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Guidelines for the design of mitigated riparian habitat and other uses in Detention Basins of Pima County, AZ, with demonstration at the Kolb Road Basin

By Matthew Bossler

A Thesis submitted to the Faculty of the COLLEGE OF ARCHITECTURE AND LANDSCAPE ARCHITECTURE In Partial Fulfillment of the Requirements For the Degree of MASTER OF LANDSCAPE ARCHITECTURE In the Graduate College THE UNIVERSITY OF ARIZONA

2010


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Acknowledgements This thesis was made possible thanks to the financial, academic, and professional support of The Garden Club of America, Granite Construction Company, Pima County Regional Flood Control District, Design Collaborations, Ltd., David Confer, and the University of Arizona Department of Landscape Architecture.


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dedication This thesis report is dedicated to those mentors who have helped me to understand and communicate environmental processes throughout my life: • Dr. Margaret Livingston, professor, University of Arizona Department of Landscape Architecture, who has been my professional sounding board throughout my masters education and primary advisor to this research • John Anderson, botanist, Arizona State Office – Bureau of Land Management, who taught me to be unashamed of my inner plant nerd • Dr. Dan Ritschoff, professor, Duke University Marine Lab, who taught me that science communication is all about simplification and joy • Charles Bossler, father, who taught me to appreciate the wilderness without • Patricia Bossler, mother, who taught me to create the wilderness within


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table of contents 1. LIST OF TABLES...................................................................................................page 5 2. LIST OF FIGURES................................................................................................page 6 3. ABSTRACT........................................................................................................page 22 4. INTRODUCTION...............................................................................................page 23 5. LITERATURE REVIEW.........................................................................................page 27 6. POLICY SETTING...............................................................................................page 37 7. CASE STUDIES..................................................................................................page 39 8. DESIGN GUIDELINES.........................................................................................page 60 1. RIPARIAN ECOLOGY...............................................................................page 63 2. ADJACENT PARCELS...............................................................................page 67 3. STREET-SIDE BASINS................................................................................page 71 4. LOT-BOTTOM BASINS..............................................................................page 75 5. INFLOW CHANNELS, DROP STRUCTURES.................................................page 79 6. SLOPE-TOPS..........................................................................................page 83 7. SAFETY AND EDUCATION........................................................................page 87 8. SIDE SLOPES..........................................................................................page 91 9. HYDRAULIC STRUCTURES.......................................................................page 95 10. INTERNAL CHANNELS, OUTLETS.............................................................page 99 11. MICROBASINS......................................................................................page 103 12. PLANTING RECOMMENDATIONS............................................................page 107 9. KOLB ROAD BASIN SITE ANALYSIS......................................................................page 111 10. KOLB ROAD BASIN DESIGN...............................................................................page 120 11. FUTURE DIRECTIONS......................................................................................page 125 12. CONCLUSION.................................................................................................page 128 13. LITERATURE CITED.........................................................................................page 131 14. IMAGERY CITED..............................................................................................page 139


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list of tables Table

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7.1

Environmental characteristics of case study metropolitan areas...................................... page 41

7.2

Uses demonstrated in case studies (by metropolitan area)..............................................page 41


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list of figures Figure

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Figure 8.1.1: Bass Canyon, Cochise County

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Figure 8.1.2: Within a typical Sonoran Desert perennial or ephemeral stream, while emergent wetland species survive in perennially inundated or saturated soils, the roots of obligate mesoriparian species must be in constant contact with groundwater, and facultative xeroriparian species can survive without perennial contact with groundwater (Pima County Regional Flood Control District 2010).

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Figure 8.1.3: Environmental and anthropogenic factors influence how close groundwater is to the surface. Gaining reaches occur where aquifer recharge exceeds withdrawal and/or groundwater is pushed towards the surface by proximate subsurface impermeable bedrock, resulting in stretches of hydro- and mesoriparian vegetation, a condition that is analogous to the dam of a detention basin.

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Figure 8.1.4: Floodplains are dynamic systems that are altered over time by the hydraulic energy and sediment transport within them. Vegetation is altered as erosion occurs along the high-energy outside of meanders, while deposition occurs on the low-energy inside, and in point bars. Detention basins are opportunities for this dynamic process to alter the form of riparian habitat over its life (Daniels, 2008, p. 51).

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Figure 8.1.5: Eastern Pima County lies on an ecological transition zone between the Sonoran and Chihuahuan biogeographic provinces, or biomes, each of which is characterized by a different set of plant species. Site location within these provinces should inform the plant selection for riparian basins (image modified from Brown, 1994, p. 13).

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Figure 8.1.6: “Patches” of habitat with a high ratio of area to edge are undisturbed preserves of biological diversity and abundance whose value can be greatly enhanced by linear biological “corridors” connecting them. Disconnected patches between are also of value as “stepping stones” for wildlife, particularly flying animals, to inhabit between large “patches.”

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Figure 8.1.7: Barriers to animal passage and stream process along riparian habitat networks can take the form of hardscape structures or denuded areas such as bare side-slopes, decreasing the value of habitat on both sides. While flying animals can pass over them, terrestrial animals may be reluctant to pass these open areas.

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Figure 8.1.8: Interior habitat is generally a refuge for sensitive species that are easily

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disturbed by factors associated with edges with disturbed areas, such as motion disturbance, noise, and introduced species. Therefore, dense thickets of riparian scrub, aquatic plants, and riparian obligate species, due to their high habitat value, are best positioned within undisturbed interiors of habitat patches. Figure 8.1.9: Inserting trails or other areas of human circulation into habitat patches typically downgrades high-quality interior habitat to low-quality edge habitat, though community use of these areas can foster appreciation, a sense of public ownership and pride, and ultimately, civic support for their continued existence.

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Figure 8.1.10: The model of habitat patches and corridors is analogous to the paths and nodes of Kevin Lynch’s ‘Image of the City’ model of human communities. In it, circulatory paths, activity nodes, and edges, among other features, shape the way that humans move and congregate within and urban area. Detention basins can serve as nodes of human activity (Lynch, 1960).

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Figure 8.2.1: Adjacent Parcels (in blue)

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Figure 8.2.2: Small areas of drainage not designed for (in blue) can cause numerous, large erosion problems (in orange,) as at Kolb Road Basin in Pima County, AZ.

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Figure 8.2.3: When the drainage from adjacent parcels is unaccounted for, side-slope rill erosion can develop and head-cut into slope-top improvements such as multi-use paths or building foundations (PCRFCD 2008 b).

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Figures 8.2.4 (top,) 8.2.5 (right): Narrow, curvilinear paved surfaces, and parcels sited with respect to contour allow for area on private parcels, increasing infiltration, and reducing runoff. Two examples of this effect in Tucson are Colonia Solana (right, City of Tucson Planning Department et al. 1994) built in the 1920s in which parcel size is large, and Sonora CoHousing Community, completed in 2000, in which parcel size is relatively small.

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Figures 8.2.6 (top right,) 8.2.7 (top left): Many special zoning overlay zones exist throughout metropolitan areas, and restrict building type and land use within them. In the example illustrated above, the Approach-Departure Corridor, also known as the “flight paddle” of Davis Monthan Air Force Base, prohibits residential, commercial, office, and active recreational/gathering area land use at the Kolb Road Basin, due to sound levels between 60-70 decibels, risk of a crash, and the potential for bird kill and resultant plane malfunction (Davis Monthan Air Force Base 2003). At right, though portions of the Guadalupe River Park lay within the flight paddle of San Jose International Airport, passive recreational use and hydroriparian habitat areas are allowed and enjoyed.

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Figure 8.2.8 (above): Reading areas of the Southeast Regional Library in Gilbert, AZ,

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overlook a recreational pond of the Riparian Preserve at Water Ranch (C.F. Shuler, Inc. 2010).

Figure 8.2.9 (right): A conference room in a business park adjacent to Granite Regional Park is enhanced by a window view of a water feature within a retention pond.

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Figure 8.2.10: Skyscrapers holding Acer, T & C Productions, and Paolo’s Restaurant in downtown San Jose, CA, are oriented towards the Guadalupe River Park, demonstrating an appealing transition between geometric and naturalistic form through the use of planting terraces, stairs, and recreational pathway.

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Figure 8.2.11: At the Paradise Apartments along Greenway Wash in Phoenix, AZ, residents are treated to window views and a turfed seating and recreation area overlooking the riparian habitat below. Curbing on the left side of the concrete path conveys water to drains located at bump-outs to the left, which also serve as overlook points.

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Figure 8.2.12: Patrons at the Wolfgang Puck Restaurant at the Springs Preserve in Las Vegas, NV, enjoy an overlook of the formal landscape and riparian habitat below (Luchessi, Galati, Inc./Natural Systems International).

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Figure 8.3.1: Street-side basins (in blue)

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Figure 8.3.2 (left,) 8.3.3 (top): Basins abutting the pavement are only appropriate along small residential or rural roads, as depicted at left. Basin series extending from natural drainages are of higher habitat value than those separated by constructed barriers. Basins along arterial streets are more appropriate in medians or offset from the roads, which expand in size with increased traffic demand.

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Figure 8.3.4: Urban street-side basins created by curb-cutting should be contained, along with a sidewalk or other pedestrian space, within the road right-of-way.

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Figure 8.3.6: In a rural, no-curb setting, a vegetation-free utility operational zone should be located between the road edge and street-side basins. When the road is down-cut from the surrounding grade, up-slope of the street-side basin, erosion control measures such as side-slope basins and slope-top diversion basin series can help prevent side slope erosion. (Design Collaborations, Ltd. 2009).

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Figure 8.3.7: Deep rectangular vegetated detention basin adjacent to impervious parking lot at Vernola Family Park, Riverside, CA.

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Figure 8.3.5: At the Confer private residence in the Colonia Solana neighborhood of Tucson, AZ, narrow streets (~24’) drain into a series of slightly-depressed basins. When one of these fills to capacity, water bypasses it and flows into the next in the series.

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Figure 8.3.8: Traffic circle: A parking area at the northern end of Columbus Boulevard in Tucson, AZ is designed around a concave, landscaped, pervious cul-de-sac that retains and infiltrates low-flows draining from the road, while providing a designed centerpiece of sculptural landscape. Figure 8.3.9: Curb-cut water-harvesting basins: By cutting away sections of an existing curb, low-flows are directed into shallow water-harvesting basins immediately adjacent to this residential street, and support hardy xeroriparian plants, at The Nature Conservancy water-harvesting demonstration site in Tucson, AZ (Watershed Management Group).

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Figure 8.3.10: Basins in chicanes: In the Rincon Heights neighborhood of Tucson, AZ, water-harvesting basins are colocated within curb bump-outs, otherwise known as chicanes, which help slow the flow of traffic on streets of overdesigned width, and shade the street and sidewalk, reducing urban heat island effect (Silins 2010).

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Figure 8.3.11: Street-side water harvesting/retention basins should be dug to a depth of 6-12,” depending on subsurface improvements, to ensure adequate drainage.

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Figure 8.3.12: Street-side detention basins to varying depths can contain “nested” water harvesting/retention basins located below the bottom of the outlet pipe. Overflow occurs via the curb-cut inlet.

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Figure 8.4.1: Lot-bottom basins (in blue)

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Figure 8.4.2 (top,) 8.4.3 (bottom): In order to achieve the same capacity, a detention basin’s surface profile can vary from a steep drop and short, flat run, to an even-sloped, extended-run, which is more conducive to mitigated habitat.

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Figure 8.4.4: Partial flow diversion of flowing waters is the essence of diversion canal agriculture in both temperate/tropical areas, as seen here in South China, and arid and semi-arid regions such as the Sonoran Desert, the home of the early canal-based protohistoric Hohokam civilization. Linear Terrace: direct series of overflow terraces; develop graphic or use image of rice paddies on slope (China Forum 2010).

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Figure 8.4.5: A pool and riffle arrangement mimics the natural analog wherein pooling areas overflow through intermediate riffles or cascades. These can be created by bedrock intrusions or cobble deposits, as seen here in the Tabletop Wilderness, AZ. Note the density of vegetation located to the sides of the sandy deposit areas.

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Figure 8.4.6: In Clarkdale, AZ, the Verde River currently runs south of ruins of the Tuzigoot Sinagua civilization, during which time the river ran around the north. This old river channel has become Peck’s Lake, a natural oxbow supplemented by waste water from an adjacent mining facility in town. Within it, Tavasci Marsh, a hydroriparian wetland and

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Figure 8.4.7: Pool and riffle: The Las Vegas Springs Preserve (Luchessi Galati, Inc./Natural Systems International) in Las Vegas, NV, concentrates hydroriparian plantings around successively lower perennial pooling areas consistently sloped towards their center, and riffle streams connecting them. In small storm events, vegetated overbank areas of both become inundated.

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Figure 8.4.8: Curved Terrace, all flows: wide basins wrap around side slopes taking total volume of all storms, with no central/bypass negative space (overflow basin,) as in this multi-use master plan for Strathern Pit in Los Angeles (Natural Systems International).

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Figure 8.4.9: Subdivided terracing: Fine-scale grading of each microbasin should allow it to fill to capacity from low-flows emanating from its feeder inlet, then overflow to adjacent microbasins without “hogging” the full amount, in order to maximize the temporary pooling and saturation areas.

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Figure 8.4.10: Low-flow channel, off-line component detention basins: At the Erie Lakes Detention Basin, CO, low flows (dark blue) are contained to a low-flow channel and water quality treatment pond, while, in large events, high-flows (light blue) back up at the outlet and overflow to an adjacent, off-line detention basin. This mimics the natural analog of a slough or oxbow lake in the overbank areas of a floodplain.

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Figure 8.5.1: Inflow channels, drop structures

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Figure 8.5.2: Basins above 1/5 acre in size or those with inlets separated from outlets by more than 100 feet are subject to policy TECH-009, which requires a 12’ physical access corridor adjacent to the inflow channel and no woody plants around the inlet and outlet.

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Figure 8.5.3: Below-grade metal pipes and culverts can safely deliver incoming flows basins where above-ground conveyance is impossible, as shown here at Vista Hermosa Park, Los Angeles, CA (Mia Lehrer Associates,) and Regency Park, North Natomas/Sacramento, CA.

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Figure 8.5.4: Flows from small drainage areas can be conveyed to the basin via narrow channels armored with concrete or rip-rap, as at Ladera Ranch, CA, and in suburban Pima County, AZ, at right.

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Figure 8.5.5: The primary parkway of Ladera Ranch community in Orange County, CA, is flanked by a dual conveyance system, named the Sienna Botanica, that drains the entire development to a lot-bottom basin, provides an intermediate habitat-value biological corridor from the vegetated basin to wilderness located above the development, and improves water quality and infiltration along its length. These benefits, in sum, satisfy the development’s habitat mitigation requirements.

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mesoriparian forest, provides ideal habitat for many bird species.


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Figure 8.5.6: The Los Angeles River Revitalization Master Plan, designed by Tetra Tech, Inc., Mia Lehrer Associates, Civitas, Inc. and Wenk Associates, calls for a stream profile that contains concrete step terracing for with access ramps leading to a low-flow environment containing emergent vegetation and pool and riffle flow (City of Los Angeles 2007). Figure 8.5.7: Runoff from an adjacent residential area arrives at the Greenway Wash through a concrete slip in low-flow conditions, swelling over a gabion walls in higher flows. The terrace created by these walls provides a xeroriparian planting area.

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Figure 8.5.8: Inflows into a constructed wash that drains the Oro Valley Marketplace are dissipated by concrete blocks, a drop in elevation, and a rip-rapped isthmus of land that splits the flow.

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Figure 8.5.9: Falls, boulders set in concrete dam: At the Erie Lakes Detention Basin in Erie, Colorado, boulders from a local quarry were set into concrete in order to create 18� vertical drops that, along with adjacent hydroriparian plant growth, absorb hydraulic energy while re-creating points of natural wonder along a neighborhood greenway (Belt Collins West.)

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Figure 8.5.10: Concrete dam + boulders: At Horseshoe Park in Denver, CO, hydraulic energy from an inlet channel is dissipated by instream vegetation, an approximately 2’ dam, and boulders set above and below the dam (Wenk Associates).

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Figure 8.5.11: Cascade: Shop Creek outcrop soil cement slip into plunge pool, Off-set site soil-cement lifts: Curved, stratified drop structures created by site soil cement lifts enhance the appearance of water-quality wetlands and allow for natural observation along Shop Creek in Denver, CO (Wenk Associates).

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Figure 8.6.1: Slope-tops (in tan)

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Figure 8.6.2: Runoff from adjacent parcels can be collected in diversion swales or basins parallel to the top of the slope of the basin, and safely conveyed to a designed inlet. Diversion areas can be contained by compacted berms or multi-use paths.

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Figure 8.6.3: A crown ditch installed at the top of this Sonoran desert roadway cutbank diverts sheet flow from adjacent lands to the right, preventing rill erosion on the designed side-slopes. (Arizona Department of Transportation 2008).

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Figure 8.6.4: At Bluff Lake Nature Center in Denver, CO, a perimeter trail is punctuated by scenic overlooks such as this, which give a sense of place, and an opportunity to reflect upon the features below.

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Figure 8.6.5: Shade, a safe walking surface, and areas for discovery and play are important

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features of slope-top recreational trails, as seen in this proposed image of The Los Angeles River Revitalization Master Plan, designed by Tetra Tech. Inc., Mia Lehrer Associates, Civitas, Inc., and Wenk Associates (City of Los Angeles 2007). Figure 8.6.6: This photo by the Arizona Wildlife Linkages Workgroup demonstrates the barrier to terrestrial animal passage posed by traditional culvert/scupper design, and the necessity for collaborative design between a project’s civil engineering and landscape architectural designers (The Arizona Wildlife Linkages Workgroup 2006).

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Figure 8.6.7: At the Star Valley Basin 4 park of the Star Valley Village subdivision in south- west Tucson, constructed inlet channels flow over the surface of perpendicular pathways through dips in the paving, an appropriate solution when the upstream channel does not retain ecological integrity (Novak Environmental, Inc. 2010).

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Figure 8.6.8: At Milagro Cohousing Community in unincorporated Pima County west of Tucson, tributary washes pass underneath pathway bridges, preserving hydrologic dynamism and the passage of small animals.

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Figure 8.6.9: Following an assessment of elk-vehicle collisions on AZ-SR 260 along the Mogollon Rim, Arizona Department of Transportation installed riparian underpasses that preserves passage through the flow channel and dry banks of Christopher Creek (The Arizona Wildlife Linkages Workgroup 2006).

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Figure 8.7.1: Safety and education

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Figure 8.7.2: At the Anthem Hills multi-use basin in Henderson, NV, this sign, repeated around the basin’s perimeter, informs users of the risk of drowning during rain storms, in both English and Spanish, and through symbolic figures.

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Figure 8.7.3: Signage at a conservation area at the West Branch of the Santa Cruz River in Pima County informs the public of sensitive habitat value and use restrictions through text and images associated with riparian life (Burnham 2010).

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Figure 8.7.4: Riparian biotic process can be communicated non-verbally through symbolic sculpture, as along a greenway in the North Natomas neighborhood of Sacramento, CA.

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Figure 8.7.5: Gowan Basins, Las Vegas, concrete ramp that communicates depth of floodwaters both during flood events and the function of the basin throughout the rest of the year.

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Figure 8.7.6 (near right): Sculptural gestures of flow draw the eye to the function of a small contributing open channel at the Springs Preserve in Las Vegas, NM (Luchessi, Galati, Inc.).

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Figure 8.7.7 (far right): This recirculating water feature at Vista Hermosa Park in Los Angeles makes a gesture of active riparian process throughout the year (Mia Lehrer Associates).

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Figure 8.7.8: Fencing separating the user from sensitive or dangerous environments should seek to enhance understanding of views below, as seen at this fishing pond at Gilbert, AZ’s Water Ranch (C.F. Shuler, Inc.).

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Figure 8.7.9: If the area is to be commonly used by visitors, investment in fencing types that contribute to the surrounding visual resources is most appropriate, as seen here in the form of a concrete seat wall, pipe and cable fence, and fencing composed of COR-10 t-bar posts, cable, and steel pipe railing (Luchessi, Galati, Inc.).

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Figure 8.8.1: Side-slopes (in yellow)

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Figure 8.8.2: Basin side slopes of an overall ratio of 3 to 1 are difficult and expensive to vegetate and may require costly erosion control measures on steeper portions (rip-rap).

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Figure 8.8.3: Basin side slopes of an overall ratio of 6 to 1 allow for relatively inexpensive micro-grading to support vegetation along them.

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Figure 8.8.4: Asphalt ramp, stairs trail: At the Bluff Lake Nature Center in Denver, Colorado, access down steep bluffs to an observational gazebo overlooking the natural riparian basin below can be accomplished either by descending a gently sloping asphalt ramp or a more steeply-graded trail of decomposed granite with wide steps retained by wooden beams.

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Figure 8.8.5: Decomposed granite walking trails descend the side slopes of the Springs Preserve along switchbacks which are built overtop of a minor-contributing drainage composed of stretches of vegetated ditch, caliche block check dams, and culvert pipes (Natural Systems International, Luchessi, Galati, Inc.).

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Figure 8.8.6: On-contour berms: At the Arizona Cancer Center in Tucson, AZ, building and slope runoff is retained by mid-slope shallow water-harvesting basins contained by an on-contour berm. Within this environment, mesquite, creosote, and desert willow have been established. Exceeding the capacity of this basin, overflow is directed through a naturalized concrete ditch to the street-side storm drain. This feature, along with inorganic rock mulch, prevents erosion rills from forming (Ten Eyck).

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Figure 8.8.7: Cross-cut slope ditch, unvegetated; mini-benching: At the recentlycompleted City of Chandler, AZ, Paseo Vista Park, rip-rapped ditches cross-cutting the steep side-slopes intercept small amounts of runoff from open slopes, which have temporarily been roughened with on-contour microberms to improve the success of

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hydroseeding. Larger flows from adjacent lands to the right of this picture are conveyed directly down the slope through rip-rapped channels perpendicular to the contour of the slope.

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Figure 8.8.8: Retaining wall terraces: The Guadalupe River Park in San Jose, CA, designed by Hargreaves Associates, is an active channel that runs through the heart of the city’s downtown. Base flows run through a naturalized central corridor. Peak event flows then inundate, a series of even-graded terraces contained by human-scaled retaining walls, which serve as easily-accessible, vegetated lunch-spots for local employees in base conditions.

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Figure 8.8.9: By following the slope contour, large “bioswales” can intercept, roughen, slow the velocity, biologically treat, and infiltrate runoff from the upslope (State of Oregon DEQ 2003).

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Figure 8.8.10: On-contour microberms: At Del Paso Park in Sacramento, CA, a steeplysloped area adjacent to a recreational vernal pool detention basin was graded to include human-scaled, back-graded berms parallel to the contour of the slope, and successfully vegetated with container plantings and volunteer growth (The HLA Group and Foothill Associates).

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Figure 8.8.11: Pocket plantings/berms: Vernola Family Park in Riverside County, CA, uses small berms surrounding container plantings on side-slopes, preventing drip irrigation from escaping a “pocket” for the establishment of the tree’s rooting system, but doing little to retard and infiltrate runoff flow into this rooting zone, making this an inferior method of side-slope grading..

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Figure 8.9.1: Hydraulic Structures

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Figure 8.9.2 (left): The function of a sediment trap can be improved by the growth of non- woody annual vegetation that can assist in the process of aggradation, is nearly impossible to prevent or control, and poses no obstruction to vehicular maintenance, as seen here at the Kolb Road Basin, in Pima County, AZ. This exception to TECH-009 does not apply to woody vegetation, which can obstruct access.

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Figure 8.9.3 (top): In a community setting, weedy plant growth can be controlled by “destructive” active use, as seen here in the form of a childrens’ BMX play-space at the Anthem Hills Park, in Henderson, NV.

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Figure 8.9.4: At the Oro Valley Marketplace in Oro Valley, AZ, incoming floodwaters from an arterial street above are dissipated of energy through a series of blocks, a rip-rap lined flow bifurcator, and a slight plunge pool in which sediment is trapped. In the flow energy shadow between the gully, xeroriparian trees have been planted.

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Figure 8.9.5: This view of the sediment trap of the Erie Lakes Detention Basin, also depicted at left, demonstrates how moderate amounts of grass growing within the pooled water of the concrete catch-basin can help roughen flow, catch incoming sediments, biofilter the water, and mitigate the industrial nature of the structure, within easy access of a multi-use path. The water quality treatment pond below provides as a naturalistic view from the neighboring RV park (Belt Collins West).

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Figure 8.9.6: Channel bend, formalized: The hydraulic energy of inflows along this portion of Westerly Creek at Lowry Parks is absorbed by concrete walls along a severe bend of the creek. As shown, these walls slope down along with the direction of flow, allowing recreational access and appreciation of emergent wetland vegetation, which is planted within low-energy “shadows� of the ends of the wall sections (Wenk Associates).

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Figure 8.9.7: Channel bend, naturalistic: At the Rillito River/Swan Wetlands Restoration Project in Tucson, AZ, hydraulic energy of a tributary inflow channel is dissipated at severe bends of flow by stretches of soil-cemented bank terraces. Note that this terrace continues upstream, losing the soil cement, and adding riparian planting areas (RECON Environmental).

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Figure 8.9.8: Along daylighted Westerly Creek in the Stapleton neighborhood of Denver, CO, low-flows draining from an adjacent parcel are diverted into a water-quality treatment pond, while large-event flows bypass directly into the creek (EDAW).

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Figure 8.9.9: Storm surges arriving at Anthem Hills Park in Henderson, NV, a combined- use active recreational detention basin, are split and slowed by a single terraced rise, at right, mirroring the wide stair-step form of the rest of the drop structure, at left, which doubles as stairs to an open greenway channel internal to the neighborhood located upstream.

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Figure 8.9.10: Below pipe: As large amounts of runoff flow in from an upstream housing development along Shop Creek, in Denver, CO, through a road box culvert, cubic blocks of concrete capture the eye and roughen the pipe flows arriving at a series of water quality treatment wetlands filled with cattails and surrounded by cottonwood and riparian scrub (Wenk Associates).

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Figure 8.9.11: Below open channel: Along Goldsmith Gulch, at George Wallace Park, this formal drop and energy dissipation structure absorbs significant hydraulic energy among large colored-concrete blocks that serve as a playful amphitheater of seating within an inspirational, sculpturally abstract environment. Base flows spill out of a rectangular concrete channel, creating an elegant falls (Wenk Associates).

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Figure 8.9.12: Further up Goldsmith Gulch, this combination drop/energy dissipation structure contains rough-hewn boulders set in an invisible concrete base, creating a

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naturalistic cascade along the riparian stream (Wenk Associates 2009).

Figure 8.10.1: Internal channels, outlets

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Figure 8.10.2: At the Las Vegas Springs Preserve in Las Vegas, NV, urban drool and low- flows from small events are filtered and diverted into a series of permanent and ephemeral pools.

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Figure 8.10.3: The grading design (Luchessi Galati, Inc./Natural Systems, International,) ensures that the delicately-designed riparian habitat in the microbasins and its complementary passive recreational features will not be destroyed by high flows from large events by diverting these flows near the entry of the basin into a high-flow channel embanked by a large berm (in white).

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Figure 8.10.4: An intermediate flow (3-8 cfs) inlet diverts flows from small storm events into the second pond of the system, creating a pastoral scene (diverter at right).

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Figures 8.10.5: Incoming flows at the University of Colorado-Boulder Research Park wetland detention basin are subdivided into base (0-3 cfs, in dark blue) intermediate (3-8 cfs, in true blue) and high flows (8+ cfs, in light blue) with the use of flow diverters (in maroon) and large berms (in white.) 100-year storm event flows back up at the outlet and inundate 23 acres (in red hatching,) avoiding developments (in purple).

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Figure 8.10.6 (above): When channel water is of poor quality or supports habitat of high quality, barriers to entry may be appropriate (Kino Ecological Research Project, Tucson, AZ).

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Figure 8.10.7 (right): Pedestrian bridge over hydroriparian low-flow channel, Las Vegas Springs Preserve (Natural Systems International).

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Figure 8.10.8: At Regency Park in North Natomas, Sacramento, CA, the outlet of a water- quality treatment pond and detention basin is hidden from view by concrete walls and kept free of vegetation with deep water.

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Figure 8.10.9: Outlets can be disguised from view by hedge screening if they do not contribute to the aesthetic appeal of the system (Ladera Ranch, CA).

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Figure 8.10.10: Where water resources are available, the incorporation of an above-ground stream can bring drama and a full array of riparian biotic communities to the side-slopes of a site. These designed watercourses should drain only a minimal watershed, as their built features and emergent streambank growth can be destroyed by large events. At the Riparian Preserve at Water Ranch in Gilbert, AZ, this channel lined with cobbles set in concrete connects a desert overlook with a fishing pond below (C.F. Shuler, Inc.).

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Figure 8.11.1: Microbasins (in blue)

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Figure 8.11.2: In wrap-around terracing, low-flow channel, or subdivided terracing, each microbasin should be offset 6 or more inches below of or at grade with upstream microbasins in order to ensure timely drainage.

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Figure 8.11.3: Micropooling areas at the Kolb Road Detention Basin in southeast Tucson receive fine sediments and saturate the lower trunks of the vegetation growing within them, precluding woody growth. Woody vegetation thrives in adjacent areas that are slightly elevated and drain relatively quickly, allowing the shoots to trunks to stay dry and the roots to access moister soils.

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Figure 8.11.4: In the middle of a open channel at Oro Valley Marketplace in the Town of Oro Valley, AZ, slightly elevated planting islands serve as point bars within the wash where instream vegetation is allowed to grow, buffered from hydraulic energy by the upstream earth of the island.

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Figure 8.11.5: Slightly elevated planting islands within microbasins should be wide enough to accommodate a full-statured woody tree and understory shrubs surrounding it, but narrow enough to allow for these root systems to reach adjacent, slightly deeper pooling areas. In order to prevent trunk rot, the base of the tree’s trunk is out of the pooling area, which is mulched to prevent clay sealing.

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Figure 8.11.6: Following grubbing of a riparian area to be disturbed, topsoils to a depth of 4 to 6 inches can be salvaged, temporarily stockpiled, and used to create an upper organic soil horizon in microbasins, giving the basin a “kick-start� of fertility, native seeds, and beneficial soil organisms.

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Figure 8.11.7: French drains increase the storage capacity of the proximate soil profile by using coarse-grained, rough-edged, evenly-sized riprap in order to create maximum pore space. Infiltration rate and total capacity of microbasins is improved with this method, causing adjacent soils to be saturated for longer periods of time, benefiting deep-rooted woody growth.

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Figure 8.11.8: Impermeable liners located just below the targeted rooting zone can increase the time of soil saturation when site soil conditions are too permeable, without creating problem pooling above the surface. These can be made from bentonite clay and geomembrane plastics, and should be designed to allow for inevitable root penetration. A disadvantage of liners is that roots are contained for the most part within the lined volume, and can be susceptible to root rot.

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Figure 8.12.1: Plantings


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Figure 8.12.2: Planting zone codes: The zones of a detention basin are characterized by frequency of inundation, and can, in this way, be compared to a natural floodplain analog. Plant species can withstand varying periods of inundation, and have been categorized by the following zonation: Figure 8.12.3 (top left,) 8.12.4 (top center): Long pots, such as these provided by Stuewe and Sons, allow for desert leguminous tree seedlings to grow to saplings much as they do in natural conditions, extending a deep tap root to reach available groundwater, as demonstrated by the three-month seedling at right. Traditional bucket pots, as deep as they are across, promote shallow roots that can become bound too tightly for optimal field planting.

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Figure 8.12.5 (top right): Within water harvesting basins located on a riparian terrace of the Rillito River/Swan Wetlands Ecosystem Restoration Project, hydroseeded saltbush (Atriplex,) following broadcast sprinkler irrigation, has established thick mono-typic stands, though, overall, species evenness is low.

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Figure 8.12.6: Four of the most common and invasive exotic plant species in Pima County that should be controlled within riparian habitat areas include (from right, clockwise,) arundo, salt cedar/tamarisk, and fountain grass, and buffelgrass. Arundo outcompetes native emergent plants, while the latter three can grow into profuse monotypic stands with limited water resources.

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Figure 9.1.1: Deep headcutting erosion rills developed over the life of the basin, as documented by this PCRFCD filed visit in early 2008 (PCRFCD 2008).

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Figure 9.1.2: Rills such as the one to the left were temporarily resolved by PCRFCD Infrastructure Management staff in 2008, through slope regrading and the installation of an uncompacted slope-top berm diverting sheet flow to rip-rapped gullies at points of heavy flow. This picture from November, 2009 demonstrates continued rilling to the left and right of a gully.

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Figure 9.1.3 (left): Erosion rills continue to sacrifice the passability of the slope-top maintenance road.

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Figure 9.1.4 (above): Aerial oblique photo of side-slope erosion rills prior to PCRFCD Infrastructure Management maintenance (Microsoft Bing 2009).

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Figure 9.1.5 (left): Deposition of soils is storm events occurs as floodwaters from both designed inlets and erosion rills loses hydraulic energy and falls out of suspension. These have taken the form similar to the delta of a river.

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Figure 9.1.6 (right): Analysis of drainage at the Kolb Road Basin reveals problem drainage

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areas on adjacent parcels that were unaccounted for in original design, leading to side-slope rill erosion and soil deposition areas within the basin bottom. Figure 9.2.1: In shallow depressed areas of the basin bottom, sediment has collected, forming pools of above-ground water that supports only shallow-rooted annual grasses, forbs, and weeds. Adjacent elevated areas that do not receive this pooling water support mature velvet mesquite (Prosopis velutina) and desert broom (Baccharis sarothroides).

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Figure 9.2.2: Large areas of the basin bottom are elevated in relation to the pooling areas seen at left. These areas, therefore, receive little infiltration, and supports only low brushy growth of primarily velvet mesquite (Prosopis velutina). These areas are ideal for potential revegetation.

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Figure 9.2.3 (left): Semi-desert grassland representative species such as cane beardgrass (Bothriochloa barbinodis) are present in man-made depressions along the railroad tracks near the basin, along with abundant desert broom (Baccharis sarothroides).

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Figure 9.2.4 (left): Tall stands of invasive Johnson grass (Sorghum halapense) replace velvet mesquite (Prosopis velutina) and desert broom (Baccharis sarothroides) in the high-energy zones at the base of designed inlets. This annual, rhizomatous grass is blown down in major storm events, and should be targeted for removal.

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Figure 9.2.5 (below): This photo, taken from the middle designed inlet shows riparian vegetation circled in red both within the basin bottom and in the upstream channel. Red areas below correlate to green areas at right. Blue areas signify areas of sparse growth, correlated with tan areas at right.

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Figure 9.2.6 (right): Existing vegetation at the Kolb Road Basin has been categorized into xeroriparian vegetation within the basin bottom and external drainages, and denuded areas on the side slopes, basin bottom, and external areas.

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Figure 9.3.1: Within a 2.5 mile service radius (purple buffer) of the Kolb Road Basin (in blue line) lies many existing and proposed/approved residential developments (blue underlay) that are currently underserved by parks (in red and yellow.) However, decibel levels from the DMAFB approach-departure corridor (grey scale) will approach 60 db. As such, the Kolb Road basin is ideally positioned to be a passive recreational metro park to serve these neighborhoods.

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Figure 9.3.2 (left): 60 decibels of noise is roughly equivalent to conversational speech or the clatter of a business office (DMAFB 2003).

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Figure 9.3.3 (below): The Julian Wash Greenway has been designed along the northwestern and northeastern slope-tops of the Kolb Road Basin by Olsson Associates, under contract

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with the City of Tucson Parks and Recreation Department. Parallel trails enter on the north side of the outlet structure, and are punctuated with interpretive nodes on both sides of a bridge at inlet #3, with excellent views of the southeastern side slopes and the basin bottom. Figure 9.3.4 (right): The UA Tech Park Master Land Use Plan, developed by The Planning Center, calls for industrial and open space usage within the flight paddle (red line,) and hospitality and public land use around Kolb Road Basin, at upper left.

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Figure 9.4.1: The Julian Wash proposal, designed by Olsson Associates, contains a multi-use path composed of a 95% compacted subgrade and a “Apache Brown� decomposed granite pathway (Olsson Associates 2009).

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Figure 9.4.2: The UASTP road meets Kolb Road across from an industrial complex, and currently is flanked by native desert scrub vegetation and mesquite plantings.

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Figure 9.4.3: The Julian Wash Greenway (proposed) will transform provide maintenance access for PCRFCD staff along an asphalt trail that will replace the existing maintenance road along the slope tops. In addition, the existing fence will be removed and replaced with a new barricade railing located closer to the top of the side-slopes than the existing fence. A controlled access gate will be installed where the green star is located, allowing for continued access to the southeastern portion of the perimeter road to PCRFCD staff. Interpretive nodes will be located at the circular features below (modified from Olsson Associates 2009).

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Figure 9.4.4 (right): Existing maintenance access to the basin occurs along levees, and the internal perimeter along the slope-tops. The Julian Wash Greenway will replace the northwestern portion of this access road.

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Figure 10.1.1 (right): Existing maintenance access to the basin occurs along levees, and the internal perimeter along the slope-tops. The Julian Wash Greenway will replace the northwestern portion of this access road.

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Figure 10.1.2 (right): Off-site sheet flow runoff is diverted by a compacted berm on the inside of the access road, and conveyed along the road until it meets an existing inlet or rip-rapped channel. Rain falling directly on the side-slopes is conveyed in a similar fashion by two more uncompacted wide berms closer further down-slope. Runoff reaching the bottom is both directed to existing pooling areas, and proposed shallow basins excavated to a similar depth.

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Figure 10.1.3. Cross section AA: : During phase 1, soil will be excavated to an approximate depth of one foot from microbasins in the bottom of the master basin, in which 17 acres of xeroriparian habitat will be planted. This fill will be transported and

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stockpiled along the side slopes, and backgraded to direct runoff to existing rip-rapped gullies. Maintenance access will be preserved along the existing slope-top road, and a compacted berm will be constructed on the edge of this road to prevent side-slope rill erosion.

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Figure 10.2.1 (right): Passerines Park combines large-scale interior habitat areas of phase 1 with highly-interactive slope-top and side-slope improvements that clearly reveal the techniques employed to create riparian experience.

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Figure 10.2.2 (right): Phase 2 will utilize stockpiled fill soil from phase 1 to expand access along the side slopes, which will be hydrated by the diversion of all flows from drainage problem areas and low-flows from existing designed inlets. Each microbasin will overtop to the next through energy dissipators that will prevent erosion headcutting and slow the flow.

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Figure 10.2.3. Cross section AA: : The visitor to Passerines Park will have a variety of riparian experiences to choose among, from shaded, sweeping vistas along the busy circulatory overlook along the top to the peace and solitude of the wooded canopy below.

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ABSTRACT Keywords: stormwater, multiple-use, riparian restoration Urban stormwaters can be managed for flood control and conveyance, active and passive recreation, aquifer recharge, wildlife habitat, mosquito control, irrigation, water quality treatment, and environmental education. Communities invest in multiple single-use facilities and parks to accomplish these goals where a single combined-use design solution is more appropriate. Passive recreation and environmental education opportunities of a riparian nature are under-represented in urban and suburban areas of cities that contain these single-use detention basins. Institutional differences between involved professions and agencies must be overcome to design and maintain these more complex, functional systems. Case studies, literature review and interview of professionals from the arid and semi-arid urban desert southwest have informed the creation of design guidelines for riparian habitat mitigation strategies within detention basins of Pima County, AZ. These have been applied to a multi-phased retrofit design of the Kolb Road Basin, an existing regional detention basin with public and private interests in metropolitan Tucson, Arizona.


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InTroduction As a young child in suburban Richmond, VA, every afternoon, from the time my friends and I departed the bus to the time the sun went down, was filled with the same adventurous routine. We first hopped on our bikes, raced down our street, and veered off into the woods through a long-abandoned colonial-era coal mining area littered with open pits, poison-ivy vines, and malformed trees, making our way to our afternoon treat at the local 7-11, usually in the form of a box of Gobstoppers or a Snickers bar. Properly sugared-up, we would race back to our houses, ditch our bikes, and cross the threshold from the manicured crape myrtles, oaks, and grass lawns of our parent’s homes through a thicket of briars and tulip poplars saplings, into the deep, dark canopy of the creek forest. This was “our” territory, where we spent most of our time precisely because we could “own” the area as the land of our kids’ club, without the interference of our parents or anyone else. We built forts in the trees and in the clay, cut willow poles to vault back and forth across the stream, and mapped out and named all the bluffs, quick-sands, fern patches, and storm sewer entrances. We also had fist-fights, built false banks on the sides of the creek to “trap” kids from the competing boys’ tribe, and once threw a copperhead snake into a bucket, doused it with glow-stick fluid, buried it for weeks, dug it back up, and paraded around the neighborhood like the “Lord of the Flies.” We used this forgotten landscape, circled on the neighborhood plat as a natural floodplain, as our first landscape of discovery, socialization, and outdoor exercise. When suburban development occurred upstream, we saw how our stream clogged up with deposited sand, changing the biota, and with the next major storm flush, miraculously returned to its previous condition. During and after each rain storm, we flocked to the creek to navigate a world transformed, one of strongly-scented, boggy, ephemeral pools teeming with shimmering black tadpoles, tiny sunfish, and mosquito larvae, of normally dry overbank areas inundated with a foot of water that we waded through like intrepid jungle explorers. Over time, we were able to form a concept of the impact of our activities of our play, as our cut-bank booby traps slowly eroded into unvegetated scars, the willow patch became thinned out by our efforts, and the holes we dug began to take on the form of the coal pits that remained from another generation’s use of the land some two-hundred years prior. In essence, we formed our earliest impressions of hydrology, soil erosion, plant communities, animal growth, and the interconnectedness of these processes by directly interacting with and altering it. Kids are destructive. Thinking back to this time in my life some twenty years later, I am fully aware that these experiences were the starting point of a career and life pursuit focused on the exploration of wild places and their creation on the doorsteps of our built landscapes. On morning walks of my neighborhood in central Tucson, I am astounded by its beauty, but constantly reminded of how completely transformed this urban landscape is from the natural processes which define flows of energy, nutrients, and life in the desert washes and streams that surround our city. Occasionally, I make it out to the fringe of the metropolitan area, where leap-frog suburbs have popped up in unincorporated Pima County, miles from the incorporated limits of the city, and am alternately dismayed or impressed with the degree to which natural drainages have been preserved for the flow of floodwaters and the fun and exploration of young children, and adults such as myself who feel relaxed and restored by a few minutes of time walking along the banks of, or through the channel of dry, intermittent, and perennial streams.


24 Pima County’s Riparian Habitat Protection Ordinance recognizes the value of these integral biotic communities as essential to the health of the regional ecosystem, and requires all properties to either preserve or mitigate for the destruction of regulated riparian habitat within them. In some developments, where natural drainages are preserved or conveyance channels are constructed in an open way, mitigation can occur within the flow channels. In other areas, where the designers of residential, industrial, and commercial developments must, or choose to destroy riparian habitat and/or minimize the areal extent of conveyance channels, these channels must remain denuded to properly serve their function and not risk the flooding of adjacent developed parcels. In these latter cases, the quickly conveyed runoff must be detained at the bottom of the development per Pima County code in detention or retention basins. For too many years, these basins have also been treated, unnecessarily, as single-function infrastructure: to detain floodwaters in such a way that the controlled release of waters from their outlets meets the pre-disturbance rate of drainage, to the exclusion of natural processes and human enjoyment. These detention basins represent an opportunity to not only restore riparian habitat per the Pima County Riparian Habitat Protection Ordinance, but also to create an all-too-uncommon interface between riparian process and human understanding and appreciation. By recognizing the additional benefits that these basins can bring to the developer and resident, their design can become more complex, and maintenance and management can be valued as important expenses to create the ambience, aesthetics, and recreational use of a residential or commercial development. This report, therefore, will review bodies of literature that inform detention basin, riparian mitigation, and recreational design in the urban southwestern U.S., introduce the reader to a multitude of comparable case studies from this region, and outline an easily understandable series of design considerations, general specifications, and built examples from Tucson, Pima County, and other arid and semi-arid urban areas of the southwestern U.S. that can guide the design of combined-use detention basins with an emphasis on riparian habitat mitigation. It is intended to be a manual that developers, civil engineers, landscape architects, environmental consultants, and home-owner associations can pick up “off the shelf ” of the Pima County Regional Flood Control District’s offices or website, as they lay out the design of their development in a way that can provide combined-use functions to these basins, reducing overall development expense. Following this, the report will describe the analysis and multi-phased retrofit design of the Kolb Road Basin, a regional detention basin in southeastern metropolitan Tucson, that is managed by the Pima County Regional Flood Control District (PCRFCD) as a regional detention basin containing runoff from the Upper Julian Wash watershed, which includes both the Rita Ranch subdivision and the University of Arizona Science and Technology Park (UASTP,) among other developments. Phase one consists of the construction of 17 acres of mitigated xeroriparian habitat within the existing basin’s bottom, as well as a simple shortterm solution for drainage problems that are occurring on its side-slopes. Phase two, recognizing the future construction of the Julian Wash Greenway along the western and northern slope-tops of the basin, extends this recreational use around the southern remainder and into the basin bottom through a series of lowflow diversion channels, pools, and drop structures along the southern and eastern side slope, and opens the basin for recreational use as a public natural resource park. Recommendations for future phases of design suggest building upon this public investment by siting a hotel, conference center, park and ride, fire station, light commerce, disc golf course, upland desert preserve, and a land use research center entitled the Southwestern Lands Innovation Center, emphasizing water-wise development, as the east anchor for the future growth of the UASTP. The aim of all three is to transform a forgotten landscape into a community amenity while preserving its capacity to detain floodwaters.


25

Problem Statement and Significance Stormwater detention basins within the Tucson basin and beyond are often engineered, constructed and maintained for a single purpose: safe control of urban floodwaters during storms of high magnitude. However, the simple “accepted design practices” of designers of these basins are not robust enough to include other programmatic goals, including active and passive recreation, aquifer recharge, wildlife habitat, mosquito control, off-site irrigation, water treatment, and environmental education within an urban setting (Haan 1994, p.4). While under-utilized, designs providing for these other uses are not appropriate in each case due to a variety of physical, biological, and social factors. While certain guides do exist for the design of stormwater detention basins from an engineering perspective (Haan 1994; Mays 2001,) a landscape architecture perspective (Strom 1998,) and that of a home-owner (Lancaster 2008, a, b,) there is a lack of “state-of-the-art” guidance for the multi-purpose design of detention basins from the scale of the neighborhood to the regional detention basin. The Pima County-owned and operated Kolb Road Detention Basin in southeast Tucson is an example of a regional detention basin that was built solely for flood control and conveyance in the early 1980s. In the time since, little further development has occurred in the upstream watershed, though sparse to lush xeroriparian vegetation has reestablished within the basin and in the diversion areas outside of the basin. Surrounding parcels have recently been partially designed to include a public greenway, golf course, open space, hotels, conference center, fire station, and park and ride. There is an opportunity to immediately restore approximately 17 acres of xeroriparian habitat in the basin and to plan for the establishment of further habitat, recreational design, and aesthetic form as the upstream watershed is developed.

Goals There were two major goals of this research. First is the development of design guidelines for the construction of private and public retrofitted and newly designed multiple use urban detention basins from the scale of the neighborhood or commercial complex to the regional detention basin. These guidelines include a categorized graphic design typology of solutions. Second is the development of a master plan for a three-phased retrofit design of the Kolb Road Basin, including a 17-acre restored xeroriparian habitat. Design guidelines and master plan were expanded in scope beyond riparian habitat mitigation, of primary interest to PCRFCD, to include the programming elements of passive recreation and aesthetics, as well as connections with adjacent development parcels. The results of this study will illuminate opportunities for public-private and inter-agency partnerships to accomplish disparate goals, and provide design guidelines for combined-use detention basins. Using this study as an example and taking advantage of similar overlooked opportunities, southwestern U.S. cities will be able to save money while providing beautiful, local outdoor destinations for their urban constituents. To begin, literature regarding design of the most common functions of stormwater infrastructure, as well as the design of business parks, has been summarized to introduce the reader to some of the major considerations inherent in combined-use detention basin design. Following this, a series of questions regarding the policy setting of combined-use stormwater design are described. These were posed to leading designers and regulators of nine major southwestern U.S. arid and semi-arid metropolitan areas. The answers to these questions are then summarized, along with a brief description of the environmental setting


26 of each of these areas, and case study designs within them that were visited by the researcher. Design guidelines for riparian habitat within detention basins of Pima County, with consideration for other uses, follows this. These have been organized into twelve sections that describe the design of a particular component of a typical development’s drainage infrastructure, through an in-depth text description, and enumerated and titled subsections of major design considerations illustrated by figures of typical dimensional relationships and photos of exemplary case studies. Each section also contains a box entitled “Key Questions for Design Decision” which can be used by designers to get a quick overview of recommended design approach for the particular component. Another box, entitled “Permitting, Maintenance, Monitoring,” is intended to serve as a similarly streamlined summary of use for regulators and maintenance professionals of these systems. Finally, “Additional Resources” recommends a few of the best print or online sources of information that be consulted by the designer to learn more about a particular component’s design. The following sections include a site analysis of the Kolb Road Basin and two phases of design imagery for the site. The “Future Directions” section will describe, in text, a potential third phase of design of adjacent parcels of the UASTP. Finally, concluding remarks summarize the findings of this research and recommend a policy approach that Pima County can follow to encourage future combined-use stormwater infrastructure design.


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literature review


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Floodplains In the arid and semi-arid southwestern U.S., the majority of rains occur in infrequent events that turn dry washes into high-energy, inundated flood channels. In upper elevations at the base of the ranges, the scouring action of these floodwaters, over millennia, has created deeply-dissected canyons of a 4% grade or greater, in which waters pass through erosion-resistant hard-rock intrusions that cause upstream pooling areas, and through less-durable soils in which flow passes less violently through riffles. The hydraulic energy of streams of this type is dissipated by a combination of the drop from these “step pools,” and through channel roughness from both organic and inorganic material. However, most urban development in the southwestern U.S. has occurred within gently-sloping (4% or lower) alluvial plains of the valleys between mountain ranges. Storm-event flows through this more erosive material have carved more meandering drainages (Zeedyk and Clothier 2009). A floodplain can be defined as “a naturally occurring stream-side feature (created by the river) where the river safely spills excess flow during flood events” (Zeedyk and Clothier 2009; figure 8.1.2). Floodplains of water flow are alternately affected by the opposite forces of erosion (floodplain soil loss) and deposition (floodplain soil gain.) These forces, respectively, increase or decrease the amount of soil suspended in the flow. Conditions promoting erosion, in general, occur where high-energy, turbid flow of sediment poor water is directed towards, and scours from, a mass of floodplain soil. Alternately, deposition tends to occur when water flows slow down, flatten out, and are directed away from high-elevation land masses. An additional factor affecting this flow is the complexity and resultant roughness coefficient of the river bottom. Vegetation on the margins of stream-flow channels is usually limited to annual growth that can successfully colonize the available ecological niche between major storm-events or can withstand the high flow velocities during these events. When these events occur, however, plant growth and large-grain cobbles within the channel create turbid, complex flow, resulting in the formation of braided streams, point bars from deposited sediment, and sinuous, back and forth flow. These forces can cause stream flow to “hydraulically jump” from the flow channel onto adjacent floodplains that are typically vegetated with woody tree and shrub growth that further slows down the velocity of storm-flows. In urban areas, the design of constructed stormwater channels typically prohibits the growth of woody plant material because it increases roughness coefficient of the stream, in turn increasing the risk that conveyed stormwater will “jump” the banks of the channel and cause damage to adjacent property (Phillips and Tadayon 2007). In this case, the energy of these stormwaters is dissipated at detention basins along their length, or not at all. However, floodplains of a “rough” nature, when preserved or designed, can continue to dissipate the energy of floodwaters in-stream, reducing the risk of danger from high-energy flows further downstream in urban areas. They can also continue to provide habitat function, which will be addressed further in the following section. Functional floodplains exhibiting these forces exist along stable meandering rivers and streams less steep than 4% that have not been or are not presently adversely affected by anthropogenic forces such as cattle grazing, urbanization, or channelization (Zeedyk and Clothier 2009; Brown, 1994).

Riparian Habitat Soils are hydrated, in one way or another, by rainfall. The upper zone of a soil profile is hydrated when rain is falling directly onto it or when standing or running water is located immediately above it.


29 Riparian biotic communities are those lands, in drainage ways and adjacent floodplains, whose soils are hydrated for longer periods of time than adjacent lands due to prolonged submergence from channelized flow, dispersed flow, or ponding of runoff from adjacent lands (Brown 1994). Another factor that extends this soil saturation is the presence of highly permeable soils which can retain much more water in a short duration than soils with lesser pore-space. This former soil type results from the settlement of heavy, coarse-grained sands, gravels, and cobbles at low-energy riffles, point-bars, or channel banks, depending upon the stream morphology, while finer-grained silt is carried further downstream, remaining in suspension. As a result of this increased availability of soil moisture, vegetation within riparian areas is often denser and taller than adjacent uplands (PCRFCD 2008). The cover and seed source provided by this concentration of botanical diversity and abundance, as well as the linear, networked connectivity of these systems across vast deserts, make these biotic communities particularly good habitat for a diverse array of both invertebrate and vertebrate animals disproportionate to their limited geographic extent (Brown 1994). Throughout the Sonoran desert and the semi-arid grasslands of the Southwestern U.S. and Northwestern Mexico, there exists a range of riparian and wetland ecosystem types. While these riparian communities were already rare in the arid and semi-arid landscape prior to the establishment of agricultural, industrial, and residential land uses, they have increasingly disappeared under the pressures of agricultural clearing, water diversion, flood control and water storage, lowering of groundwater tables, and the cutting of wood for fuel (Brown 1994; Zeedyk and Clothier 2009). Riparian communities are generally described as being hydroriparian, mesoriparian, or xeroriparian. The primary difference in environmental condition between these ecosystem types is the proximity of the groundwater table to the soil surface (Debano and Schmidt 2004). Hydroriparian systems are characterized by perennial above-ground water that allows for emergent, riparian-obligate or -preferential wetland species such as cattail (Typha,) rush (Juncus,) and bulrush (Scirpus) to grow in the understory, and riparian obligate tree species such as cottonwood (Populus fremontii) and willow (Salix) from the understory to canopy (PCRFCD 2008). Essentially, the roots of plants in hydroriparian areas must always be in contact with a saturated soil. Mesoriparian species are characterized by a subterranean water table located at a depth close enough that the roots of preferential and xeric tree species (Fraxinis, Celtis pallida; Prosopis velutina, Olneya tesota, Acacia constricta) are able to reach it. For example, in order for velvet mesquite (Prosopis velutina) to reach full maturity height (up to 15 meters,) their roots, which can extend up to 14 m (~45’) below the surface, must be able to reach groundwater (Brown 1994; Judd et al 1971). Xeroriparian habitat is primarily characterized by limited, ephemeral water supply above ground and throughout the rooting zone, which is more often dry than saturated. In Pima County, xeroriparian habitat is further subdivided into classes A, B, C, and D based upon density and plant associations (PCRFCD 2008). Within the metropolitan areas covered in this study, a range of these biotic communities exist. Using the terminology of both Brown’s “Biotic Communities, Southwestern United States and Northwestern Mexico,” and the classes of riparian communities defined by Pima County Riparian ordinance, these include, from most to least mesic, hydroriparian ecosystems [Californian maritime and interior marshlands (Los Angeles, Orange County, Riverside, Davis/Sacramento, San Jose, CA,) Montane, plains, and Great Basin marshlands (Las Vegas, NV; Denver/Boulder, CO,) Plains and Great Basin riparian wetlands (Las Vegas, NV; Denver/Boulder, CO) Sonoran and Sinaloan interior marshlands and submergent communities (Tucson, Phoenix, AZ; Las Vegas, NV,)] mesoriparian ecosystems [Sonoran riparian deciduous forest and woodlands (Tucson, Phoenix, AZ, Las Vegas, NV,) Warm-temperate riparian scrublands (Las Vegas, NV; ) Sonoran riparian scrubland (Tucson, Phoenix, AZ;)] and xeroriparian ecosystems [Warmtemperate interior strands (Tucson, AZ,) and Sonoran interior strands (Tucson, Phoenix, AZ.)] In Pima County, as discussed above, most development occurs along alluvial plains that are dissected


30 by perennial, intermittent, and ephemeral streams. Due to river channelization, and receded groundwater tables, the most typical biotic communities within these are mesoriparian or xeroriparian in nature (Sonoran riparian deciduous forest and woodlands, Sonoran riparian scrubland, Warm-temperate interior strands and Sonoran interior strands). In the drainages of small watersheds, at the transition from sheet flow to channelization, and within larger drainages in which the groundwater table is far removed from the surface, Sonoran riparian scrubland consisting of sporadic woody tree and shrub growth, is most common. Leguminous trees typically provide the most canopy cover, thorny, impenetrable refuge from predation, nesting/roosting sites, and nutritious seed, and include catclaw acacia (Acacia greggii,) whitethorn acacia (Acacia constricta,) blue palo verde (Parkinsonia floridum,) baby bonnets (Coursetia glandulosa,) the occasional ironwood (Olneya tesota,) and the highly facultative velvet mesquite (Prosopis velutina.) Four-wing saltbush (Atriplex canescens,) and quailbush (Atriplex lentiformes,) also provide dense cover and abundant seed, and are particularly good habitat for quail. Seep willow (Baccharis salicifolia,) the ubiquitous, and sometimes weedy desert broom (Baccharis sarothroides,) desert hackberry (Celtis pallida,) creosote bush (Larrea tridentata,) wolfberry (Lycium, multiple species,) burrobrush (Hymenoclea monogyra,) and gray thorn (Ziziphus obtusifolia,) round out the typical shrubby growth within these systems (Bowers 1993; Brown 1994). Riparian strands are influenced by pronounced “fluctuations in water level” over the course of a year. Along the banks of channels with above-ground flow, or within the channel during periods of drought, plant communities are dominated by herbaceous annual species and composites, including sacred datura (Datura meteloides,) seep willow (Baccharis salicifolia,) desert broom (Baccharis sarothroides,) sunflower (Helianthus, multiple species,) and cocklebur (Xanthium strumarium.) Along perennial streams, marshlands and submergent communities fringed by dense growth of emergent vegetation such as Typha, Juncus, and Scirpus can be found, though most of these areas are under protection of preserve status by the county or federal government, and are unlikely sites for development. Within the zone adjacent to and elevated from the banks of perennial and intermittent channels, also known as the overbank area, both Sonoran riparian scrubland and Sonoran riparian deciduous forest and woodlands are common. Species composition of the latter is very similar to the former, though it also includes riparian obligate species, including Fremont cottonwood (Populus fremontii,) Goodding’s willow (Salix gooddingii.) In higher elevation areas of the county, velvet ash (Fraxinus pennsylvanica var. velutina,) Mexican elder (Sambucus mexicana,) netleaf hackberry (Celtis reticulata,) Arizona sycamore (Platanus wrightii,) and Arizona walnut (Juglans major,) may be encountered. Desert grasses are another important component of Sonoran and Chihuahuan riparian ecosystems that help support abundant insect, bird, and grazing animal populations. Within periodically inundated areas of cienegas, or headwater marshlands generally located in the drainages of semi-desert grasslands, sacaton (Sporobolus wrightii) forms dense thickets that provide excellent habitat for reptiles, amphibians, and mammals. Along stream riffles, bullgrass (Muhlenbergia emersleyi,) and deergrass (Muhlenbergia rigens) are common. In lower elevations, desert grasses such as bush muhly (Muhlenbergia porteri,) and big galleta (Hilaria rigida,) are commonly found along dry desert washes. These plant communities also often include cane beardgrass (Bothriocloa barbinodis,) sideoats grama (Bouteloua curtipendula,) tobosa grass (Hilaria mutica,) green sprangletop (Leptochloa dubia,) spike dropseed (Sporobolus contractus,) sand dropseed (Sporobolus cryptandrus). Other non-woody forbs and small shrubs that are common in the understory of these systems include triangle-leaf bursage (Ambrosia deltoidea,) canyon ragweed (Ambrosia ambrosiodes,) desert marigold (Baileya multiradiata,) bricklebush (Brickellia, multiple species,) desert senna (Cassia covesii,) blue dicks (Dichelostemma pulchellum,) dogweed (Dyssodia pentachaeta,) brittlebush (Encelia farinosa,) Goodding’s verbena


31 (Glandularia gooddingii,) tansyleaf spine aster (Machaeracantha tanacetafolia,) Cooper’s paperflower (Psilostrophe tagetina,) desert globemallow (Sphaeralcea ambigua,) and desert zinnia (Zinnia grandiflora.) Many of these plants provide additional forage and cover to large grazing mammals, small mammals, insects, reptiles, and amphibians.

Drainage, Flood Control, andWater Quality Management Urbanization, or the conversion of wildlands/greenfields to urban or suburban land cover, dramatically decreases the water infiltration capacity of landscapes. In essence, the replacement of porous soils composed of some mixture or clay, silt, sand, and loam with impervious materials such as building rooftops, asphalt, concrete, and fine-particled rock mulch results in increased water runoff that concentrates into the existing system of natural drainages, often resulting in severe downstream flooding that imperils homes, lives and infrastructure. In addition, these urban waters also contain high levels of pollutants. In response to these challenges, most metropolitan areas of the U.S. have organized flood control districts to work with the Army Corps of Engineers, municipal governments, and private-sector civil engineers to design stormwater drainage channels and retention/detention basins to contain 100-year floodwaters within engineered floodplains inside of which no habitable construction is allowed. Detention basins temporarily detain excessive urban floodwaters in one spot along a drainage, and outlet only a rate of flow (Q) equal to the cubic feet per second that passed through that point prior to urbanization, or some other calculated amount. Many detention basins and armored, channelized washes were designed and built in the 1970s and 1980s in response to rapid urbanization and a series of catastrophic flood events, but most often do not serve other functions such as wildlife habitat, aesthetic appeal, or recreational use. Erosion of steep, newly-cut slopes of detention basins often pose maintenance issues to access roads. Arizona Department of Transportation drainage design guidelines recommend incorporating “crown ditches...installed at the tops of slopes to divert sheet flow from adjacent undisturbed slopes.� In order to improve or remediate the quality of stormwater passing through the system, a system of filters, weirs, and leach fields can be implemented to slow the water and promote the settling of solids. However, the slowing process of water remediation is counter to the primary goal, conveyance (Bergue 2000). In order to serve both purposes, a more intricate systems of collapsible detention gates or dams can be employed to allow for water to be solely diverted into a linear system of treatment basins, grass strips, filters, and intensive chemical treatment in times of low flow, while changing to a system of diverging flows in high-flow events, when, once a maximum capacity has been met within the remediation diverted system, the rest overflows a detention gate and proceeds, untreated, downstream (DeCook 1983).

Water-harvesting Concentrating on the tops of watersheds, this principle encourages the recontouring of pervious surfaces within an urban matrix in order to temporarily detain and infiltrate runoff from impervious surfaces before it reaches the municipal stormwater system. The resultant vegetation growth within these saturated soils can support residential energy efficiency, wildlife habitat, recreational comfort and edible landscapes (City of Tucson 2005; Lancaster 2008, a, b). Water harvesting techniques, while limited in their applicability to large-scale, lot-bottom and regional detention basins because of their focus on small amounts


32 of runoff at the private residence scale, are extremely valuable for the development of fine-scale components of the design guidelines, including street-side basins, micro-basins, and planting recommendations. Principles, history, and design examples and components of water-harvesting basins and earthworks will be discussed in greater detail in the “Case study” and “Design Guidelines” sections below.

Vector-borne Disease and Mosquito Control In the year 2003, the Centers for Disease Control received 9862 reports of human cases of WestNile virus, making it the most widespread vector-borne disease in the United States (Gambarini 2004). This formerly tropical disease causes mild to severe illness in humans and illness or death in mammals and birds. While this disease has only been widely observed in North America within this decade, the extent to which it has influenced public and municipal attitudes towards constructed wetlands, retention basins, and other urban stormwater basins has been great. Within the Tucson basin, the Sweetwater Preserve constructed wetland project has been forced to adopt extremely expensive mitigation measures in order to control mosquito breeding. This unexpected cost has called the economic validity of treatment wetlands into question, and is likely negatively influencing the further construction of these types of facilities in the urban matrix (Glenn 2008). Willott (2003) makes the case that wetlands have justifiably been eliminated from urban areas since the 1800s, given the correlation between their disappearance and the reduction of malaria and other mosquito-borne illnesses in the time since. While she admits that other factors, including better nutrition and advances in health care, have also likely contributed to this improving public health condition, she maintains that, by adopting a risk tolerance method of government, mosquito-breeding habitat should be contained to ex-urban wilderness areas that are difficult to explore and are therefore avoided by most people. In other words, mosquito habitat only belongs in these “risk-averse” and should be avoided in urban areas. While much public, scientific, and regulatory attention has been placed on controlling mosquito habitat in municipal facilities whose total management schemes can be quickly altered by government intervention, much, and perhaps most of the problem is diffusely rooted across the city in micro-pool environments, including plant trays, wheelbarrows, tires, and bird baths (City of Tucson 2005). Prior to the emergence of West-Nile virus, a team of Arizona public health researchers studied the presence of mosquito species Aedes aegypti, a tropical, domestic carrier of yellow and dengue fevers, in five different zones of Tucson (north, east, south, west, and central) and determined that 49.5% of trapped mosquitoes were found in Central Tucson (Fink et al 1998). This zone includes neither the Sweetwater wetland nor any of the large-scale county-maintained stormwater retention or detention basins. Multiple studies have reviewed the relationship between physical structure of stormwater detention basins and proprietary flood control features and mosquito production and have determined two consistent characteristics that create shallow, standing water: siltification and subsequent long-term micro-pooling within basins immediately down-stream of culvert outlet structures (often within a zone of rip-rap,) and buildup of thick vegetation within basins as a result of irregular maintenance (Gambarini 2004; Knight 2003; Metzger 2002). Some simple design recommendations have resulted from these studies, including a minimum slope for the side of basins (4:1,) a recommendation of constant grade within basin bottoms, use of water motion devices such as fountains, creation of deep-water pockets within basins in order to support aquatic predator populations, and choice of emergent plant species that allow for aquatic and airborne predatory access to juvenile mosquitoes. The City of Tucson’s Water Harvesting Guidance Manual recommends that all water-harvesting earthworks be constructed to allow for complete infiltration within


33 12 hours, less than the life cycle of a mosquito (City of Tucson 2005). Synthesizing the recommendations above with the goal of creating mitigated riparian habitat within detention basins, we are left with a seeming contradiction between the creation of steep slopes to prevent breeding grounds and the creation of pooling areas for infiltration. Hydro-riparian pooling areas whose goal is the growth of emergent vegetation, by nature, will breed mosquitoes, as is the case in semi-arid region water quality treatment wetlands, where the groundwater table is close to the surface. However, with the proper design of sediment traps within basins, and open-channel design promoting the deposition of suspended solids in low-energy areas of flow, clay-sealing of pooling areas, and subsequent long-term pooling, can be avoided, but not completely prevented. Therefore, the public-health cost of increased mosquito vectors should be balanced against the environmental services (water quality treatment and wildlife habitat) and recreational, educational, and aesthetic benefits of such systems as they are being sited and designed. In some metropolitan areas, as will be discussed in the “case studies� section below, the benefits of these systems outweigh the risks. For example, as soon as cases of West Nile Virus rose to particularly high levels in the Boulder area, and public sentiment was very wary of its spread, University grounds crews worked to cut vegetation close to the ground, and eliminate areas of standing water near residences (University of Colorado-Boulder 2003). However, fears of the virus did not result in the draining of natural or constructed pools and lakes, such as those at the University of Colorado-Boulder Research Park. The environmental and quality of life services provided by greenway wetlands is one of the characteristics of the city that makes it unique and a desirable place to live, and following the initial hysteria surrounding the disease, these benefits were deemed too valuable to eliminate in order to create a disease-free city (Love 2009). The recommendation made by Gambarini (2004,) Knight (2003,) and Metzger (2002,) should be taken with a grain of salt, as they were published in the peak of these fears following the arrival of the disease, and fail to recognize that detention basins within areas where the groundwater table is far removed from the surface, as opposed to the considered areas of long-term pooling such as lakes and ponds, quickly drain both through infiltration and outlet discharge. As such, 4:1 or steeper banks are not recommended for Pima County, as this would either create erosion problems, or necessitate costly soil-retaining walls, and would prevent recreational accessibility to the basin bottoms. However, micro-basin pooling areas should still be designed in a way that drains water from them within 24-48 hours. In the absence of infiltration capacity-increasing soil amendments or subsurface constructed improvements, microbasin depths should be restricted to 6 inches or shallower. When these infiltration capacity-increasing improvements are in place, designed depths can increase, subject to the review of the District.

Combined Use: Recreation, Aesthetics, and Environmental Services

Through the leadership of the Army Corps, flood control districts, and designers, metropolitan areas of the southwestern U.S. have seen varying degrees of success either retrofitting existing channels and basins, or designing new systems in order to incorporate recreational use, wildlife habitat, off-site irrigation use, and aesthetic design. Success is generally characterized by flexibility and leadership in partnering between municipal agencies charged with separate public functions. In order for residential subdivision developers to consider incorporating riparian habitat into their


34 communities, it must be proven that resultant home sale values and sale frequency rise. A technique called hedonic analysis compares sale prices of homes within close proximity to amenities such as riparian resources to those not as close. In the Chagrin River Watershed of Ohio, it was found that those homes with riparian setbacks, or restricted portions of properties in which development could not occur under normal conditions, sold for approximately the same amount as those without. It was postulated that the degree to which the environmentally sensitive riparian habitats were considered amenities was evenly outweighed by the dis-amenity of tight building restrictions within the riparian setback (Mikelbank 2000). However, in Tucson, AZ, within a study area northeast of North Swan Road and Broadway Boulevard, homebuyers were shown to be willing to pay significantly more for homes in close proximity to “woody-plant species-rich washes,” washes that supported “tall leafy groundwater-dependent trees,” and areas where a riparian habitat was connected, without physical obstruction, to adjacent upland areas, than those homes without those characteristics. However, home prices were significantly lower for homes in close proximity to “densely vegetated habitats” (Bark 2009). The implications of this research leave much to be answered regarding homeowner’s perception of riparian areas. Taken together, these results indicate that while intact, diverse riparian areas including hydro-/mesoriparian tree species are valued, homogenous, overgrown areas, such as those with weeds or monocultures of a particular species, are seen as “disamenities.” Perhaps this is because dense, thorny meso-/xeroriparian areas are difficult to walk through and enjoy in comparison to cottonwood gallery forests, and therefore become “forgotten” landscapes only inhabited by children or the homeless. Further research comparing leafy riparian areas to meso-/xeroriparian areas in which easily accessible recreational use has been designed may reveal more similar preferences of homebuyers. Many recreational uses are possible in stormwater retention and detention basins. These include on-site active recreational fields (baseball, soccer, etc.,) irrigated by flooding or sprinklers, passive recreational amenities such as trails and ramadas shaded by irrigated trees, and surrounded with groundwater-supported and xeric plants, and fishing within retention ponds. In no case should retention basin uses include swimming or wading due to the pollution of the stormwaters (Bergue 2000). Similarly, infiltration or other filtration areas of detention basins, as will be explained below, should be removed from recreational programming. In the Tucson, Phoenix, Denver/Boulder, and other metropolitan areas, greenways or “linear parks” along drainages have become a popular park form that significantly increases the perimeter of a region’s park system, decreasing distance to the system from any point in the urban area, and allowing for a low or no-traffic alternative for bicycle and pedestrian travel through the city, adjacent to aesthetically-pleasing riparian ecosystems.

Business Parks As the Kolb Road Basin is surrounded by lands owned by the University of Arizona Science and Technology Park (UASTP,) synergistic benefit and integration of this amenity into future research parks designs will be considered. The goals of UASTP, like many university research parks, are to attract multiple high-tech research and development (R&D) business tenants via the creation of a flexible, pleasant, “office-style” research community benefiting from strong academic relationships with the university and other similar companies, facilities appropriate for high-tech industry and a generally conducive business environment. Parks of this type are most often located outside of established town centers, where land is cheap and without infrastructural restrictions, and, in many cases throughout the U.S. and France, located within close proximity to research universities and offer comparable campus-style environments.


35 In general, the office buildings of these parks are very deep, allowing for myriad office and industrial arrangements (Burt 1991). While the thought of the traditional business park often brings to mind large industrial or office buildings, expansive parking lots, and vast, gratuitous swaths of turf and water, there is a trend afoot to bring more useful amenities to these facilities in order to integrate them into their surrounding communities. While many of the business parks built in the 1970s by large corporations such as IBM and General Motors, relied upon the personal car, they lacked a sense of place. More recent business parks seem to be bucking this trend. More light manufacturing and warehouse space, as well as “flex space” or work space which can be adapted to multiple uses depending upon the needs of the tenants have complemented the primary office buildings. Parking areas (from 4-6 spaces per 200-square-feet of office space), as primary entryways through which all employees and visitors enter, are being designed to cohesively integrate with the park-like landscapes surrounding them, and public transportation options are being incorporated in order to give employees transportation options beyond the personal automobile (Freij 2001). Hacienda Business Park in Pleasanton, CA, outside of San Francisco, for example, as of 1995, offered free local bus service, a shuttle bus to Bay Area Rapid Transit (BART) stations, and a program to match car-poolers (Pennington 1995). Investment in quality-of-life amenities is also seen as a necessary step in order to attract a skilled workforce. Factors such as opportunities for outdoor recreation and a rich cultural life can help create the sense of place that attracts the brightest minds. The Irvine Spectrum business park in Irvine, for instance, boasts a 700,000square-foot destination entertainment center that includes a multiplex cinema and restaurants (Freij 2001). Interlocken, in Broomfield, Colorado, has office buildings and a conference center nestled among the links of a 27-hole golf course. A survey conducted in 1995 by Conway Data, found that, individually, meeting and conference rooms, a sandwich shop, a full-service restaurant, and a jogging trail were found in 41-48% of office parks, including science and mixed-use parks, and approximately 25% of office parks contained a hotel, day-care center, sports fitness center, printing center, residential housing, and shopping centers (Pennington 1995). In essence, instead of accepting their place as a place of work on the edge of town, these office parks have become the town (Mazullo 2001). In recognition of their generation of high-quality jobs, some municipalities have become directly involved in the formation of business parks and have provided tax incentives or financing assistance to developers in order to encourage the location of businesses to these parks (Freij 2001). Beyond financial incentives, one can imagine that coordinated planning and design efforts for adjacent public facilities such as libraries, waterways, parks, would also be a way in which municipalities could help “kick-start” economic development within the park by providing for an environmental infrastructure and community character upon which businesses could be located. The information age has also significantly changed the concept of the business park. For both those businesses producing tangible goods via industrial manufacturing, and for those providing technical, financial, and other services, quick speed of delivery is necessary for successful enterprise. Those businesses producing tangible goods require nearby transportation networks such as rail, airports, and highways, and proximity to primary markets. As the primary venture of university research parks is R&D, access to high-tech infrastructure such as cable and fiber-optic lines is essential, and some parks now include onsite educational and training facilities. In addition, the prevalent uses of wireless devices such as laptop computers, cell phones, and blackberries for allows for some work tasks to be extended to outdoor gathering areas as a refreshing alternative to indoor office life (Freij 2001). In the late ‘90s, posed with a potential relocation of cable-television testing firm Acterna to Research Triangle Park, NC, City of Indianapolis planners informally introduced a master-plan for the


36 InTech business park to Acterna representatives. Acterna was greatly impressed, particularly, by design elements such as basketball courts, a picnic area, day-care facilities, 2.5 miles of walking paths connecting to adjacent public parks, 13 acres of waterways, shops, a bank, and restaurants, and soon thereafter, became the first tenant (Freij 2001; Mazullo 2001). Turning stormwater and natural spaces into amenities, Ratio Architects sited park buildings around focal-point storm-water wetland ponds and an eight-acre woodland preserve, and included ecoswales within the parking areas as point-source pollution cleansers and aesthetically-pleasing planting areas (Freij 2001). Legacy Business Park, developed by Electronic Data Systems, is unique in that, following the establishment of corporate clients on the prime parcels, and the resultant employment of 36,000 people, development shifted to a centralized town center. Beginning with a 404-room Doubletree hotel and conference center, the town center master plan, developed using a mixed-use, new urbanist model by RKTL Associates and Duany-Plater Zyberk, has now seen the construction of 384 loft apartments, 20 small ground-level retailers, and top-floor office space; future phases of development are slated to include a Dallas Area Rapid Transit Center, and at least 2,100 more residences (Freij 2001; Mazullo 2001). Legacy, at 2,665 acres, with one major corporate tenant, and a destination hotel, is in many ways comparable to the goals of UASTP.


37

policy setting


38 In order to understand regional patterns of design application beyond the professional literature, one must compare the political differences between regions of consideration. In the case of multiple-use detention basin design, Flood Control District detention and retention basin design manuals and other associated policies both within the Districts and without, offer revealing differences both in terms of degree of detail of consideration, recognition of the need to partner with other agencies and ease of “off-the-shelf ” application by designers and regulators. Beyond analysis of written policy, institutional culture influences design reality. In order to better understand the degree to which the combined-use design environment is influenced by the nature of collaboration between Flood Control Districts and other agencies, regulators and designers were interviewed. The questions posed within these interviews are summarized in the following paragraphs. In order to analyze interview responses, this document will borrow a metaphor from property rights literature: the bundle of rights, or, in this case, the bundle of uses. Within property rights law, it is useful to think of the rights of a given piece of land, including the water rights, the sub-surface development rights, the airspace, the surface development rights, utility easements, etc., as a bundle of sticks, with each stick being an individual right (Ostrom 1990; McCay and Acheson 1996). It follows that for an individual piece of land, multiple individuals can own sticks (rights) of that bundle (the sum of all property rights.) Similarly, the management and design of lands influenced by stormwater can be thought of as a bundle of sticks, or uses/functions. For the purpose of this report, these uses/functions will be limited to flood control and conveyance, stormwater quality treatment, aquifer recharge, riparian habitat, recreation, and landscape aesthetics. In general, the metropolitan case study areas can be compared in terms of the degree to which institutional flexibility of systems of governance allow for the accomplishment of integrated stormwater design and management. Whereas the Flood Control Districts of all eight metropolitan areas are charged with flood control and conveyance, some are also the primary regulators of stormwater quality treatment, riparian habitat protection, and recreational use within the floodplain, whereas, in other metropolitan areas, other agencies are responsible for these uses. Understanding how many agencies are responsible for these uses within a metropolitan area is important for understanding inherent institutional flexibility in accomplishing combined-use design. Therefore, the first question of importance regarding policy setting is which agencies control which uses. A particularly important sub-question is whether the same agency that controls flood control and conveyance also regulates riparian habitat. The second question of importance regarding policy setting is whether combined-use is specifically addressed within the design manual or other policy. Beyond this, it is important to know to what extent these sections of the design manual are used. A sub-question is whether the agency which controls flood control and conveyance also is charged with recreation or aesthetics in their mission statement, but simply has not developed any guidelines or standards for recreation to be considered. The third question of importance is how well, given the responses of designers within the metropolitan area, do agencies assigned with one or more rights work with other agencies assigned with other rights to accomplish combined-use stormwater systems? Responses to these questions will first be summarily organized in tables 1, 2, and 3, and, in the section entitled “Case Study Descriptive Introduction,” the metropolitan areas of this study will be further described in terms of policy characteristics (project goals, agencies involved, makeup of design team,) and environmental characteristics (average annual precipitation and temperature.) In the section entitled “Design Guidelines,” components of these case studies will be further described by water sources employed, hydraulic flow routing, biotic communities represented, and details of an aesthetic, engineering, and recreational character.


39

case studies


40

Case Study Selection Criteria In order to identify exemplary case studies of multiple-use detention basins throughout the arid and semi-arid Southwestern U.S., multiple visits to combined-use detention basin sites and offices of the companies who designed them, within eight major metropolitan areas, were undertaken in 2009 and 2010. The eight metropolitan areas chosen (Las Vegas, NV, Phoenix, AZ, Riverside, CA, Tucson, AZ, San Jose, CA, Los Angeles, CA, Denver/Boulder, CO, and Davis/Sacramento, CA) are primary or secondary cities within their respective states, and are located either within arid basins or on the high plains just prior to the rise of the Rocky Mountains. Additional sites which are referred to once within the design guidelines were also visited, but will not be described in this section. The focus of site type in all metropolitan areas was towards combined-use, lot-bottom and regional basins, as these were the ones most commonly understood by agency and design firm staff, and were most easily accessible in the limited time available to the researcher. Where possible, street-side basins and openchannel designs were also visited, particularly within the Tucson metropolitan area, where the researcher resides. Environmentally, average annual temperatures range from 50.1 degrees (Denver/Boulder) to 72.6 degrees (Phoenix,) annual precipitation (P) ranges from 4.16 inches (Las Vegas) to 15.81 inches (Denver/ Boulder.) In addition, the aquifers of some of these cities receive significant recharge from nearby snowmelt, resulting in a closer depth to groundwater, whereas the soil profile in other cities is dry to much greater depths. A simple categorization commonly used by U.S. Geological Survey is based solely on average annual precipitation: “arid lands have less than 250 millimeters (about 10 inches) of annual rainfall, and semiarid lands have a mean annual precipitation of between 250 and 500 millimeters (between about 10 and 20 inches; USGS 2006). Metropolitan areas are therefore categorized into arid (0-10 inches/year,) semi-arid (10-15 inches/year,) and semi-arid (15-20 inches/year.) By these definitions, the primary urban growth area of eastern Pima County (Tucson metropolitan area) is considered semi-arid, while less developed western Pima County (Ajo area) is considered arid (0-10 inches/year.) Arid metropolitan areas of Las Vegas and Phoenix have been considered in this study in light of climate predictions of increased aridity in southern Arizona (insert reference; Arizona Riparian Council Proceedings, 2006.) Semi-arid (15-20 inches/year) metropolitan areas of Los Angeles/Riverside, Boulder/Denver, and Davis/Sacramento were included primarily because they have been at the leading edge of combined use drainage and detention basin design. The comparative aridity of these case studies should be considered in terms of their appropriateness to designs within Pima County as the reader/designer encounters examples from them throughout the design guidelines. These environmental characteristics of case study metropolitan areas have been summarized in table 7.1. Additional characteristics including average annual temperature, proximity of groundwater table, winds, and potential evapotranspiration rate should also be considered in the design of a site. In addition to environmental characteristics, the case study metropolitan areas have been characterized by the frequency of particular uses found within detention basins, and are summarized in table 7.2.


41 Metropolitan Area

Average Annual Precipitation (P, inches/yr.)

USGS (modified) Aridity Average Annual TemCategories perature (째F)

Las Vegas, NV

4.16

Arid (0-10 inches)

67.1

Phoenix, AZ

7.7

Arid (0-10 inches)

72.6

Riverside, CA

10.2

66.0

Tucson, AZ

12.17

Orange County, CA

13.1

San Jose, CA

14.66

Los Angeles, CA

15.04

Denver/Boulder, CO

15.81

Davis/Sacramento, CA

17.28-17.7

Semi-Arid (10-15 inches) Semi-Arid (10-15 inches) Semi-Arid (10-15 inches) Semi-Arid (10-15 inches) Semi-Arid (15-20 inches) Semi-Arid (15-20 inches) Semi-Arid (15-20 inches)

68.7 70 60.3 63.0 50.1 60.8-62.0

Table 7.1: Environmental characteristics of case study metropolitan areas

Metropolitan Flood Area Control and Conveyance Las Vegas, Yes NV Phoenix, AZ Yes Riverside, CA Tucson, AZ San Jose, CA Los Angeles, CA Denver/ Boulder, CO Davis/ Sacramento, CA

Water Quality Treatment Some

Aquifer Recharge

Riparian Habitat

Recreation

Landscape Aesthetics

Some

Some

Some

Some

Some

Some

Yes

None

None

None

Active, Passive Active, Passive Active

Yes

Some

Some

Most

Yes Yes

Some Some

None Some

All Some

Yes

Most

Most

All

Yes

Most

Some

All

Table 7.2: Uses demonstrated in case studies (by metropolitan area)

Active, Passive Passive Active, Passive Passive Active, Passive

Some All Some All All All Some


42

Arid (0-10 inches/year,) Metropolitan areas The arid metropolitan areas of Las Vegas, NV, and Phoenix, AZ, provide multiple examples of combined-use regional basins emphasizing active and/or passive recreation and traditional plant palettes (turf and shade trees,) or native plant palettes. Due to the limited rainfall and high potential evapotranspiration, all of the designs within these metropolitan areas either irrigated plants with municipal water sources or took advantage of urban drool emanating from the over-watered landscapes and carwashing activities of surrounding suburban areas.

LasVegas Metropolitan Area

Clark County, in which the Cities of Las Vegas and Henderson, NV are located, oversees the design and maintenance of all regional detention basins through the Clark County Regional Flood Control District. As Tim Sutko, District Environmental Mitigation Manager described, his personal philosophy of drainage design, which is reflected by many of his peers in the district, is that if he can get through a year without a single person drowning in the district’s infrastructure, he can sleep soundly as a public servant (Sutko 2009). While the District’s design manual mentions combined-use briefly, it is limited to one page and contains no graphics, illustrating their commitment to this ideal by policy. However, while the district was originally reluctant to include human use within these basins, they began to experiment, at the encouragement of suburban designers, with the incorporation of ball-fields within Desert Breeze Park (Las Vegas,) the Gowan Detention Basins (Las Vegas,) and Anthem Hills Park (Henderson.) Sutko described their process of alternative design generation by remarking that these basins would be “in an ideal world, codesigned, but in reality, back and forth with review,” portraying an iterative process between agencies and design professions with different objectives that was mostly bound by cost. All three are characterized by completely open access coupled with stern signage warning users of the flood control function and associated drowning risk of the basins. When asked about whether the District had considered any high-tech solutions for flood risk warning, such as remote controlled gate closures linked with weather data systems, Sutko expressed a high degree of reluctance, explaining that Murphy’s Law would likely find its way to cause failure in such a system, and, at the advice of County lawyers, he recommends that warning signage is the most effective and least liable solution to public safety. Incoming flows in the former and latter first inundate a grass-filled low-flow channel, while playing fields are located on adjacent, elevated terraces. The inlet and energy dissipation structure of the latter is particularly elegant, and serves as a model for how course concrete form can add to the aesthetic interest of a combined-use facility. This is likely due to strict design criteria for recreational-use within basins developed by the City of Henderson, in which the public works department is in healthy communication with their parks department (Sutko 2009). In essence, these three cases provide safe, active-recreational use to their surrounding communities, but do nothing to create and interpret riparian habitat. This is perhaps due to limited financial resources of the county’s maintenance staff, as indicated by Sutko’s comment that “passive operation” was the goal of District infrastructure so as to make it fail-safe. In the absence of other funding sources, this goal is understandable. Expanding funding and maintenance sources, perhaps encouraged by the experimental success of these three basins, the district engaged with the Southern Nevada Water Authority, City of Las Vegas, the


43 Las Vegas Valley Water District, and other municipal entities, in the retrofit design of an existing regional detention basin, first completed in 1989, located just a few miles to the north-east of “The Strip.” The resultant Springs Preserve, designed by Luchessi, Galati, Inc. and Natural Systems International, is a highly educational complex focusing upon water resources. It is one of the best examples encountered within the case study review of retrofitted regional detention basin design that incorporates xero-, meso-, and hydroriparian restoration, and passive recreational paths, along a series of pools and riffles fed by filtered urban drool and diversion of low flows within storm events, while protecting these improvements from damage in large events via a high-flow bypass channel. In extremely large events where incoming flow rate exceeds the outlet flow rate, contained water backs up to inundate the mitigated areas in a lowenergy capacity. Most importantly, the whole system is within view of the multi-story Nevada State History Museum, which focuses on the environmental history of the Las Vegas Valley’s water and biological resources, and in which visitors are encouraged to explore the basin in order to gain an understanding of the riparian resources associated with the Las Vegas Springs that no longer exists, and the ways in which environmental design can reintroduce them into the life of the community. Jeff Roberts, Project Manager of the overall design, and Luchessi, Galati, Inc. architect, describes the master-planning effort as being driven by the Southern Nevada Water Authority, who had access to a large funding pool from the Southern Nevada Public Lands Management Act, which directs 10% of the sale of BLM lands within the state to conservation, restoration, and outdoor recreation (USDI 2010). At the time, the Clark County Regional Flood Control District was eager to increase the capacity of the basin, which at 4’ deep, was not containing all runoff in large events, resulting in flooding on Charleston Road located downstream. Additionally, there were concerns about the contaminated nature of incoming urban drool and floodwaters in first-flush events. To address these two primary concerns, Michael Roberts, civil engineering lead of Natural Systems International, redesigned the basin to be dug 5’ deeper, and to include a device just upstream of the inlet to capture the urban drool and low flows, treat them with a sand filter, and divert them into the a series of hydro-riparian pools. These pools, which are unlined, were first supplemented with a dozen truckloads of “wash muck” from a functioning riparian area nearby. Following container planting, a drip irrigation system was used to establish the plants until such time as their root systems could reach the saturated soil profile. Recreation is directed from an interpretive overlook in to the basin along a side-slope switchback bordered by a man-made “fake-rock” outcropping, a design component that Roberts describes as highly resisted by Flood Control District staff, who, at first, preferred for the basin to remain uninhabited by visitors (Roberts 2009). From this point, approximately 6’ wide gravel pathways and modest footbridges carry the visitor past and over both hydro-, meso-, and xeroriparian biotic communities, bringing the visitor back to the top of the side-slopes with a gently-curving gravel pathway lined by caliche boulders reclaimed from the site. A compromise that was struck in order to ensure the safety of visitors is that they are only allowed in the combined-use basin when Preserve staff are present. The riparian system has been remarkably successful at providing habitat for a variety of bird species. As Jeff Roberts describes it, “the original numbers prior to the wetlands design when it was a barren flood control basin was less than 10 species of birds documented in the 30 acres and they were all raptor species. The last spring count I was informed of there is now been over 200 different species documented in the cienega/wetlands (Roberts 2010).” One final design detail of relevance is the manner in which the preserve gives thanks to the donors that made the project possible. As the visitor approaches the museum from the parking lot, they pass through an aisle of brass plaques in the form of wild animals that recognizes the governmental agencies and politicians who spearheaded the effort. The atrium of the museum, centered by a dazzling cube depicting


44 monsoonal storm condensation and rain, is flanked by metallic cattails inscribed with the names of private donors, creating the overall effect of an interior sanctum of donorship. In summary, the Las Vegas metropolitan area tells a story of an evolving relationship between a traditionally-conservative flood control district and private and public entities that have sought greater use of regional detention basins. As Pima County becomes more arid, the Las Vegas region and the combineduse basin designs existing today, and in the future, should be looked to as an example of what can be in an arid metropolis.

Phoenix Metropolitan Area The Lower Salt River Valley in central Arizona holds the Cities of Mesa, Tempe, Scottsdale, Phoenix, and Glendale, among others. Originally founded as a town of the territory of Arizona in the 1860s, Phoenix grew to become a modern metropolis throughout the 20th century. This rapid increase in impermeable surface, by the 1970s, was causing severe overbank flooding along the Salt River and other metropolitan rivers, leading to arroyo and river channelization efforts undertaken by the Army Corps of Engineers and the Maricopa County Flood Control District. One such watercourse is the Greenway Wash in north Phoenix, that, while channelized, combines a fair amount of xeroriparian vegetation, including many mature mesquites, with a parallel recreational pathway. Banks of this watercourse are armored with long stretches of visually-appealing gabion walls, and this form is carried up along the side of concrete-slip drop structure inlets at tributary drainages from neighboring residential areas. Aside from Colorado River water received via the Central Arizona Project canal, this large metropolitan area also receives much of its water from a series of reservoirs on the Salt River. The resultant damming, evaporation, and municipal water use of the Salt, by the 1990s, resulted in the disappearance of above-ground flow in the Salt River channel in the vicinity of the Mesa/Tempe boundary. In 1999, following many years of valley-wide planning for a transformative flood control, habitat, and recreation overhaul of the Salt entitled the Rio Salado Project, the City of Tempe finished construction of Tempe Town Lake, a reservoir made within the river channel with an inflatable dam, encircled by beach-parks, marinas, condominiums, and offices. The lake today receives water from both the Salt River Project Canal, flood pulses along the river, and visitors from the City of Tempe. Plantings along the Salt River levee banks, including at Tempe Town Lake, are free of five common native desert leguminous trees per the Maricopa County Flood Control District, including ironwood and mesquite, in order to avoid bank failure caused by void space left after the tree dies and it’s roots decay, though exceptions have inexplicably been made in certain cases such as the Tempe Arts Center (Kimbrell 2010). Downstream of the lake, the Salt River channel lies within the flight path of Sky Harbor Airport. In order to keep the river from pooling and attracting birds within this air-space, the river has been highly channelized through this stretch. Further downstream, however, approximately 5 miles of the river channel within the City of Phoenix has been transformed into the Rio Salado Habitat Restoration Area, via the installation of subsurface impermeable liners, and the planting of a mix of meso- and hydroriparian vegetation, including aquatic strand species along the project’s low-flow channel (City of Phoenix 2007). This park and habitat area provides a diverse and abundant bit of wild and accessible ecology to an underserved area of the city . Outside of the levees of the Salt River, most of the streetscapes and parks of residential areas outside of the urban core have a general tendency for the use of turf-grass and shade trees. However, acceptance and appreciation of modernist coarse form, xeriscape plantings, and materials such as COR-10 steel, glass, and concrete has become the norm in commercial and downtown settings, and this has begun to influence the design of residential parks as well. Two parks in the East Valley, while not detention basins, are


45 examples of this contemporary design ethic, and contain components that are of particular interest. Located adjacent to a water quality treatment plant, the Riparian Preserve at Water Ranch is a complex system of groundwater recharge ponds that have been surrounded by passive recreational amenities of a desert riparian and upland nature. The park was built on the site of a former agricultural field, and has been re-sculpted with deep depressions and promontory hills formed from the excavated soil. In general, higher activity level areas are located near the edges of the surrounding arterial roads, including parking areas and playgrounds, leaving the center of the site as undisturbed as possible for visiting and resident waterfowl and other birds, and for the peace and quiet of visitors. A perennial reservoir which serves as a fishing lake is located near one corner of the site, surrounded by concrete wharves, a pier, the overlooking Southeast Regional Library, and multi-use paths. A portion of the reservoir is pumped to the top of the highest hill, and circulated down a channel that transitions from a concrete, rock-inset stream near a trail intersection to a delta of emergent wetland vegetation on the margins of the lake. 17 “snapshots” of varying Arizona habitat types are represented and interpreted at the site, including some upland plant communities that require more water resources than are available in the valley. For these areas, such as an Upper Sonoran Desert jojoba thicket, drip irrigation extracted from the reservoir is used. The remaining seven ponds are alternately filled depending upon the availability of reclaimed water from the neighboring water treatment pond. When regional demand for reclaimed water peaks during summer months, the perennial lake is fed by the adjacent Eastern Canal of the Central Arizona Project. In order to prevent the breeding of mosquitoes both within these ponds and the perennial lake, water levels are fluctuated daily, surface- and lake-bottom-level aerators oxygenate and circulate the water, and marshy areas are regularly maintained by flushing them with water, removing weeds, and discing the accumulated finesediment crust to increase permeability (Shuler 2009). Aside from the complex water resources, this park stands out for it’s diversity of plants of both riparian and upland nature, network of recreational pathways and overlooks along which to interact with them, and educational experience of the water recharge system and associated ecology both through ecorevelatory design and signage. This project builds upon The City of Chandler’s experimental leadership within riparian habitat design to create a regional riparian park that many area residents are able to enjoy. The second park within the City of Chandler that was considered for this study is the newlycompleted Paseo Vista park. This park was constructed on the site of a decommissioned landfill that towers above the surrounding landscape of agricultural fields and suburbs. The steep side-slopes of this park are of an approximately 3:1 grade that, when visited by the researcher, had just been fine-scale graded with mini-benches and either planted with cholla, Santa Rita prickly pear, ocotillo, mesquite, or hop-bush, or hydroseeded along these slopes (which, it must be noted, are never inundated.) Also along these slopes were wide rip-rapped flow channels draining the top of the hill, that either cross-cut the slope or plunged directly down, perpendicular to the contour. In some cases, these channels were paralleled by multi-use paths and disc golf holes. Overall, the coarse form of these side-slopes produced the effect of a low-desert mountain, austere, yet powerfully gripping.


46

Semi-arid (10-15 inches/year,) metropolitan areas The metropolitan areas within this category share a similar precipitation range with eastern unincorporated Pima County. Riverside is very similar to Tucson in terms of mean annual temperature and proximity of groundwater table, and regular exposure to hot desert winds. San Jose significantly differs in all three, due to its higher latitude, low elevation and close proximity to the southernmost, marshy end of the San Francisco Bay.

Riverside, CA Metropolitan Area

An interagency agreement between the Riverside County Parks and Recreation District and Flood Control and Water Conservation District facilitates the design and maintenance of combined-use, offline detention basins. Private developers can acquire a development license with the Parks and Recreation Department to allow for recreational use within them (Anderson 2010). Two such cases were visited in this study, and both were of extremely simple grading and planting design, and contained no riparian habitat. One contained a few components that are of interest. The Vernola Family Park is a recently-constructed combined-use, offline detention basin managed by Riverside County that incorporates non-native trees, turf, and traditional active recreational uses, including a parking area, playground, picnic shelters, basketball courts, and ball-fields. Relevant components of this design include side-slope pocket plantings for container trees, and a bioswale draining the parking area.

Tucson, AZ Metropolitan Area

As the purpose of this report is to provide guidance to Pima County’s development future, historical, political, and contemporary design research of the metropolitan area of Tucson, the most significant urban area within the county, has been completed in depth in order to identify the policy setting, environmental conditions, and design environment and trends for comparison to other metropolitan areas. A retrospective look at the growth of the city reveals a community with archaic roots in the Hohokam/ Pima/O’odham continuum along the Santa Cruz River and major drainages, the establishment and fall of a Spanish presidio, and a centuries-old synthesis of Mexican cultural landscape traditions of stock grazing, diversionary agriculture, and row-houses with groundwater-extractive, modern, suburban Anglo traditions (Logan 2002; Sheridan 2006). Most of this early suburban development occurred along a traditional grid layout, an effective and efficient design response to the relatively flat valley lands with roots in both Mormon and Spanish colonial urban design, and contained wide setbacks for yards between the fronts of houses and the streets, with liberal use of exotic vegetation (City of Tucson Planning Department et al. 1994). In order to attract affluent easterners, planners and architects in the early part of the 20th century began to borrow from Californian Bungalow, Santa Fe/Pueblo, and mission revival styles, to create a distinctive Southwestern residential architectural type in the image of a romantic sense of place. As much of these affluent subdivisions were encroaching into the foothills of the Catalina Mountains, planning traditions also shifted at this time to curvilinear streets and natural drainage-ways. The prestigious and innovative


47 Colonia Solana neighborhood incorporated narrow, curvilinear streets following the gently-sloping contours of the land, adjacent to Arroyo Chico, which was preserved for drainage and as a quality-of-life amenity (figure 8.2.6). Following disastrous flooding of the Salt, Santa Cruz and Rillito rivers in the late 1970s, the Arizona State Legislature passed legislation forming county-wide flood control districts to mitigate flooding problems and regulate all future development to reduce off-site runoff (Logan 2002; PCRFCD 2010 a, b). The Pima County Flood Control district was founded in 1978, and quickly went about the work of armoring the rivers with soil cement and levees, preparing hydrology studies of the major tributary watersheds, and creating regional detention basins along them (PCRFCD 2010, b; Pima County Department of Transportation and Flood Control District 1982). In the early 1980s, Pima County Department of Transportation and Flood Control District and City of Tucson developed a “Stormwater Detention/Retention Manual” to guide and standardize the design of detention basins within private developments (Pima County Department of Transportation and Flood Control District and City of Tucson 1987). “Guidelines for the Development of Regional Multiple-Use Detention/Retention Basins in Pima County, AZ,” were prepared for the District by landscape architects Susan J. Hebel and Donald K. McGann in 1986, but were perhaps not adopted by the design community because of their emphasis on landscape architectural approaches to design, or its minimal distribution by the District, hard-to-find reference deep within the text of the “Stormwater Detention/Retention Manual,” and subsequent lack of awareness of its existence. More likely, though, these guidelines did not gain traction because few publicly-owned regional basins were built following its publication. The exception to this is the Kino Ecological Restoration Project (KERP,) a combined-use, retrofitted design of the Ajo Detention Basin, in central Tucson. The KERP system collects and treats stormwater from a large, highly-polluted urban watershed through a series of sieves and biofiltration ponds. Low-flow channels between ponds and portions of the margins of the ponds have been planted with cattail (Typha,) Fremont cottonwood (Populus fremontii,) and velvet mesquite (Prosopis velutina,) and a range of riparian shrubs in order to help treat the polluted waters through microbial action and to create an urban hydroriparian ecosystem. 28 acres of riparian habitat, while abundant, is separated from recreational use by a distance of at least 30 feet by railings that use a specific shade of light purple to indicate reclaimed water unsafe for human contact. This purple motif is carried throughout the park, including over the pedestrian bridge that parallels the flow of water to the baseball fields of the adjacent Tucson Electric Park. While this facility is commendable for its water quality treatment, off-site reclaimed water use, and creation of riparian habitat, it leaves much to be desired in terms of recreational use and appreciation of the created wetlands. Official access, as mentioned above, is limited to a paved exercise path circumventing the riparian basins at the top of the slope. Most of this pathway is located at least 100 feet from the riparian areas and is flanked by either traditional shade trees, turf, and shade structures, or creosote bush, and, by observation of the researcher, is infrequently used. The one portion of the trail that approached within approximately 30 feet of the riparian areas has poor views of the hydroriparian resources due to thick growth of mesquite and shrubby vegetation. Anecdotal evidence and presence of social trails indicate that many users of the facility disregard the “authorized personnel only” signage and barriers to entry and walk along the maintenance trails that closely approach the riparian areas. According to PCRFCD staff who were involved in the design, requirements of the U.S. Army Corps of Engineers Ecosystem Restoration Division prohibited human disturbance of riparian habitat and contact with potentially hazardous, polluted water. “Guidelines for the Development of Regional Multiple-Use Detention/Retention Basins in Pima County, AZ” were apparently not consulted by the designers, Tetra Tech, Inc (Becker 2009). Additionally, the original master plan called for a golf course to be placed in the


48 grounds between the treatment ponds and the exercise trail. This design component was later struck, which perhaps explains why this otherwise exceptional project seems to tease the visitor with far-off views of lush habitat, but never gives them a chance to experience it from within. In the 1990s, Pima County Parks and recreation department sponsored the design of many miles of linear “greenway” river-parks along the channelized stretches of the Santa Cruz and Rillito rivers, providing a natural resource-focused, passive-recreational, urban alternative to traditional turf and shade tree parks, and improving bicycle circulation throughout the city. In 2006, the City of Tucson conducted a comparative study of park system characteristics of six other southwestern U.S. cities and found that Tucson contained the lowest number of miles of trails at zero. In response, 103 miles of trail were planned for purchase and designed for linkages with 31 miles of existing Pima County River Trails, including a River Park Pathway on Julian Wash (City of Tucson 2006). Beginning in the late 80s and continuing to the present, community activists and politicians such as David Yetman, water-harvesting proponent Brad Lancaster, and the Watershed Management Group, and residential designers of CoHousing communities and the Civano neighborhood, have promoted a Tucson design ethic of water conservation, energy efficiency, sensitive riparian habitat protection, and integrated design. In collaborative response, the planning agencies of incorporated cities have adopted a variety of policy changes. The Pima County Riparian Habitat Protection Ordinance requires all new developments within unincorporated Pima County to either preserve or mitigate for the destruction of site riparian habitat through the restoration of riparian habitat either on-site or off-site. From 1994 until the present, the District has developed “Regulated Riparian Habitat Mitigation Standards and Implementation Guidelines,” through contract with landscape architectural firms McGann and Associates, Inc., and, more recently, Novak Environmental, Inc., the latter of whom served as a primary mentor in the preparation of this thesis report (PCRFCD 2010). This report, among other topics, describes the Ordinance in detail, guides the developer through the site analysis and permitting process for riparian disturbance, and gives general recommendations on plant and irrigation system installation methods, monitoring protocol, and plant palettes, but provides little guidance on the use of passive water-harvesting techniques and other design components specifically oriented to the mitigation of riparian habitat within detention basins. The Sonoran Desert Conservation Plan is an interagency (municipal, state and federal,) regional master-plan that has identified sensitive habitat patches and corridors for protection, directed urban growth to the least sensitive areas (Pima County Administrator’s Office 2010). This plan has improved the Riparian Ordinance, as well, as riparian areas of Pima County were better located through improved remote and field analysis techniques. Another important aspect of this ethic is the inclusion of rain/stormwater-harvesting basins and earthworks within individual residential parcels in order to prevent individual lot runoff, enhance the quality of residential life, and recharge the aquifer (City of Tucson 2005; Lancaster 2008 a, b,) including, most notably, the City of Tucson’s commercial rainwater-harvesting ordinance of 2010, which will require that half of the landscape water budget of all new commercial developments come from harvested rainwater (City of Tucson 2010). Additionally, the City of Tucson has adopted a standard for street-side water harvesting basins along curbed urban streets via the use of curb-cuts. As mentioned above, CoHousing residential developments provide very good examples of detention basins integrated within and in the bottom of developments, at multiple scales. In addition, they demonstrate that trained maintenance staff, in their case the residents themselves, can understand and manage for the complexities of combined-use basins. Sonora CoHousing Community is a residential development in urban Tucson, corroboratively designed by residents and Floerchinger, Sadler, Steele, and


49 Baken, that is communally managed and maintained. The design of this town-home village incorporates small-scale water harvesting in the pathways between homes, xeroriparian open channels, an internal, turfed, active recreational detention basin, and a lot-bottom passive recreational, xeroriparian retention basin. Milagro CoHousing is a residential community in the foothills to the west of Tucson in unincorporated Pima County in which runoff is detained in a series of shallow combined-use detention areas, before it drains to preserved xeroriparian channels, along which recreational paths parallel. The Briamonte subdivision, while not a CoHousing community, has been designed and developed by the civil engineer designer of Milagro, David Confer, and the landscape architecture firm Design Collaborations, Ltd., the latter of whom employed the researcher on the design of this subdivision. The proposed streetscape design includes an innovative series of water harvesting basins along a rural, no-curb street, that preserves a utility access-corridor between street edge and basin, and re-grades adjacent, steep road-cuts in a manner that reduces erosion and promotes native vegetation growth by directing runoff from adjacent lands into a variety of scales of swales and microbasins parallel to the top of the slope and road. The Oro Valley marketplace is a recently-constructed shopping center in the incorporated Town of Oro Valley, within the metropolitan area of Tucson, AZ. All parcels of this development drains towards an aesthetically-pleasing, central, xeroriparian, open channel that includes elevated planting islands, naturalized energy dissipation structures, and observational trails and nodes along the top of the channel. Additionally, steep side-slopes between the development parcels and the neighboring surface streets exhibit a variety of side-slope stabilization techniques. In summary, comparison of the state of Tucson’s combined-use green infrastructure, institutional division of the “bundle of uses” identified above, and character of inter-agency interaction between these use-controlling government divisions, to other major metropolitan areas of the southwestern U.S. will be used to reveal important institutional arrangements that allow for particular combined-use design outcomes to be achieved.

Orange County, CA Metropolitan Area

Orange County contains rapidly growing suburban areas along Interstates 5 and 405, southeast of the city of Los Angeles, between the Pacific Ocean and the Santa Ana Mountains. Santa Ana winds and arid conditions often combine to create wildfires within the grassland foothills, which are increasingly being built into by residential master-planned communities such as Ladera Ranch. Within the past ten years, the City of Irvine, an affluent area of office parks and suburbs, has planned and begun the construction of the Orange County Great Park. These two case studies were investigated in depth, and reveal unique residential drainage design alternatives and political solutions, respectively. In 1943, El Toro Marine Corps Air Station was commissioned by the U.S. government outside of Irvine, CA. For sixty years, this Orange County Naval base served as a practice and staging facility for the bombers and fighter jets. In 1999, the base was decommissioned; soon thereafter, Orange County voters approved an initiative that changed the future development plans from a regional airport to a multi-partner Orange County Central Park and Nature Preserve (Orange County Great Park Corporation 2007). The land was subsequently auctioned to the Lennar Corporation, who, along with the department of the Navy and the City of Irvine, began planning for a mixed development of 1,300 acres of public space and a masterplanned community filling the remaining approximately 3,300 acres. Ken Smith Landscape Architect, who received previous attention for his synthetic rooftop garden at New York’s Metropolitan Museum of Art, was chosen in 2005 to lead the master plan of the Great


50 Park. Smith and the Great Park Corporation envision the park as an urban anchor for Orange County in much the same way as nearby Balboa Park in San Diego and Golden Gate Park in San Francisco. Using an over-arching motif of post-modern orange accents, Smith has proposed a 2.5 mile ecologically-based wilderness canyon to be day-lighted and reconstructed after years of passing through underground culverts, exhibiting concentrated activity development around the banks of a 20-acre off-line lake, a military museum documenting the history of the park, sports fields, and a wildlife corridor linking the protected Santa Ana mountain landscape of the Cleveland National Forest with the coastal sage scrub hills of Laguna Coast Wilderness Park (Vernon 2007). Smith describes the rehabilitation of this land as such: “This is an old military base. The ecology is repressed and the site is really barren and it’s not comfortable. We have to heal the place and bring life back” (Smith 2006). The wildlife corridor of California sycamore, willow, and cottonwood, entitled the Agua Chinon zone, is unique in its isolation from human activities, thus minimizing the disturbing effects of human traffic and activity upon habitat disruption. Between this corridor and the recreational canyon are located two nodes of living laboratories, including cultivation facilities, orchards, a natural treatment facility, and a 55-acre botanical garden. Mia Lehrer, a member of the design team, describes the proposed, adjacent multi-cultural centers, museums, and conference centers as essential pieces that make the park economically sustainable (Chang 2007). Surrounding the site is a series of transit-oriented developments located on a local train line for those looking for a home with Great Park and public transportation access. The history of the park’s development sheds light on the design environment between regulating agencies of the County. The Orange County Great Park Corporation (OCGPC,) a subsidiary of the City of Irvine, is an agency solely charged with developing and managing the park that was necessary to create in order to “hold harmless” the Orange County Flood Control District should recreational injury occur within the park. According to Glen Worthington, Manager of Planning of OCGPC, the District, as has been the typical case throughout this study, was originally reluctant to include recreational use and was opposed to riparian habitat within detention basins because it often increases beyond its designed size, is declared endangered species habitat by the California Department of Fish and Game, the regulator of riparian habitat within the state, and becomes off-limits for maintenance activities (Worthington 2009). In essence, success of habitat breeds encroachment on maintenance ability. The Fish and Game Department, on the other hand, felt that recreational disturbance of required habitat acreage would lower it’s quality. Looking back on the process, Worthington recognize a significant difference between the Flood Control District’s standards for complex, braided streams, the standards that the designers built to, and the realistic maintenance abilities of the OCGP, which resulted in their disapproval and the need for redesign. As such, he suggests that the designers of future combined-use detention basins of this scale consult with the permitting Flood Control District and Fish and Game Department at the beginning of the design process in order to avoid reiterations, and clearly define maintenance responsibility from the beginning. Additionally, while the wildlife corridor was originally buffered from residential disturbance by a proposed golf course, the latter was eliminated due to cost. Worthington describes that this has led to unhappiness among the neighborhood association of the master-planned community, who perceive the wildlife corridor to be a disamenity, perhaps reflecting a value system particular to this affluent and conservative part of Southern California. A final note of recommendation from Worthington was that designers should seek historic stream flow data early in the process, and not completely rely upon the occurrence intervals of 5-year, 25-year and 100-year events provided by the Flood Control District when designing flow diversion devices, such as is used to hydrate portions of the riparian design at the park. The challenge of the OCGP is to enhance the abundant adjacent natural resources that exist by


51 restoring that which has been lost within it. The proposed design, on the periphery of an urban area contains elements of open space and riparian canyon function, as well as borders with two major preserves. As such, it has high value as a wildlife corridor between these two areas. With the programmatic intention to increase interaction between people and natural elements in order to increase the value of the land by the community user groups, this “great” park is a fine example of how a combined-use approach to drainage design can be transformative to a community. Ladera Ranch, a master-planned community in the foothills of the Santa Ana Mountains, contains an innovative design that incorporates a street-side, dual-course drainage, entitled the “Sienna Botanica,” designed by Land Concern (landscape architects and planners,) and Hall and Foreman (civil engineers). A visible riparian bioswale parallels the primary arterial boulevard of the development and a recreational pathway, handles all base flows, and even receives base flows from a storm culvert located under the road, which drains the urban drool and runoff from other smaller watersheds of the site. In large storm events, flows are diverted from the bioswale into the culvert, keeping the street passable, and preventing destruction of the plantings and recreational amenities. The riparian system ranges from native bunch grasses and sycamore trees to cattail thickets, and have greatly evolved in biotic community type over the approximately 7 year history of the development. The linear system terminates in the Horno Detention Basin, which is subdivided between five water quality treatment basins, some of a hydroriparian nature with no liner, others fully constructed with no vegetation and a concrete liner, and an offline detention basin. Unfortunately, none of these riparian amenities are accessible for recreation, though they are in full view of some housing within the development. The cattail has proven to pose the most maintenance headaches, as its rhizomatous form quickly invades any area of standing water or saturated soils, including inlet and outlet pipes and culverts. Maintenance of such system has consisted of large teams of hired laborers manually pulling out the decayed, putrefied plant material within the anoxic environment. Because of the complexity of the system, an extensive manual on system ecology and hydraulic function was prepared by the design and engineering consultants and has served as the guide of the community’s landscape maintenance contractors, Mosaic, but, as proven by the cattail problem, the maintenance team has had to deal with the unexpected (Steffy 2009). In summary, Orange County, CA’s similarity to Pima County in terms of characteristics of both the natural and design environments, and the nature of development growth both retrofitting infill parcels and residentially expanding into foothills, makes it an ideal comparative metropolitan region from which to borrow regional lot-bottom basin and residential street-side channel designs, and lessons on the political interagency process of accomplishing a combined-use system.

San Jose, CA Metropolitan Area Due to its location within the rain shadow of the Santa Cruz mountains to the east, San Jose receives an average of a scant 14.66 inches of rain per year. Average annual temperatures hover at 60.3 degrees F, partially moderated by the southernmost, marshy extent of the San Francisco Bay. The city of San Jose and neighboring cities extend from the edge of the bay, across the flat valley floor, and into the low, wooded foothills. A portion of these foothills and beyond drain into the Guadalupe River, a shallow, perennial river that runs through the midst of the downtown, high-rise business district. This watercourse was redesigned in 1989 by Hargreaves Associates for eleven miles of its length to create the Guadalupe River Park (City of San Jose 2010). While this linear greenway does not include any detention basins along it’s designed length, it has been included in this study because it demonstrates how a public greenway of sculptural hardscape


52 design, passive recreational pathways, and riparian habitat, all within the floodplain, can create a sense of place and destination on the doorstep of executive hotels and high-tech workplaces. Recreational, vegetated side-slope terracing types, a base-flow natural river channel of mesoriparian vegetation, and an inhabitable concrete confluence of a major tributary forms the southeast border of McEnery Park, where employees of Adobe often take lunch. This space is extremely dynamic in light storm events, as waters from the tributary meet the Guadalupe River channel, which itself swells to inundate the areas that were inhabited hours, if not minutes before, an occurrence captures in video at <<http://www.sjparks.org/Trails/GRiver/ FloodControl.mov>> (City of San Jose 2010).


53

Semi-arid (15-20 inches/year,) metropolitan areas Environmental conditions of the metropolitan areas within this category are significantly different than the preceding group. Aside from the precipitation range, the water table of each of these cities is significantly closer to the ground surface, as evidenced by large areas of permanent standing water (insert figure of Boulder lakes and greenways) and streams with perennial base flows. This is due to significant snowpack and characteristics of the aquifer in the upstream watershed, and/or the low elevation and resultant close proximity to tidal areas. Also, as a result of the proximate groundwater table and other environmental conditions such as steady winds and average annual temperature, potential evapotranspiration (PET) rates are significantly lower.

Los Angeles, CA Metropolitan Area

Following catastrophic flooding in the 1930s, the Army Corps of Engineers excavated and channelized the Los Angeles river with concrete in the 50s and 60s, eliminating riparian habitat and creating a public eyesore (City of Los Angeles 2007). In 2005, the Los Angeles City Council hired Tetra Tech, Inc., Wenk Associates, and Mia Lehrer Associates to engage with the City’s Office of the Mayor, Bureau of Department of Public Works, and Department of Water and Power, and the Army Corps of Engineers, to create a “Los Angeles River Revitalization Master Plan” that aims to completely reconfigure the barren ditch to include riparian vegetation and recreational use, and aesthetic contribution to the community (City of Los Angeles 2007). Among the analyses undertaken in this plan was a characterization of flow velocities along the river, description of ecological processes, water quality problems, and an analysis of community needs. Recommendations based upon these analyses are a series of combined-use detention/ retention basins, and recontoured channels that allow for vegetative growth and recreational use through the installation of biofiltration terracing and planting areas within shadows of hydraulic energy (Dyer 2009; Wenk 2009). These have also been applied to the City of Compton’s Compton Creek “Garden Park Master Plan.” Among the more innovative components of this former master plan is the current development of a zoning overlay entitled the “Los Angeles River Improvement Overlay (LA-RIO,)” that will regulate future design and construction of all parcels within a specified buffer distance from the river within the 32 miles that it passes through the City, without using eminent domain. In order to be approved for a building permit, a development must reach a points threshold from “three design categories: Watershed, Urban Design, and Mobility (City of Los Angeles 2007; Dyer, 2009). Another project that is under current development is the retrofit design of the 45-acre Strathern Pit, a gravel pit that has been used as an inert landfill in recent years. With the primary purpose of “water quality cleansing and flood control management,” the master plan for this design, developed by PSOMAS Engineering, Natural Systems International, and RJM Design, Inc. landscape architects, includes a wraparound series of broad terraces in which low-flows will be retained by a 60 millimeter treaded HDPE liner covered by emergent hydroriparian vegetation. Each ponding area is contained by berms which also serve as recreational paths. In large storm events, the entire pit is filled to capacity. Vista Hermosa Park, designed by Mia Lehrer Associates, captures the visitor through a series of


54 interpretive displays of water sources and associated biotic communities of the region. Within it is a small detention basin that serves as a turfed seating area overlooking downtown Los Angeles. In general, the city of Los Angeles and other municipalities within Los Angeles County, along with active community groups and prominent landscape designers, have shown incredible leadership in building a vision for the regionâ&#x20AC;&#x2122;s future that includes the retrofit design of built-out drainage ways to include recreational access to functioning ecosystems, an uncommon occurrence at present, within safe floodplains.

Denver/Boulder, CO Metropolitan Area

The Front Range metropolitan region of Colorado lies to the east of the Front Range of the Colorado Rockies on semi-arid grassland plains. Contained within this region are the Cities of Denver and Boulder, and the Town of Erie. Flood control and conveyance in all three municipalities is managed by the regional Urban Drainage and Flood Control District (UDFCD). As this area is characterized by groundwater tables close to the surface, perennial base flows exist in many streams, and there are many naturally-occurring ponds and lakes. Due to the potential of runoff contamination of these above-ground water resources, water quality treatment is a major concern that is also managed by UDFCD. While wetlands are also protected by law, and mitigation required in case of disturbance, they are abundant within the region, and so are perhaps not as highly prized and protected. Perhaps due to the abundance of these linear and nodal riparian communities, and a community nature that revolves around outdoor recreation, The City of Boulder has become world-renowned for its interconnected network of greenways that provide both an internal system of walking and biking paths, and a growth-limiting perimeter characterized by agricultural landscapes of production and natural drainage features. In the City of Denver, parks and recreation departments have worked hand-in-hand with UDFCD, civil engineers, and landscape architects for years, resulting in many urban parks that combine traditional and native plant palettes with naturalized and highly abstract concrete structures (Wenk 2009). The resulting combined-use design environment in the Denver/Boulder area, therefore, stresses four uses: flood control and conveyance, water quality treatment, and recreation, and aesthetics. In the City of Denver and surrounding suburbs, Bill Wenk Associates have designed many intriguing new and retrofitted, combined-use greenways, detention basins, and water quality treatment pond systems, that superbly demonstrate how creative grading, aesthetically designed drop and energy dissipation structures, and hydroriparian biotic communities can be combined into captivating combineduse landscapes. George Wallace Park is a linear greenway along Goldsmith Gulch that separates a residential community from a busy surface street and the Denver Tech Center, for which a special district was organized to maintain the park. This retrofit design incorporates traditional turf and shade trees within an open channel whose low-point is elegantly designed with a rectangular, concrete, low-flow channel. The energy of high-flows in large storm events is dissipated at two locations by 3â&#x20AC;&#x2122; drop structures, a concrete chute, and an array of orthogonally-abstract concrete blocks below. During low-flow conditions, water from this channel elegantly falls over these simple drops, and the energy dissipation blocks serve as seating and play areas that create the overall effect of an amphitheater. During a visit in September, 2009, these locations were used by families with small children taking baby portraits, and by a group of young adults playing Frisbee. The bottom of this system serves as a detention basin, within which lies a hydro-riparian wetland that also functions for water-quality treatment. The work environment is improved by the Denver Tech Center by window views of open space, a nearby park in which to take lunch breaks, and a functional greenway by which employees can arrive by bike.


55 Shop Creek lies within the eastern portion of the metropolitan area. Here, Wenk Associates designed a restored hydro-, meso-, and xeroriparian, and meadow habitat along a series of water quality treatment retention ponds separated by cascading soil-cemented drop structures that have the appearance of natural outcrop stratigraphy. Paralleling this drainage is a multi-use recreational trail with spurs to the drop structures and adjacent residential communities. This design, like George Wallace Park, is exemplary in that the drop structures are intriguing to the eye and fun to climb on and observe the wildlife from in low-flow conditions. Lowry Parks, also designed by Wenk, is a community park surrounded by the newly-constructed residential community of Lowry. The rear slopes of the Westerly Creek Dam, which contains all waters of Westerly Creek just upstream of the park complex, were re-graded in gently-curving terraces, branded “fillets” by Wenk Associates, that allow for visitors to ascend to the scenic top of the dam by foot or bike. Further downstream, the Kelly Dam also retains the flow of the creek in a water-quality treatment hydroriparian wetland that lies adjacent to one of the arterial streets of the development. Between the two dams, the stream has been daylighted from underground culverts to an above-ground open channel. Further downstream from the Kelly Dam, following the passage of floodwaters under another arterial street, the creek curves approximately 45 degrees, where the banks are armored by a series of long, rectangular concrete blocks that gracefully disappear within the channel, creating small backwaters in which emergent hydro-riparian vegetation is growing, and allowing visitors to descend from the turfed adjacent parcels to the riparian growth below. This latter component is an ideal example of how flow-directing devices can enhance the recreational and aesthetic value of a channel, while simultaneously accomplishing energy dissipation. Further downstream on Westerly Creek, EDAW helped to retrofit design a portion of the decommissioned Stapleton airport into a residential community. Westerly Creek Park is a centrally-located greenway conveying and retaining runoff from adjacent homes. This greenway and basin system is paralleled by concrete pedestrian trails and residential roads which criss-cross back and forth across the reconstructed stream. Low-flow areas and basin margins are planted with cottonwoods and willows, while uplands are planted with native grasses, wildflowers, and upland tree species. Stabilized, decomposed granite trails spur from the concrete paths to private contemplation spaces that overlook these riparian areas, within the floodplain. Bluff Lake Nature Center stands on a short-grass prairie bluff overlooking a 9-acre lake adjacent to Sand Creek Regional Greenway. Described as the “cornerstone” of the greenway, this riparian system was, for many years, inaccessible to the public, as it lay within the “crash zone” of the Stapleton Airport. Following the decommission of the airport, the City and County of Denver, and the Sierra Club opened access to the preserve, and have gradually added recreational improvements, including granite access trails traversing the steep slopes of the bluff, a small-event ramada located half-way down the slope, and scenic overlooks, a parking lot, and a modest nature center along the top rim (Bluff Lake Nature Center 2008). When visited in September, 2009, many joggers and day-hikers were encountered within the basin, who seemed to be using the park more as a beautiful exercise location more than an environmental education center. This case is of particular interest as it demonstrates a successful greenway node/natural resource park. In Erie, CO, east of Boulder and north of Denver, Erie Lakes Regional Detention Facility was designed in the middle 2000s in response to rapid residential development. The contributing basin, also known as the upstream watershed, like much of the Front Range area, had historically been flattened for agricultural fields, with runoff conveyed through irrigation canals. As the adjacent lands began to be urbanized, the Town of Erie and the Urban Drainage and Flood Control District contracted Civil


56 Engineering firm Love Associates to design a regional detention facility. The proposed and accepted design generally incorporates stormwater quality treatment, flood control and conveyance, riparian habitat, aesthetically-pleasing structures, and passive recreational trails through a three-zone design. Zone 1 includes an open-flow channel vegetated with cat-tail (Typha) and willow (Salix,) punctuated by naturalistic drop structures, and flanked by a recreational path. This channel leads to zone 2, a water quality treatment basin perennially retaining pooled water and fringed by cat-tails, that can easily be approached by straying from the recreational path. These first two zones additionally provide a naturalistic middle-ground view from the rear windows of the adjacent houses. Zone 3 is an offline detention basin that is kept out of sight of the first two recreational zones by a large berm. Within the City of Boulder, The University of Colorado-Boulder Research Park campus is built on a backbone of water quality treatment wetlands within a series of stormwater detention basins. Two major drainages of the city, Skunk Creek and Boulder Creek, historically converged at this site. During a period of agricultural production, fields to the north diverted water from Boulder Creek through an irrigation canal that was later delineated by the Flood Control District as the primary channel of Boulder Creek. This arrangement, in essence, relocated the confluence of the creeks to a point further downstream of the site. However, both creeks still ran through the site, which the University had acquired in the 1950s. Wishing to develop the site as a center of innovation, but recognizing that 96 of the 100 acres were within the 100-year floodplain, UC-Boulder contracted Love Associates, a civil engineering firm, and architecture/planning firm Downing, Thorpe, and James to design a research park master plan that would free up 77 acres for development while enhancing the riparian and recreational amenities in between. The first tenant, Baby Bell US West, now Qwest Communications, had coincidentally just experienced severe flooding to a facility in the Tucson area and was therefore greatly interested in avoiding a similar fate with its next development (Love 2009). The key feature of the design is the variable direction of waters from both creeks through either a series of four wetland ponds or along their respective channels, depending upon the flood conditions. Base flows of Skunk Creek up to 3 cfs are diverted into a 2â&#x20AC;&#x2122; deep, rectangular, low-flow-channel that supplies water to the first pond. Waters exceeding the capacity of this first pond overflow into the second pond, and so on through all four ponds. When the capacity of the fourth and final pond is exceeded, water overflows back into the Skunk Creek Drainage. When storm flows exceed 3 cfs, the next 5 cfs (3-8 cfs of storm surge) bypasses the first diversion structure (and first pond) and is carried by the Skunk Creek bypass channel, which is lined by rock in order to maintain flow and prevent erosion, through a box culvert into pond 2. Exceeding 8 cfs, waters bypass the second diversion structure and continue to flow down the Skunk Creek bypass channel through another box culvert which drains underneath a parkway and off-site. When incoming flows exceed 10 cfs, the Skunk Creek bypass channel begins to back up at this outlet, overbanking the channel. In a 100-year event, flows back up within the Skunk Creek channel and beyond into a greater low-slope detention basin which contains the channel and four ponds, and which is located fully outside of the building envelopes. This detention basin will also receive peak flows of the adjacent Boulder Creek, that, in lower flows, remains within its banks.

Davis/Sacramento, CA Metropolitan Area In the City of Sacramento, a full-service city, flood control and conveyance is the responsibility of the Cityâ&#x20AC;&#x2122;s Department of Utilities, and recreation and aesthetics of public land is controlled by the Parks and Recreation Department. In recognition of limited developable space left within the city, and the expense


57 of public infrastructure, in 2007, the two city departments undertook a memorandum of understanding entailing an “agreement under which a stormwater detention &/or conveyance facility qualifies to be recognized as a city park or to receive funding for recreational improvements” (City of Sacramento 2007). This agreement splits the design, development, and maintenance responsibility of these joint-use facilities between “drainage” and “park” components. Similar to other California cities, sensitive biological habitat protection and restoration are controlled by the California Department of Fish and Game. As Gary Hyden, supervisory landscape architect of the City of Sacramento Parks and Recreation Department describes, the early agricultural settlement of the Sacramento area was characterized by the draining and reclamation of wetlands for use as productive fields. By the time environmental awareness of the protection of riparian habitat arose, most wetlands had already been destroyed. From his perspective, Fish and Game exerted more control over the protection of mature oak and willow trees in savanna and riparian ecosystems, respectively, as opposed to the protection of biotic communities such as riparian habitat. However, at this time, new developments must undergo streambed alteration agreement permitting with the Fish and Game department that requires a 3:1 area replanting ratio for riparian preserves created versus those destroyed in development (Hyden 2010). As a result, reviewing the metropolitan area’s “joint-use” detention basins, two characteristic types were encountered: those that incorporated riparian preserves and those that did not. Both contained design components that are relevant to this study. The simplest of traditional active-recreation detention basins that were encountered was the Cosumnes River College Park, which is a simple, turfed basin with active recreation playing fields, an evengraded basin bottom and a typical side-slope-paralleling access ramp. In a newly-built residential area near the intersection of 29th Street and Meadowview Road, another simple basin with turf on an even-graded bottom was encountered. This basin is of interest due to the steep side slopes which have been stabilized by formal plantings of brushy shrubs, and its purpose as a play and special-event space at the front of houses that surround it. Granite Regional Park in eastern Sacramento was the most complex system encountered. This park, funded by City of Sacramento, with help from the California Clean Water, Clean Air, Safe Neighborhood Parks, and Coastal Protection Act of 2002, is not a detention basin, but rather a deep former sand and gravel pit of the Granite Construction Company that is located 200+ yards from the local tributary stream. While many components of the recreational design are impressive, the two characteristics that are of most importance to this study are the developed slope-tops, and side-slope road access. All park developments within the bottom of the pit, including a fishing retention pond, water quality treatment retention pond, skate park, and playing fields, are within full view of the business park perched on the slope-tops above, which includes a courthouse, other municipal and state government offices, and private offices. Parking for the office park is located at the base of a steep side-slope separating the recreational park from the business park, so that visitors and employees must descend the slope in order to park their vehicle. This can be accomplished along one of two roads. One is subtractive from the existing slope, requiring regrading and bank stabilization as the road roughly parallels the perimeter of the basin and transverses the slope in a steep manner. The other is additive, extending from the slope-top to the basin bottom along a gently-descending berm that is perpendicular to the pit’s perimeter. In the neighborhood of North Natomas, a broad open channel drains a large residential watershed, and also serves as a greenway along which residents stroll, ride their bikes, and pass through on their way to neighbor’s houses. Along these pathways are planar metallic sculptures inset with photos of wetlands and colorful sculptural forms of riparian flora and fauna. These symbolize the biofiltration wetland that was originally constructed within the low-flow channel, but user complaints during the early years of its


58 inhabitation forced the development company to remove these riparian amenities and replace them with a concrete ditch. Reasons for this re-design could be many, including the formal tastes of the residents, fears of West Nile Virus, and failure of signage to properly explain the function of the wetlands. The open channel greenway drains to a lot-bottom retention basin which also serves as a water quality treatment pond and bird habitat. Del Paso Park in Northeast Sacramento is an offline detention basin along a tributary drainage that is designed to recreate a vernal pool biotic community. From basin bottom to top of side-slopes, this basin used three planting strategies. The even-graded basin bottom seems to have either been hydroseeded or allowed to establish via volunteer growth; most vegetation within it is emergent clumping grass that seems resistant to long periods of inundation. Along the portions of the side slope that are inundated in large storm events, container plantings have been placed within slight, approximately 2’ diameter circular terraces with shallow berms located just down-slope, a configuration that has previously been described as “pocket” plantings. These plantings, for the most part, looked dead when visited in January, while lowstatured grasses grew well in the intermediate space between plantings. In comparison, above the highwater line, the slope continues, and has been graded with a series of human-scaled (1’ tall, 2’ wide) berms on-contour. While this area did not appear to have been planted with trees, it did successfully support not only the afore-mentioned low-statured grass, but also a variety of heath-like shrubs and forbs, perhaps due to the increased water availability. Village Homes, a single-family residential development built in Davis, CA, was designed and constructed in the 1970s by Michael and Judy Corbett with energy-efficiency and sense of community as the primary design goals. Michael Corbett describes the early design process as follows: “When I first presented the concept plan for Village Homes to the then city planning director for the City of Davis, she sat back in her chair and started to laugh. ‘This goes against everything I learned in planning school. Change all of it and come back and then we can talk,’ she responded. What is remarkable, I was able to get 90 percent of what was on the original plan” (Francis 2003, quoting a lecture by Mike Corbett on Village Homes at UC Davis in 1988). Among many concerns for the marketability of the development was the abundance of common space at the expense of lot size. Linear common areas are located to the rear of private parcels within open channel drainages, and are paralleled by multi-use pathways from which maintenance can occur. In essence, this design borrowed from garden city design tenets that run counter to New Urbanism design principles: focusing community attention upon its interior as opposed to its public face, the streets and front entrances of buildings. The Homeowners Association was arranged “to allow residents to design and build landscape areas,” with HOA funds, within the common area that they live adjacent to. This immediately forced neighbors to interact and develop a functional understanding and “sense of symbolic ownership” of these combined-use areas that has provided for knowledgeable maintenance of these areas to this day (Francis 2003). This design also eliminates the need for sidewalks along the sides of streets, as pedestrian circulatory function is accomplished by the multi-use paths. The community has been a great success in terms of resident occupancy, property value, and sense of community. “Residents report having twice as many friends and three times more social contacts than residents in a conventional control neighborhood in Davis” (Francis 2003, quoting T. Lenz, A PostOccupancy Evaluation of Village Homes, Davis, California. Unpublished Master’s Thesis. Technical University of Munich 1990). Most importantly, like the Tucson-area CoHousing communities described above, Village Homes demonstrates how an internal linear design and HOA maintenance can accomplish flood control and conveyance function in a combined-use setting. In summary, the Sacramento metropolitan area demonstrates how flood control facilities can


59 provide wildlife habitat, water quality treatment, and active and passive recreation. Much of this was likely possible due to the interagency policy agreement undertaken between the flood control district and parks and recreation department, a policy device that should be considered in any metropolitan area wanting to create a conducive design environment for combined-use detention basins and conveyance channels. Village Homes within the City of Davis provides a testament to the effectiveness of integrated flood control open channels/greenways through residential neighborhoods.


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design guidelines Pima County Regional Flood Control District 97 E. Congress St., 3rd Floor Tucson, AZ 85701-1791 (520) 243-1800


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Introduction Pima County Policy requires land developers to not only limit site runoff volume to pre-disturbance levels during storm events, but also requires developers to mitigate for on-site disturbance of riparian areas. Mitigation requirements can be met either on-site within detention basins or other areas or via off-site mitigation, through retrofitting an existing regional or site detention basin. Integrating riparian habitat within residential, commercial, and regional detention basins can provide many additional site benefits, such as shading/cooling of neighboring buildings and paved surfaces, creating outdoor spaces for relaxation, contemplation, and interaction with nature, and can raise property values of neighboring homes, in much the same way as small-scale water harvesting basins (Bark et al. 2009; Lancaster 2008, a, b). Recognizing that non-saleable acreage in landscape is costly to the developer of new residential and commercial properties, investment in land, grading, and fine-scale components of detention basins containing riparian habitat can form the backbone of a site’s open-space landscape, while reducing the overall acreage necessary to accomplish seemingly disparate zoning requirements (Glassman 2010). Confusion exists regarding definitions of detention basins, retention basins, and water harvesting basins among designers and the public, and what specifications apply to each; this manual will clarify these differences and illustrate how water-harvesting basins can be a component of a functional detention basin. The intended audience of professions of this report include civil engineers, landscape architects, environmental consultants, biologists/botanists, hydrologists, land owners, developers, and planners. The intended audience of agencies includes Pima County Regional Flood Control District, Pima County Parks and Recreation Department, Pima County Development Services Department. The report has been informed by arid and semi-arid southwestern U.S. metropolitan areas, is intended for use in Pima County, and is also useful to arid and semi-arid metropolitan areas within the U.S. and internationally. This report will be made available in hard copy at the District office, and in digital form via a link on Pima County Subdivision and Improvement Plan Review webpage (http://rfcd.pima.gov/pdd/review. htm.)

Recommended Design Process

Proper design of any site should be preceded by an exhaustive analysis of site conditions. This begins with an inventory of elevation, solar aspect, average annual rainfall, depth to groundwater, biotic community, and existing level of disturbance. In order to determine the range of habitat improvements that are possible on site, the designer should seek to identify reference riparian habitat, or undisturbed, well-functioning riparian sites with similar environmental parameters within the watershed or closely neighboring watersheds. This can be done using ArcGIS, or other map-overlay method (trace paper, Adobe Illustrator/Photoshop, etc.) Information for these analyses should be should be generated from a site field inventory and/or consultation of a combination of ecological and botanical manual and online resources. Sources of this information that have proven reliable in earlier designs include the following: • Biotic Communities: Southwestern U.S. and Northwestern Mexico, Brown et al. • Plants of Arizona, Anne Orth Epple • Google Earth, << http://earth.google.com/>>


62 • Pima County Map Guide, <<http://www.dot.pima.gov/gis/maps/mapguide/>> • Arizona Department of Water Resources well registry viewer, <https://gisweb.azwater.gov/ waterresourcedata/WellRegistry.aspx>> Basins of pooling water such as those created by detention basins are uncommon along contemporary riparian corridors dissecting the alluvial plains/bajadas upon which most development in Pima County occurs due to the scarcity of bedrock outcrops along these gradients and the channelizing effects of erosional water flow and streambank stabilization in an era of receded groundwater tables and flood prevention. Because basins essentially increase the duration and quantity of water saturation of the soils within them, appropriate reference riparian habitat for sites built within the Tucson Basin should err on the side of slightly higher elevation, higher annual rainfall, and closer groundwater table than the site. Areas where these occur are generally at the top of alluvial slopes, just downstream of the mouth of surrounding canyons. In the Tucson basin, accessible and appropriate reference riparian habitat include, among others, in counter-clockwise direction starting in the south, Sycamore Canyon, Cienega Creek Natural Area, Upper Tanque Verde Wash, Agua Caliente Wash, Bear Creek, Sabino Creek, Ventana Canyon, Pontatoc Canyon, Pima Wash, Sutherland Wash, Cañada del Oro, Big Wash, Ruelas Canyon, Sweetwater Draw,Yetman Wash, and the West Fork of the Santa Cruz River. Ajo-area reference riparian habitat include portions the Cuerda de Leña and Ten-mile washes, as well as numerous smaller washes emanating from the Little Ajo Mountains. In the Arivaca area, Sopori wash is a fairly undisturbed riparian habitat for reference. If possible, the designer of the detention basin should visit one or more reference riparian habitats and make field notes on plant community composition using the guides recommended above. Field botanical observations at reference riparian habitat/s should be cross-referenced with the recommended plant list to select an appropriate plant palette, including grasses, forbs, small shrubs, large shrubs, and trees, for the detention basin to be designed.


63 riparian ecology

riparian ecology


riparian ecology

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riparian ecology

Figure 8.1.1: Bass Canyon, Cochise County

Riparian systems of Pima County floodplains provide refuge to native plant and animal communities both within and outside of developed areas, and, when biologically functional, exhibit the following characteristics:

Riparian biotic communities are those lands, in drainage ways and adjacent floodplains, whose generally porous soils are hydrated for longer periods of time than adjacent lands due to prolonged submergence from flooding, dispersed flow, or ponding of runoff from adjacent lands (Brown 1994). As a result of this increased availability of soil moisture, vegetation within riparian areas is often denser, taller, and more diverse than adjacent uplands (PCRFCD 2008, a). Small-scale (cover, seed source) and regional (linear connectivity within deserts) structural qualities bestow a habitat value to these systems disproportionate to their limited geographic extent (Brown 1994). Terrestrial animals are highly dependent upon connectedness, while native bird density in Tucson is correlated with high vegetative volumes in urban washes (The Arizona Wildlife Linkages Workgroup 2006; Mills et. al 1989). Riparian communities are generally classified as either hydroriparian, mesoriparian, or xeroriparian. The primary difference in

environmental condition between these ecosystem types is the proximity of the groundwater table to the soil surface, and result in varying levels of total amount of vegetation, which have been delineated via remote sending and field measurement. Xeroriparian habitat is primarily characterized by limited, ephemeral water supply above ground and throughout the rooting zone, and is found in riparian strands and scrubland; it is further categorized by the county into classes A, B, C, and D based upon density and plant associations. Mesoriparian habitat is associated with shallow ground water and are found in riparian deciduous forest, woodlands, and scrubland. Hydroriparian habitat is associated with perennial watercourses, and are found in interior marshlands and submergent communities (Brown 1994; Pima County Department of Transportation and Flood Control District 1993; PCRFCD 2008, a). Field determination of class type of disturbed habitat must correlate with the acreage to be mitigated (PCRFCD 2008, a).


65 Figure 8.1.2: Within a typical Sonoran Desert perennial or ephemeral stream, while emergent wetland species survive in perennially inundated or saturated soils, the roots of obligate mesoriparian species must be in constant contact with groundwater, and facultative xeroriparian species can survive without perennial contact with groundwater (Pima County Regional Flood Control District 2010).

2. Hydraulic Dynamism

1. Geomorphology and Habitat Structure

Figure 8.1.4: Floodplains are dynamic systems that are altered over time by the hydraulic energy and sediment transport within them. Vegetation is altered as erosion occurs along the high-energy outside of meanders, while deposition occurs on the low-energy inside, and in point bars. Detention basins are opportunities for this dynamic process to alter the form of riparian habitat over its life (Daniels 2008, p. 51).

3. Biome

Figure 8.1.5: Eastern Pima County lies on an ecological transition zone between the Sonoran and Chihuahuan biogeographic provinces, or biomes, each of which is characterized by a different set of plant species. Site location within these provinces should inform the plant selection for riparian basins (image modified from Brown 1994, p. 13).

Key Questions for Design Decision Figure 8.1.3: Environmental and anthropogenic factors influence how close groundwater is to the surface. Gaining reaches occur where aquifer recharge exceeds withdrawal and/or groundwater is pushed towards the surface by proximate subsurface impermeable bedrock, resulting in stretches of hydro- and mesoriparian vegetation, a condition that is analogous to the dam of a detention basin.

1. What is the nearest biologically-functioning ecological network (major river, minor wash, etc.?) 2. What biotic communities exist on-site or locally and how might the diversity of the local ecosystem structure be improved? 3. How can the design minimize barriers to wildlife movement between the basin

and adjacent corridors and biologicallyfunctional uplands? 4. What is the required habitat mitigation acreage and what are the benefits to be had by introducing elements of human circulation? How can these two design goals be synthesized in a mutually beneficial manner?


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Permitting, Maintenance, & Monitoring 1. Permit review of adjacent developments should emphasize connectivity of functional biological corridors through the use of open channels. 2. Pruning and brush removal should be limited to the recreational buffer along the perimeter of interior habitat areas in order to minimize edge effects.

Figure 8.1.6: “Patches” of habitat with a high ratio of area to edge are undisturbed preserves of biological diversity and abundance whose value can be greatly enhanced by linear biological “corridors” connecting them. Disconnected patches between are also of value as “stepping stones” for wildlife, particularly flying animals, to inhabit between large “patches.”

3. Natural stream dynamics (deposition areas, cut banks) should be allowed within the basin and inflow channels where they do not cause flooding risks. 4. As climate and water resources change regionally, plant palettes may need to be revised to accommodate altered environmental conditions.

Figure 8.1.7: Barriers to animal passage and stream process along riparian habitat networks can take the form of hardscape structures or denuded areas such as bare side-slopes, decreasing the value of habitat on both sides. While flying animals can pass over them, terrestrial animals may be reluctant to pass these open areas.

4. Connectivity Figure 8.1.10: The model of habitat patches and corridors is analogous to the paths and nodes of Kevin Lynch’s ‘Image of the City’ model of human communities. In it, circulatory paths, activity nodes, and edges, among other features, shape the way that humans move and congregate within and urban area. Detention basins can serve as nodes of human activity (Lynch 1960).

5. Edge Effects

Additional Resources DeBano, Leonard F., and Larry J. Schmidt. “Definitions and Classifications,” in Riparian Areas of the Southwestern Unites States: Hydrology, Ecology, and Management, ed. Malchus B. Baker, Jr., Peter F. Ffolliott, Leonard F. DeBano, Daniel G. Neary. Boca Raton: CRC Press, 2004. Figure 8.1.8: Interior habitat is generally a refuge for sensitive species that are easily disturbed by factors associated with edges with disturbed areas, such as motion disturbance, noise, and introduced species. Therefore, dense thickets of riparian scrub, aquatic plants, and riparian obligate species, due to their high habitat value, are best positioned within undisturbed interiors of habitat patches.

Figure 8.1.9: Inserting trails or other areas of human circulation into habitat patches typically downgrades high-quality interior habitat to low-quality edge habitat, though community use of these areas can foster appreciation, a sense of public ownership and pride, and ultimately, civic support for their continued existence.

Dramstad, Wenche E., James D. Olson, and Richard T.T. Foreman. Landscape Ecology Principles in Landscape Architecture and Land-Use Planning. Washington, D.C.: Island Press, 1996.

Harris, Larry D. “Edge Effects and Conservation of Biotic Diversity,” Conservation Biology v. 2:4 (1988): 330-332. Hellmund, Paul C. and Daniel S. Smith. Designing Greenways: Sustainable Landscapes for Nature and People. Island Press, Washington, D.C. 2006. Lynch, Kevin. The Image of the City. MIT Press, Cambridge, 1960.


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adjacent parcels adjacent parcels


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adjacent parcels

adjacent parcels

Figure 8.2.1: Adjacent Parcels (in blue)

The form of a riparian detention basinâ&#x20AC;&#x2122;s interior and edges is greatly influenced by the hydrological, biological, and developed nature of adjacent lands. Design should therefore be mindful of the following attributes of the site:

Prior to designing a detention basin, great care must be applied to analyzing the contributing watershed. Design should consider multiple, separate, contributing watersheds, from the primary upstream inlet taking the vast majority of the volume, to smaller-scale watersheds along the sides of the designed basin, with seemingly insignificant sources of flow. If unaccounted for, these latter areas can become drainage problem areas by developing erosion rills that can headcut into maintenance rights-of-way, multi-use trails, and planting areas on the slope-top, or into adjacent property parcels. In order to properly maintain form, capacity, and strength of a basin, all contributing watersheds, regardless of size, should either be made non-contributing by complete retention in storms up to 100-year storms by water-harvesting tanks and earthworks, and/or retention basins internal to the site, or be directed into designed inlets through a combination of levees, berms, swales, and microbasins that prevent them from forming their own erosive routes over

the side-slopes. The quality of life of places of work, residence, or outdoor gathering in adjacent parcels can be greatly improved by views on to the riparian basin. These developments can range from utilitarian, agricultural landscapes to traditional, residential communities to urban multi-storied hotels and offices. A common complaint about successful riparian growth in stormwater infrastructure in Pima County is that it looks overgrown in comparison to the manicured landscape of the home, and appears to be a hinterland that attracts inhabitation by the homeless and unsupervised youth. Therefore, in order to improve public perception and acceptance of riparian areas as socially-beneficial amenities, the transition zone between the neighboring building and manicured landscape should either be gently transitioned from formal to natural or designed in a way that embraces the contrast between the two as a positive element of design instead of an accidental, uncomfortable clash.


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Figure 8.2.2: Small areas of drainage not designed for (in blue) can cause numerous, large erosion problems (in orange,) as at Kolb Road Basin in Pima County, AZ.

Figure 8.2.3: When the drainage from adjacent parcels is unaccounted for, side-slope rill erosion can develop and head-cut into slope-top improvements such as multi-use paths or building foundations (PCRFCD 2008, b).

3. Special Zoning Overlays 1. Drainage Flow 2. Permeability

Figures 8.2.6 (top right,) 8.2.7 (top left): Many special zoning overlay zones exist throughout metropolitan areas, and restrict building type and land use within them. In the example illustrated above, the Approach-Departure Corridor, also known as the â&#x20AC;&#x153;flight paddleâ&#x20AC;? of Davis Monthan Air Force Base, prohibits residential, commercial, office, and active recreational/gathering area land use at the Kolb Road Basin, due to sound levels between 60-70 decibels, risk of a crash, and the potential for bird kill and resultant plane malfunction (Davis Monthan Air Force Base 2003). At right, though portions of the Guadalupe River Park lay within the flight paddle of San Jose International Airport, passive recreational use and hydroriparian habitat areas are allowed and enjoyed.

Key Questions for Design Decision 1. How is stormwater draining from secondary (not primary upstream wash ) adjacent areas going to be controlled? 2. What are the views on site from neighboring developments and how can they be designed for positive perception? 3. Are the building exteriors and proximate landscape of neighboring developments Figure 8.2.4 (top,) 8.2.5 (right): Narrow, curvilinear paved surfaces, and parcels sited with respect to contour allow for area on private parcels, increasing infiltration, and reducing runoff. Two examples of this effect in Tucson are Colonia Solana (right, City of Tucson Planning Department et al. 1994) built in the 1920s in which parcel size is large, and Sonora CoHousing Community, completed in 2000, in which parcel size is relatively small.

formal/informal, vernacular or naturalistic? 4. How can the transition between the neighboring developments be best designed through the incorporation of contrast or smooth gradient design characteristics to improve positive perception of the designed riparian system?


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Permitting, Maintenance, & Monitoring

1. Where erosion rills from drainage problem areas threaten buildings, paths, or other infrastructure, their contributing watershed should be redesigned with diversion berms, swales, and/or basins to capture water upslope and concentrate flows into designed inlets. 2. Permit review of new adjacent

developments should emphasize the preservation of sight-lines towards riparian visual amenities and on-site detention of increased runoff. 3. Revision of overlay zones, such as airport flight paddles, should consider the wildlife habitat value, and resultant waterfowl population, of sites within them.

Figure 8.2.8 (above): Reading areas of the Southeast Regional Library in Gilbert, AZ, overlook a recreational pond of the Riparian Preserve at Water Ranch (C.F. Shuler, Inc. 2010). Figure 8.2.9 (right): A conference room in a business park adjacent to Granite Regional Park is enhanced by a window view of a water feature within a retention pond.

Figure 8.2.12: Patrons at the Wolfgang Puck Restaurant at the Springs Preserve in Las Vegas, NV, enjoy an overlook of the formal landscape and riparian habitat below (Luchessi, Galati, Inc./Natural Systems International).

4.Views onto Site 5.Transition of Form

Additional Resources Davis Monthan Air Force Base. Arizona Military Regional Compatibility Project. Davis-Monthan Air Force Base/Tucson Joint Land Use Study. Public Informational Meeting, September, 2003. Figure 8.2.10: Skyscrapers holding Acer, T & C Productions, and Paoloâ&#x20AC;&#x2122;s Restaurant in downtown San Jose, CA, are oriented towards the Guadalupe River Park, demonstrating an appealing transition between geometric and naturalistic form through the use of planting terraces, stairs, and recreational pathway.

Figure 8.2.11: At the Paradise Apartments along Greenway Wash in Phoenix, AZ, residents are treated to window views and a turfed seating and recreation area overlooking the riparian habitat below. Curbing on the left side of the concrete path conveys water to drains located at bump-outs to the left, which also serve as overlook points.

Pima County Regional Flood Control District, City of Tucson, 2008. DRAFT Ordinance No. 2008FC____. An Ordinance of the Board of the Directors of the Pima County Flood Control District relating to Floodplain Management codifying the

Pima County floodplain and erosion hazard management ordinance as Title 16 of the Pima County Code. Tucson, AZ.


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Street-side basins

street-side basins


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street-side basins

street-side basins

Figure 8.3.1: Street-side basins (in blue)

Street-side basin series can create a network of accessible, maintainable, riparian corridors of intermediate habitat value and beneficial community use, and should be designed according to the following guidelines:

Detention basins integrated within the matrix of a residential, commercial, or residential development primarily represent opportunities for the growth of native trees that can both create riparian corridors and improve the quality of life of residents or employees through the creation of shade, the lowering of ambient temperatures, and increasing aesthetic appeal. If riparian streetside basins are located in a continuous series connected to a tributary or regional watercourse, they can expand the regional ecological network by extending minor biological corridors from the core of the network into the matrix of the development. When disconnected from the regional ecological network by a road or other constructed barrier, the value of this habitat is lowered, though they still contribute to the ecological function of the region by serving as â&#x20AC;&#x153;stepping stonesâ&#x20AC;? for flying animals. (see figure 8.1.9). Therefore, while the human benefit of integrated mitigated habitat within detention basins is very valuable throughout a developed matrix, habitat value is lowered as the

basin becomes more internal to the developed area. Most existing developed areas within the developed areas of Pima County are bounded by streets with concrete curbs which contain stormwaters that have arrived into the street until it is conveyed to a storm sewer, or channel. If a site is to be redeveloped, detention requirements are often increased. If existing streets are planned for continued use, they can be retrofitted with cutting or removal of curbs. Curb cuts are openings cut into the concrete to the level of the street at points along the curb to allow for stormwater conveyed by the street to be directed into street-side basins. Completely new developments, however, can skip the expense of curbing, shifting conveyance, as well as detention, into linear series of basins adjacent to the both the street and developed parcels. Because of their small size, street-side basins should concentrate woody plantings on slightly elevated extensions of side-slopes instead of internal planting islands.


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3a. No-curb Alternative (Street Even with Lot)

Figure 8.3.2 (left,) 8.3.3 (top): Basins abutting the pavement are only appropriate along small residential or rural roads, as depicted at left. Basin series extending from natural drainages are of higher habitat value than those separated by constructed barriers. Basins along arterial streets are more appropriate in medians or offset from the roads, which expand in size with increased traffic demand.

1. Street Scale

Figure 8.3.5: At the Confer private residence in the Colonia Solana neighborhood of Tucson, AZ, narrow streets (~24â&#x20AC;&#x2122;) drain into a series of slightly-depressed basins. When one of these fills to capacity, water bypasses it and flows into the next in the series.

2. ROW Zonation

Figure 8.3.6: In a rural, no-curb setting, a vegetation-free utility operational zone should be located between the road edge and street-side basins. When the road is down-cut from the surrounding grade, up-slope of the street-side basin, erosion control measures such as side-slope basins and slope-top diversion basin series can help prevent side slope erosion. (Design Collaborations, Ltd. 2009).

Key Questions for Design Decision

Figure 8.3.4: Urban street-side basins created by curb-cutting should be contained, along with a sidewalk or other pedestrian space, within the road right-of-way.

if a retrofit development: 1. Is it necessary to keep absolute stormwater control function of street? to keep curbs? 2. Are basin excavations compatible with existing underground and aboveground utility line location and maintenance zones? 3. Will placement of curb cuts degrade roadway pavement?

if a new development: 1. How is stormwater draining from secondary (not primary upstream wash ) adjacent areas going to be controlled? 2. What are the views on site from neighboring developments and how can they be designed for positive perception? 3. What is the form of the landscape of neighboring developments formal/


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Permitting, Maintenance, & Monitoring 1. Ideally, individual basins within a series should all be easily approached by vehicle and of a consistent form in order for simplification of maintenance strategy. 2. Outlets and inlets should be kept clear of clogging by accumulated brush of rhizomatous vegetation such as

Figure 8.3.7: Deep rectangular vegetated detention basin adjacent to impervious parking lot at Vernola Family Park, Riverside, CA.

Figure 8.3.8: Traffic circle: A parking area at the northern end of Columbus Boulevard in Tucson, AZ is designed around a concave, landscaped, pervious cul-de-sac that retains and infiltrates low-flows draining from the road, while providing a designed centerpiece of sculptural landscape.

3b. No-curb Alternative

5. Detention Basin orWater Harvesting Basin?

4. Curbed Alternative

cattail through manual removal (nonvehicular). 3. Maintenance responsibility lies with HOAs, facilities management staff, or municipal staff, depending on site location, but is never the responsibility of the individual homeowner of the private residential lot.

Additional Resources

City of Tucson. Department of Transportation. Stormwater Management Section, Water Harvesting Guidance Manual. Ann Audrey Phillips. Ordinance number 10210. 2005. Figure 8.3.11: Street-side water harvesting/retention basins should be dug to a depth of 6-12,” depending on subsurface improvements, to ensure adequate drainage.

Lancaster, Brad. Rainwater Harvesting for Drylands and Beyond;Vol. 2:Water-Harvesting Earthworks, Tucson: Rainsource Press, 2008. Waterfall, Patricia H. “Harvesting Rainwater for Landscape Use.” University of Arizona Cooperative Extension. <<http://ag.arizona. edu/pubs/water/az1344.pdf>> last revised 2006.

Figure 8.3.9: Curb-cut water-harvesting basins: By cutting away sections of an existing curb, low-flows are directed into shallow water-harvesting basins immediately adjacent to this residential street, and support hardy xeroriparian plants, at The Nature Conservancy water-harvesting demonstration site in Tucson, AZ (Watershed Management Group).

Figure 8.3.10: Basins in chicanes: In the Rincon Heights neighborhood of Tucson, AZ, water-harvesting basins are colocated within curb bumpouts, otherwise known as chicanes, which help slow the flow of traffic on streets of overdesigned width, and shade the street and sidewalk, reducing urban heat island effect (Silins 2010).

Figure 8.3.12: Street-side detention basins to varying depths can contain “nested” water harvesting/retention basins located below the bottom of the outlet pipe. Overflow occurs via the curb-cut inlet.

Watershed Management Group. “Guidelines for working in the right-of-way.” << http://www. watershedmg.org/sites/default/files/docs/ wmg_public_right_of_way_handout.pdf>> last revised 2008.


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lot-bottom basins

lot-bottom basins


76

LOt-bottom basins

lot-bottom basins

Figure 8.4.1: Lot-bottom basins (in blue)

Many basins detain runoff from large impermeable areas at the lowest point of a development or previously-developed region of the county. Basins of this size can take a variety of forms to support the growth of riparian habitat:

Basins located at the bottom of an intermediate-sized development or regional watershed catch excess runoff not detained and infiltrated within the matrix of the developed site. A benefit of locating riparian habitat within basins of this type is that they are generally located down-slope from impacted areas and are generally closer to tributary or regional watercourses that serve as major and minor biological corridors. Therefore, the creation of a riparian habitat mitigation area within one of these basins essentially contributes a connected node to an existing ecological network. While all detention basins are inundated by storm-water runoff, other sources of water should be considered. Residential, public, and golf course landscape overwatering, commonly known as â&#x20AC;&#x153;urban drool,â&#x20AC;? filtered or unfiltered, can be directed to planting areas. Other water sources that can irrigate plantings include

reclaimed water from industrial processing or the treatment of effluent, or actively-harvested water stored in tanks. Before designing a detention basin, the flow velocity and frequency of flow events through inlets should be modelled. Highvelocity storm surges should be slowed by some combination of open-flow channels, drop structures, and energy dissipation structures should be designed in order to protect downstream microbasin planting areas from destruction. Low-flows should be directed through a series of shallow terraces or microbasins. As a rule of thumb, the shallower the terraces or microbasins, the more area within them can be covered in small events. The floor of microbasins closer to feeder inlets should be at or above the floor elevation of those microbasins further from feeder inlets to allow for successive overflow.


77 Figure 8.4.2 (top,) 8.4.3 (bottom): In order to achieve the same capacity, a detention basinâ&#x20AC;&#x2122;s surface profile can vary from a steep drop and short, flat run, to an even-sloped, extendedrun, which is more conducive to mitigated habitat.

3. Natural Analogs

1. Bottom-profile Basics

2. Agricultural Analogs

Figure 8.4.5: A pool and riffle arrangement mimics the natural analog wherein pooling areas overflow through intermediate riffles or cascades. These can be created by bedrock intrusions or cobble deposits, as seen here in the Tabletop Wilderness, AZ. Note the density of vegetation located to the sides of the sandy deposit areas.

Figure 8.4.6: In Clarkdale, AZ, the Verde River currently runs south of ruins of the Tuzigoot Sinagua civilization, during which time the river ran around the north. This old river channel has become Peckâ&#x20AC;&#x2122;s Lake, a natural oxbow supplemented by waste water from an adjacent mining facility in town. Within it, Tavasci Marsh, a hydroriparian wetland and mesoriparian forest, provides ideal habitat for many bird species.

Key Questions for Design Decision Figure 8.4.4: Partial flow diversion of flowing waters is the essence of diversion canal agriculture in both temperate/tropical areas, as seen here in South China, and arid and semi-arid regions such as the Sonoran Desert, the home of the early canal-based protohistoric Hohokam civilization. Linear Terrace: direct series of overflow terraces; develop graphic or use image of rice paddies on slope (China Forum 2010).

1. What do available annual storm series data tell you about the relative frequency of small and large storm events? 2. What capacity must the master detention basin contain to handle a 100-year event? 3. What is the project budget? Can the master-plan allow for construction of a first phase without sacrificing the function of

future phases of development? 4. Are sensitive planting areas or recreational amenities to be included? Can the design of flow-diversion structures and offline systems protect these components? 5. Is the total detention basin to be visible and accessible? If not, is the design of an outof-sight offline detention basin appropriate?


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Permitting, Maintenance, & Monitoring 1. The maintenance of lot-bottom basins, as they are infrastructure internal to a development, lies with the neighborhood/ home-owners association, or the facilities management staff. 2. Maintenance personnel, whether they are residents, facilities staff, or contracted crew, must be educated as to the proper Figure 8.4.7: Pool and riffle: The Las Vegas Springs Preserve (Luchessi Galati, Inc./Natural Systems International) in Las Vegas, NV, concentrates hydroriparian plantings around successively lower perennial pooling areas consistently sloped towards their center, and riffle streams connecting them. In small storm events, vegetated overbank areas of both become inundated.

Figure 8.4.8: Curved Terrace, all flows: wide basins wrap around side slopes taking total volume of all storms, with no central/bypass negative space (overflow basin,) as in this multi-use master plan for Strathern Pit in Los Angeles (Natural Systems International).

4. Designed Flow Regimes

Additional Resources Campbell, Craig S. and Michael H. Ogden. Constructed Wetlands in the Sustainable Landscape. New York: John Wiley & Sons, Inc. 1999. Haan, C.T. B.J. Barfield, an J.C. Hayes. Design Hydrology and Sedimentology for Small Catchments. Academic Press, Inc., San Diego, 1994. Harris, Charles W. and Nicholas T. Dines. TimeSaver Standards for Landscape Architecture: second edition. New York: McGraw-Hill Publishing Company, 1998.

Figure 8.4.9: Subdivided terracing: Fine-scale grading of each microbasin should allow it to fill to capacity from low-flows emanating from its feeder inlet, then overflow to adjacent microbasins without â&#x20AC;&#x153;hoggingâ&#x20AC;? the full amount, in order to maximize the temporary pooling and saturation areas.

Figure 8.4.10: Low-flow channel, off-line component detention basins: At the Erie Lakes Detention Basin, CO, low flows (dark blue) are contained to a low-flow channel and water quality treatment pond, while, in large events, high-flows (light blue) back up at the outlet and overflow to an adjacent, off-line detention basin. This mimics the natural analog of a slough or oxbow lake in the overbank areas of a floodplain.

functioning condition of the designed riparian habitat, which is vastly different than typical residential, commercial, or park landscapes. Education can occur via on-site signage, site maintenance manual, and/or direct education of crew by the groundskeeper.

Kincade-Levario, Heather. Design forWater: Rainwater Harvesting, Stormwater Catchment, and Alternate Water Reuse. Gabriola Island, Canada: New Society Publishers, 2007. Lancaster, Brad. Rainwater Harvesting for Drylands and Beyond;Vol. 2:Water-Harvesting Earthworks, Tucson: Rainsource Press, 2008.

Mays, Larry W. Stormwater Collection Systems Design Handbook. McGraw-Hill, San Francisco, 2001 Pima County Department of Transportation and Flood Control District. Guidelines for the Development of Regional Multiple-Use Detention/ Retention Basins in Pima County, AZ . Prepared by Susan J. Hebel and Donald K. McGann. Pima County Department of Transportation and Flood Control District, Tucson, AZ, 1986. Pima County Department of Transportation and Flood Control District, and City of Tucson. Stormwater Detention/Retention Manual. Pima County Department of Transportation and Flood Control District, Tucson, AZ, 1987. Strom, Steven S. Site Engineering for Landscape Architects. Wiley Publishers, New York, 1998.


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Inflow Channels, drop structures

inflow channels, drop structures


inflow channels, , drop structures

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Inflow channels, drop structures

Figure 8.5.1: Inflow channels, drop structures

Inflow channels convey runoff to a detention basin, and, along with drop structures, can absorb energy, connect habitat, assist with sediment deposition, and create intriguing drama. In their design, the following should be considered:

Inlets to detention/retention basins can be one or many. In order to minimize erosion, all contributing watersheds, even minor ones to the side of the basin, should be directed into designed inlets. The type of inlet designed is highly dependent upon the form of the master plan. The first two components of an inlet, in order of the direction of flow, are the inflow channel/spillway, and drop structure. Generally, constructed infow channels should be kept free of vegetation to ensure proper conveyance. Open-channel inlet design begins with the concept that designed conveyance channels can serve secondary purposes, such as infiltration, recreation, and habitat, by slowing the passage of water through wider, easily accessible channels that contain vegetation. At Village Homes in Davis, CA, all residential lots drain to the rear of the property into open channels that are paralleled and crossed by walking paths, creating an interconnected network of common areas that are commonly used by home-owners and their children, fostering a

sense of community (Francis 2003). The success of this has influenced other community designs in California, Colorado and Arizona, in which open channels parallel the front of lots and the road, or within the median of a road. If the inflow channel continues upstream as a properly-functioning biological corridor, the spillway and drop structure should be designed in a way that encourages passage of terrestrial animals between the vegetated refugia of the channel above and the basin below. Additionally, as the upstream “tail” of the basin is lengthened, and the inflow channel within it is roughened with in-channel and overbank vegetation and either retained in original sinuous form or designed so, the energy of the incoming floodwaters is lessened and suspended sediment is given multiple opportunities to settle in low-energy areas of flow, requiring less of an engineered hardscape solution (Zeedyk and Clothier 2009). Pima County Technical Policy 009 bounds the design of inflow channels by requiring “a 12’


81 physical access corridor adjacent to the inflow channel and within the 16’ access easement for maintenance purposes.” Additionally, “no plantings, volunteer or otherwise, within 20’ radius of basin inlet or outlet, as measured from the edge of the structure,” are allowed in large basins, so that inlet or outlet structures that may require maintenance can be accessed by a utility truck or other heavy machinery (see figure 8.5.2). For smaller detention basins that can be maintained using smaller maintenance vehicles or by hand, landscaping may be allowed within a 20’ radius from the basin inlet and/or outlet on a case-by-case basis, subject to District review and approval.

Figure 8.5.2: Basins above 1/5 acre in size or those with inlets separated from outlets by more than 100 feet are subject to policy TECH-009, which requires a 12’ physical access corridor adjacent to the inflow channel and no woody plants around the inlet and outlet.

4. Open Channels

1. Maintenance Access 2. Culverts

3. Constructed Channels

Figure 8.5.5: The primary parkway of Ladera Ranch community in Orange County, CA, is flanked by a dual conveyance system, named the Sienna Botanica, that drains the entire development to a lot-bottom basin, provides an intermediate habitat-value biological corridor from the vegetated basin to wilderness located above the development, and improves water quality and infiltration along its length. These benefits, in sum, satisfy the development’s habitat mitigation requirements.

Figure 8.5.6: The Los Angeles River Revitalization Master Plan, designed by Tetra Tech, Inc., Mia Lehrer Associates, Civitas, Inc. and Wenk Associates, calls for a stream profile that contains concrete step terracing for with access ramps leading to a lowflow environment containing emergent vegetation and pool and riffle flow (City of Los Angeles 2007).

Key Questions for Design Decision

Figure 8.5.3: Below-grade metal pipes and culverts can safely deliver incoming flows basins where above-ground conveyance is impossible, as shown here at Vista Hermosa Park, Los Angeles, CA (Mia Lehrer Associates,) and Regency Park, North Natomas/Sacramento, CA.

Figure 8.5.4: Flows from small drainage areas can be conveyed to the basin via narrow channels armored with concrete or riprap, as at Ladera Ranch, CA, and in suburban Pima County, AZ, at right.

1. Do inlet channels retain ecological integrity? If so, can spillways and drop structures be designed in a way that accomplishes long-term hydraulic function and wildlife passage? 2. Can the basin be used to improve the quality of life of the development? Can the arrival and hydraulic management of

low-flows be sculpted into intriguing, ecorevelatory art? 3. Is sensitive use such as water quality treatment wetlands or lush mesoriparian woodlands designed within the immediate vicinity of the inlet? If so, can incoming hydraulic energy be absorbed by hardscape instream, or drop onto splash pads?


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Permitting, Maintenance, & Monitoring 1. Remove any volunteer plants from constructed inflow channels, but not from open flow channels or intentional planting areas. 2. Following major events, inspect drop structures for undercutting and the development of erosion channels other than the designed flow channel.

Figure 8.5.7: Runoff from an adjacent residential area arrives at the Greenway Wash through a concrete slip in low-flow conditions, swelling over a gabion walls in higher flows. The terrace created by these walls provides a xeroriparian planting area.

5. Concrete Slip and Gabion

3. Following major events, remove coarse woody debris and large inorganic trash such as tires and appliances to ensure proper hydraulic function

Figure 8.5.8: Inflows into a constructed wash that drains the Oro Valley Marketplace are dissipated by concrete blocks, a drop in elevation, and a rip-rapped isthmus of land that splits the flow.

5. Naturalized Cascade

6. Combined

7. Naturalized Concrete Dams

Figure 8.5.11: Cascade: Shop Creek outcrop soil cement slip into plunge pool, Off-set site soil-cement lifts: Curved, stratified drop structures created by site soil cement lifts enhance the appearance of water-quality wetlands and allow for natural observation along Shop Creek in Denver, CO (Wenk Associates).

Additional Resources The Arizona Wildlife Linkages Workgroup. Arizona’s Wildlife Linkages Assessment. Phoenix: Arizona Department of Transportation, 2006.

Figure 8.5.9: Falls, boulders set in concrete dam: At the Erie Lakes Detention Basin in Erie, Colorado, boulders from a local quarry were set into concrete in order to create 18” vertical drops that, along with adjacent hydroriparian plant growth, absorb hydraulic energy while re-creating points of natural wonder along a neighborhood greenway (Belt Collins West).

Figure 8.5.10: Concrete dam + boulders: At Horseshoe Park in Denver, CO, hydraulic energy from an inlet channel is dissipated by instream vegetation, an approximately 2’ dam, and boulders set above and below the dam (Wenk Associates).

City of Los Angeles. Los Angeles River Revitalization Master Plan. 2007. City of Tucson. Water Harvesting Guidance Manual. Ed. Anne Audrey Phillips. 2005.

Francis, Mark. Village Homes: A community by design. Washington: Island Press, 2003. Urban Drainage and Flood Control District. Drainage Criteria Manual (v. 3): chapter 4, Structural Best Management Practices Zeedyk, Bill and Van Clothier. 2009. Let theWater do theWork: Induced Meandering, an Evolving Method for Restoring Incised Channels. The Quivira Coalition, Santa Fe, NM.


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slope-tops

slope tops


slope-tops

84

slope-tops

Figure 8.6.1: Slope-tops (in tan)

The form of a riparian detention basinâ&#x20AC;&#x2122;s interior and edges is greatly influenced by the hydrological, biological, and developed nature of adjacent lands, and the transition to basin side slopes, which can take the following forms:

Minimally, the tops of detention basins must provide maintenance access and concentrate sheet flowing from minor adjacent watersheds into designed inlets. In order to accomplish the former, the tops all basins should preserve a 12â&#x20AC;&#x2122; maintenance access corridor within a 16â&#x20AC;&#x2122; maintenance easement (TECH-009). The transition between the side slope, which drains towards the basin bottom, and the inside of the flat or back-graded top is an area where head-cut erosion will often occur, dependent upon the degree to which adjacent runoff is concentrated into inlets. Maintenance of these head-cuts, most commonly done by regrading, can infringe upon functional areas along the top, including maintenance access/recreational pathways, safety barriers, and planting areas. In addition to erosion-prevention measures along the side slopes, the designer should also create a buffer space appropriately scaled to the height and slope of the side-slope for frequent re-grading between the steepest pitch of the side-slope and the beginning

of slope-top improvements. In this area, designed elements should be restricted to small shrubs and other elements that can be easily removed or replaced without significantly impacting the design. Maintenance access corridors along slope tops can double as recreational paths, and diversion swales and basins can enhance the ecological connectivity between the basin bottom and functionally-riparian inlet channels. Depending upon the size of the contributing watershed, waters flowing perpendicular or near perpendicular to the direction of the edge of the side slope should be diverted into a designed inlet structure through above-grade compacted berms, crown ditch swales, and/or a series of microbasins along this swale. Functionally-riparian inlet channels should be crossed over by bridging perpendicular roads and pathways in order to continue uninterrupted hydrologic processes and wildlife passage. Denuded inlet channels can be constructed more affordably to pass over top of the surface of the pathway.


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3. Recreational Amenities

Figure 8.6.2: Runoff from adjacent parcels can be collected in diversion swales or basins parallel to the top of the slope of the basin, and safely conveyed to a designed inlet. Diversion areas can be contained by compacted berms or multi-use paths.

1. Berm and Basin

Figure 8.6.4: At Bluff Lake Nature Center in Denver, CO, a perimeter trail is punctuated by scenic overlooks such as this, which give a sense of place, and an opportunity to reflect upon the features below.

2. Crown Ditch

Figure 8.6.5: Shade, a safe walking surface, and areas for discovery and play are important features of slope-top recreational trails, as seen in this proposed image of The Los Angeles River Revitalization Master Plan, designed by Tetra Tech. Inc., Mia Lehrer Associates, Civitas, Inc., and Wenk Associates (City of Los Angeles 2007).

Key Questions for Design Decision

Figure 8.6.3: A crown ditch installed at the top of this Sonoran desert roadway cutbank diverts sheet flow from adjacent lands to the right, preventing rill erosion on the designed side-slopes. (Arizona Department of Transportation 2008).

1. Is side-slope erosion from drainage problem areas in adjacent parcels likely without some sort of slope-top diversion? 2. Are the soils of the side-slope highly erosive? If so, does the soil of top-of-slope diversion structures need to be compacted to prevent undercutting? 3. Is the basin located along a river park, greenway, or other recreational path? If

so, how can this path be sited along the slope-top to maximize field of view of the riparian amenities below and help concentrate runoff into designed inlets? 4. Can slope-top diversion areas also be infiltration and riparian habitat areas? Can trees growing among them help to shade existing paths?


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Permitting, Maintenance, & Monitoring 1. After major storm events, pathways may have been damaged at intersections with channels, or sediment deposits may have settled in undesirable places. Monitor at least once yearly, after the monsoon system, and make necessary repairs. 2. Paved and gravel pathways can erode and settle from sinkholes, and should be refilled

Figure 8.6.6: This photo by the Arizona Wildlife Linkages Workgroup demonstrates the barrier to terrestrial animal passage posed by traditional culvert/scupper design, and the necessity for collaborative design between a project’s civil engineering and landscape architectural designers (The Arizona Wildlife Linkages Workgroup 2006).

Figure 8.6.7: At the Star Valley Basin 4 park of the Star Valley Village subdivision in southwest Tucson, constructed inlet channels flow over the surface of perpendicular pathways through dips in the paving, an appropriate solution when the upstream channel does not retain ecological integrity (Novak Environmental, Inc. 2010).

4. Pathway/Inlet Channel Intersection

Additional Resources Arizona Department of Transportation. Guidelines for Highways on Bureau of Land Management and U.S. Forest Service Lands. Phoenix: Arizona Department of Transportation, 2008, http://www. azdot.gov/Highways/Roadway_Engineering/ Roadside_Development/HwyBLM_USFS.asp (accessed 2010). The Arizona Wildlife Linkages Workgroup. Arizona’s Wildlife Linkages Assessment. Phoenix: Arizona Department of Transportation, 2006. Campbell, Craig S. and Michael H. Ogden. Constructed Wetlands in the Sustainable Landscape. New York: John Wiley & Sons, Inc. 1999.

Figure 8.6.8: At Milagro Cohousing Community in unincorporated Pima County west of Tucson, tributary washes pass underneath pathway bridges, preserving hydrologic dynamism and the passage of small animals.

and/or compacted with the base material when this occurs. 3. Maintain a vegetation free zone of 2’ to each side of the 12’ wide, slope-top, multiuse path. Clear overhanging branches if and only if they obstruct the necessary passage of maintenance vehicles at the time of maintenance.

Figure 8.6.9: Following an assessment of elk-vehicle collisions on AZ-SR 260 along the Mogollon Rim, Arizona Department of Transportation installed riparian underpasses that preserves passage through the flow channel and dry banks of Christopher Creek (The Arizona Wildlife Linkages Workgroup 2006).

Haan, C.T. B.J. Barfield, an J.C. Hayes. Design Hydrology and Sedimentology for Small Catchments. Academic Press, Inc., San Diego, 1994. Lancaster, Brad. Rainwater Harvesting for Drylands

and Beyond;Vol. 2:Water-Harvesting Earthworks, Tucson: Rainsource Press, 2008. Pima County Department of Transportation and Flood Control District, and City of Tucson. Stormwater Detention/Retention Manual. Pima County Department of Transportation and Flood Control District, Tucson, AZ, 1987. Zeedyk, Bill and Van Clothier. 2009. Let theWater do theWork: Induced Meandering, an Evolving Method for Restoring Incised Channels. The Quivira Coalition, Santa Fe, NM.


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safety and education

safety and education


88

safety and education

Safety and education

Figure 8.7.1: Safety and education

Acceptance, appreciation, and safe use of riparian basins by the public, maintenance staff, police and elected officials are essential for their successful function and maintenance, and can be promoted with the following techniques:

By its nature, recreational use within floodplains poses a risk of bodily harm. This is most pronounced in steep inflow channels, where flow velocities are greatest, and â&#x20AC;&#x153;wallsâ&#x20AC;? of water can arrive within instants, not providing a person enough time to escape from the nearest, sometimes far-away access point. For this reason, recreational use is not recommended within steep-walled inflow channels, and is instead focused to their slope-top banks. Detention basins differ from inflow channels in that, at the arrival of these high velocity floodwaters to a detention basin, they are instantly spread across a great amount of area, and the hydraulic energy of these flows is quickly dissipated both through this spreading, re-orientation of direction of flow downward over drop structures, and energy dissipation structures below on which they can splash. For these reasons, high-flows of inflow channels should either be directed to bypass channels that are not programmed for recreational use, or directed into an area in which they can

quickly be spread. In large storm events, slightly elevated berms of component microbasins will be the last soil within the basin bottom to become inundated, and are therefore ideal locations for walking trails. However, due to the vast area of the basin, inundation happens over a period of time in which visitors should be able to safely exit the basin. At worst, they may need to wade through water to reach an exit, but the time it takes to do so is minimal in comparison to the time it takes for the basin to fill to levels in which drowning would be likely. Due to this potential harm and the resultant liability that the managers of the site take on, and the opportunity for public education, design of these basins should seek to inform the visitor of the risk and the ecology of the site through verbal and symbolic communication. Landscape maintenance manuals should seek to educate the maintenance staff on the complex hydraulics and ecology of the site, as they are much different than traditional sites.


89 Figure 8.7.2: At the Anthem Hills multi-use basin in Henderson, NV, this sign, repeated around the basinâ&#x20AC;&#x2122;s perimeter, informs users of the risk of drowning during rain storms, in both English and Spanish, and through symbolic figures.

3. Non-verbal Signage

1. Signage Alerting Risks 2. Signage Informing Purpose

Figure 8.7.4: Riparian biotic process can be communicated nonverbally through symbolic sculpture, as along a greenway in the North Natomas neighborhood of Sacramento, CA.

Figure 8.7.5: At the Gowan Basins, in Las Vegas, NV, a line of concrete along the side-slopes communicates depth of floodwaters during flood events and function of the basin throughout the rest of the year.

Key Questions for Design Decision

Figure 8.7.3: Signage at a conservation area at the West Branch of the Santa Cruz River in Pima County informs the public of sensitive habitat value and use restrictions through text and images associated with riparian life (Burnham 2010).

1. What are the risks to the visitor during storm events and how can they best be prevented? 2. What is the metropolitanâ&#x20AC;&#x2122;s standard of legal liability of risk and recreational injury prevention for combined-use facilities? Is explicit signage the only acceptable form of communication per the law?

3. Can eco-revelatory art and/or non-verbal symbolism communicate risk and riparian process better than signage, which is often ignored?


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Permitting, Maintenance, & Monitoring 1. Fencing should be field-visited after major storm events, checked for damage from erosion, and repaired as necessary. 2. Signage should be cleaned or replaced when graffitied. 3. Remove flammable non-native vegetation (buffelgrass, fountain grass) to prevent wildfires in otherwise non-flammable

Figure 8.7.6 (near right): Sculptural gestures of flow draw the eye to the function of a small contributing open channel at the Springs Preserve in Las Vegas, NM (Luchessi, Galati, Inc.). Figure 8.7.7 (far right): This recirculating water feature at Vista Hermosa Park in Los Angeles makes a gesture of active riparian process throughout the year (Mia Lehrer Associates).

4. Symbols of Process 5. Fencing

Additional Resources Hall and Foreman, Inc./Mosaic Consulting, Inc., “Ladera Ranch: Sienna Botanica Maintenance Guidelines, Second Draft.” internal publication. April 16, 2001. Harris, Charles W. and Nicholas T. Dines. TimeSaver Standards for Landscape Architecture: second edition. New York: McGraw-Hill Publishing Company, 1998. Kincade-Levario, Heather. Design forWater: Rainwater Harvesting, Stormwater Catchment, and Alternate Water Reuse. Gabriola Island, Canada: New Society Publishers, 2007.

Figure 8.7.8: Fencing separating the user from sensitive or dangerous environments should seek to enhance understanding of views below, as seen at this fishing pond at Gilbert, AZ’s Water Ranch (C.F. Shuler, Inc.).

Figure 8.7.9: If the area is to be commonly used by visitors, investment in fencing types that contribute to the surrounding visual resources is most appropriate, as seen here in the form of a concrete seat wall, pipe and cable fence, and fencing composed of COR-10 t-bar posts, cable, and steel pipe railing (Luchessi, Galati, Inc.).

riparian communities. 4. Shade and cover encourage inhabitation by people, including the homeless and teenagers. Discouragement of this type of use can occur through frequent community use and/or police presence if a crime has been committed, but removal of vegetation within interior habitat is not allowed.

Lancaster, Brad. Rainwater Harvesting for Drylands and Beyond;Vol. 2:Water-Harvesting Earthworks, Tucson: Rainsource Press, 2008. Pima County Department of Transportation and Flood Control District. Guidelines for the

Development of Regional Multiple-Use Detention/ Retention Basins in Pima County, AZ . Prepared by Susan J. Hebel and Donald K. McGann. Pima County Department of Transportation and Flood Control District, Tucson, AZ, 1986. Pima County Department of Transportation and Flood Control District, and City of Tucson. Stormwater Detention/Retention Manual. Pima County Department of Transportation and Flood Control District, Tucson, AZ, 1987. Zeedyk, Bill and Van Clothier. 2009. Let the Water do the Work: Induced Meandering, an Evolving Method for Restoring Incised Channels. Chapter 8: Monitoring, Modification, and Maintenance. The Quivira Coalition, Santa Fe, NM.


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side-slopes

side-slopes


92

side sliopes

side-slopes

Figure 8.8.1: Side-slopes (in yellow)

Side-slopes of detention basins can be either separate or connect habitat and human use depending upon hydrologic routing, and the design of plantings and access paths. Primary considerations in the design of side slopes are:

Side slopes must serve at least two functions, maintenance access and drainage, and, preferably, a third function, habitat connectivity between functioning biological corridor above and habitat patch within the basin below. Traditionally, side-slopes and their component inlet drop structures have been designed as denuded hardscapes, that disconnect ecological networks and are susceptible to severe erosion (see figure 8.2.3). The form, function, and expense of detention basin side slopes are highly dependent upon the master plan type chosen (see “lot-bottom basins”). Often, in order to adequately dissipate incoming hydraulic energy, steep, rigid drop structures and coarse concrete energy dissipation structures are necessary at primary inlets (see sections ““Hydraulic Structures.”) However, portions of side-slopes that do not convey upstream drainage should not be built with steep slopes, as they do not need to dissipate hydraulic energy. In general, erosion is reduced and vegetation promoted when side slopes are less severe than

a 4:1 ratio, avoiding costly erosion-protection measures (City of Chandler 2002). However, as slopes become less severe, more land area is needed to create the same basin capacity, increasing cost. Side slopes are also the most common barrier to recreational access from adjacent residents, due to their severe slopes and unfriendly appearance. Multi-use pathways, terracing, finescale grading, and aesthetically-appealing vegetation improvements along side-slopes can transform these utilitarian spaces into recreational areas in which residents can interact with nature. These combined-use spaces can count as buffer-yard acreage as required by Pima County development code, and represent one of the best ways that developers can save money by reducing overall non-saleable acreage. (Pima County Development Services, Planning Division 1985).


93 Figure 8.8.2: Basin side slopes of an overall ratio of 3 to 1 are difficult and expensive to vegetate and may require costly erosion control measures on steeper portions (rip-rap).

3. Large-scale Drainage Features

Figure 8.8.3: Basin side slopes of an overall ratio of 6 to 1 allow for relatively inexpensive micro-grading to support vegetation along them.

1. (Habitat) Connectivity 2. Access

Figure 8.8.6: On-contour berms: At the Arizona Cancer Center in Tucson, AZ, building and slope runoff is retained by mid-slope shallow water-harvesting basins contained by an on-contour berm. Within this environment, mesquite, creosote, and desert willow have been established. Exceeding the capacity of this basin, overflow is directed through a naturalized concrete ditch to the street-side storm drain. This feature, along with inorganic rock mulch, prevents erosion rills from forming (Ten Eyck).

Figure 8.8.7: Cross-cut slope ditch, unvegetated; minibenching: At the recently-completed City of Chandler, AZ, Paseo Vista Park, rip-rapped ditches cross-cutting the steep side-slopes intercept small amounts of runoff from open slopes, which have temporarily been roughened with on-contour microberms to improve the success of hydroseeding. Larger flows from adjacent lands to the right of this picture are conveyed directly down the slope through rip-rapped channels perpendicular to the contour of the slope.

Key Questions for Design Decision

Figure 8.8.4: Asphalt ramp, stairs trail: At the Bluff Lake Nature Center in Denver, Colorado, access down steep bluffs to an observational gazebo overlooking the natural riparian basin below can be accomplished either by descending a gently sloping asphalt ramp or a more steeply-graded trail of decomposed granite with wide steps retained by wooden beams.

Figure 8.8.5: Decomposed granite walking trails descend the side slopes of the Springs Preserve along switchbacks which are built overtop of a minor-contributing drainage composed of stretches of vegetated ditch, caliche block check dams, and culvert pipes (Natural Systems International, Luchessi, Galati, Inc.) .

1. How much space is available in the development for detention? By overlapping bufferyard, recreational, and mitigated habitat acreage within the detention basin, can this area be increased to allow for shallower slopes? 2. Where are the primary and secondary inflow channels to be located along the side

slope? Is it possible to redirect secondary channels or divert base flows from primary channels along the slope via a cross-cut channel to increase planting conditions? 3. How will the basin bottom be accessed by maintenance staff and visitors? 4. Can cross-cut channel berms also serve as a path?


94 Figure 8.8.9: By following the slope contour, large “bioswales” can intercept, roughen, slow the velocity, biologically treat, and infiltrate runoff from the upslope (State of Oregon DEQ 2003).

2. crosscut channels

Permitting, Maintenance, & Monitoring 1. In order to slow the migration of soils from these side-slopes less steep than a 4:1 ratio, live plants, deadfall and litter from plants should be left in place. Prunings from recreational buffer zones or adjacent parcels can be placed on top of bare soil areas. Slopes steeper than a 4:1 ratio, though not recommended, should be

Figure 8.8.8: Retaining wall terraces: The Guadalupe River Park in San Jose, CA, designed by Hargreaves Associates, is an active channel that runs through the heart of the city’s downtown. Base flows run through a naturalized central corridor. Peak event flows then inundate, a series of even-graded terraces contained by human-scaled retaining walls, which serve as easilyaccessible, vegetated lunch-spots for local employees in base conditions.

4. Small-scale Drainage Features

Additional Resources Arizona Department of Transportation. Guidelines for Highways on Bureau of Land Management and U.S. Forest Service Lands. Phoenix: Arizona Department of Transportation, 2008, http://www. azdot.gov/Highways/Roadway_Engineering/ Roadside_Development/HwyBLM_USFS.asp (accessed 2010). City of San Jose. Department of Parks, Recreation and Neighborhoods Services. “Guadalupe River Trail.” << http://www.sjparks.org/Trails/ GRiver/index.asp>>, accessed April 12, 2010, last modified March 16, 2010. Pima County Development Services, Planning Division. Landscape Design Manual. 1985.

Figure 8.8.10: On-contour microberms: At Del Paso Park in Sacramento, CA, a steeply-sloped area adjacent to a recreational vernal pool detention basin was graded to include human-scaled, back-graded berms parallel to the contour of the slope, and successfully vegetated with container plantings and volunteer growth (The HLA Group and Foothill Associates).

Figure 8.8.11: Pocket plantings/berms: Vernola Family Park in Riverside County, CA, uses small berms surrounding container plantings on side-slopes, preventing drip irrigation from escaping a “pocket” for the establishment of the tree’s rooting system, but doing little to retard and infiltrate runoff flow into this rooting zone, making this an inferior method of side-slope grading..

stabilized by inorganic rip-rap. 2. In poorly-designed basins, rill erosion may create headcuts damaging or threatening to damage slope-top improvements or adjacent buildings. Deep rills should be re-graded and upstream drainage problem areas diverted to designed inlets.

Pima County Regional Flood Control District, City of Tucson, 2008. DRAFT Ordinance No. 2008FC____. An Ordinance of the Board of the Directors of the Pima County Flood Control District

relating to Floodplain Management codifying the Pima County floodplain and erosion hazard management ordinance as Title 16 of the Pima County Code. Tucson, AZ. <<http://www.sjparks.org/Trails/GRiver/index. asp>>


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hydraulic structures

hydrraulic structures


96

hydraulic structures

Figure 8.9.1: Hydraulic Structures

hydraulic structures

Hydraulic energy and sediment load of incoming stormwater flows have the potential to destroy the fine-scale grading and infiltration ability of microbasins. To mitigate these effects in an aesthetic manner, consider the following:

If the inlet channel continues upstream as a properly-functioning biological corridor, the spillway and drop structure should be designed in a way that encourages passage of terrestrial animals between the vegetated refugia of the channel above and the basin below (see figures 8.1.7, 8.8.31). Additionally, as the upstream “tail” of the basin is lengthened, and the inlet channel within it is roughened with in-channel and overbank vegetation and either retained in original sinuous form or designed so, the energy of the incoming floodwaters is absorbed and suspended sediment is given multiple opportunities to settle in low-energy areas of flow, requiring less of an engineered hardscape solution (Zeedyk and Clothier 2009). Along with drop structures, energy dissipators are one of the best opportunities to design moments of drama and hydrologic interpretation, as points of change of hydraulic energy states that are on the visible edge of riparian basins. As mentioned above, hydraulic energy

and sediment load of stormwater flows entering a detention basin following a sudden drop in elevation is highly dependent on master plan configuration and upstream channel design. In general, the less the contributing watershed and inlet channel is engineered, the more hydraulic energy can be absorbed by it, and the less that needs to be addressed upon arriving at the basin. As mentioned above, Pima County Policy TECH-009 requires a 20’ access buffer surrounding the drop structure. Energy dissipators and sediment traps can be located within the first 10’, with an additional 10’ allowed for vehicle access. As discussed in the section below entitled “Microbasins,” sedimentation leading to the formation of an impermeable surficial clay layer is a condition that greatly decreases the rate of soil infiltration and the ability of riparian vegetation to take root. A sediment trap prevents these fine sediments from reaching them, and is therefore an important component of a functional riparian detention basin.


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2. Inflow Channel Energy Dissipators

Figure 8.9.2 (left): The function of a sediment trap can be improved by the growth of non-woody annual vegetation that can assist in the process of aggradation, is nearly impossible to prevent or control, and poses no obstruction to vehicular maintenance, as seen here at the Kolb Road Basin, in Pima County, AZ. This exception to TECH-009 does not apply to woody vegetation, which can obstruct access. Figure 8.9.3 (top): In a community setting, weedy plant growth can be controlled by “destructive” active use, as seen here in the form of a childrens’ BMX play-space at the Anthem Hills Park, in Henderson, NV.

1. Sediment Traps

Figure 8.9.6: Channel bend, formalized: The hydraulic energy of inflows along this portion of Westerly Creek at Lowry Parks is absorbed by concrete walls along a severe bend of the creek. As shown, these walls slope down along with the direction of flow, allowing recreational access and appreciation of emergent wetland vegetation, which is planted within low-energy “shadows” of the ends of the wall sections (Wenk Associates).

Figure 8.9.7: Channel bend, naturalistic: At the Rillito River/ Swan Wetlands Restoration Project in Tucson, AZ, hydraulic energy of a tributary inflow channel is dissipated at severe bends of flow by stretches of soil-cemented bank terraces. Note that this terrace continues upstream, losing the soil cement, and adding riparian planting areas (RECON Environmental).

Key Questions for Design Decision

Figure 8.9.4: At the Oro Valley Marketplace in Oro Valley, AZ, incoming floodwaters from an arterial street above are dissipated of energy through a series of blocks, a rip-rap lined flow bifurcator, and a slight plunge pool in which sediment is trapped. In the flow energy shadow between the gully, xeroriparian trees have been planted.

Figure 8.9.5: This view of the sediment trap of the Erie Lakes Detention Basin, also depicted at left, demonstrates how moderate amounts of grass growing within the pooled water of the concrete catch-basin can help roughen flow, catch incoming sediments, biofilter the water, and mitigate the industrial nature of the structure, within easy access of a multi-use path. The water quality treatment pond below provides as a naturalistic view from the neighboring RV park (Belt Collins West).

1. What is the flow velocity within primary and secondary inflow channels? Can it be slowed within the inflow channel through natural cutbanks or designed energy dissipators? 2. Are there designed planting areas within the immediate vicinity of the arrival of inflows that can be damage by their

velocity? If so, as flows arrive at these points, can they be slowed through drop structures and/or energy dissipators that enhance the naturalistic or formal design of the basin and slope-top improvements? 3. Is incoming water laden with sediment? Can energy dissipators encourage settlement at downstream sediment traps?


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Permitting, Maintenance, & Monitoring 1. Woody vegetation in basins above 1/5 acre in size or those in which the distance between inlet and outlet is 100â&#x20AC;&#x2122; or greater is prohibited per TECH 009 policy (see figure X.X) 2. Though the Sonoran desert biome is vegetated mostly of small-statured plants, coarse woody debris and trash may accuFigure 8.9.8: Along daylighted Westerly Creek in the Stapleton neighborhood of Denver, CO, low-flows draining from an adjacent parcel are diverted into a water-quality treatment pond, while large-event flows bypass directly into the creek (EDAW).

mulate in energy dissipation structures with narrow interstitial space. These should be removed periodically; organic matter can be placed within interior habitat areas in the basins below, provided that the process of moving them there does not disturb them.

Figure 8.9.9: Storm surges arriving at Anthem Hills Park in Henderson, NV, a combined-use active recreational detention basin, are split and slowed by a single terraced rise, at right, mirroring the wide stair-step form of the rest of the drop structure, at left, which doubles as stairs to an open greenway channel internal to the neighborhood located upstream.

3. Flow Diverters 4. Energy Dissipation Structures

Figure 8.9.12: Further up Goldsmith Gulch, this combination drop/energy dissipation structure contains rough-hewn boulders set in an invisible concrete base, creating a naturalistic cascade along the riparian stream (Wenk Associates 2009).

Additional Resources The Arizona Wildlife Linkages Workgroup. Arizonaâ&#x20AC;&#x2122;s Wildlife Linkages Assessment. Phoenix: Arizona Department of Transportation, 2006. Figure 8.9.10: Below pipe: As large amounts of runoff flow in from an upstream housing development along Shop Creek, in Denver, CO, through a road box culvert, cubic blocks of concrete capture the eye and roughen the pipe flows arriving at a series of water quality treatment wetlands filled with cattails and surrounded by cottonwood and riparian scrub (Wenk Associates).

Figure 8.9.11: Below open channel: Along Goldsmith Gulch, at George Wallace Park, this formal drop and energy dissipation structure absorbs significant hydraulic energy among large colored-concrete blocks that serve as a playful amphitheater of seating within an inspirational, sculpturally abstract environment. Base flows spill out of a rectangular concrete channel, creating an elegant falls (Wenk Associates).

Haan, C.T. B.J. Barfield, an J.C. Hayes. Design Hydrology and Sedimentology for Small Catchments. Academic Press, Inc., San Diego, 1994. Pima County Department of Transportation and

Flood Control District, and City of Tucson. Stormwater Detention/Retention Manual. Pima County Department of Transportation and Flood Control District, Tucson, AZ, 1987. Zeedyk, Bill and Van Clothier. 2009. Let the Water do the Work: Induced Meandering, an Evolving Method for Restoring Incised Channels. The Quivira Coalition, Santa Fe, NM.


99

internal channels, outlets

internal channels, outlets


100

internal channels, outlets Channels internal to a detention basin either convey water between microbasins, or away from habitat areas that could be damaged by the hydraulic energy of high flows. Characteristic types are: Figure 8.10.1: Internal channels, outlets

internal channels, outlets

Channels within detention basins are necessary design components only when the master plan is of a type that requires them. Generally, small street-side basins only require channels between them, and design should follow open-channel or pipe recommendations outlined in the Pima County sections 3.1.6, Inlet Standards. As discussed above, vegetation in constructed conveyance channels is prohibited by TECH-009 since these channels are designed with the assumption of smooth sides. Often times a master-plan requires the divergence of base or low-flows from storm surge or high-flows. High flow channels within detention basins, in essence, are conveyance channels whose disrupted function and subsequent flooding may imperil adjacent parcels. In addition, high velocity flows within these channels can rip out any established vegetation within them. As such, mitigated riparian vegetation should not be planted within these

channels, either. Low-flow channels within detention basins, on the other hand, while important for distributing incoming floodwaters between vegetated micro-basins, do not carry an inherent risk to adjacent parcels outside of the floodplain, and therefore may contain vegetation. While the amount of flow passing between off-line, low-flow microbasins may be slight, the passage of water between them can cause erosion. Spillways between basins should be constructed from the top of a higher microbasin to the bottom of the next basin in the series. These may need to be constructed and lined with rock to manage prevent erosion headcutting from sacrificing the storage capacity of the higher microbasin (City of Tucson 2005).


101 Figure 8.10.2: At the Las Vegas Springs Preserve in Las Vegas, NV, urban drool and low-flows from small events are filtered and diverted into a series of permanent and ephemeral pools.

1. Separation of High and Low Flows, cont.

Figures 8.10.5: Incoming flows at the University of Colorado-Boulder Research Park wetland detention basin are subdivided into base (0-3 cfs, in dark blue) intermediate (3-8 cfs, in true blue) and high flows (8+ cfs, in light blue) with the use of flow diverters (in maroon) and large berms (in white.) 100-year storm event flows back up at the outlet and inundate 23 acres (in red hatching,) avoiding developments (in purple).

1. Separation of High and Low Flows Figure 8.10.3: The grading design (Luchessi Galati, Inc./Natural Systems, International,) ensures that the delicately-designed riparian habitat in the microbasins and its complementary passive recreational features will not be destroyed by high flows from large events by diverting these flows near the entry of the basin into a high-flow channel embanked by a large berm (in white).

Figure 8.10.4: An intermediate flow (3-8 cfs) inlet diverts flows from small storm events into the second pond of the system, creating a pastoral scene (diverter at right).

Key Questions for Design Decision 1. If the master-plan of the lot-bottom basin necessitates separation of flow, can a highflow bypass channel be contained by a high earthen berm? 2. Is there a series of microbasins or water quality treatment ponds? How much drop in grade is there between them? In order to prevent channels between them

from headcutting into the relatively upper pooling area, how much horizontal distance is needed to create a slope of less than 2%? 3. Are there trails in the basin? How can these cross channels without damaging them? 4. How can the outlet be positioned so that it is accessible, free of vegetation, and out of sight?


102

Permitting, Maintenance, & Monitoring 1. Repair channels between pooling areas by regrading or installing rigid hardscape if they headcut into upper pooling areas, causing them to fully drain. 2. Improve the strength of berms/levees of high-flow bypass channels with rip-rap or soil cement where their structural strength appears compromised.

3. Grub out vegetation and remove coarse debris within a 20 foot radius of large basins (>1/5 acre) and proportionally smaller radius for smaller basins to allow for proper drainage. 4. Re-grout portions of concrete-lined channels that appear to be breaking up.

Figure 8.10.6 (above): When channel water is of poor quality or supports habitat of high quality, barriers to entry may be appropriate (Kino Ecological Research Project, Tucson, AZ). Figure 8.10.7 (right): Pedestrian bridge over hydroriparian low-flow channel, Las Vegas Springs Preserve (Natural Systems International).

4. Recirculating Stream

2. Low-flow Channel

Figure 8.10.10: Where water resources are available, the incorporation of an above-ground stream can bring drama and a full array of riparian biotic communities to the sideslopes of a site. These designed watercourses should drain only a minimal watershed, as their built features and emergent streambank growth can be destroyed by large events. At the Riparian Preserve at Water Ranch in Gilbert, AZ, this channel lined with cobbles set in concrete connects a desert overlook with a fishing pond below (C.F. Shuler, Inc.).

3. Outlets

Additional Resources City of Tucson. Department of Transportation. Stormwater Management Section, Water Harvesting Guidance Manual. Ann Audrey Phillips. Ordinance number 10210. 2005. Figure 8.10.8: At Regency Park in North Natomas, Sacramento, CA, the outlet of a water-quality treatment pond and detention basin is hidden from view by concrete walls and kept free of vegetation with deep water.

Figure 8.10.9: Outlets can be disguised from view by hedge screening if they do not contribute to the aesthetic appeal of the system (Ladera Ranch, CA).

Hall and Foreman, Inc./Mosaic Consulting, Inc., â&#x20AC;&#x153;Ladera Ranch: Sienna Botanica Maintenance Guidelines, Second Draft.â&#x20AC;? internal publication. April 16, 2001.

University of Colorado-Boulder. UC-Boulder Research Park Master Site Development Plan and Flood Mitigation Plan. prepared by Downing, Thorpe and James. << http:// fm.colorado.edu/planning/projects/ResearchPark/documents/MasterSiteDevelopmentPlan. pdf>> 1987.


103 microbasins

micro-basins


micro-basins

104

micro-basins

Figure 8.11.1: Microbasins (in blue)

The goal of microbasin design is to create multiple microclimates for diverse riparian growth without creating long-term pooling. Finescale grading and soil profiles should therefore be guided by the following site components:

Microbasins are nested, shallow basins (often referred to as water harvesting basins,) within a larger master detention basin, that drain down through soil infiltration, but not out through a controlled-flow outlet, in order to increase the time of soil saturation optimal for riparian growth. In order to ensure drainage from these pooling areas within a 24-72 hour period, the minimum time needed for the life cycle of a mosquito, two primary factors, depth and sub-surface porosity, can be altered. Depth between the surface of the microbasin bottom and the elevation of the surrounding grade or basin berm should generally not exceed approximately 6â&#x20AC;?. However, when the soil profile below the surface of the basin has been improved by manual soil-loosening/aeration/ scarification, the addition of French drains or dry wells, and/or deep-mulching, the soil infiltration rate is increased, allowing for rapid drainage from a basin depth greater than 6â&#x20AC;?. Such cases are allowable on a case-by-case basis, subject to District review and approval.

As discussed above, clay sealing through repeated deposition events is a common problem in basins that causes water to pool without infiltration for long periods of time. Though sediment traps can help prevent sediments from reaching microbasins, some fine sediment will make its way to the microbasins over time, particularly during large inundation events in which the master detention basin is filled. Basin-bottom mulching primarily improves the condition of the growing areas when sediment does reach them, providing a decomposing, highly variable three-dimensional matrix in which they can deposit. Organic mulching also lowers the temperature and raises the carbon and other nutrient content within the soil, mirroring the organic catchment of natural drainages and making for a preferable growing medium for riparian plants. Once plants establish, their root structure further perforates and aerates the surficial crust, so that infiltration will increase over time as riparian communities establish.


105

2. Planting Islands

Figure 8.11.2: In wrap-around terracing, low-flow channel, or subdivided terracing, each microbasin should be offset 6 or more inches below of or at grade with upstream microbasins in order to ensure timely drainage.

1. Relative Depths Figure 8.11.4: In the middle of an open channel at Oro Valley Marketplace in the Town of Oro Valley, AZ, slightly elevated planting islands serve as point bars within the wash where instream vegetation is allowed to grow, buffered from hydraulic energy by the upstream earth of the island.

Mitigated micro-basin areas, since they restore native habitat, can be counted as landscape bufferyard per Pima County code (Pima County Development Services 1985). They can also be counted as water-harvesting catchment areas to gain points towards certification as a Pima County Regional Residential Green Building (Pima County Green Building Program 2009).

Figure 8.11.3: Micropooling areas at the Kolb Road Detention Basin in southeast Tucson receive fine sediments and saturate the lower trunks of the vegetation growing within them, precluding woody growth. Woody vegetation thrives in adjacent areas that are slightly elevated and drain relatively quickly, allowing the shoots to trunks to stay dry and the roots to access moister soils.

Figure 8.11.5: Slightly elevated planting islands within microbasins should be wide enough to accommodate a full-statured woody tree and understory shrubs surrounding it, but narrow enough to allow for these root systems to reach adjacent, slightly deeper pooling areas. In order to prevent trunk rot, the base of the treeâ&#x20AC;&#x2122;s trunk is out of the pooling area, which is mulched to prevent clay sealing.

Key Questions for Design Decision

1. How wide is the canopy of my target tree plantings? 2. How wide is my detention basin? 3. In what manner of master plan will the low-flows be subdivided into microbasins? 4. How many planting islands across will my microbasins be? 5. Is a sediment trap or other deposition area Figure 2: .

located upstream? Will the microbasins receive much sediment? 6. What is porosity of the site soil? Will it infiltrate and percolate too fast to support riparian vegetation? to slow to prevent mosquito breeding? If so, can soil and subsurface treatments generate appropriate soil infiltration conditions within budget?


106

3. Soil and Subsurface Treatments 2. surface profile Figure 8.11.6: Following grubbing of a riparian area to be disturbed, topsoils to a depth of 4 to 6 inches can be salvaged, temporarily stockpiled, and used to create an upper organic soil horizon in microbasins, giving the basin a “kick-start” of fertility, native seeds, and beneficial soil organisms.

Permitting, Maintenance, & Monitoring 1. “Bust the crust:” If microbasin bottoms become sealed with clay and silt, increase the pore space of the top soil by blading, using hand tools, and/or placing prunings and brush on top in order to promote proper soil infiltration. 2. Pooling areas will contain smaller interior strand species, and are necessary for

Figure 8.11.9: Organic mulch placed on top of site soil to a depth of approximately four inches, such as seen at this demonstration site on the NE corner of Country Club and Broadway in Tucson, will reduce evaporation and extend the period of soil saturation. As it decomposes, soil fertility will be enhanced until such time that established vegetation contributes leaf litter and deadfall.

Figure 8.11.7: French drains increase the storage capacity of the proximate soil profile by using coarse-grained, rough-edged, evenly-sized riprap in order to create maximum pore space. Infiltration rate and total capacity of microbasins is improved with this method, causing adjacent soils to be saturated for longer periods of time, benefiting deep-rooted woody growth.

Figure 8.11.8: Impermeable liners located just below the targeted rooting zone can increase the time of soil saturation when site soil conditions are too permeable, without creating problem pooling above the surface. These can be made from bentonite clay and geomembrane plastics, and should be designed to allow for inevitable root penetration. A disadvantage of liners is that roots are contained for the most part within the lined volume, and can be susceptible to root rot.

the success of trees on adjacent planting islands. Both areas should be counted as riparian habitat acreage. 3. Remove invasive weeds (see figure 8.12.6) 4. For the most part, microbasins should be left to go wild. These are the areas of interior habitat, and the more structural diversity, the better!

Additional Resources City of Tucson. Water Harvesting Guidance Manual. Ed. Anne Audrey Phillips. 2005. Lancaster, Brad. Rainwater Harvesting for Dry Lands and Beyond, Volume 2: Water-Harvesting Earthworks. Rainsource Press. 2008. Pima County Regional Flood Control District, City of Tucson, 2010. Regulated Riparian Habitat Mitigation Standards

and Implementation Guidelines. http://www.harvestingrainwater.com Waterfall, Patricia H. Harvesting Rainwater for Landscape Use. University of Arizona Cooperative Extension. 1998. (http://ag.arizona.edu/pubs/ water/az1052)


107

planting recommendations planting recommendations


108

planting Recommendations planting Recommendations

Mitigated riparian plantings, once established, must sustain without supplemental irrigation. The following species lists and planting techniques should guide the planting design of these habitats: Figure 8.12.1: Plantings

As discussed in the section above entitled “Riparian Ecology,” a process of regional, local, and site analysis of ecophysiological conditions should be undertaken in order to identify one or more target biotic communities to be designed within the detention basin, with the recognition that hydrologic processes and dynamic successional growth can alter the relative percentages of these related communities over time. In most cases, designed biotic community type should be the same as that which has been disturbed. The plant list of a site should include canopy trees, understory shrubs, and annual grasses and forbs, and should be further subdivided into planting zones. “Deep rooted” nursery stock are preferred for canopy tree container plants. Using this technique, desert leguminous tree seeds/ seedlings are grown in approximately 2’ long, narrow, soil-filled tubes, perforated on the bottom to allow for drainage and aeration. The benefit of this type in comparison to traditional, “bucket” plantings is that the root growth of the developing plant

is focused upon the extension of a deep tap root, mirroring the manner in which these plants would grow in field conditions, improving the chances of survival once it is planted at a habitat mitigation site with minimal establishment irrigation (localized drip, subsurface mat irrigation, or other approved method near the rootball of container plantings for the first few growing seasons (1-2 years)). The “shotgun” approach to plant seeding, where a seed mix with a wide variety of species affiliated with the target biotic community are broadcast over areas in which container plants have not been dug, and some species successfully establish while others don’t, takes much of the guess work out of site analysis and plant selection. Following seeding, broadcast sprinkler irrigation should be avoided in order to prevent the rapid growth of weedy plants that can “crowd out” the growth of species within the seed mix that are appropriate for the site conditions, by completely exhausting available solar, soil, and water resources, (and the seeds’ limited viability).


109

Figure 8.12.2: Planting zone codes: The zones of a detention basin are characterized by frequency of inundation, and can, in this way, be compared to a natural floodplain analog. Plant species can withstand varying periods of inundation, and have been categorized by the following zonation:

1. Planting Zones 2.Tall Pots

3. Hydroseeding

â&#x20AC;˘ Microbasin Bottom (MB): analogous to naturally-occurring depressions, these areas are subject to long periods of inundation and fine sediment deposits; generally, species in this group are non-woody and annual. â&#x20AC;˘ Microbasin Terrace (MT) and Channel Bank (CB): analogous to the margins of depression and streams, these areas are inundated only in times of moderate to large storm events. Plant species within them can withstand temporary inundation, and depend up increased water availability in the soils of adjacent zones for root growth. â&#x20AC;˘ Upland Inundated (UI): analogous to upland areas that experience rare sheet flow inundation, the species within this zone must be able to withstand rare inundation from the master detention basin in large events, and are either non-woody, succulent, or woody. Sonoran desert species common to dry hillsides are excluded from this group.

Key Questions for Design Decision

Figure 8.12.3 (top left,) 8.12.4 (top center): Long pots, such as these provided by Stuewe and Sons, allow for desert leguminous tree seedlings to grow to saplings much as they do in natural conditions, extending a deep tap root to reach available groundwater, as demonstrated by the three-month seedling at right. Traditional bucket pots, as deep as they are across, promote shallow roots that can become bound too tightly for optimal field planting.

Figure 8.12.5 (top right): Within water harvesting basins located on a riparian terrace of the Rillito River/Swan Wetlands Ecosystem Restoration Project, hydroseeded saltbush (Atriplex,) following broadcast sprinkler irrigation, has established thick mono-typic stands, though, overall, species evenness is low.

1. Which zones of the site will experience high-velocity flow, preventing plant growth? 2. In which areas must maintenance vehicles be able to pass? 3. Which zones of the site will experience frequent inundation? infrequent inundation? no inundation?

4. Based upon site soil conditions, subsurface improvements, and volume of inflow, how long will the rooting zone remain saturated over the course of the year? What is the target plant community based upon these conditions? 5. Are there invasive plant species in the contributing watershed?


110 As in a natural system, seeds in developed watersheds travel by wind, animal carrier, or, mostly, by water flow. Therefore, it is essential that the contributing watershed of basins which are designed for mitigated riparian habitat, including adjacent parcels, must not be planted with invasive non-native plants. While many invasive species are present throughout Pima County, a select few are hardy enough to establish significant stands within riparian basins. These are: • • • • • •

Permitting, Maintenance, & Monitoring 1. Remove invasive non-natives against which there is a fighting chance. Focus on buffelgrass, fountain grass, arundo, and tamarisk through manual (hand-tools, skidsteer loader,) and herbicidal removal (Basal bark, foliar, and/or cut stump application.) The rhizomal nature of Bermuda grass and Johnson grass makes them nearly

Buffelgrass (Pennisetum ciliare) Fountain grass (Pennisetum setaceum) Giant Cane (Arundo donax) Johnson Grass (Sorghum halapense) Salt Cedar (Tamarix ramosissima) Bermuda grass (Cynodon dactylon)

Figure 8.12.6: Four of the most common and invasive exotic plant species in Pima County that should be controlled within riparian habitat areas include (from right, clockwise,) arundo, salt cedar/tamarisk, and fountain grass, and buffelgrass. Arundo outcompetes native emergent plants, while the latter three can grow into profuse monotypic stands with limited water resources.

4. Invasive Species 5. Seed Mix List • Larrea tridentata: creosote bush (UI) • Atriplex canescens: fourwing saltbush (MB, MT, CB, UI) • Hymenoclea monogyra: burrobrush (MB, MT, CB) • Anisacanthus thurberi: chuparosa (MB, MT) • Encelia farinosa: brittlebush (UI) • Ambrosia deltoidea: triangle-leaf bursage (UI) • Ambrosia ambrosiodes: canyon ragweed (MB, MT, CB) • Sphaeralcea ambigua: desert globemallow (UI) • Cassia covesii: desert senna (UI) • Baileya multiradiata: desert marigold (UI) • Zinnia grandiflora: desert zinnia (UI) • Psilostrophe tagetina: Cooper’s paperflower (UI) • Machaeracantha tanacetifolia: tansyleaf spine aster (MB, CB, UI) • Glandularia gooddingii: Goodding’s verbena (MB, MT, CB) • Dyssodia pentachaeta: dogweed (MB, MT, CB, UI) • Bothriochloa barbinodis: cane beardgrass (MB, UI)

• • • • • • • • •

Bouteloua curtipendula: sideoats grama (MB, MT, CB) Sporobolus cryptandrus: sand dropseed (MB) Sporobolus contractus: spike dropseed (UI) Sporobolus wrightii: sacaton (MB) Leptochloa dubia: green sprangletop (MT, CB, UI) Hilaria mutica: tobosa grass (MB, MT, CB, UI) Hilaria rigida: big galleta (MB, MT, CB) Muhlenbergia emersleyi: bullgrass (MT, CB) Dichelostemma pulchellum: blue dicks (MB, MT, CB)

impossible to remove in a basin setting. 2. While deep-rooted trees can cause failure in constructed soils through root growth, they reduce slope erosion through the retention of soil by root networks and coarse litter. On excavated basin sideslopes, let them grow and leave the downfall!

6. Container Plant List

• Prosopis velutina: velvet mesquite (MT, CB, UI) • Parkinsonia floridum: blue palo verde (MT, CB) • Parkinsonia microphyllum: foothills palo verde (UI) • Chilopsis linearis: desert willow (MT, CB) • Olneya tesota: ironwood (MT, CB) • Acacia constricta: whitethorn acacia (MT, CB) • Acacia greggii: catclaw acacia (MT, CB, UI) • Lycium andersonii: Anderson’s wolfberry (MT, CB, UI)

• • • •

• • • •

Celtis pallida: desert hackberry (MT, CB) Larrea tridentata: creosote bush (UI) Baccharis salicifolia: seepwillow (MT, CB) Atriplex canescens: fourwing saltbush (MB, MT, CB, UI) Coursetia glandulosa: baby-bonnets (MT, CB) Aloysia wrightii: beebush (UI) Dalea Pulchra: dalea (UI) Ziziphus obtusifolia: gray thorn (MT, CB)

Additional Resources Bowers, Janice Emily. Shrubs and Trees of the Southwest Deserts. Tucson: Western National Parks Association, 1993.

Epple, Anne Orth. A Field Guide to the Plants of Arizona. Guilford, CT: The Globe Pequot Press, 1995.

Brown, David E. Biotic Communities: Southwestern United States and Northwestern Mexico. Salt Lake City: University of Utah Press, 1994.

Lancaster, Brad. Rainwater Harvesting for Drylands and Beyond;Vol. 2:Water-Harvesting Earthworks, Tucson: Rainsource Press, 2008.

Coronado RC&D Area, Inc. and Conservation Districts of Southeastern Arizona. Grasses of Southeastern Arizona. undated.

Arizona-Sonora Desert Museum. Steven J. Phillips and Patricia Wentworth Comus eds. A Natural History of the Sonoran Desert. Tucson: Arizona-Sonora Desert Museum Press, 2000.


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kolb road basin site analysis


112

Drainage Stormwater from UASTP, Rita Ranch, and the access road enters the Kolb Road Basin at three ~20â&#x20AC;&#x2122; inlet drop structures, as marked in red at left. Riprapped splash-pads at the bottom of the three inlets and adjacent areas appear to have partially siltified with a surface layer of fine sediment (areas in yellow.) The composition of these deposits seems to differ, resulting in variable plant growth among the three areas. Drainage from three adjacent areas was not considered in the original 1982 design, and this has caused multiple headcut rills (zig-zags in orange at left) along the

Figure 9.1.1: Deep headcutting erosion rills developed over the life of the basin, as documented by this PCRFCD filed visit in early 2008 (PCRFCD 2008).

side slopes of the basin as the collected stormwaters pass over the top and down the side of the basin side-slopes, creating maintenance access problems (see photo below and to right.) PCRFCD has filled these headcuts with rip-rap, which only serves as a temporary solution as rills appear to the sides of the rock soon thereafter (see photo at bottom right.)

Figure 9.1.2: Rills such as the one to the left were temporarily resolved by PCRFCD Infrastructure Management staff in 2008, through slope regrading and the installation of an uncompacted slope-top berm diverting sheet flow to rip-rapped gullies at points of heavy flow. This picture from November, 2009 demonstrates continued rilling to the left and right of a gully.


113 Figure 9.1.6 (right): Analysis of drainage at the Kolb Road Basin reveals problem drainage areas on adjacent parcels that were unaccounted for in original design, leading to side-slope rill erosion and soil deposition areas within the basin bottom. Figure 9.1.3 (left): Erosion rills continue to sacrifice the passability of the slope-top maintenance road.

Figure 9.1.4 (above): Aerial oblique photo of sideslope erosion rills prior to PCRFCD Infrastructure Management maintenance (Microsoft Bing 2009).

Figure 9.1.5 (left): Deposition of soils is storm events occurs as floodwaters from both designed inlets and erosion rills loses hydraulic energy and falls out of suspension. These have taken the form similar to the delta of a river.


114

vegetation Significant volunteer regrowth of xeroriparian scrub vegetation exists throughout the basinâ&#x20AC;&#x2122;s interior and along the inlet channels, as seen in green at far right. The basin top, levees, some adjacent parcels by Kolb Road, and major portions of the basin bottom, as shown in beige, have remained denuded since original disturbance. Clay-rich sedimentation and maintenance access disturbance has prevented regrowth at the base of the side slopes. Aside from the dominant Prosopis velutina and Baccharis sarothroides, representative plants of xeric scrub, interior strand, and semi-desert grassland communities occur throughout the site. Small stands of non-native Johnson grass and buffelgrass occur at the base of existing inlets. The nearby Rita Ranch Retention Basin supports dense thickets of mesquite and cottonwood, suggesting that a similar plant community could be

supported at Kolb by producing improved retention capacity and resultant infiltration. Taking a cue from the hydrological and soil conditions on site that have shown successful regrowth (see below,) these microbasins will need to be excavated to the same elevation as existing pooling areas, and be interspersed with planting islands on which xeroriparian trees may be container-planted. Field analysis of adjacent riparian washes and pooling areas revealed the growth of semi-desert grassland grass species such as Bothriochloa barbinodis, riparian annuals such as Datura meteloides and Ambrosia ambrosiodes, and a few more tree species including Parkinsonia microphylla and Acacia constricta. Other areas that were formerly desert scrub, but had been made riparian by were may take the form of existing pooling areas ponds to infiltrate increasing amounts of stormwater.

Figure 9.2.1: In shallow depressed areas of the basin bottom, sediment has collected, forming pools of above-ground water that supports only shallow-rooted annual grasses, forbs, and weeds. Adjacent elevated areas that do not receive this pooling water support mature velvet mesquite (Prosopis velutina) and desert broom (Baccharis sarothroides).

Figure 9.2.2: Large areas of the basin bottom are elevated in relation to the pooling areas seen at left. These areas, therefore, receive little infiltration, and supports only low brushy growth of primarily velvet mesquite (Prosopis velutina). These areas are ideal for potential revegetation.


115 Figure 9.2.6 (right): Existing vegetation at the Kolb Road Basin has been categorized into xeroriparian vegetation within the basin bottom and external drainages, and denuded areas on the side slopes, basin bottom, and external areas.

Figure 9.2.3 (left): Semi-desert grassland representative species such as cane beardgrass (Bothriochloa barbinodis) are present in man-made depressions along the railroad tracks near the basin, along with abundant desert broom (Baccharis sarothroides.)

Figure 9.2.4 (left): Tall stands of invasive Johnson grass (Sorghum halapense) replace velvet mesquite (Prosopis velutina) and desert broom (Baccharis sarothroides) in the high-energy zones at the base of designed inlets. This annual, rhizomatous grass is blown down in major storm events, and should be targeted for removal.

Figure 9.2.5 (below): This photo, taken from the middle designed inlet shows riparian vegetation circled in red both within the basin bottom and in the upstream channel. Red areas below correlate to green areas at right. Blue areas signify areas of sparse growth, correlated with tan areas at right.


116

planning context Current features adjacent to the site include a Burlington Northern Santa Fe/Amtrak railroad track, Kolb Road and the access road for the University of Arizona Science and Technology Park (UASTP.) The City of Tucson contracted Olsson Associates to design the dual-trail Julian Wash Greenway that extends the length of the wash, including a stretch in which it follows the northwestern and northeastern sides of the Kolb Road Basin. These plans include two interpretive stations just east of the basin. UASTP contracted The Planning Center (TPC) to create a master land use plan to drive and guide future development. At the time of this report, surrounding the basin, these plans include a public park-andride facility, a cell phone tower, a fire station, two

hotels, and a conference center. The flight departure corridor of the Davis Monthan Air Force base, due to the decibel level of noise, prohibits many human uses, including gathering areas. Plans for this area have wavered from a golf-course utilizing reclaimed water, to a preserve incorporating solar arrays and walking paths. To the south of the UASTP access road, KB Homes plans to build approximately 70 acres of single-family housing. Development of an additional residential area across Kolb Road is also underway. Additional planned uses for the eastern area of the park include a University of Arizona extension campus (UA South,) an experimental solar array, and other additional industrial development pads.

Figure 9.3.1: Within a 2.5 mile service radius (purple buffer) of the Kolb Road Basin (in blue line) lies many existing and proposed/ approved residential developments (blue underlay) that are currently underserved by parks (in red and yellow.) However, decibel levels from the DMAFB approachdeparture corridor (greyscale) will approach 60 db. As such, the Kolb Road basin is ideally positioned to be a passive recreational metro park to serve these neighborhoods.


117 Figure 9.3.2 (left): 60 decibels of noise is roughly equivalent to conversational speech or the clatter of a business office (DMAFB 2003).

Figure 9.3.4 (right): The UA Tech Park Master Land Use Plan, developed by The Planning Center, calls for industrial and open space usage within the flight paddle (red line,) and hospitality and public land use around Kolb Road Basin, at upper left.

Figure 9.3.3 (below): The Julian Wash Greenway has been designed along the northwestern and northeastern slope-tops of the Kolb Road Basin by Olsson Associates, under contract with the City of Tucson Parks and Recreation Department. Parallel trails enter on the north side of the outlet structure, and are punctuated with interpretive nodes on both sides of a bridge at inlet #3, with excellent views of the southeastern side slopes and the basin bottom.


118

circulation Kolb Road is a major N-S arterial in SE Tucson that lies to the west of the site. Entry to the UASTP from Kolb is through the UASTP Road, which is seen at the bottom of the image at left. The basin, and slope-top maintenance road, can be accessed by maintenance staff either from Kolb Road, through a levee road turning off of the UASTP road, or by a gasline road paralleling the railroad track (shown in small black dashed line at far right). This access road currently veers away from the basin top between drop structures 2 and 3 through a drainage easement intersecting UASTP land. Olsson Associates has designed the Julian Wash Greenway to parallel the northwest side of the basin, mount the levee to the north, and cross the diversion channel on its way southeast, as shown by the dashed red line at left and the construction document at right. Maintenance vehicles will be able

Figure 9.4.1: The Julian Wash proposal, designed by Olsson Associates, contains a multi-use path composed of a 95% compacted subgrade and a “Apache Brown” decomposed granite pathway (Olsson Associates 2009).

to drive upon the paved path, and enter the basin top at a proposed access gate (green star.) Another trail will be surfaced with 2 inches of 1/4”-minus granite over leveled, 95% compacted native fill. Designed improvements for the Kolb Road Basin should consider continuity with the design type of the Julian Wash Greenway if it is to become an extension of it.


119 Figure 9.4.4 (right): Existing maintenance access to the basin occurs along levees, and the internal perimeter along the slopetops. The Julian Wash Greenway will replace the northwestern portion of this access road.

Figure 9.4.2: The UASTP road meets Kolb Road across from an industrial complex, and currently is flanked by native desert scrub vegetation and mesquite plantings.

Figure 9.4.3: The Julian Wash Greenway (proposed) will transform provide maintenance access for PCRFCD staff along an asphalt trail that will replace the existing maintenance road along the slope tops. In addition, the existing fence will be removed and replaced with a new barricade railing located closer to the top of the side-slopes than the existing fence. A controlled access gate will be installed where the green star is located, allowing for continued access to the southeastern portion of the perimeter road to PCRFCD staff. Interpretive nodes will be located at the circular features below (modified from Olsson Associates 2009).


120

kolb road basin design


121

Phase 1: xeroriparian mitigation Phase 1 of the design includes a xeroriparian habitat mitigation area within the Kolb Road Basin parcel that will preserve the capacity of the ultimate detention basin, resolve erosion problems on the side slopes of the basin, allow maintenance access by Pima County Flood Control District Infrastructure Management staff, and allow passive recreational use by visitors.

Grading:

Sixteen acres of xeroriparian habitat will be planted within 4 Shallow Basins excavated to a depth of 6”-1’ from the existing basin bottom. These shallow basins will be contoured with pooling areas and planting islands as described in the “Microbasins” subsection of the “Design Guidelines” above. Salvaged riparian topsoil from the Airport Wash disturbance site will be imported to the surface profile of these Shallow Basins, to allow for greater infiltration of soils by pooling water, and improve growing conditions. Soil excavated to a depth of 1.5’ across the 16 acres of the Shallow Basins will be stockpiled along the side-slopes, in two large berms that will gently drain slope runoff toward existing inlets 1-3, and rip-rapped gullies (see figure 10.1.X). A compacted berm will also be located along the top of the side-slope to solidify the existing drainage strategy diverting sheet flow into these designed sideslope drainages.

Access: Maintenance access to the basin will continue from the gas pipeline road paralleling the railroad, from the N-S trending levee arriving at the central inlet, and from the southwest corner, and also from the proposed Julian Wash Greenway, when it is built. Perimeter maintenance access will be preserved along the slope-tops, which will be protected from further rill erosion. Access to the basin bottom for both maintenance staff and visitors will continue to be served by the gently-sloping existing inlets. Additional Walking Trails encircling the shallow basins will provide further opportunities for observation of wildlife and the water-harvesting features.

Phasing: Recognizing financial and political constraints, the zones of the master plan have been divided into two phases. The designed improvements of phase 1 can function with little maintenance, and can be constructed without compromising the construction feasibility or function of zones included in later phases. Excavated soil material stockpiled along the side slopes in phase 1 can be used as fill and recontoured to create an expanded side-slope design, explained in phase 2. Figure 10.1.1 (right): Existing maintenance access to the basin occurs along levees, and the internal perimeter along the slope-tops. The Julian Wash Greenway will replace the northwestern portion of this access road.


122 Figure 10.1.2 (right): Off-site sheet flow runoff is diverted by a compacted berm on the inside of the access road, and conveyed along the road until it meets an existing inlet or rip-rapped channel. Rain falling directly on the side-slopes is conveyed in a similar fashion by two more uncompacted wide berms closer further down-slope. Runoff reaching the bottom is both directed to existing pooling areas, and proposed shallow basins excavated to a similar depth.

Figure 10.1.3. Cross section AA: : During phase 1, soil will be excavated to an approximate depth of one foot from microbasins in the bottom of the master basin, in which 17 acres of xeroriparian habitat will be planted. This fill will be transported and stockpiled along the side slopes, and backgraded to direct runoff to existing rip-rapped gullies. Maintenance access will be preserved along the existing slopetop road, and a compacted berm will be constructed on the edge of this road to prevent side-slope rill erosion.


123

Phase 2: passerines park Phase 2 of the design will take advantage of the excavated soils from phase 1 to create more extensive diversion and sideslope improvements. An expanded slope-top pathway will seamlessly connect the proposed Julian Wash Greenway to a perimeter loop of passive-recreational nature, with a parallel swale punctuated by water-harvesting basins to encourage further riparian growth. Rip-rapped channels will be removed, and low-flow diversion devices installed within existing inlets, and the ends of the vegetated runoff swales, directing them into a low-flow channel transversing the side-slope, and will be paralleled by multi-use paths and walking paths for observation and demonstration of the riparian habitat mitigation design.

Grading: Four Low-Flow Channel Areas (~2 acres) will be constructed along the side slopes, and Off-site Runoff Basins/Swales (~1 acre) capturing nuisance off-site runoff and concentrating it into multiple Feeder Channels (<1 acre) leading to the larger low-flow channels. Side-slope areas between these larger-scaled features will be gently terraced with back-sloped On-Contour Berms to promote upland revegetation. Incoming flows from 2-year events or lesser at the three current inlets will be diverted as they crest the top of the basin through hardened structures to low-flow channels which gently descend along courses roughly parallel to the side slopes. Waters passing through these low-flow channels, contained

by a slight berm, will collect in a series of micro-basins separated by smaller drop structures of 2-3â&#x20AC;&#x2122; (see figure 10.2.3). Smaller â&#x20AC;&#x153;feederâ&#x20AC;? flows entering from the drainage problem areas or falling directly onto the side slopes will be directed into these low-flow channels through lesser bermed channels. Depending upon budget, french drains may be installed below the channels and basins of the side slope and basin top in order to enhance infiltration and encourage soilstabilizing root growth. Flows occurring in events greater than the 2-year event will bypass these low-flow channels, instead flowing directly over top of the diversion structures, and will be quickly spread by sculptural energy dissipation devices at their base in order to protect sensitive planting areas, and provide an intriguing, playful observation area. Flows of all sizes will then be directed into the Shallow Basins constructed in phase 1. The amount of soil needed to be added to the proposed side-slope improvements of phase 2 is ~ 1,027,000 cubic feet. This amount will be available on-site from the excavated material from the off-site runoff swales, and the stockpiled fill from phase 1. French drains increase the pore space of the underlying soil, and would increase the capacity of the basin under which they lay by approximately 1/3 to 1/2 of the volume of the drain. Figure 10.2.1 (right): Passerines Park combines large-scale interior habitat areas of phase 1 with highly-interactive slope-top and side-slope improvements that clearly reveal the techniques employed to create riparian experience.


124 Figure 10.2.2 (right): Phase 2 will utilize stockpiled fill soil from phase 1 to expand access along the side slopes, which will be hydrated by the diversion of all flows from drainage problem areas and low-flows from existing designed inlets. Each microbasin will overtop to the next through energy dissipators that will prevent erosion headcutting and slow the flow.

Access: The perimeter road from phase 1 will be moved in towards the center of the basin, and improved to recreational use standards. Multi-Use Path/Access Roads will descend into the basin from the proposed Julian Wash Greenway entry gate and the southwest corner and will provide pedestrian, bicycle, and maintenance vehicle access to the mitigation areas and hardened structures; another will be located along the top of the side slope. Hardened structures will be designed such that they will also serve as climbable vista points for bird watchers and other recreationists. Additional Walking Trails encircling the shallow basins and following the low-flow channels will provide further opportunities for observation of wildlife and the water-harvesting features.

Phasing: Recognizing financial and political constraints, the zones of the master plan have been divided into two phases. Improvements in phase two are of a mostly recreational and aesthetic nature, and therefore must be funded by parks and recreation funds or as part of a public-private agreement with UASTP.

Figure 10.2.3. Cross section AA: : The visitor to Passerines Park will have a variety of riparian experiences to choose among, from shaded, sweeping vistas along the busy circulatory overlook along the top to the peace and solitude of the wooded canopy below. ..


125

future directions


126

Southwestern Lands Innovation Center

The University of Arizona Science and Technology Park is uniquely positioned to become the innovation hub of alternative energies and sustainable arid-land design. Tucson lies at the crossroads between cultures, nations, states, and ecosystems, and boasts an internationally-renown cadre of scientists and designers at the University of Arizona and regional companies such as Raytheon, Intuit, and UASTP’s own, IBM. As the University breaks ground on the Arizona Bioscience Park, planned to become the a state and regional leader in biotech research, the University has struggled to find additional space within its confined boundaries for the type of land-intensive research necessary for solar, wind, and hydrological technologies. UASTP currently holds 140 million square feet of commercial property on undeveloped acreage contiguous to an already-thriving computer software and hardware development laboratory at it east end. Much of this acreage lies within the departure corridor of the Davis Monthan Air Force Base, and, due to ambient noise levels exceeding 65 decibels from engine noise, is undevelopable for offices, residential, or commercial use. Currently, the park lies on the eastern fringe of residential development in the city, and both City of Tucson and Pima County project plan for the lands surrounding it to be built out as the metropolitan area reaches it threshold long-term capacity given available groundwater resources. As such, the traditionally undevelopable lands at UASTP within the flight paddle serve as an ideal opportunity for large, experimental solar, water and productive land use technologies, and industrial auxiliary buildings, set in the middle of a large potential future work force, with pre-built communications and utility infrastructure of the park, and easy freight access to both the Burlington Northern Santa Fe Railroad and Interstate 10. Those lands outside of the flight paddle, including the majority of lands along the proposed Science and Technology Park Road, are ideal locations for associated support offices, light commerce, residential, hospitality, park and ride, and fire station, and has been master-planned as such by The Planning Center within recent years. Like many university research parks, UASTP has been seeking the right combination of business sectors, hotel and conference capacity, and quality-of-life amenities to make it attractive to small and large businesses seeking to expand their operations. Three ideas in particular have been suggested by UASTP and The Planning Center staff over the years, to address these needs. One of these original ideas forwarded to make the park more attractive to businesses was the creation of an 18-hole golf course, in the flight paddle, adjacent to a pro shop, conference center, and two hotels. This model of business park has seen success in many of the early business parks of the late 70s, 80s, and 90s, as it creates a pastoral grounds setting in which park employees and hotel/conference visitors can stroll, recreate, and project wealth and order in a highly formalized, business-appropriate setting. While this traditional type of business park is common in areas with more abundant resources, such as the east coast, Midwest, and West Coast, fewer examples of this type exist in the southwestern U.S., primarily due to cost of water resources. Among them are the Interlocken development of Louisville, CO, and numerous developments of Phoenix, AZ. However, Tucson has a mean annual rainfall of 13 inches/year, a population base that is reaching its capacity for growth in order to maintain a sustainable yield of the valley’s aquifer, and a city development department that controls the ratio of golf courses to population so that local recreational need is met but a greater tourist draw is discouraged. As such, the enormous use of water resources, even if it is from reclaimed sources, should be heavily questioned. Recently, the leaders of UASTP and the designers and planners at The Planning Center have latched onto a new direction to guide the park’s future development. Their goal, now, is to make the UASTP the “greenest” university research park in the nation, one who’s physical design and business recruitment is


127 geared towards energy efficiency, prudent natural resource use, and further sustainable innovation. The first concrete manifestation of this new goal has been designed at the eastern entrance of the park, where a solar plaza, solar array company/startup, serving as an eastern solar anchor to define the park’s green commitment. In order to synthesize both the old dream of a hotel and conference center with the new proposed designs of the solar plaza, UASTP should build upon the water-wise development of both the Kolb Road Basin Xeroriparian Mitigation Area and Passerines Park, and anchor both the western half of the park with a motif of hydrological innovation. This development can be use both the design recommendations and site analysis from this report as guidelines for the siting of parcels. Imagine becoming fixed in discussion with a doctoral candidate of subsurface irrigation technology, picking his brain on his novel methods, and inviting him to join you for a desert dining experience on the first-floor back-porch restaurant patio, enjoying a burbling stream emanating from a gorgeous interior tinaja grotto, and watching the sun set over the city of Tucson and it’s mountains beyond, as torches alight to your sides to keep you warm against the cool, creosote-soaked breezes wafting down the Julian Wash. The next morning, you step out on to your northern-facing balcony with the morning’s cup of coffee and complimentary newspaper, as you breath in the moisture of a Sonoran desert morning, and chase the path of a mating pair of phainopepla until you fix upon the brilliant foliage of a Vermilion flycatcher tucked between the canopy of a mesquite and the robust shrubbery of a salt-bush. Satisfied, you then throw on your power suit, zip down eight floors, and begin the day’s first event, detailing the fluid mechanics of passive solar home technologies. Following the day’s proceedings, at the personal suggestion of the keynote speaker, you and your group join him for a round of Disc golf, using discs complimentary borrowed to you by the front desk. With disc satchel and bottle of water in hand, you all stride past the restaurant porch on to the slopetop recreational loop, pausing to admire and comprehend the recreated desert wash system below at one of many interpretive nodes. Finally, you arrive at your destination, hole 1, beginning on top of the former spoils pile, once again given the opportunity to take into a panoramic view of the Tucson Valley, experimental developments already established at the tech park, and delineated building pads that, from this perspective, seem like they may be ideal locations for your company’s next endeavor. The next morning, before you leave, you once again take in the beauty of the site by lacing up your running shoes to take a 5 mile loop around the basin, east along the Julian Wash Greenway, and back around an interior loop that allows you to get a closer view of the parcels you spied the day before.


128

conclusion


129 In order to truly create a design environment conducive to combined-use detention basin design, the municipal, state, and federal agencies of a metropolitan region, including the flood control district, parks and recreation departments, fish and game agencies, Army Corps of Engineers, and Bureau of Reclamation, must not only have policy encourages inter-agency, cross-professional, collaborative work, but also must exhibit leadership from both the internal regulatory and external design professions to accomplish this goal. Risk-averse flood control districts, most importantly, must be charged with the additional uses of riparian habitat, recreation, water treatment, and landscape aesthetics from the “bundle of sticks,” and should seek the involvement of fish and game departments, parks and recreation departments, and the Army Corps of Engineers in order to acquire additional funding to accomplish these more expensive designs in publiclyowned basins. Private developers, when approaching a project, should be incentivized to create these combined-use systems by allowing them to meet overlapping code requirements of habitat mitigation, landscape buffers, recreational space, and open space within detention basins. Finally, during the design process of publicly-owned basins, needs assessments of local neighborhoods and adjacent private landowners should be considered, so that the ultimate design of the combined-use basin encourages community, environmental education, and private investment development. When compared to other southwestern U.S. arid and semi-arid metropolitan areas, Pima County has shown leadership in combining two of these uses, flood control and conveyance and riparian habitat, but falls short of encouraging interactive riparian experience and recreational use of detention basins. The Riparian Habitat Protection Ordinance has successfully prioritized a use that has always been within the charter of the Regional Flood Control District, but the “integrated program of natural resource management and flood and erosion hazard reduction” called for in Pima County Code, section 16.04.030, “to maintain a balanced and cooperative relationship between human communities and the land and resources that sustain them,” through “maintenance of natural hydrologic and hydraulic stream flow processes, with consideration for groundwater recharge, aesthetics, natural open space, recreation areas, and flora, fauna, and other wildlife habitat resources,” has marginalized the contributions that both the County’s and incorporated cities’ parks and recreation departments, and the profession of landscape architecture, can make. The Kino Ecological Research Project, held by the district as an example of this integrated approach, while being a positive step towards combined-use design with federal involvement, fails to integrate sanctioned, riparian-focused recreational use and education or a sense of aesthetic. The support of the District in creating this report, in particular the design guidelines for mitigated riparian habitat with detention basins, demonstrates a willingness to improve the design and development environment to better serve the residents of the county. These guidelines, by demonstrating a method by which riparian habitat can not only be incorporated into a site’s detention basin/s, but also improve a site’s livability and marketability, will hopefully serve as a starting point for further policy improvement and interagency collaboration in order to accomplish true integration between natural resource managers, flood control engineers, and landscape designers. Additionally, phase 1 of the Kolb Road Basin retrofit demonstrates a willingness on the part of the District to advance detention basin use in concrete form, by directing Granite Construction Company mitigation dollars from the disturbance of Upper Airport Wash into an off-site mitigation of 17 acres of xeroriparian habitat. While the designer of this project is disappointed that a more combined-use approach with collaborative involvement with parks and recreation departments and the University of Arizona Science and Technology Park was not adopted, it is hoped that the district remains committed to future phases of this design, which will truly extend its value from riparian habitat mitigation to environmental education, community recreational use, and synergistic economic benefit to the UASTP. Likewise, it is hoped that parks and recreation departments, UASTP, and their design and planning consultant, The Planning Center,


130 consider the ideas put forth in this report as they continue to design and define what the Julian Wash Greenway, the UASTP, and the Kolb Road Basin is to become.


131

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138 Worthington, Glen. Personal Communication. Orange County Great Park Corporation. 2010. Zeedyk, Bill and Van Clothier. Let theWater do theWork: Induced Meandering, an Evolving Method for Restoring Incised Channels. Santa Fe: The Quivira Coalition, 2009.


139

imagery cited


140 Figure 8.1.2: Pima County Regional Flood Control District. “Species change with increasing depth to groundwater in a Sonoran riparian ecosystem.” 2010. Figure 8.1.4: Daniels, Alan. “Flow of a River,” p. 51, from: Jenkins, Matt “Just add water.” Nature Conservancy Magazine, 58, no. 2 (Summer 2008): 45-55. Figure 8.1.5: modified from “Figure 3: Biogeographics Provinces of the Southwest,” p. 13, from: Brown, David E. ed. Biotic Communities: Southwestern United States and Northwestern Mexico. Salt Lake City: University of Utah Press, 1994. Figure 8.1.11: Lynch, Kevin. The Image of the City. Cambridge: M.I.T. Press, 1960. acquired from Sundilson, Ethan, “Kevin Lynch: City Elements Create Images in Our Mind, 1960” <<http://www.csiss. org/classics/content/62>> University of California, Santa Barbara: Center for Spatially Integrated Science. 2009. Figure 8.2.3: Pima County Regional Flood Control District. “Field Report for: Kolb Road Basin.” 2008. Figure 8.2.5: City of Tucson Planning Department, Pima County, the University of Arizona. Joesler & Murphey: An Architectural Legacy for Tucson. City of Tucson Planning Department, Tucson, AZ, 1994. Figure 8.2.6: Davis Monthan Air Force Base. Arizona Military Regional Compatibility Project. DavisMonthan Air Force Base/Tucson Joint Land Use Study. Public Informational Meeting, September, 2003. Figure 8.2.8: C.F. Shuler, Inc. “Riparian Preserve at Water Ranch, Town of Gilbert, AZ.” 2010 Figure 8.3.6: Design Collaborations, Ltd. from Street Edge Water Harvesting: Green Corridors for Our Community. 2009. Figure 8.3.10: Silins, Joe. “Chicane.” Watershed Management Group. 2010. Figure 8.4.4: China Forum. “ricepaddy2.” <<http://bbs.chinadaily.com.cn/redirect.php?gid=2&fid=6&t id=554951&goto=nextnewset,%20>> accessed March 29, 2010. Figure 8.5.6: City of Los Angeles. Los Angeles River Revitalization Master Plan. 2007. Figure 8.6.5: City of Los Angeles. Los Angeles River Revitalization Master Plan. 2007. Figure 8.6.6: The Arizona Wildlife Linkages Workgroup. Arizona’sWildlife Linkages Assessment. Arizona Department of Transportation. 2006. Figure 8.6.7: Novak Environmental, Inc. 2010. Figure 8.6.8: The Arizona Wildlife Linkages Workgroup. Arizona’sWildlife Linkages Assessment. Arizona Department of Transportation. 2006.


141 Figure 8.7.3: Burnham, Dave. Pima County Graphic Services. 2010. Figure 8.8.9: State of Oregon Department of Environmental Quality. “Biofilters (Bioswales, Vegetative Buffers, & Constructed Wetlands) For Storm Water Discharge and Pollution Removal.” 2003. Figure 8.9.12: Wenk Associates, “GoldsmithGulch.DropStructure.” 2009. Figure 9.1.1: Pima County Regional Flood Control District. “Field Report for: Kolb Road Basin.” 2008. Figure 9.1.4 (above): Microsoft Bing. 2009. Figure 9.3.2: Davis Monthan Air Force Base. Arizona Military Regional Compatibility Project. DavisMonthan Air Force Base/Tucson Joint Land Use Study. Public Informational Meeting, September, 2003. Figure 9.4.2: “Granite Path.” Sheet D-5, Julian Wash Greenway. Olsson Associates. 2009. Figure 9.4.3: “Site Plan 4 and 5” Julian Wash Greenway, Olsson Associates. 2009.

Guidelines for the design of multiple-use Detention Basins in Pima County, AZ  

Case studies, literature review and interview of pros from the arid and semi-arid urban desert southwest have informed the creation of desig...

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