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Andropogon Associates, Ltd. h'(ofogim/ Plallt/iug (0' Design

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Philadelphia PA 19128

A Program for Open Space Management and Habitat Restoration for Stapleton Development Plan Western High Plains Region Prepared for the Stapleton Redevelopment Foundation and the City of Denver Denver, Colorado by Andropogon Associates, Ltd. Philadelphia, Pennsylvania 18 October 1994

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Habitat Restoration and Open Space Managment Table of Contents 1.

Overview of the Proposed Habitats

II.

The Habitat Plan 1. Introduction 2. Habitat pages a. Upland Types Short Grass Prairie Sandhills Prairie Blowout Depression b. Riparian Types Sandbar channels Streamside Prairie Playa Lake Bottoms Playa Lake Fringes c. Modified Habitat Types Woody Draw Prairie Turf 3. Image Plans include brief description 4. Overlay Plan include legend and brief descriptions

III. The High Plains Vocabulary 1. Drainage 2. Circulation 3. Parks and Active Recreation Areas 4. Institutional Land/Special Large Sites IV. Open Space Management Program V. Restoration Stategies VII. Phase I Construction including the Restoration of Westerly Creek


1. Overview of the Proposed Habitats


Habitat Restoration and Open Space Management for Stapleton Overview of the Proposed Habitats Until very recently, the native High Plains landscape was virtually ignored as a landscape value in the course of the development of Denver, which looked instead to the landscapes of the east and of the midwest for inspiration. The vegetation of the Stapleton site today, has been so modified that, with the exception of a few patches along Sand Creek, virtually all the historic vegetation has been eliminated. As a result, only degraded remnants of the native prairie and riparian habitats are left and these fail to capture any of the drama, scale or beauty of the original landscape. These fragments also are neither large enough nor continuous enough to sustain the indigenous plant and animal communities of the region. Redevelopment of the Stapleton site offers the opportunity to restore the patterns and the functions of the larger ecosystem that will be required if these natural values are to be sustained into the future within the Denver metropolitan area. The commitment to sustainability at Stapleton will be most visible in the habitat restorations of the open space system which will celebrate the regional landscapes of Denver. The extensive open space system offers a unique combination of natural habitats, parks and recreational and scenic values that can be found nowhere else so close to the center of town. The landscape character of the redevelopment of Stapleton represents one of the most powerful strategies for attracting both people and investors to this site. Familiar landscape types such as golf courses, park drives and residential streets will be retained but subtly modified to reflect the goals of sustainability. The management of these landscapes will foster native plants and animals and also serve as models for reduced irrigation demand as well as innovative and cost effective stormwater control and pollutant reduction. More than any other feature, the restoration of the landscapes of the High Plains will effect the kind of transformation of the whole site that is crucial to building the vision of the new Stapleton. The sustainability of indigenous landscapes depends not only on the restoration and protection of significant natural areas but also on maintaining vital biotic corridors throughout the fabric of development and on landscape management practices that sustain the natural processes of the larger ecosystem. The goal is to restore and manage the indigenous plant and animal communities of the Western High Plains within a renewed urban fabric. This will be realized at many scales throughout the fabric of Stapleton, from a regional scale reestablishment of sandhi lis prairie and restoration of the historic forested stream channels of Sand and Westerly Creeks to the smallest habitat recreations in a garden or schoolyard. There are five major types of landscapes, each offering different opportunities to integrate landscapes of the High Plains into the community of Stapleton. page---l


Core Natural Habitats The central components of the open space system are the Core Natural Areas where the goal is to bring back representative examples of the major native plant communities of the region, including sandhills, shortgrass and mixed prairie types as well as the sandbar cl1annels and playa lakes of the historic riparian landscapes. Prairie Park and the corridors of Sand and Westerly Creeks and their tributaries create the primary landscape setting for the neighborhoods of Stapleton. The stormwater drainage system will be integrated with the natural prairie landscapes and integrated into the management program to help support the proposed native communities.

Transitional Public Landscapes There are three major components of the public open space system where functional requirements preclude their use as natural habitat parks but which afford the opportunity to demonstrate a new integration of native plant communities in their landscape settings. They are the golf course the traditional parklands and the park drives. The conventional management of these landscapes in the past has relied on irrigated turf and trees and shrubs more typical of eastern forests. At Stapleton they will demonstrate reduced irrigation using shortgrass prairie lawns and, in addition to indigenous trees and shrubs, a more diverse array of plants that volunteer naturally in the larger region of the Rockies whenever there is more abundant moisture available.

Quasi-Public Landscapes There are also many acres of institutional and large scale private lands that are expansive enough to support dramatic and low maintenance natural landscapes, including portions of school grounds, governmental sites and larger developments such as office parks and industrial sites. The use of the expanded range of regionally native species in these landscapes can contribute enormously toward expanding the sense of open space on the site and help create a strong regional flavor to the landscapes of the Stapleton community.

Smaller Scale Greenways The continuous network of drainage swales and roadways that thread through the site offer the opportunity to provide integral connections for both wildlife and plants as well as people, also using the landscape vocabulary of the High Plains.

The Private Landscape It is hoped that the demonstration of the use of dramatic native plant communities throughout the open space system will provide inspiration and guidance for the homeowner and private landholder who wishes to reduce costs while contributing toward sustaining the natural landscapes of the region into the future.

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The next sections of this report describe a plan and program for the realization of this integrated vision for habitat restoration. The sections are:

The Habitat Plan which includes descriptions of the major proposed habitats and illustrative plans of the habitats of the open space system of each major precinct of Stapleton, as well as a habitat overlay map for the entire site. The High Plains Landscape Vocabulary which illustrates how the major habitat types are integrated with the urban landscape. It is intended as a design vocabulary that blends both innovative uses of native communities with the more traditional and familiar landscape features such as parks, roads, drainageways and residential streets. Open Space Management Program that describes the administrative structure and management regimes that are needed to realize the vision establishing and maintaining the native habitats in the open space system as well as the kind of public education that will foster the use of sustainable landscapes on quasi-public and private lands. Restoration Strategies which include more detailed descriptions of the habitats and the species that comprise them as well as strategies for establishing and maintaining these habitats in the long term.

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II.

T11e Habitat Plan 1. Introduction 2. Habitat pages a. Upland Types Short Grass Prairie Sandhills Prairie Blowout Depression b. Riparian Types Sandbar channels Streamside Prairie Playa Lake Bottoms Playa Lake Fringes c. Modified Habitat Types Woody Draw Prairie Turf 3. Image Plans include brief description 4. Overlay Plan include lege11d a11d brief descriptions


The Habitat Plan The objective of habitat restoration at Stapleton is to bring back representative portions of the major native plant communities at Stapleton and as much as possible of their associated animal life. These communities change along a gradient that reflects the amount of moisture available to the plants. The vegetation of the Stapleton site once consisted of a matrix of mixed prairie types that continued unbroken between the narrow corridors of woody vegetation that occurred along the watercourses. The grasslands changed on a gradient from tall grasses on the wetter, sandier soils to short grasses on the drier, clayey soils. A mixed grass prairie was found in the transition areas. Trees were confined to the sandbar channels where coarser and wetter soils were found along the riverbanks and on the floodplains. Shrubs intermingled with the grasses on steep, shaded river banks where lingering snow banks recharged soil moisture along the southeastern slopes of the sandhills. Where the watertable was close to or at the surface throughout the year, a diverse array of wetland species occurred and supported abundant wildlife. At the margins of these wetlands where water was more intermittent the species changed in response to the amount of available moisture, which is the key to High Plains landscapes. Where natural rainfall is augmented by additional water from sources such as irrigation or where streams are significantly modified by drop structures to retain more water in the channel, a variety of species can be supported which would otherwise not occur at Stapleton. These include many trees and shrubs that characterize the High Plains landscapes of the foothills of the Rockies and similar landscapes in New Mexico. They can be used to greatly enrich the local plant opportunities without requiring the intensive levels of irrigation or maintenance that are needed to sustain many of the more familiar landscape plants used in Denver that corne from the east coast and other places where rainfall is substantially greater. The following pages outline the major habitats of Stapleton and the character and species of these landscape types.


Upland Habitats Shortgrass Prairie The Shortgrass Prairie, characterized by shorter, more drought resistant grasses, occurs where there are heavier, finer-textured clay soils, that prevent water from percolating to depth. In the larger open spaces in the southern part of the Stapleton site, Shortgrass Prairie can be restored adjacent to Sand and Westerly Creeks. It could also be used at the farthest margins of drainage corridors in this portion of the site and along landscape edges where an alternative to turf is desired. The primary species are short Grama grasses, such as side-oats grama (Bouteloua curtipendula) and blue grama and a shorter plant, buffalo grass. These grasses are mixed with a variety of other rhizomanous, stoloniferous and bunch grasses, as well as a number of forbs, to create a striking texture that is due to the irregular patterns of these different species.

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Upland Habitats Sandhills Prairie The Sand hills Prairie will be the primary prairie landscape of Stapleton, with its centerpiece at Prairie Park. The terrain consists of gently undulating hills oriented to and created by the prevailing winds. Tallgrass prairie occurs in the High Plains where the more permeable soils allow moisture to percolate deep into the sand. These hills, probably fossil dunes, are stabilized by tall, deep-rooted grasses such as sand bluestem, prairie sand-reed (Calamovilfa longifolia), needle-andthread and sand dropseed (Sporobolus Gn)ptalldra). The Sandhills Prairie is the only grassland type at Stapleton that supports a wide array of shrubs such as three-leaf sumac (Rhus trilobata), sagebrush (Artemisia filifolia), chokecherry (Prunus virginiana), wild plum (Prunus americana), Arkansas rose (Rosa arkansiana), snow berry (Symphoricarpos albus) and golden currant (Ribes aureum).

, Sand Reedgrass Calamovilfa longifolia

Detail of Plan, "Sandhills Prairie Park"

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Needle-and-Thread Stipa comata

Sand Dropseed Sporobolus crl)ptandra


Upland Habitats Sandhill Prairie

Rabbit Brush is aile of the wildflowers that will be seell ill the Prairie Path.

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Upland Habitats Sandhills Prairie Sa Ild Blowou ts Within the Sandhills Prairie occasional "sand blowouts" can be found on the windward side ofthe dunes, on the northwest corners of the sand ridges. These features are small bowl-shaped depressions of loose sand which support a special plant and animal community of their own. The creation of one or more "sand blowouts" can give variety to this landscape and provide an educational experience for park users. These "blowouts" are emphemeral features that will have to be maintained to prevent return to a tall grass prairie. Blowout grass (Redfieldia f!exllosa) , heliotrope (Heliotrope spp.J, ring grass and sandsage are typical of these sites.

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Upland Habitats Sandhills Prairie Sandhills Depressions Within the Sandhills Prairie, where the landforms are created by wind, depressions are occasionally formed between the hills. In these depressions, where there is no natural outlet for water, soil fines sometimes settle out and seal the bottom, creating a wetter area. These small circular depressions can support wetland vegetation, such as spike rush, an aquatic liverwort (Mars ilea mucro/rata), sa ltgrass (DistichUs spicata) and even rings of cottonwoods, which provide an unexpected sheltered oasis in the midst of the expansive prairie.

Spike Rush Eleocharis palustris

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Cottonwood Populus deltoides


Riparian Habitats Sandbar Channels All the drainageways within the larger open space system of Stapleton are modelled on sandbar channels-free-flowing, wide, flat, main channels, within which minor channels are free to braid and meander. With conventional drainage, flow is confined to a single channel, increasing velocity and erosion and necessitating the use of drop structures to absorb energy. Conventional confined channels prevent the reproduction of native woody vegetation, which requires bare mineral soil exposed by the shifting channels, to germinate. Sinuous lines of cottonwoods grow on higher ground and thick patches of sandbar willows with occasional peachleaf willows grow within the channels. Weed problems may occur here, particularly with leafy spurge (Euphorbia esula!. The sandbar corridors are home to a multitude of water- â&#x20AC;˘ fowl (sandpipers and blue herons) and butterflies (Weidemeyer's Admiral, Mourning Cloak, etc.)

Pet1chlea! Willow Salix amygdaloides

Sandbar Willow Salix exigud

Populus deltoides

Detail of Plan with Sandbar Channel, Precincts V, VI VII, Northcentral Section

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Riparian Habitats Sandbar Channels

Sal1d Bar Willow will be a feature of Sal1d Bar Chal1l1els throughout the site.

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Riparian Habitats Streamside Prairie Switchgrass (PalliewlI virgatlllll) covers the entire ground except where the stream channel is actively eroding. Swi tchgrass should be established early on so as the site gets wetter the plants can spread. Prairie cordgrass can be planted across the bottom of the channel as it will grow in standing water. Western wheatgrass has a wide range of tolerance and can be planted when the channel is still relatively dry. Later it will be able to tolerate flooding and will grow even instandingwater .

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Switehgrass Panicum virgatlllll

Prairie Cordgrass Spartina pectinata

Western Wheatgrass Agropyron smithii

Detail of plan showing areas of Streamside Prairie, Precinct III, Southeast Section

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Riparian Habitats Playa Lake Bottom Where a basin is constructed for storm water management, either to improve water quality or to control flooding, the model will be the playa lake. Playa lakes are ep hemeral waterbodies that are found throughout the plains region. The playa lakes at Stapleton will be designed to maintain ground water contact and to build up the 'ground water mound' that will develop beneath the basin. This will be accomplished by the use of a ground water plug or underground dam that inhibits downslope ground water movement. The playa lakes will have a wetness gradient related to the groundwater plume. Continuous groundwater contact allows the basin bottom to support a rush meadow, that will reduce pollutants and improve water quality. The predominant species is soft-s temmed rush.

Soft-Stemmed Rllsh Scirplls validlls

Detail of Plan, Precinct V, VI & VII, Northcentral Section

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Bille Vervain Verbwa hastata


Riparian Habitats Playa Lake Fringes Where a basin is co nstruc ted for stormwa ter management, either to improve water quality or to control flooding, the model will be the playa lake. Playa lakes are ephemeral waterbodies, dry most of the time, that are found throughout the plains region. At the upper reaches of the playa basins and along their margins there will be less frequent contact with groundwater and the moisture regimen will fluctuate more dramatically. These fringes are characterized by spike rush and dense stands of prairie cordgrass.

Prairie Cordgrass Spartina pectinata

Spike rush Eleocharis paillstris

Detail of Plan, Precinct V, VI & VII, Northcentral Section

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Modified Habitat Types Woody Draw-Trees and Shrubs

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Serviceberry Amelanchier alnifolia

American Elm Ulmus Americana

Red-osier Dogwood Cornus stolonifera

Bur Oak Quercus macrocarpa Ponderosa Pine Pinus ponderosa

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Modified Habitat Types Prairie Turf Buffalo grass is the toughest of the grasses and takes the most foot traffic, yet has the softest and most even texture. It covers more quickly than the others, then lives the longest. If you sow it profusely in soil (not caliche), water it three times a day, and arange for good warm weather, you can have a thick and sturdy stand that can be mowed only one month later. On caliche it takes longer to establish. Just sow extra thickly for a quicker cover. Those who have established buffalo grass lawns rarely water or mow them,

Blue grama is a fine-leaved turf grass that gets its name from the blue cast of its seed heads. Blue grama is often mixed with buffalo grass, and together they give excellent cover and provide a lawn so soft and smooth tha titsa tisfies thecravings of people who love to walk barefoot on the grass. Although this type of lawn must be watered to maintain its softness and springiness in the summer, I've been told that the amount of water necessary is a half to a third of that needed just to keep Kentucky bluegrass alive. It sometimes spreads by rhizomes, but rather timidly, which is why it is called sub-rhizomatous.

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Western wheatgrass stands out because of its handsome bluish-green color. And you get an added bonus-it stays looking that colorful all winter. It prefers cool summers and a little bit of watering is necessary in the summer to keep it from going dormant. If it gets aggressive, you have given it too much water. Its only drawback is that it cannot beused for a wildflower meadow. The sod is extraordinarily tight, and its vigorous winter growth outcompetes wildflower rosettes. Of course, it outcompetes weeds, too. People who have used it describe it as a good, tough, turf grass.

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Text and photographs adapted from "Native Texas Plants: Landscaping Region by Region" by Sally Wasowski with Andy Wasowski, 1988: Gulf Publishing Company, 406 pp.

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Habitat Image Plans The Habitat Image Plans are enlarged sections of the overall Stapleton plan at a scale of 1" to 400, (reduced to 1" to 800' in the report), developed to explore and illustrate the habitats that wiII be established throughout the site both in the open space system and in the body of the development. The park elements and other plan features were illustrated to show scale and locate different habitat types. The Habitat Image Plans shown here are as follows: 1. Precincts I & II. (Southwest section.) 2. Precinct III. (Southeast section.) 3. Precinct IV. (Central section.) 4. Precincts V, VI & VII. (Northcentral Section.) 5. Precinct VIII. (Section 10.)

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Descriptions of the Habitat Image Plans 1. Precincts I and II: Southwest Area This area, which includes the Terminal building and surrounding facili ties and buildings, is currently the most developed part of the site. While many building and runways will be demolished, the new development will remain more urban in character than the rest of the site. There is little existing natural habitat. Sand and Westerly creeks are on the fringes of the area. The main habitats will be in community and city parks of a more traditional character including a major city park on the east boundary, parkways and water quality treatment areas. The latter will be used to treat water from existing storm sewers before they enter Sand or Westerly Creeks. The restoration of Westerly Creek will be a significant landscape restoration project that may be done in conjunction vvith the first phase of construction which will most likely be Precinct I.

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Descriptions of the Habitat Image Plans 2. Precinct III: Southeast Area Precinct ill is the south east corner of the site and is bounded both by Sand and Westerly creeks on the north and west. The city of Aurora forms the southern boundary. The precinct is adjacent to the most significant natural areas on the site, Bluff Lake and the least disturbed parts of Sand Creek. This section is also the highest part of the site and the bluffs, which run along the south side of the creek, afford magnificent views of the Front Range, downtown Denver, and (for the present) the Stapleton Terminal area. The topography here is the steepest on the site and is curious in that most of the drainage is towards Westerly Creek rather than Sand Creek because the uplifted bluffs area interrupts drainage to Sand Creek for most of the area. The plan reflects this factor by having a parkway / drainage swale following the drainage direction towards Westerly Creek. The bluff tops provide a major habitat area which will be representative of short grass prairie and there will be an overlook park on the western point of the bluffs near Westerly Creek. Several wetland/water bodies will be constructed as water quality treatment areas, notably adjacent to Westerly Creek which will treat water from an Aurora storm sewer that flows through the Precinct.

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Descriptions of the Habitat Image Plans 3. Precinct IV: Central Section This area crosses the entire site and lies between Interstate 70 to the north and the railroad and Sand Creek to the south and is somewhat isolated from the other parts of Stapleton by these boundary features. The area itself is also split into three sections: the western part lies between Sand Creek and 1-70 and will be separated from the eastern areas by a reinstated Yosemite Street. The area immediately west of Yosemite is high since it is on existing runway fill. The far eastern area drops some 15 to 20 feet lower and is bounded by Havana Street on the east. Regrading is suggested in all three parts to address the fragmented nature of the area and other problems. The overfilled banks of Sand Creek should be regraded in the western section to more natural stable slopes and restored to native habitat. This area will be developed as a lighted ballfield complex with irrigated fields and landscape. The area east of Yosemite will be regraded to minimize the differences between the high and low area and to improve drainage the low area. Drainage will be redirected to the north and swale and storage/water quality facilities developed as a landscaped amenity buffer along I 70.

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Descriptions of the Habitat Image Plans 4. Precincts V, VI and VII: Northcentral Section These precincts occupy the large north-central section of the site. The main habitat feature of this area will be a newly created drainage way designed to divert stormwater to Sand Creek that will run roughly from the north-east at 56th street to the south-west corner of the area near the junction of Quebec and I 270. This drainage way is required because there is no adequate drainage outfall from the area. It will form a major open space amenity and a wildlife and open space connection from the Arsenal to Sand Creek. This system provides for major flood storage, both for Stapleton and some off-site flood flows, and has other park and recreation amenities such as trails, scenic park drives and a golf course. Within the developed parts of the area there are extensive drainage swales with habitats developed as amenities. Within the residential neighborhoods there will be 'sustainable' versions of the traditional Denver parkways, community parks, schools and other large sites in which open spaces will have habitats established.

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Descriptions of the Habitat Image Plans 5. Precinct VIII: Northern Area, (Section 10). Precinct VIII occupies the whole of the area known as Section 10, north of 56th Street. Apart from the far northern end of the north-south runways this area is currently open land abutting the Arsenal Preserve. Though extensively re-graded for the airport this land was originally thought to be mainly sandhills prairie. The 1948 aerial photographs show some agricultural activity. The Sand Creek Lateral of the High Line Canal still existed at that time and can be clearly seen on the photo. A large section of this precinct is dedicated to the establishment of a "Prairie Park". This park is a primary link connecting the Arsenal Preserve through Stapleton to Sand Creek, providing corridors for wildlife and a prairie experience and interpretation within the community. Trails run through the park where the visitor can experience different aspects of the sandhills prairie such as sand blowouts and sandhills depressions. Sightlines along the trails are arranged so that the visitor can find places where ridgelines hide outside views and give the experience of being wholly in the open prairie. Other trails run on ridges that will give spectacular views to the Arsenal and the Front Range. Part of the golf course (holes 5 and 6) extends to this section with access under 56th Street via an underpass. This part of the course will have the most "prairie like" character where it abuts the Prairie Park. There are also extensive riparian habitats in the Precinct along drainage ways and at points of historic outflow from the section. Since no primary outfall channels exist, large amounts of storage and infiltration will be needed at the old outflow points so as not to exceed historic flows. As in other parts of the site these will be 'playa lake' type habitats-meadows of rushes and grasses that will be prime habitat for bird life.

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The Stapleton Habitat Overlay Map The habitat overlay map shows the habitat types proposed for establishment on the Stapleton site. To emphasize the sustainable aspects of the Stapleton Development Plan, habitats have been shoW11 over the entire site, including both open space and developed areas. These are shown as black and white hatches in the reduced sized report version of the map and in color on the full sized 1" to 800' scale map. The map legend is broken down into three general land type categories with sub-categories of specific land uses and plant community types:

1. Landscape Types Managed as Natural Habitats Extensive areas of regional native habitats will be established in the main open space corridors, drainage areas and in the existing natural areas of Sand and Westerly creeks. These habitats will be mostly on public lands managed and maintained by different public agencies such as Urban Drainage, Parks and Recreation, or possibly land conservancies set up to manage special areas such as the Prairie Park.

2. Transitional Parklands This category includes all parks, such as city and community parks, ballfields, golf courses and parkways. These parklands are essentially traditional Denver parkland types modified to achieve greater sustainability. Each type will contain a mixture of habitats taken from an extended regional plant vocabulary such as the "woody draw", modified native plant types such as "prairie turf" (selected prairie grass species mown as turf), "sustainable irrigated turf", or mixtures of native habitat types.

3. Developed Lands This category includes institutional lands, such as schools and "opportunity sites", which are defined as parcels of land large enough to include substantial open space such as a corporate campus, and all remaining developed land and streets. The developed areas cover the major portion of the site and although city agencies will have no direct control over the management of these lands it is assumed that guidelines will be established for the management of habitats within this area such as front and back yards, street tree planting strips and minor drainage ways, etc., to encourage sustainable practices.

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Sustainable Site Development Stapleton Open Space Plan Denver, Colorado

The Stapleton Redevelopment Plan offers an opportunity to restore and resettle derelict urban lands. The central open space area of approximately 1400 acres is the heart of the new community and is the biggest single addition to the Denver Parks System in fifty years. It symbolizes the rebirth of this iract of land as an urban settlement in partnership with natural communities. Open space at Stapleton integrates various uses, such as golf courses, bike paths, trails and several distinct park types such as traditional green community parks, active sports centers and natural parks. An extensive stormwater management system using indigenous riparian habitats is the spine of the open space system and is fully integrated into the recreational facilities.

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STAPLETON HABITAT PLAN LEGEND GENERAL LAND TYPES LANDSCAPE TYPES MANAGED AS NATURAL HABITATS

LAND USE TYPES AT STAPLETON

PLANT COMMUNITY TYPES

BLUFF LAKE PRAIRIE PARK

UPLAND TYPES SHORT GRASS PRAIRIE

PRAIRIE BLUFFS

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RIPARIAN TYPES STREAMSIDE PRAIRIE

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PLAYA LAKE BOTTOMS

PLAY A LAKE FRINGE

page-12


TRANSITIONAL HABITATS

TRANsmONAL PARKLANDS

WOODY DRAW PRAIRIE TURF SUSTAINABLE IRRIGATED TURF MIXED NATURAL HABITATS GOLF COURSES

ALL LAND USE MAPPING UNITS UNDER THIS CATEGORY ARE MIXTURES OF THE ABOVE PLANT COM路 MUNITY TYPES

PARKWAYS

PARKS

DEVELOPED LANDS

INSTITUTIONAL & OPPORTUNITY SITES

REMAINING DEVELOPED LAND & STREETS

page-13


III. The High Plains Vocabulary 1. Drainage 2. Circulation 3. Parks and Active Recreation Areas 4. Institutional Land/Special Large Sites


High Plains Vocabulary Drainage Main Swale Main swale

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100 year outlet/spillway structure ---,---"",

Diagrammatic Plan of Main Swale / Golf Course illustrating how flood control can be integrated with golf use Golf green

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Diagrammatic Long Section of Main Swale

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Main swale fall

page-14


High Plains Vocabulary Drainage Col/ection Swale All swales in the main drainage system for Stapleton will be based on the naturally occurring 'sandbar channel' for maximum habitat establishment potential. Natural swales in this arid region are very wide and shallow and all Stapleton swales have been given ample width to accommodate the establishment of a similar natural fonn. During stonn events, a system of meandering and braided sub-channels with sand bars is created within the body of the main channel. Different plants become rapidly established on

bars forming a rich ribboning of native vegetation including cottonwoods and sandbar willows. In Stapleton, swales may remain dry for long periods before full developmen t occurs and increases runoff. Such swales would be initially planted with grasses and other plants suitable for the drier conditions. Some swales might be planted with the extended volcabulary of the 'woody draw' such as green ash, American elm and box elder This example shows a collection swale of medium size. Larger swales would simply be

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Cut bank Deposition Bank

Meandering channel

use The proposed natural drainage system integrates sitedrainageand stormwater management intoa continuous system ofvegetated swales, wetlands and sediment ponds which outfall to regional lake basins. ThiG also provides significant gains in flood storage, infiltration and water quality. The land area used, while greater than the area required for a piped system, becomes an important recreational and open space amenity for the community and provides habitat for native plants and wildlife.

Section of collector swale with smaller meandering channels to slow flow and create habitat

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Detail of Plan of Precincts V, VI and VII: Northcentral Section

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Andropogon Associates, Ltd.

page-1S


High Plains Vocabulary Drainage Playa Lake/Water Quality Site The 'Playa Lake' is the habitat model for all of the open ponded areas on the site regardless of whether they are for storm water storage or water quality improvement although there may be structural differences depending on the specific use and location, maintenance requirements, etc. The Playa Lake is essentially an ephemeral pond that fills with water after storms. Ponds would be designed to empty in a 48 hour period to conform with storm water detention requirements, however, for habitat purposes, a shallow damp bottom would be maintained in which a meadow of rushes can be established.

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This would be achieved with several techniques used individually or in combination. One method would be to partially impound the ground water plume with a sub-surface barrier as shown. Another would be to supply the the pond with a small base flow such as that available from the Montbello drain, or other re-use sources. The basin shape would be a very shallow bowl shape that would allow lake bottom and lake fringe species to vary in their locations depending on groundwater availability.

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Longitudinal section through a Playa Lake shOWing the integration of flood control with wetland habitats

Detail of Plan of Precinct IV showing Playa Lakes

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Andropogon Associates, Ltd.


High Plains Vocabulary Drainage Playa Lake/Water Quality Site The cross section of the playa lake, as proposed on Stapleton, will differ slightly from the recommended section proposed in the Urban Drainage Manual under structural best management practices, (BMP's) to encourage the establishmen\ of preferred habitats. The recommended cross section is a very shallow bowl rather than a flat bottom with steep sides. In the early stages of the development of Stapleton many of the water re-

ten tion facilities will bequite dry for considerable periods if no supplemental base flow water is available. The shallow bowl allows the boundary between the playa lake bottom rush meadow and the playa lake fringe species to change over time as the lakes get wetter. The shallow vegetated banks will also require less structural reinforcement with rip-rap as shown on the BMP section.

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page-17


High Plains Vocabulary Circulation Arterial Road

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page-J8


High Plains Vocabulary Circulation Parkways

Perspective drawing of Parkway showing lIIedian strip with shallow swale and plantings of informal groupings of trees

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Andropogon Associates, Ltd.

page-19


High Plains Vocabulary Circulation Parkways The Stapleton version of the traditional Denver parkway has subtle differences that create a more sustainable environment. The typical tree-lined medians and roadside planting areas are slightly depressed rather than raised to collect and impound the maximum amount of storm water for increased soil moisture. Small vegetated swales run down the wider medians that drain to inlets in the medians before intersections. The plants used are chosen from an extended palette of regionally native species which are more drought tolerant the traditional Denver Park plantings that require full irrigation.

The edges of the medians and areas bordering sidewalks can be bordered with a mowed strip of buffalo grass, otherwise, prairie grasses, wildflowers and shrubs can cover the ground and be used in combination with recommended vines and ground covers. Trees should be planted in informal groups or 'looseallees' rather than strictly regular avenues. In this way, variation in growth habits and occasional death of individual specimens can occur without spoiling the overall planted effect.

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Cross section through Parkway showing median strip with swale & connection to stormwater system

Detail of Plan from Precinct I & II: South and Southwest Section

Andropogon Associates, Ltd.

page-20


High Plains Vocabulary Circulation Park Drives Park Drives are infonnal winding pleasure dri ves that follow the edges of the main open space corridors forming a transition between the neighorhood street grid and the more natural forms of the open space. Park drives vary in character from area to area depending on the environment they are passing through. This example borders the golf course in the north-central area and has a narrow tree-lined canal which

recalls the feeling of the early irrigation ditches, such as the Sand Creek La teral of the High Line Canal which once passed through this area. The feasibility of the canal would depend on theavailability of appropriate re-use water. Regional and local trails also follow Park Drives. In low traffic areas, Park Drives would be rurbless and swaled at the sides.

Canal water used to irrigate golf course

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Main a en s ace corridor with draina e and golf course

Park drive with bikewa ,

Cross Section of Park Drive Adjacent to Golf Course and Residential Area

Detail of Plan, Precincts V, VI and VII: Northcentral Section

1'' 1

Andropogon Associates, Ltd.

page--21


High Plains Vocabulary Circulation Residential Streets While residential streets do not show up a significant open space on the plan the cumulative effect of many small private decisions by homeowners in their own yards and street frontages has a big overall impact. The typical planting strip along the street is shown as slightly depressed instead of raised to encourage infiltration of runoff. It is planted with drought tolerant trees from the 'extended regional vocabulary' and 'prairie turf. During storms, these areas would fill and overflow to conventional street gutters and inlets. This water could be supplemented by yard and roof

Two lane residential roadwa with curbs, planted edge and and sidewalks

catchment water. Similarly, planted parts of the front and back yards and alleys could be depressed to harvest runoff. Alleys could have center soft strips instead of being all concrete. While the amount of extra water available to plants is small and intennittent, it does make a difference. If supplemental irrigation is used, more soaks into the ground and less water is wasted by running off into gutters and drains.

Residential ard area

Section through residential street with sustainability modIfications

Detail of plan of Precinct III, Southeast Section showing local streets, residential land and alleys

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Andropogon Associates, Ltd.

page-22


High Plains Vocabulary Parks al1d Active Recreation Areas Prairie Park

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Salldhills prairie

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Section of Prairie Park alld adjacent park drive with sustainable drainage modificatiolls

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Andropogoll Associates, Ltd.

page-23


High Plains Vocabulary Parks and Active Recreation Areas Golf Course The Stapleton golf course is designed as an integral part of the main open space system between Precincts VI and VII. From a proposed c1ub house location linked to the village center in Precinct VI, the course extends with nine holes along the open space spine south towards Sand Creek and nine holes running north to 56th Street and into Section 10 via an underpass. The golf course is in a varied setting of rolling sandhills prairie terrain, steamside prairie, playa lakes and the sandbar channel habitat of the main drainage swale. Fairways will be prairie turf and the roughs and general setting of streamside prairie. In places the fairways will be within the 100 year flood plain of the main swale. Greens and tees

will be raised above the flood plain and will be irrigated turf. Irrigation will be from reuse water which will probably be a separate systern from the general storm drainage system of swales and ponds. Current health regulations in Colorado require any irrigation water ponds to be fenced (not shown on the section as details of this system are not yet developed). Local swales, such as along the parkway edge, provide additional landscape interest with the use of plants from the extended vocabulary. The character of the golf course could reflect the general environmental gradient of the site becoming more prairie-like in the north.

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Parking

page-24


High Plains VocabuLnnj Parks and Active Recreation Areas City Park and Canal at Westerly Creek

Perspective drawing of canal and canal walk at park adjacellt 10 Westerly Creek

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Andropogoll Associates, Lid.

page-25


High Plains Vocabulary Parks and Active Recreation Areas City Park at Westerly Creek Loose allee in grass swale

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Westerly Creek with sandbar> channel and prairie streamside habitats

Cross section through collector street, park with bike path and canal walk, and creek showing potential for irrigating with stormwater

Detail of plan of Precinct III, Southeast Section showing major park

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Andropogon Associates, Ltd.

page-26


High Plains Vocabulary Parks and Active Recreation Areas City Park at Westerly Creek

A stream and trail similar to that proposed for Stapleton along Sand Creek, Westerly Creek and the mam open space area.

I'r/J Andropogon Associates, Ltd.

page-27


High Plains Vocabulary Institutional Land/Special Sites Schoolyards Opportunities for habitat restoration and establishment exist in many areas outside of the public open space system, in quasi-public sites and private sites with significant open space. In this example, (based on an actual design by Keammerer Ecological Consultants) a small prairie habitat has been established in a school yard for educational and recreational purposes. A tiny running stream was created by tapping groundwater with a french drain (called locally a 'burrito drain').

The habitat includes both riparian and upland plants including rushes, grasses, wildflowers, woody plants and trees. Paths, stepping stones and a board walk are included in the design which is tucked into a small drainage area between conventional playing fields. The area is fenced but accessible by small gates. The habitat is continously used by classes and is eagerly sought by students for unsupervised play.

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Detail of Plan, Precinct III, Southeast Section showing typical schoolyard with habitat area that also functions as stormwater management

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Andropogon Associates, Ltd.

page-28


High Plains Vocabulary InstitutionaL Land/SpeciaL Sites SchooLyards

Path through a Prairie Habitat Restoration at a schooL.

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Andropogon Associates, Ltd.

page-29


High Plains Vocabulary Institutional Land/Special Sites Corporate Sites Large sites used for corporate headquarters, office parks, etc., can have different natural habitats in lieu of large areas of irrigated turf. Other sustainability modifications can also be included. This section shows a bordering natural swale as a frontage landscape to an arterial road with banks planted with prairie sandhills species behind. With theuseofliners in part of the pond, the playa lake is modified to form a permanent water featureand retention facility as well as a habitat area. Parking can be shaded with trellis structures and

Tall grassed berms Water feature "Playa Lake" Drainage swale handles vegetates frontage

vines which provides a pleasant landscape experience with less water demand. Trees can be from the extended vocabulary of plants and grasses can be" prairie turf'. If regular turf grasses are strongly desired they should be placed only in areas close to where people enter the building and other high profile parts of the site. Irrigation should be the most efficient type, such as underground drip irrigation-not sprinkiers. Reuse water should be used where available.

Shaded parking & walkways

Groves & loose allees of trees

using trellises & vines Arterial road with frontage

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Cross section of a corporate site fronting on an arterial road

Andropogon Associates, Ltd.

page-3D


'Rest 'ation of


Open Space Management Sustaining and restoring the natural landscapes of a region is a goal of many communities as they to realize what has been lost in the way of local character and environment, and at what cost. This is the challenge for Stapleton and its realization is a learning process. Two concepts are fundamental to its realization:

1. Real sustainability requires an informed and involved community. Education is of paramount importance and can and should be incorporated into virtually all open space activities. The landscape users must understand the consequences of their own actions and their impacts on the quality of their environment over time.

2. The success of this effort is dependent on good science and effective site monitoring. Landscape restoration is a heuristic process where the participants learn from the site as it is managed and monitored. There is no fixed program, but rather an evolving an incremental one that is informed over time by the landscape as it changes. This will foster a very responsive management program that is rooted in reality and in what is actually occurring on the land. Several new administrative structures and programs are recommended to help ensure the realization of the vision of restoring and sustaining the High Plains landscapes at Stapleton:

Natural Areas Advisory Group This is a first priority recommendation. Because of the complexities of integrating site restoration with all other phases of planning, design, and construction, it is imperative to have a team of advisors with the breadth of experience necessary to make appropriate management recommendations under these conditions. The scope of this effort will require a level of expertise and coordination that will go far beyond what can be achieved by staffing, especially at the outset. It is important that those who are already most expert in these areas be involved in overseeing the entire habitat restoration. A Natural Area Advisory Group should be established to direct the interim management of the site and to continue to serve as advisors to the proposed Sandhills Prairie Institute once it is established. This group could also advise Denver Parks and Recreation for all natural areas management. Quarterly field reviews are recommended. Several local and regional experts should be included, among them: Ed Redente, Department of Rangeland Ecosystem Science, Colorado State University, Ft. Collins. CO 80523 (303-491-6542). He is an expert in prairie seeding techniques and

soil management. David Cooper, 2680 Lafayette Drive, Boulder, CO, 80303. (303-491-7905) He is already involved in the project and has experience in establishing both prairie and riparian systems. He has also worked at the Arsenal.

page-31


Carl Mackey, Morris Knudsen Corp., 1700 Lincoln Street, Suite 4800, Denver, CO, (303860-8621). He is directing and monitoring the prairie and wetland restoration programs at the Arsenal and has extensive field experience very close to the Stapleton site. Deborah Keammerer and Warren Keammerer, Keammerer Ecological Consultants, 5858 Woodbourne Hollow Road, Boulder, CO 80301 (303-530-1783). Deborah is an expert in seed collection and propagation of native prairie species and has experience in prairie restoration at all scales. She is also presently working with Urban Drainage on vegetated swales. Warren is an ecologist with extensive grasslands experience and completed the botanical inventory for the Arsenal restoration. Carol Bylsma, Colorado Dept. of Wildlife, Project Wild. She also is involved in habitat education at the High Line Butterfly Center. She is highly recommended by R. M. Pyle (author of The Thunder Tree and butterfly expert). Paul Opler, 3353 Valley Oak Drive, Loveland CO 80538 (303-493-8401). He is a biologist with the US Fish and Wildlife Service and is also recommended by Dr. Pyle.

The Sandhills Prairie Conservancy This is also an immediate priority that will be instrumental in realizing all of the programs described in this report. As a private, non-profit conservancy, this organization would work as an adjunct to the Denver Department of Parks & Recreation and the Sandhills Prairie Institute and would playa key role in fundraising, coordination and public education. The Friends of Sand Creek is a good example of a successful local friends group.

The Sandhills Prairie Network This is the third high priority activity necessary to ensure that the expertise and planning will be there as it is needed. The art and science of restoration are being developed right now. There are no time tested methodologies or best practices but rather an evolving understanding that is rooted in research and development. The importance of networking is vital when the knowledge base is growing so rapidly. The creation of a formal network and possibly an on-line database and bulletin board offer opportunities to involve a wide array of people in this effort. The following is a list of institutions with prairie-related programs and/or restorations that can serve as a starting point. Colorado State Univ., Ft. Collins, CO, in particular Rangeland and Ecosystem Science. National Grasslands, US Dept. of Agric., US Forest Service Bureau of Land Management University of Colorado, Boulder, CO, in particular the Museum and Herbarium Colorado Nature Conservancy, Denver CO, Colorado Natural Heritage Inventory

page-32


Colorado State Dept. of Natural Resources, Natural Areas Program Denver Botanic Gardens, Denver CO Rocky Mountain National Wildlife Area, Denver CO Pawnee National Grasslands City of Boulder, Open Space Dept., managing Natural Areas in Boulder. The Denver Audubon Society, Grasslands Institute Plains Conservation Center

The Sandhiils Prairie Institu Ie This is a longer range goal that can be realized once the other structures are in place. This organization would function as a bioregional arboretum with a primary emphasis on the natural areas management and programming for the High Plains Landscapes of Stapleton. The Institute could potentially be located at the northwest corner of Havana and 56th Avenue. Its mission would be to integrate as many aspects of community life as possible with the restoration and management of the natural landscape systems. Its activities would range from directing habitat establishment and management, educational programming on site and coordinating volunteer activities to providing employment and job training in restoration and sustainable landscape maintenance. Maintenance facilities and equipment will also be required. It is recommended that the Prairie Institute serve as the coordinating agency with overall responsibility for the management of the Stapleton natural areas to ensure that the site can be viewed as integrated whole. This is presently the arrangement for the management of Central Park and Prospect Park in New York City. This effort must be carefully coordinated with Susan Edwards of the Denver Department of Parks and Recreation. In order to fulfill this mission, several key staff roles should be considered in addition to the administration:

1. Staff ecologist: general expertise in prairie systems and familiarity with local wildlife, plants, soils, and hydrology. This individual would also be responsible for establishing the monitoring program and maintaining the site database. 2. Project manager: experience in overseeing large scale landscape projects to ensure adequate coordination with on-gOing construction. 3. Landscape manager: experience in propagation, plant establishment and management practices such as burning. This individual could coordinate with the Stapleton Tree Nursery on site to expand its mission to include plants for the restoration effort. 4. Volunteer coordinator: experience in habitat restoration to work with local groups such as Volunteers for Colorado as well as larger organizations such as the National Civilian Community Corps which has one of its four training campuses at Lowry Air Force Base.

page-33


5. Environmental education coordinator: experience in prairie landscapes. Beyond onsite programming, this individual should coordinate with the Denver school system to develop a curriculum to address sustainablity. The issues that are shaping the current master planning and the restoration effort are of great importance to Denver's children. They should be involved in hands-on projects related to monitoring, propagation, planting and a variety of other projects that could be started now. 6. Planner/designer: in-house consultant coordinator with other planners and designers on the site to ensure appropriate integration with the habitat restoration. Several research needs should be given high priority to ensure that the appropriate information is available when the more detailed design development is undertaken. a. A soil survey-The current lack of an up-to-date soil survey of the site could have very costly consequences for implementation so one should be undertaken immediately. This terrain has been highly modified by grading and is essentially an unknown commodity at this time. In addition, those areas where more natural soils structures persist represent important resources that might otherwise be overlooked. This is crucial piece of missing information that will be invaluable for restoration and all landscape applications. A soil survey should be undertaken immediately and before final grading plans are completed. This information may also be crucial to determining appropriate site phasing. b. Depth to watertable-The research effort should include monitoring the seasonal changes in depth to watertable which will provide data that is necessary for design development of the water management system, including all of the swales, channels, wetlands and ponds. c. An inventory of sandhills prairie remnants-both upland and riparian-The remaining sandhills remnants represent irreplaceable biotic and scientific resources. They should be inventoried to determine their status and location to ensure that these vital pieces are sustained for the future. These habitats should be monitored in parallel with the Stapleton sites to serve, not only as models to emulate, but also as standards for measuring success. Sites both in Colorado as well as adjacent states should be included due to the paucity of remaining habitat. d. Applied field research on propagation, establishment and management techniques for Sandhills Prairie plants-Small-scale plots should be established as soon as possible in those areas designated as natural areas that are least likely to be graded in the course of redevelopment. The specific sites and demonstration projects should be determined by the Natural Areas Advisory Group. Some propagation could be carried out at the Stapleton Tree Nursery as well as advance growing for those native species that are not available in the trade.

page-34


The Learning Curve The restoration and sustainability of indigenous habitats at Stapleton is dependent on realizing a vision that is truly innovative. Creating an extensive open space system that returns the High Plains to Denver and fostering sustainable landscape practices that use native species and minimize water consumptive would be a remarkable demonstration of reinhabiting the city that would serve a model worldwide. The program that has been proposed to accomplish this is not like a conventional master plan which spells out a detailed menu of projects. Rather it is a process whereby the participants learn by doing as they manage the site with a high degree of public involvement and scientific expertise. It is an investment in monitoring, training, networking and field trials on the ground rather than elaborate plans on paper. It is an investment in people and place.

page-35


V. Restoration Stategies


Restoration Strategies-Proposed Major Habitats for the Site Upland Landscapes and Habitats Slwrtgrass Prairie The short grass prairie was the most common landscape in the larger High Plains and occurred on the heavier, finer-textured soils, the clays that did not allow water to percolate to depth and were therefore subject to more evaporation and supported shorter, tougher grasses. The Shortgrass Prairie has been very much reduced in extent throughout the region. This flatter terrain was irrigated and used for agriculture or replaced by development. More than half of the remnant shortgrass prairies extant now support a number of invasive exotic species that persist at the expense of native communities. Where larger open spaces can be reestablished in the areas of heavy soils a shortgrass prairie can be restored. Patches of mixed tall and shortgrass species will occur in the transitions. Shortgrass prairie is proposed for the driest landscapes and will occur primarily at the farthest margins of drainage corridors and along landscape edges where an alternative to turf is desired. The primary species are short Grama grasses, such as side-oats grama (Baute/aua curtipendula) , blue grama (Baute/oua gracilis) and buffalo grass (Buchlae dacty/aides) that are mixed with a variety of other grasses and forbs. Typical associates include June grass (Kaeleria macrantha ) and western wheatgrass (Agropyron smithii). This grassland, comprised of rhizomatous grasses and bunchgrasses, is strikingly textured due to the irregular patterns of the varied species.

Mixed Prairie Mixed prairie will develop naturally over time as a transition between shortgrass and sandhills prairie.

Sandhills Prairie The sandhills prairie, a tallgrass prairie type, was probably the most extensive landscape type in the area that is now Stapleton Airport, occurring largely north of Sand Creek. Tallgrasses grew wherever more permeable soils afforded moisture at depth. The areas of the Sandhill Prairie that were more hilly probably were not used for agriculture but were grazed. They show evidence of substantial degradation and have been invaded by exotic eurasian annual grasses that are very persistent and now comprise more than half the present grassland. Extensive damage occurred during the grading to accommodate the expansion of the runways and other airport support facilities which flattened the subtle variations of the terrain. Sandhills Prairie is proposed as the primary prairie landscape of Stapleton with its centerpiece at Prairie Park. Sand bluestem (Andrapogan hal/ii) , prairie sand reed page---36


(Calamovilfa longifoUa) and needle-and-thread (Stipa comala) , big bluestem (Andropogon gerardiiJ , little bluestem (Schizachyrium scoparium ) and sand dropseed (Sporobolus cryptandra) are the most common species. This is the only local prairie type that also supports a wide array of woody plants including shrubs such as three-leaf sumac (Rhus trilobata) , sagebrush (Artemisia fiUfolia) , chokecherry (Prunus virginiana), wild plum (Prunus americana), Wood's and Arkansas roses (Rosa woodsii, R. arkansiana), snowberry (Symphoricarpos albus) and golden current (Ribes aurcwn ) . These same woody species might be found wherever snow banks persist to provide stored moisture such as on the southeastern sides of steeper sand ridges and sandbanks. The terrain consisted of gently undulating hills oriented to and created by the movement of the prevailing winds from the northwest to southeast across the site. With the regrading of portions of the watershed to recreate, to the extent feasible, the historic "dune" terrain and drainage patterns, the drama of the tall grass prairie of the Sandhills will be restored to a significant portion of the site. The small circular wetlands that once occurred between the low hills can also be recreated to afford small oases of woody plants in the midst of expansive prairie, supporting spike rush (Eleocharis palustris) an aquatic liverwort (Marsilea mucronata), saltgrass (Distichlis spicata) and possibly even rings of cottonwoods (Populus delta ides) . The landscape will also be accented with occasional blowouts on the sandy hills, typically on the northwest corners of sand ridges. Blowout grass (Redfieldia flexuosa) heliotrope (Heliotrope spp.) as well as ring grass(Muhlenbergia pungens) and sandsage (Artemisia filifolia). These are ephemeral features that will eventually return to sand bluestem. The reestablishment of the rolling terrain that characterized the dune landscape of the Sandhills will be an aesthetically important aspect of the scenery and will create variations in environmental conditions that are a part of the richness of this prairie. This is the only grassland type with dense shrub growth affording visual interest and added cover. Some animal and insect species that are uncommon locally could probably be supported here, including Brewer's and Vesper's sparrow and populations of prairie chickens. Meadowlarks, horned larks, and buntings would be found in the tall and mixed grasslands, while rap tors might be found throughout the landscape. Management can be focused to favor selected wildlife by encouraging the proliferation of host species and food sources. Suitable butterflies would include satyrs and wood nymphs, crescents, checkers and coppers. Dr. Robert Pyle author of "The Thunder Tree" suggests that reintroducing the "lovely" Olympia marblewing would make a great project.

Riparian Landscapes and Habitats As the uplands were shaped by wind, fire and soil type, the lowlands were shaped by water. The indigenous riparian vegetation of the High Plains reflects the dynamics of the floodplain environment. This is the landscape of the flashy creek that suddenly swells from a rivulet inches deep to a wide torrent that weaves across its floodplain and leaves behind sandbars that are swiftly colonized by sandbar and peachleaf willows.

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These sandbar channels once occurred at all scales, from Sand Creek to Cherry Creek and countless smaller streams, most of which no longer run free, except outside Denver, but are constrained by drop structures and confined by narrowed floodplains. The remnant natural landscapes of Sand Creek represent the most intact, relic, indigenous landscapes on the site and should receive the highest level of protection and restoration. A key objective for the open space system is to provide for the opportunity to recreate the riparian habitats that once characterized the High Plains Denver landscape and to restore the plant and animal populations that they supported. Reestablishment of the historic hydrologic regimen is the most important step in restoring historic plant and animal communities. The open space system for the redevelopment of Stapleton has been designed to allow free-flowing streams in natural floodplains to develop in the open space corridors at two different scales-the mid-size scale of a drainage swale and the larger stream landscapes such as those of Sand and Westerly Creeks. A basin system will be used to further regulate drainage flows at points of designated outfalls to ensure compliance with existing requirements. At Stapleton we have the opportunity to go beyond maintaining functioning natural systems, to restore those presently degraded components of the natural infrastructure by incorporating the patterns of the local hydrology into the fabric of the development.

Sandbar Channels Neither the geometry of conventional development nor the geometry of conventional drainage permits the floodplain processes that are basic to sustaining the plant and animal communities of this region to be retained. Most of the cottonwoods along Sand Creek, for example, date from the flooding that occurred in 1965, but these trees will grow old and die without reproducing themselves unless more historic drainage patterns are restored. As the hydrology of the site is modified by dams, the historic plant communities are being replaced by species native elsewhere such as the Green ash(Fraxinus pennsylvanica) as well as exotic species such as Kentucky bluegrass (Poa pratensis) and downy chess grass (Bro111us tectarum ). All the drainageways in the larger scale open space system are proposed to be modeled on natural, free-flowing sandbar channels. The landscapes are comprised of very wide, flat channels that may often flow often an inch or two deep. They are lined with cottonwood (Papulus deltoides), as well as sandbar and peachleaf "villows (Salix exigua, S. amygdaloides) . Switchgrass(Panicu111 virgatum) can be used in the channel area that will grade into the prairie landscape types at the margins of the wetlands. These corridors will attract multitudes of waterfowl such as herons and egrets and skies filled with butterflies, including Weidemeyer'S admiral, mourning cloak, and tiger swallowtail, which can be a major feature of the restored landscape. Cherry Creek near Parker, Colorado, beyond the channelization of the stream in Denver has a broad sandbed that could serve as a model for Sand Creek. Often there is about an inch of water in it, as well as abundant wildlife. Sand Creek at it's lowest part in Aurora,

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where it crosses 1-225, flows in a restored sand bed which also could provide a model for the restoration of Westerly Creek.

Playa Lakes: Playa Lake Bottom Where a basin is constructed for flood management the model will be the playa lake bottom, a relatively permanent water feature supported by a mound of groundwater. The watertable fluctuates seasonally but is close enough for extended periods to support a diverse array of wetland species. The most common plants are likely to be the soft-stemmed rush (funeus validus ) and alkali bulrush ( Seirpus maritimus ) which are very beneficial to water quality. Blue vervain (Verbena hostata) is also present. Aquatic species in the shallow water environment include Sago pondweed (Potamogeton peetinatus) and Marestail (Myriophyllum sibiriewl1).

Playa Lakes: Playa Lake Fringe At the upper reaches of the playa lakes and at the drier margins where the water table is more variable seasonally and the moisture regimen fluctuates more dramatically the vegetation will be characterized by spike rush (Eleocharis palustris) , smartweed (Persicaria amphibium ) and prairie cordgrass (Spartina pectinata) . Leafy spurge (Euphorbia esula ) can be a problematic exotic that requires management.

Transitional Habitats Woody Draw While the natural landscapes are intended to be supported without supplemental watering, there are also opportuni ties to use regionally native species that require only minimal irrigation, to greatly expand the plant vocabulary for both public and private landscapes. Such an extended native vocabulary would include the shrubs and small trees of the lower foothills of the Front Range of the Rocky Mountains, just west of Denver as well as selected plants native to analogous habitats in Montana and New Mexico where there is slightly higher rainfall. In the High Plains of eastern Montana, for example, stream channels that are relatively undisturbed gradually succeed from cottonwood to a more varied wooded landscapes. Many of these species can be supported in Denver with minimal inputs of recycled greywater or by moisture from a drainage swale. In many cases supplemental watering is only required during the establishment period. The following list is illustrative of some of the most typical species that could be used to create shade and variety and color with a dramatically reduced water demand. Ponderosa pine (Pinus ponderosa), limber pine (P. flexilis), common juniper (Juniperus communis), Mountain mahogany (Cercocarpus montanus) ,American elm (Ulmus americana ), box elder (Aeer negundo ) , green ash (Fraxinus pennsylvaniea) , bur oak (Quercus maerocarpa) , Gambtel oak (Q. gambreli) , sand cherry (Prunus bassey) ,thin-

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leaved alder (Alnus incana lenUlfolia ) , serviceberry (Amelanchier alnifolia );, hawthorn (Crataegus erythropoda) , red osier dogwood (Comus stoloniferus) ,western snowberry (Symphoricarpos .occidel1lalis ) , smooth sumac (R. glabra ), Buckbrush (Ceonothus fel1dlerii), western virgin's bower (Clematis ligusticifolia), grape (Vilis riparia), Virginia creeper (Parthel1ocissus inserta), kinnikinnick (Arctostaphylos uva-ursi), pussy toes (Antennaria rosea).

Prairie Turf There has been a growing trend to use some grass species from the shortgrass prairie to create a kind of modified lawn that requires significantly less irrigation and mowing Both buffalo grass and western wheatgrass have been used successfully throughout the west and offer an important transitional landscape type between unirrigated prairie and fully irrigated turf.

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Implementation Strategies for Upland Landscapes The establishment of high quality native grasslands as a central aesthetic feature of Stapleton will be a gradual process that should be initiated as soon as possible. The site is largely barren at this time and it will take several years to create satisfying landscapes. While some on-ground experience in reestablishing short grass prairie has been obtained at the Arsenal and elsewhere, there has never been a sandhills prairie restoration. Many of the same species and techniques, however, will be used. The quality of the restoration will depend of the strength of the science. This effort should have a strong scientific footing from the outset. The following steps should be initiated immediately:

Interim management It is important that adequate mowing be maintained until a more prairie-oriented management program is developed. Although degraded, the grasslands at Stapleton do not at present because of the regular mowing support dense stands of the most pernicious exotic weeds such as cheatgrass. This effort to prevent weeds from becoming entrenched will reduce the costs and time frame for prairie establishment and require less herbicide use.

Seeding A two-step seeding process is recommended to minimize the opportunity for cheatgrass establishment. The initial seeding of the warm grasses in the mix should be planted in the early summer before the soil gets too hot and just after soil preparation is completed. It is imperative that bare soil not sit around waiting to be colonized and that grading operations be appropriately timed. A second overseeding in the following spring of the cool season grasses is proposed. Because both tall grass and shortgrass species will be included in the mix, the differences in the eventual grasslands will be able to develop naturally. It may also be possible to bale hay from natural sandhills sites near Denver, such as the areas near Raggin and Colorado Springs which could be used as a mulch and seed source simultaneously. Carol Mackie is currently employing this technique to establish needle-and-thread grass at the Arsenal.

Seed collection. A local seed collection program should be initiated now and carried out on a continuing basis. The quality of the landscape will be dependent on the level of enrichment that is undertaken as this site is too isolated from native seed sources and awash in exotics. The use of local seed may reduce site modification costs as well. Recent studies at CSU reconfirm the fitness of success of local seeds in local environments. Quality seed sources in the Stapleton area, are limited and disappearing rapidly. Many of the sandhills prairie species, such as prairie sand-reed and sandhills bluestem, sand

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dropseed and needle-and-thread grass are completely unavailable. Two sites for potential seed, propagule and prairie hay collection include extensive sandhills prairies around Raggin, Colorado as well as patches near Colorado Springs, Colorado. Many of the prairie forbs (herbaceous wildflowers instead of grasses) are slow to establish and should be grown vegetatively from locally collected seed for reintroduction in the prairie complexes. Some seedlings should also be propagated, especially of strongly rhizomatous species such as Sandhills bluestem and prairieysand reed. It is important to start the incremental development of both the expertise and the facilities that will be needed to realize the Stapleton landscape vision. This work could be coordinated with school programs and volunteer groups to integrate seed supply with education and publications. A plant propagation program should also be developed as soon as possible. Rick Brune, an excellent collector who is active locally, is very highly recommende~2060 Garland St., Lakewood, CO (303-238-5078).

Watering Supplemental watering is recommended for the first season in the event of a dry season as recommended by the Natural Areas Advisory Group.

Field demonstrations A sequence of field demonstration sites should be set up from the beginning. While many areas of Stapleton may be graded at a later date, those that are unlikely to be modified could be managed from this moment forward for prairie establishment and would serve as invaluable trial sites for cost-effective prairie establishment. Initial trial sites to evaluate propagation techniques could be very small, less than one acre, while others should be large enough to evaluate the use of appropriate equipment and the modifications of grading and soil conditions, from several acres upwards.

Controlling Invasives Degraded grasslands impact the stability of the landscape. Non-native annuals grow actively during the precipitation peak (May-July). They consume the available moisture and shade out the native grasses which are shorter during this season. Later, when the dry season arrives, many of the non-native seedlings cannot survive and die leaving bare exposed soil and a more barren landscape than that of the native grassland. Cheatgrass (Bromos teetorum), and leafy spurge (Euphorbia esula) and, in the damper areas, Canada thistle (Circium arvense) must be managed during the establishment period because once entrenched they will be very difficult to eradicate. Very early burning and/or mowing may be especially useful in controlling Cheatgrass while the native grasses are becoming established. The mower blade should be set to avoid damaging native grasses.

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Fire Management-Prescribed Burning All the prairie landscapes were historically shaped by fire, both natural and _ intentionally set. The plant and animal species coevolved which is a vital fact sustaining indigenous populations. Prescribed burning which emulates natural cycles, as well as mowing where fire cannot be accommodated, will be important management tools. The Natural Areas Advisory Group should establish, evaluate, and revise the recommended regimen.

V

Fire shaped the prairie landscape and is vital to sustaining many prairie species. Fire management is the most cost-effective method for controlling most undesirable exotic species and for fostering indigenous communities coevolved with fire. Many native species germinate and become established on the seedbed created by post-fire conditions. Fire has typically been suppressed throughout developed regions, even though it has been demonstrated to provide the best long-term control of serious wildfire. The most significant obstacle is smoke, especially adjacent to roadsides. Nonetheless a fire management program can and should be developed for the larger open spaces and will provide one of the most popular community events once implemented. Burning schedules should be set to coordinate with wildlife requirements including butterflies and ground nesting birds. Boulder Colorado has established a prescribed burning program that may serve as a model. When fire management is not feasible, other methods can be used to somewhat replicate the consequences of fire, such as mowing and soil amendments.

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Implementation Strategy for Riparian Landscapes Hydrology There is a cardinal rule in restoring wetland habitats: If you get the hydrology right, a lot will happen on its own; if it's wrong, nothing will work. The most common error is overengineering the system in order to gain a little 'developable' land. The open space system at Stapleton, however, is large enough to accommodate expansive floodplains that develop naturally. Success will be less dependent on the accuracy of predictive mathematical models and more on natural processes that are allowed to operate wlimpeded. Drop structures, liners, and other structures that deviate from natural hydrologic patterns will be avoided to the extent feasible. The primary focus can be instead on enhancing the quality of these landscapes as a setting for the new community and as habitat to sustain indigenous biodiversity. Unlike the built infrastructure, this natural drainage system can become richer and more stable over time rather than requiring ever increased maintenance and eventual replacement. The relationship between the riparian habitats and the groundwater is crucial. Some permanent flow is required to sustain indigenous communities in addition to stormwater flows. The irrigation water that will be used in virtually every landscape type could provide a vital augmentation to the natural rainfall to greatly enhance the habitat opportunities of the riparian areas by providing 'baseflow'. TIlis would also help compensate for the lingering water deficit that derives in part from continued use of irrigation. At the same time, however, the total proportion of the site that is irrigated land is significantly reduced from a conventional landscape treatment.

Grading The most exacting requirement is for the grading to be essentially flat within the floodplain. This will allow the actual runoff received to take as shallow a course as possible permitting maximum infiltration to support groundwater as well as charging by groundwater. There should be minimum restraint of floodflows. To permit stream course shifting that is the essence of the sandbar channel,)/he restored and protected corridor must be large enough to accommodate natural flooding patterns and foster the development of indigenous plant and animal communities. The twenty year storm appears to be a major force in shaping the channel configuration and should be used to determine the immediate channel width. The margins of the corridor can rise topographically to enclose the broad channel visually and to provide a second tier of flood protection. Topsoil should be reserved and replaced during the grading operation. If the topsoil may have propagules of native species, it should be windrowed during storage rather than piled which would destroy all of the propagules as well as valuable soil microorganisms.

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Vegetation Because available supplies of native plants for revegetation is very limited, advance propagation of local stock will be necessary. This issue that should be addressed as early as possible in the project. Timing is the key to establishing the riparian communities of the floodplain. A substantial proportion of the desired native vegetation is likely to colonize the site naturally if the seasonal aspects of plant recruitment are exploited. Ideally, the grading for all riparian corridors should be completed as close as possible to 1st May (i.e. within 30 days or less) when the seeds of willow and cottonwood are being disseminated. For the next two months there will be a continuous supply of seeds brought in on the wind to colonize the newly graded soil by creating a condition analogous to that which follows the spring floods. Grading completed in July, however, will not invite successful native volunteers and may require interim stabilization and redisturbance the following spring.

Controlling 111vasives

"*

Some vegetation management is also required, in particular, weeding undesirable species before they become entrenched on site and more difficult to control. This includes exotics such as green ash (Fraxil1us pel1l1sy!val1ica) , smooth brome (Bromos il1ermis). and bluegrass (Poa pratel1sis) as well as aggressive native species such as cattail (Typha iatijolia), that are less characteristic of the historic sandbar channels. Switchgrass is recommended where site stabilization is required. Additional species enhancement and management should be undertaken by the agency and institutions that are established to manage the natural areas of the open space system at Stapleton in the long term, under guidelines determined by the Natural Areas Management Group.

Playa Lakes The playa lakes will also be modeled on the patterns of natural prairie basins in the historic, indigenous communities. These can best be described as 'shallowly wet'. As in the stream channels, the water is usually very shallow and serves to create and support a groundwater mound. This is a very important requirement for without groundwater close to the surface, the vegetation of the basin will be comprised of far less valuable species that tolerate severe drying out and will not sustain historic plant and animal populations. The ideal basin condition would be to sustain anaerobic soil conditions on the bottom to provide the highest level of pollutant reduction and denitrification. Soft-stemmed bulrush is desirable as the predominant species that would transpire the most oxygen into the soil, which along with saturation, would provide ideal conditions for denitrification. The system could probably be flooded to a depth of four feet for short periods for stormwater retention and flood control without unduly compromising the

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habitat potential of these created wetlands. Provisions must be made however, for wildlife nesting areas protected from temporary floodwaters. Cottonwood and sandbar willows would likely volunteer along the margins. As in the channels, control of exotics and aggressive natives is required, as well as on-going monitoring. Where groundwater is too deep, an underground barrier or plug can be used to impound groundwater movement and raise the watertable in the basin area. Where more fluctuating conditions are unavoidable, spike rush and smartweeds would be desirable for stabilization and habitat use. The most serious obstacle to this effort is the lack of information on depth to groundwater on this site. Local information in the stream and swale channels as well as in the basin areas will be necessary before design development and construction documents can be completed. Scientific names for plant species in this report have been taken from the National List of Scientific Plant Names, USDA SCS-TP-159. 1982, Smithsonian Institution, Washington, DC. Alternative nomenclature can be found in Colorado Flora: Eastern Slope by W. A. Weber, 1990, University of Colorado Press, 396 p.

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VI. Phase I Construction including the Restoration of Westerly Creek


Phase One Construction The first phase of construction of the Stapleton redevelopment plan is most likely to be the neighborhood in the south-west corner of the site. This is the area designated Precinct I on the overall Stapleton Plan. It is contiguous with existing residential neighborhoods and one of the most visible and immediately accessible parts of the site. The area currently contains several buildings related to ancillary airport uses and a portion of the main east-west runways. From a restoration perspective the area is quite complex. Virtually all the issues characteristic of the overall site are represented here. There are many structures that have to be demolished or incorporated into a new plan and a significant area of runway and taxiway to be removed and re-cycled. In addition, there are known remediation issues that will have to be dealt with before the eastern section can be developed. The most important opportunity for restoration is a portion of Westerly Creek about 1000 feet long currently piped under the runways. Under the plan, after the runway concrete is removed, this piece of the stream would be excavated and restored to a natural open channel. A large portion of the existing open part of the stream, from its confluence with Sand Creek to the Aurora line, is partially channelized or confined and would also need restoration. This project has a high priority with Urban Drainage partly because the current channel and pipe is inadequate for storm flows. The Phase One area has no significant existing natural habitat other than the degraded grasslands surrounding the runways and small portions of Westerly Creek and these latter riparian habitats are actually peripheral to the area. The soils and geology information suggest that this area was originally short grass prairie, unlike the northern part of Stapleton which was mostly sandhills prairie. The plan for this area does not propose large portions of natural habitat except for the Westerly Creek restoration but there are several parks and parkways, school sites, a 'water quality' area and a small golf course.

Key Issues Certain issues will need to be resolved if the Westerly Creek restoration project is to become an integral part of Phase I of the Stapleton Development Plan. Foremost among these issues is remediation. Known contaminant plumes exist in the area and they flow in the direction of Westerly creek. No restoration of the creek can proceed unless a strategy for dealing with the plumes is devised in advance. This project would be an excellent opportunity to deal with remediation in an open and integrated way and provide a model, not just for Stapleton, but for other reused lands throughout the country. A further reason for dealing with this issue up front is that it is highly likely that current strategies will not clean up the area fast enough for the creek restoration to be included in any early phase of the project. The restoration of the creek will, by definition, involve earth moving. Restoration techniques that could not be considered while the airport was in operation, such as soil farming, might appear more viable in combination with the creek restoration and should be investigated at an early date.

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In general Precinct I is likely to have a deficit of natural soils and a considerable amount of sub-surface urban debris. When a sub-area plan is developed and the grading examined in detail, there is likely to be a soil deficit simply in volume to replace the concrete that will have to be removed. There would appear to be advantages in combining creek restoration with the phase one development to balance the cu t and fill. In addi tion, soils from the northern part of the site are likely to be more of the sandhills type rather than the less permeable soils derived from loess deposits in the south. Depending on the availability of a detailed soil survey, there may also be advantages to using specific soils from the excavation of the main swale for soil enhancement in Phase One. Finally, any comments made about phase one should be seen in the context of the overall restoration of the site. As noted earlier, critical site information on soils and ground water must be obtained as soon as the site becomes available for thorough investigation. All the other recommendations mentioned above related to putting together an advisory team and doing early demonstration projects are even more critical for phase one.

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1 February 1994 MEMO TO:

Pete Gober, Jane Griess United States Fish and Wildlife Service, Rocky Mountain Urban Wildlife Refuge

FROM:

Carol Franklin

RE:

Materials Relevant to the Proposed Natural Systems Framework for Stapleton Airport Development

As you may know, Colin Franklin and Richard Nalbandian (from the Stapleton Team) will be at the Arsenal, Monday February 7, 1994 to meet with Kathryn Caine, a Fish and Wildlife Service employee on loan to the Army. The purpose of the meeting is to help us to understand existing contamination on the northern portion of the Stapleton site. If you are interested they would be pleased to have you join them at this meeting. In addition, we are looking forward to Fish and Wildlife participating in future Stapleton team meetings. We are sending you some material to review in preparation for the upcoming meetings on 8-10th February. Enclosed please find: 1. An initial plan of the proposed Natural Systems Framework for Stapleton Airport. 2. A copy of the Stapleton International Airport, Development Plan Draft Principles, January 19, 1994. 3. The description of the vegetation inventory. 4. Xeroxes of two maps of contamination at the Arsenal, sent to us by the Army, to illustrate potential contamination sources originating at Stapleton. 5. Draft Principles for the Creation of the Natural Systems Framework These principles represent a first attempt at bringing together a second tier of ideas which one more site specific than the Stapleton International Airport, Development Plan, Draft Principles, January 19, 1994. It would be helpful if you could review these ideas from the standpoint of the concerns of the Rocky Mountain National Wildlife Refuge and get back to us with your comments.

Design Principles-Stapleton page 1


NATURAL SYSTEMS FRAMEWORK The Natural System Framework at Stapleton will comprise the largest proportion of the land area and will provide for a wide array of site uses including natural area restoration, regional scale habitat, water management, and passive and active recreation. It will be a significant amenity of the site and provide the major "value added" component of the development. 1. Scale and Connectivity

a. The open space at Stapleton must be large and continuous. Development fragments the natural landscape and creates small island which support less diversity. Natural areas at Stapleton must be in large pieces in order to allow the greatest potential species diversity. b. To make the Stapleton Open Space a significant regional system it has to be connected to the main open spaces on or directly adjacent to the site-the Rocky Mountain Urban Wildlife Refuge and the Sand Creek Corridor. Fish and Wildlife personnel and local plant and wildlife experts should be fully involved in the planning for this natural framework. c. Functional continuity means continuity of terrain. Interconnections must be clear, unobstructed land with grade separations for railroads, arterial roads and expressways. d. While connections between the large pieces of open space are critical there must also be multiple smaller connections at every scale. 2. Representation of The Full Range of Indigenous Ecological Systems a. The open space should represent the full range of indigenous habitats that once existed on or adjacent to the site and not simply selected components recognized to be of value such as riparian habitat. b. The prairie is the main natural habitat of this region and the natural context for the entire development. While it will not be possible at this scale to support the full breath of prairie species on the available acreage, Stapleton should integrate "functional prairie" into the fabric of development at many different scales. c. Prairie Parks should be protected from the impacts of destructive uses. "Wilder" prairie parks should be located adjacent to institutional and corporate uses where the impacts of both building requirements and recreation can be more fully controlled in orderto minimize damage to Design Principles-Stapleton page 2


natural habitat and its associated wildlife. The proposed park drives should be located to protect the natural areas from adjacent development. d. Full continuity should be maintained between upland and lowland habitats. 3. Wildlife Wildlife needs mandate large scale contiguous open space. Full advantage should be takenof the large scale of the Stapleton site and special efforts should be made to insure appropriate conditions such as adequate sightlines to foster grassland dependent birds and butterflies. The wildlife corridor should function for the whole range of potential wildlife including large mammals. There should be continuous lowland connections where there is the necessary coverincluding grade separated connections at the proposed extended 56th Street and at 1-70. The nature of these connections (height and width, etc.) should be planned with Col. DOT, the Public Works Department and wildlife experts from the Rocky Mountain Urban Wildlife Refuge. 4. Multiple Use a. The open space system isn't merely preserved or restored land but should accommodate multiple site programmatic functions. These functions include: (1). Drainage--conveyance, storage and infiltration.

(2). Biological Water Treatment to upgrade water quality. (3). Synoptic representation of regional habitats and the associated microhabitats: (a). Riparian Woodland (b). Sandhill Prairie (c). Shortgrass Prairie (4). Synoptic wildlife habitats/ corridor. (5). Passive recreation including footpaths, sitting areas, scenic drives, etc. (6). Active recreation including golf course, equestrian paths, bicycle paths, ballfields, golf courses and festival areas. (7) Related Institutions including the Prairie Restoration Center

Design Principles-Stapleton page 3


and the Sustainable Design Center. 5. The "Gradient of Wildness" a. The open space system should be organized as a "gradient of wildness" across the site. This gradient should include: (1). The natural core representing the synoptic habitats of the region and be composed primarily of restored remnant plant communities. This natural core will include drainage "fingers" threading through each neighborhood.

(2). Transitional, "quasi" natural areas which border the natural core and are combined with water management (water harvesting and water treatment) and with active recreational uses. These areas are landscapes of woodlands and groves with tall grasses and wildflowers from neighboring wetter habitats and represent the increased water now present on the site. (3). Traditional formal and informal neighborhood parks and boulevards (turf and ornamentals) irrigated with gray water and treated effluent. b. The "gradient of wildness" should vary so that there are gradients of all dimensions-shallow, moderate and steep. This variation will provide contrast, allow for a greater flexibility in planning, and a wider variety of habitat and landscape experience. 6. Integrating Remediation with Restoration and Public Education Stapleton, an abandoned airport, represents a unique opportunity to integrate the clean up of poisoned soil and water with the restoration and long term management of indigenous plant and animal communities and habitats. Remediation offers real opportunities for habitat restoration, not just treatment of a problem. Remediation includes excavation, soil treatment and creation, filling, planting and water management. All of these are integral to restoration. The traditional approach has been to try to turn attention from the mistakes of the past and focus solely on an image of the site after clean-up. However, one of the most significant contributions that both the former Stapleton Airport and the former Rocky Mountain Arsenal can provide is a model for the transformation of such sites, demonstrating how remediation itself can become the vehicle for continuous site improvement. Monitoring wells and treatment systems should be part of on-going public involvement and education---explaining that remediation of degraded sites is the most significant work of the 21st Century.

Design Principles-Stapleton page 4


1. Integrated Treatment

a. Remediation is almost always better done sooner than later. With time contamination diffuses and spreads. While concentrations of toxic substances may diminish, rather than disappearing or decrease to below cleanup standards, pollutants are harder to capture. b. Soil and groundwater remediation have been constrained by the previous use of Stapleton as an airport where it was not possible to remove large volumes of contaminated soil beneath runways, aprons and terminals. As these soils are still in place, they are continuing sources of groundwater pollution and, upon discharge, as contaminated stream baseflow. While "pump and treat" systems for the treatment of contaminated groundwater will almost certainly continue to be necessary, the use of additional methods may enable considerable shortening of the cleanup period and provide a number of synergistic economies integrating the creation of new habitat with the restoration of buried stream channels, soil farming and other bioremediation techniques. c. Where feasible, cleanup at Stapleton should involve digging out and treating contaminated soil on site, which, given the volume of contaminated soil at Stapleton, will be more cost effective and less environmentally destructive than transporting the material to haz-mat landfills offsite. When the airport ceases operations alternate remediation systems can be considered. d. Wherever possible major earth moving activities should serve multiple purposes, such as the creation of basins and swales that will be parts of the natural drainage system, creation of natural habitat, creation of visual amenity and recreation areas, as well as the remediation of contaminated soil and water. e. Consideration should be given to the establishment of large-scale treatment facilities for contaminated soil and water. At present, many airport tenants own and operate underground storage tanks (USTs) that hold a variety of regulated substances. Closure of these USTs upon termination of their use, is mandated by state and federal regulations. In virtually all UST closures some quantity of contaminated soil must be disposed of. A large-scale treatment facility employing presently available techniques such as soil farming, bioremediation or HAVE could treat soils on site and save current tenants considerable transportation and disposal costs, could also produce profits for the city to offset development costs.

Design Principles-Stapleton page 5


Management and habitat restoration stapleton development plan