NYS Department of Environmental Conservation Region 3 Headquarters New Paltz, NY
Stormwater Management Plan Spring 2009
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Prepared By Cornell University
Department of Biological & Environmental Engineering - Professor Larry Geohring (ldg5@cornell.edu) Department of Landscape Architecture - Professor Jamie Vanucchi (jlv29@cornell.edu)
BEE 4740 - Watershed & Landscape Engineering Chris Keil Danielle Musa Adam Silbert
LA 6020 - Integrating Theory & Practice Su Jung Ham Eden Gallanter Lee M. Pouliot
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Table of Contents Executive Summary ................................................................. 3 Background Information ........................................................ 4 Project Objectives .................................................................... 7 Concept Development ............................................................ 8
Master Plan ............................................................................... 9 Calculations .............................................................................. 28 Recommendations & Considerations ................................ 30 Appendices ............................................................................... 31
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Executive Summary “...showcasing the organization’s understanding of water management concerns and opportunities while demonstrating that nature and development do not have to be mutually exclusive.” The Region 3 Headquarters of the NYS Department of Environmental Conservation (DEC), located in New Paltz, NY is dissatisfied with the current stormwater management system consisting of a detention & infiltration basins located at the site. These basins do not provide proper infiltration capacity or appropriately move water off site. Additionally, efforts to minimize the flow of water entering the basin system have led to on-site erosion, ponding near the building foundation, and water damage to the building itself. The following stormwater management plan will promote enhanced control over water flow on site and serve to demonstrate a number of best management practices. Elements of the plan address the on-site issues, local conditions, and attempt to create additional value going beyond simply handling the site’s stormwater. Included in the plan is detailed grading, flow path, and planting plans, and a phasing plan to prioritize the improvements and allow their associated costs to be budgeted for over time. The materials and plants, in addition to their aesthetic harmonization, were chosen to be native to Ulster County and readily available from local sources. Further recommendations and considerations address monitoring water quality and flow, a greener parking system, snow management, and landscape maintenance. Collectively, the concepts and components of this plan will transform the site into a cutting-edge model that successfully manages stormwater while serving as a teaching tool to inspire others who are concerned with stormwater management.
Proper installation and management of the proposed rain gardens and other site improvements will improve the landscape’s appearance, reduce erosion, enhance pollutant removal and water quality, increase groundwater recharge, increase habitat and vegetation, and make the storm-water management practices visible and educational. The DEC will be sending a clear message to visitors by showcasing the organization’s understanding of water management concerns and opportunities while demonstrating that nature and development do not have to be mutually exclusive.
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Background Information “...Region 3 Headquarters, has recently undergone construction to expand its facilities and significantly increase its available parking area...an increased stormwater from added impervious surface...” The project site is located at 21 South Putt Corners Road in the city of New Paltz, Ulster County. This office, the Region 3 Headquarters, has recently undergone construction to expand its facilities and significantly increase its available parking area. The mission of the NYS DEC is “…to conserve, improve and protect New York’s natural resources and environment and to prevent, abate and control water, land and air pollution, in order to enhance the health, safety and welfare of the people of the state and their overall economic and social well-being.”1
In an attempt to remedy the situation, the pipes connected to building gutters have been cut off from the system, which has diverted runoff from the building’s roof to the surrounding turf areas. This action has resulted in ponding near the foundation and water damage to the building itself. There are also locations where the high water flow, not carefully diverted, has created substantial erosion. While these management problems pose major challenges to the site, they also offer unique opportunities for the future. The National Pollutant Discharge Elimination System (NPDES) has developed a list of Best Management Practices (BMPs) for storm-water management.3 These are divided into the following six categories:
According to the EPA, “the best way to mitigate stormwater impacts from new developments is to use practices to treat, store, and infiltrate runoff onsite before it can affect water bodies downstream.”2 In response to an increased stormwater volume from added impervious surface, the DEC office initiated the design and construction of a post-construction stormwater o Public Education - BMPs for MS4s to inform individuals and households about ways to BMP. This is a particularly important action, considering that the DEC is dedicated to reduce stormwater pollution. protecting water resources and the well-being of NYS residents. o Public Involvement - BMPs for MS4s to involve the public in the development, imple mentation, and review of an MS4’s stormwater management program. The BMP design included a settling basin and a large infiltration basin. A previously forested o Illicit Discharge Detection & Elimination - BMPs for identifying and eliminating illicit dis land ‘patch’ on-site was cleared and excavated to create the system. The basins were charges and spills to storm drain systems. designed to handle the overland runoff from the parking lot as well as runoff from the o Construction - BMPs for MS4s and construction site operators to address stormwater remainder of the site via underground pipes. However, due to very shallow bedrock, the water runoff from active construction sites. is unable to vertically infiltrate to any considerable depth. Moreover, the basin is constructed o Post-construction - BMPs for MS4s, developers, and property owners to address at the edge of a major road, necessitating an impermeable liner be used to prevent the basin stormwater runoff after construction activities have completed. water from seeping under the road. This requirement further limits the level of infiltration o Pollution Prevention/Good Housekeeping possible. Thus the system is unable to infiltrate the volume of water it receives from the project site and simply ponds until overflowing into the road-side ditch system. By re-imagining the site, a new stormwater system can address current stormwater challenges and many of the goals detailed by the NPDES while allowing the site to become a valuable teaching tool at the DEC’s disposal. 1 “About DEC.” NYS Dept. of Environmental Conservation. 2009. New York State Department of Environmental Conservation. 22 April 2009 <http://www.dec.ny.gov/24.html>. 2 “Post-Construction Stormwater Management in New Development and Redevelopment.” EPA-Stormwater Menu of BMPs. 2006. U.S. Environmental Protection Agency. 22 April 2009.
3 “National Menu of Stormwater Best Management Practices.” EPA-Stormwater Menu of BMPs. 2006. U.S. Environmental Protection Agency. 22 April 2009 < http://cfpub1.epa.gov/npdes/stormwater/menuofbmps/index.cfm>.
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Current Site Plan
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Scale: 1” = 80’
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Current Conditions
Area 1: offers full sun exposure and considerable space for rain garden construction. Creating a rain garden would also reduce turf maintenance.
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Area 4: exhibits water ponding and erosion as a result of large volumes of water being released onto turf area from roof surfaces.
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Area 2: recieves only partial sun exposure offering the opportunity to showcase plants suitable to â&#x20AC;&#x2DC;shadeâ&#x20AC;&#x2122; rain gardens.
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Area 5: offers a unique opportunity to create a plant chrono-sequence beginning with dry-tolerant plants at the top of the slope, ending with wet-adapted plants below.
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Area 6: the berm behind the parking lot offers the opportunity to showcase species that can be utilized for phyto-stabilization.
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Area 3: exhibits issues with foundation water damage, ponding, and erosion.
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Area 7: the exisiting detention/infiltration basins offer the opportunity to increase bio-diversity and unique habitat in the area while reducing turf maintenance.
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Project Objectives The mission of the NYS DEC is “…to conserve, improve and protect New York’s natural resources and environment and to prevent, abate and control water, land and air pollution, in order to enhance the health, safety and welfare of the people of the state and their overall economic and social well-being.” o Delineate sub-areas based on water flow patterns, sun/ shade exposure, soil conditions, and functional possibilities.
o Reduce required site maintenance by utilizing native plants and minimizing maintenance-intensive turf.
o Maximize the site’s ability to infiltrate stormwater, reducing the amount of water flowing to the current detention/ infiltration system.
o Define a monitoring program to document improvements in water quality resulting from the new stormwater system.
o Create areas to specifically retain water, slowing the speed at which stormwater does enter the current detention/infiltration system.
o Integrate educational features into the site offering visitors a ‘take home message.’
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Concept Development The creation of a holistic stormwater system composed of modulated areas treated with different BMP techniques. Each module functions individually, but can be connected and phased in over time. Each module doubles as a model, giving the DEC an inexpensive educational toolkit for future environmental programming. Concept Diagram
Breakdown of site modules
Bio-stabilization module
Re-forestation module Vegetated swale module Dry/shade module Dry infiltration creek bed module
Dry/wet plant chrono-sequence module Sun rain garden module
Shade rain garden module New parking module Biological benchmark module Salt tolerant meadow module
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Master Plan “The creation of a holistic stormwater system composed of modulated areas treated with different BMP techniques.” This design employs rain gardens, water channeling, and other landscape modifications to successfully infiltrate enough runoff to eliminate the water damage problems around the building and reduce the amount of water entering the original detention/infiltration basin. In addition, the rain gardens and other features are designed to be demonstrative and educational, allowing the DEC to serve as a model for stormwater management practices.
From the concept diagram, module areas were described and prioritized as follows: o Sun rain garden –This relatively flat area offers the opportunity to create a rain garden that handles stormwater from a large portion of impervious roof area. This area is also the first area that visitors will encounter upon entering the site. The area is large enough to offer interaction between plants and visitors with the addition of a secondary pathway through the garden. This module is later connected with the Dry/ wet plant chrono-sequence module. o Shade rain garden – This area is divided into two sections: an area that receives partial sun and an area in full shade. The site must retain a small portion of stormwater from both sides of the building and therefore can showcase plants that are adapted to rain garden conditions and thrive in shade environments. o Dry/wet plant chrono-sequence – This large area offers unique topographic features that allow for the planting of a sequence of plant associations leading from a dry-tolerant association at the top and ending in a wet association were elevations reach their lowest values. This area showcases the interactions between various plant species and the rich diversity NYS native plants offer based on environmental factors. Once constructed this area links to the Sun rain garden module to create a holistic stormwater system. o Dry/shade – This area, located adjacent to the dry/wet plant chrono-sequence module is topographically the highest and driest of all identified module areas. This area is perfectly suited to the planting of upland canopy species that produce shade for understory plants below.
o Bio-stabilization – The berm, established during construction, is suspected to contain some level of pollutants. While the exact pollutants are currently unknown, the site is utilized as a display of species utilized in phyto-stabilization and phyto-remediation plantings. Species in this area are known to hyper-accumulate soil pollutants. o Vegetated swale – This existing stormwater structure can be enhanced to provide a visual link to the Bio-stabilization module and improve water quality before water enters the basin system. By densely planting the swale, the modules functionality is increased. o Salt tolerant meadow – This area slopes from the main entrance down to the roadway below. A curb cut added in the drop off circle will allow stormwater to enter this module instead of the pipe system to the basins. The meadow association to be planted in this area is designed to deal with high salt content, an issue typical with any plantings done in areas receiving stormwater from roadway surfaces. This low meadow transitions well to the mixed meadow/woody plant associations of the sun and shade rain gardens while reducing turf maintenance as well. o Biological benchmark – The existing basins currently lack any vegetation that could make the area valuable as a site of bio-diversity and habitat. By determining biological benchmarks, or the different plant zones based on water depth, a highly diverse planting scheme is developed that can then serve as habitat to a number of species. By planting this area, a large reduction in turf maintenance also occurs. o New parking – Plans exist to expand the parking capacity on site to an area left of the main building. Should these plans move forward, the parking lot should be designed to include new stormwater practice techniques possibly including porous pavement or pavers, infiltration islands, and the introduction of plant materials to increase shade in the parking lot.
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Master Plan
o Dry infiltration creek â&#x20AC;&#x201C; This areaâ&#x20AC;&#x2122;s current swale can be enhanced with stone to reduce current erosion problems while dealing with the large volume of stormwater coming from the back left of the building. The area can be planted to link into the salt tolerant meadow module and the re-forested module. o Re-forested module â&#x20AC;&#x201C; A large area located to the back left of the building is maintained as a large tract of turf. With no apparent function, the area should be returned to a native forest association thereby reducing turf maintenance and enhancing surrounding tracts of forest vegetation.
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Master Plan
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Perspective
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Technical Drawings
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EX −> Subsurface Subsurface −> Finished Grade
40.73yd CUT 5.05yd CUT
26.80yd FILL 30.85yd FILL
13.93yd CUT 25.80yd FILL 11.87yd Amendment
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EX −> Subsurface Subsurface −> Finished Grade
40.73yd CUT 5.05yd CUT
26.80yd FILL 30.85yd FILL
13.93yd CUT 25.80yd FILL 11.87yd Amendment
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Calculations & Phasing Description of Calculations Related to Water Flow Sizing the Rain Gardens
A, the runoff area, is approximately 0.57 acres. The accumulated runoff depth is based on the Curve Number Method and calculated as shown below.
In Chapter 5 of the NYS Stormwater Management Design Manual, bioretention areas, such as rain gardens, are designed based on the Water Quality Volume (WQV). The equation for calculating this volume is shown below. WQV = (P )( RV )( A) 12
where WQV is water quality volume (acre-ft), P is the 90% rainfall event number, A is the site area in acres, and RV = 0.05+0.009(I), where I is percent impervious cover
The following table summarizes the WQV for each of the different areas of the site. Area Sun Rain Garden Shade Rain Garden Dry-wet Chrono-sequence
Water Quality Volume (ft3) 35.5 76.5 131.4
Each of the proposed systems is graded and sized to handle the associated WQV. Sizing the Channel A constructed channel is included in our design to connect the water collection system from the west side of the building (Rear Dry to Wet Slope) to the east side of the building (Sun Rain Garden). The channel was sized based on a calculated peak flow rate. Below are calculations to determine this flow rate (using the Kirpich equation and Curve Number Method) and the associated channel dimensions. Flow rate calculations: To find a peak flow rate (Qp = (0.756(A)(Qt))/tp) requires first calculating the associated area, accumulated runoff depth, and time to peak.
( P− I a ) 2 Qt = ( P− I a + S )
where P is rainfall depth (inches) [P=1.2” (from 90% rainfall event map)], S is the potential maximum storage, and Ia is some initial abstraction (approximated as equal to 0.2S)
S is found using the equation, S =
a −b CN
where a=1000 and b=10 and CN is the curve number found by weighting the differing independent curve numbers by area. The curve number (CN) was found to be 81.7. This led to S = 2.23” and Qt = 0.19 in. The Kirpich equation allows one to determine the time of concentration (tc) as follows: tc = 0.0078(L)0.77(S)-0.385 (min) where L (ft) is the longest flow path and S is the average slope. L= 290ft S= 0.13 tc= 1.31 min Then, the time of concentration is used to determine the time to peak (tp) tp= (0.7)tc = 0.92 min These calculations resulted in a value for peak runoff as Qp = 5.34 ft3/s. Channel dimensions: A natural channel on the western lawn will carry water from its high elevation to the north end of the building where the water will be captured in perforated pipe that leads to the Sun Rain Garden. The natural channel is designed for the peak flow rate (Qp) in a triangular shape with a 20% buffer. The following calculations outline the determination of the channel dimensions.
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Calculations & Phasing For a trapezoidal channel, bd+ Zd2 2 /3 1/2 1.486 Q = (bd+ Zd ) s0 n b+ 2d Z 2 + 1 2
where n is Manning’s n coefficient for the channel, b is the bottom width (ft), d is the channel height (ft), Z is the side slope, and s0 is the channel slope.
The site conditions gave the following values: n= 0.025 (non-vegetated, winding earthen channel), b=0 for triangular channel, s0=0.01, and Z=3 to ensure maintainability. The previously determined flow rate of 5.34 ft3/s was designed to be handled with a 20% freeboard (additional depth above the normal flow depth). This resulted in a depth value (d) equal to 0.9 ft and the top width (T) is 5.5 ft. The channel will lead into a 2ft diameter clay pipe where Q=A
1.486 2 /3 1/2 R s0 n
for half full flow with area (A) equal to 1.46 ft2, hydraulic radius (R) of 0.48 and a slope of 1%.
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Recommendations & Considerations • The specifications for grading and planting have been specifically chosen for the local site characteristics, including climatic conditions, soil conditions, and native plants and materials. Any changes from the proposed design should be carefully considered to ensure its appropriateness for the particular site. • Since there is little collected data on the water quality improvements of rain gardens as bioretention facilities, Cornell University’s Biological and Environmental Engineering Department has been provided with a grant for the purpose of monitoring the success of an installed rain garden. It is recommended that monitoring equipment should be installed to collect water samples and test concentrations for the following pollutants: copper, lead, zinc, phosphorus, total Kjeldahl nitrogen (TKN), ammonium (NH4+), nitrate (NO3-), total nitrogen (TN), and calcium. Ideal locations for collecting samples would be at the water’s entrance to the rain garden, a location at the deepest, central part of the rain garden, and at the overflow to the storm drainage system.
• Consideration may also be given to the concurrent installment of monitoring equipment at similar locations (excluding the center of the rain garden) that could provide data on the amount of water entering and exiting the rain garden. This data could provide information on the effectiveness of the sizing and infiltration capacity of rain gardens. A potential method for including this monitoring would be to include short segments of pipe at the entrance and exit and attach electronic flow meters. Even if the data is recorded digitally, additional public interest could be sparked by keeping a written log at the building entrance that shows the total daily volumes, updated once a day.
o This data could be particularly valuable since few studies have yet addressed pollutant removal in bioretention basins, such as rain gardens. “A field and laboratory analysis of bioretention facilities conducted by Davis et al. (1997), showed very high removal rates (roughly 95 percent for copper, 98 percent for phosphorus, 20 percent for nitrate, and 50 percent for total Kjeldhal nitrogen (TKN). The following table shows data from two other studies of field bioretention sites in Maryland.”1 Pollutant Pollutant Removal Copper 43%-97% Lead 70%-95% Zinc 64%-95% Phosphorus 65%-87% Total Kjeldahl Nitrogen (TKN) 52-67% Ammonium (NH4+ ) 92% Nitrate (NO3-) 15%-16% Total nitrogen (TN) 49% Calcium 27%
• Consideration for installing a new parking lot provides an excellent opportunity for creating a greener parking system. Several techniques can be employed to retrofit the existing parking and add additional parking. Some of these include reducing the size of parking spaces, installing infiltration islands, and using porous pavement or alternative pavers.2
1 “Bioretention (Rain Gardens).” EPA-Stormwater Menu of BMPs. 2006. U.S. Environmental Protection Agency. 22 April 2009 <http://cfpub1.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=browse&Rbutton=detail&bmp= 72&minmeasure=5>.
2 “Green Parking.” EPA-Stormwater Menu of BMPs. 2006. U.S. Environmental Protection Agency. 22 April 2009 <http://cfpub1.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=browse&Rbutton=detail&bmp=89&minme asure=5>.
o The length and width of many parking spaces can often be reduced since most local parking codes require stall widths wider than the widest SUVs. Additionally, a number of smaller parking spaces can be included to accommodate and encourage compact vehicles.
o Porous pavement and alternative pavers allow greater infiltration and a common design for alternative pavers features a gravel or plastic grid with the gaps filled in with grass planting and a gravel layer underneath to provide structural support and greater infiltration.
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References
“About DEC.” NYS Dept. of Environmental Conservation. 2009. New York State Department of Environmental Conservation. 22 April 2009 <http://www.dec.ny.gov/24.html>. “Bioretention (Rain Gardens).” EPA-Stormwater Menu of BMPs. 2006. U.S. Environmental Protection Agency. 22 April 2009 <http://cfpub1.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=browse&Rbutton=detail&bmp=72&minmeasure=5>. “Green Parking.” EPA-Stormwater Menu of BMPs. 2006. U.S. Environmental Protection Agency. 22 April 2009 <http://cfpub1.epa.gov/npdes/stormwater/menuofbmps/index.cfm?acti on=browse&Rbutton=detail&bmp=89&minmeasure=5>. “National Menu of Stormwater Best Management Practices.” EPA-Stormwater Menu of BMPs. 2006. U.S. Environmental Protection Agency. 22 April 2009 <http://cfpub1.epa.gov/npdes/ stormwater/menuofbmps/index.cfm>.
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Plant Lists
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Plant Lists
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Plant Lists
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Plant Lists