Green Infrastructure in the Semi-Arid West

Low-Impact Development and Green Infrastructure in the Semi-Arid West

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Introduction

Low impact development (LID) is a method of building design and community development with the intention of keeping storm water runoff as uncontaminated as possible. “Slow it down, spread it out, soak it in” is the motto of LID. Slowing the flow of stormwater reduces erosion and flooding dangers. Spreading stormwater out reduces the speed of the stormwater. Allowing the stormwater to soak into the ground recharges underground aquifers and fosters environmental growth. Green infrastructure (GI) is a method of water management that is as sustainable, environmentally friendly, and cost-effective as possible. GI focuses on creating ecosystems to treat polluted stormwater runoff prior to it entering aquifers, streams, or other waterways. On-site management of stormwater is the first choice, with neighborhood or regional solutions the next preferable solutions.

When LID and GI are implemented in a semi-arid climate, attention must be paid to our unique environment. With a dry climate and large temperature differences between summer and winter, native plants that are drought tolerant and low maintenance must be chosen that can withstand the harshness of our region.

Green infrastructure in the semi-arid West can be specifically designed to address rapid freeze/thaw cycles, semi-arid conditions, and intermittent and unpredictable rainfall patterns.

Green Roofs

In Region 8 most “Green Roofs” are not actually the color green. To represent this, many green roofs in our region are referred to as “living roofs” or “eco-roofs”. Green roofs reduce the volume of storm water runoff and filter the storm water runoff that does leave the roof.

Unique Benefits

  • Green roofs create a place for stormwater to soak in, reducing the amount of stormwater runoff from a building. The foliage also slows and filters the stormwater that does runoff the roof
  • When built in urban areas, green roofs can reduce the Urban Heat Island Effect which is dangerous to human health, especially at our higher elevations. Having enough green roofs in a city can actually reduce the energy expenses of surrounding buildings as the urban temperatures are reduced
  • Region 8 experiences very warm summers and very cold winters. Green roofs reduce energy expenses for buildings by providing insulation to reduce heat loss during the winter and air-conditioned loss during the summer
  • Due to our increased elevation from sea level, buildings in Region 8 are exposed to intense solar radiation, which damages the roof membrane. Green roofs extend roof lifespan by protecting the membrane from sun damage
  • Green roofs can provide habitat for birds, butterflies, insects, etc.

Examples

Fargo, ND: Hotel Donaldson’s Sky Prairie on The Roof restaurant allows guests to enjoy the view from the roof and the garden on it as well. The vegetation is mostly on the outer edge of the roof, proving a roof does not need to be completely covered in foliage to reap the benefits of having a green roof.

Denver, CO: The REI parking garage turns a traditionally gray area into a green island in the city. This green roof reduces the Urban Heat Island Effect and creates a large area for stormwater to absorb into a garden. It also provides an attractive open space near the South Platte River.
Roof Restaurant photo

Salt Lake City, UT: Church of Jesus Christ of Latter-Day Saints (LDS) Conference Center takes advantage of their large roof to provide a fountain and walking garden for visitors to enjoy. The gardens also reduce the amount of runoff from the conference center.
LDS Green Roof

Laramie, WY: Robert and Carol Berry Biodiversity Conservation Center creates a classroom on the roof for children and students to learn about native Wyoming plants. This green roof is an ongoing experiment, testing over 60 native drought tolerant plants to see their potential for green roofs within our region. Updates about the native plants can be seen on the Berry Prairie blog.
roof photo

Denver, CO: The first publicly accessible green roof in Denver is on the roof of the Denver Botanic Gardens. The plants used are native to our region, testing their potential for use on green roofs.
Botanical Gardens roof

Denver, CO: The EPA Region 8 building contains a green roof of sedums in trays for easy irrigation. The roof also provides insulation to the building, reducing heating and cooling costs. Experiments have been done on the roof with the solar panels and the sedums. The vegetation keeps the solar panels cool and the solar panels provide shade for the plants.
Region 8 roof photo

Helena, MT: The Montana State Fund building harvests rainwater to irrigate the vegetation on the roof. The building is LEED certified Gold because of its many green innovations.
Montana State Fund building roof

Jackson Hole, WY: Jackson Hole and Greater Yellowstone Visitor Center sod roof.
Jackson Hole visitor center

Denver, CO: The former Denver Museum of Contemporary Art uses their green roof as an art exhibit as well as a vegetated area. Most of the plants are native to Colorado and only require watering a few months of the year.
Denver Museum roof

Recommended Sites

Rain Gardens

Positioned near paved surfaces or lawns, rain gardens consist of native plants that catch runoff.

Unique Benefits

  • Reduce the stormwater runoff entering streams and ponds by catching the water in the gardens. The runoff that does enter the natural water sources is filtered by the plants in the garden.
  • In arid and semi-arid regions like ours, native plants are drought resistant and hearty. Thus they require little to no maintenance once they are installed.
  • When used in public areas they can provide shade and aesthetic benefits.
  • Rain gardens can meet public landscaping requirements as well as provide stormwater benefits.

Examples

Boulder, CO Western Resource Advocates, 2260 Baseline Rd: Including a rain garden in a parking lot design provides storm water runoff control and a source of shade for cars parked in the lot. The rain garden allows the water to soak into the ground while watering plants. See cuts in the concrete to allow stormwater flow.
rain garden in a parking lot in Denver

Denver, CO: Property near Regis University uses rain gardens for the collection of stormwater. The native grasses both slow and filter the water.
rain gardens near Regis University

Fargo, ND: Microsoft uses porous pavement in their parking lot and rain gardens surrounding the lot to essentially eliminate all runoff. This combination of LID and GI results in the stormwater being cleaner when it enters the aquifer.
porous pavement in Microsoft parking lot in Fargo, ND

Fort Collins, CO: New Belgium Brewery takes advantage of a rain garden’s aesthetic qualities while also using it for runoff control. The rocks and plants in the garden create an area for the stormwater to slowly absorb and be filtered.
New Belgium Brewery invereted landscape garden

Cheyenne, WY: Antiques Central used a Nonpoint Source Pollution Control grant from the State and EPA to create rain gardens surrounding their building. Water running off of the roof of the building can be absorbed into the gardens, reducing the distance the stormwater travels, and thus improves its quality.
rain gardens surround Antiques Central building in Cheyenne, Wyoming

Denver, CO: The Denver Housing Authority uses both rain gardens and pervious pavements in their Park Avenue development. This helps the new development to be environmentally friendly as well as attractive. DHA was able to decrease stormwater infrastructure costs from $850,000 (stormwater vault) to $350,000 (bioswales and permeable pavements) at its Park Avenue site. DHA estimates that they will save $3,000,000 at its Mariposa site by using low-impact development/green infrastructure over traditional grey infrastructure (see link for stormwater/gi design charette).
Park Avenue development in Denver

Salt Lake City, UT: As a part of their Sustainable Campus Initiative the University of Utah built rain gardens to capture and filter stormwater runoff. The garden also has educational purposes as well.
University of Utah rain garden

Denver, CO: The TAXI Development uses rain gardens to filter water from their parking lots before it reaches the storm drain. The garden also features native plants and requires limited additional water. Note: there are several pictures:

Denver, CO: Central Park (Stapleton) soft running path and green infrastructure in street median.

Boulder, Colo.: Rainwater is collected in a planter box then is channeled into a rain garden. The water is collected from the gutters on the roof of the Environmental Center of the Rockies. 2 pictures.

Denver, CO: Former 1035 Cherokee, side yard where two areas are passively irrigated by storm water runoff from roof downspouts, this was a former driveway to the parking area.

Recommended Sites

Bioswales/Bioretention Cells

To filter contaminants from stormwater runoff, many communities in Region 8 choose to install bioswales, sloped drainage areas that contain vegetation. Most bioswales continue for several miles, often running next to roads or walking paths. The slope of the bioswale allows the water to drain slowly, thus increasing its filtering time. The native vegetation in the bioswale removes pollutants as the water drains. Soil preparation and soil type are key to infiltrating water effectively.

Unique Benefits

  • Since bioswales are long and often run alongside of the road they do not take up large amounts of space and can be used in urban, suburban, or rural settings.
  • The vegetation in a bioswale filters the stormwater runoff and provides an attractive vegetated area.

Examples

Denver, CO: Central Park (formerly Stapleton) Quebec Square shopping center. Bioswale between a parking lot and a road.

Fort Carson, CO: Vegetative swale
vegetative swale in Ft Carson, Colo.

Fort Carson, CO: Iris in Bioretention Pond
Iris in bioretention pond in Fort Carson, Colorado

Denver, CO: Central Park (formerly Stapleton) Greenway Park during a storm event.
Stapleton's Greenway Park during a storm event

Denver, CO: Central Park (formerly Stapleton) Greenway Park during the fall.
Stapleton's Greenway Park during the fall

Denver, CO: Northfield at (Central Park (formerly Stapleton) with Interstate 70 in the background.
Northfield at Stapleton in Denver, with I-70 in the background

Denver, CO: Westerly Creek at Central Park (formerly Stapleton). Daylighted creek that was under taxiways at Stapleton International Airport. Westerly Creek is now part of open space and has a functioning floodplain and wetlands.

Denver, CO: The South Platte River near downtown. The vegetation can be inundated in large flow events.
South Platte River near downtown Denver

Denver CO: Streetside stormwater planters (bioretention cells) and stone gabian wall benches along Brighton Blvd. in the River North (RINO) area near Interstate 70.

Golden, CO: Constructed wetlands and stone gabian walls adjacent to parking garage at the National Renewable Energy Lab.

Resources

Detention/Retention Ponds

In Region 8 flash floods are often a concern, as sudden rainfall releases large amounts of water quickly. Detention and retention ponds create a location for this rainwater to collect and infiltrate into the aquifer. During times of no rainfall the detention pond stays dry while a retention pond contains a constant amount of water.

Unique Benefits

  • Prevents flooding by creating a storage space for the large amounts of water provided from hard, sudden rainfall.
  • During dry seasons provides an open space for many animals and plants to thrive.
  • In the snowy winter months acts as a storage place for piles of snow that have been removed from sidewalks and parking lots.

Examples

Fargo, N.D.: The Woodhaven neighborhood has a large stormwater retention pond that collects stormwater runoff. The retention pond provides a large area for stormwater to spread out and drain into an underground aquifer slowly, filtering the water in the process.

Denver, CO: City Park contains several retention ponds where water levels are constant during most of the year, then rise during wet seasons. These retention ponds reduce erosion to the park and create a wetland ecosystem.

Denver, CO: A shopping center uses a retention pond to collect and filter stormwater runoff before it enters the underground aquifer. The plants surrounding the retention pond filter the water as it drains, allowing cleaner water to enter the aquifer.

Porous Pavements

Speeding stormwater runoff and fast floods are concerns in Region 8 states. Porous pavement absorbs stormwater runoff instead of increasing its speed.

Unique Benefits

  • Replenish aquifers with water that is filtered by the pavement as it drains.
  • In Region 8 we have a great risk for flash flood when there is a large storm. Porous pavements can reduce flooding risks by slowing storm water runoff, making communities safer.
  • Many types of porous pavements are unaffected by routine freezing and thawing cycles that are seen in the winters in Region 8, allowing them to be more durable than traditional nonporous concrete. Porous pavements, just like traditional asphalt and concrete, can be adapted for all types of climates.

Examples

Sioux Falls, S.D.: To prevent flooding of their office, Woodlawn Cemetery installed pervious pavement. Their office hasn’t flooded since! The water absorbs into the pavement, is filtered, and enters the underground aquifer instead of flooding and causing erosion to the surrounding area.
Woodlawn Cemetery

Rapid City, S.D.: Camp Rapid, home of the South Dakota National Guard, uses porous pavement to absorb stormwater runoff and snowmelt from the visitor parking lot. The water can absorb through the pavement.

Fort Collins, CO: Odell Brewery uses pavers and a flow through parking island planter to slow the flow of stormwater. The parking islands provide a location for the water to collect, have the contaminants removed by the plants and rocks, and then slowly absorb into the aquifer.

Billings, MT: The Northern Plains Resource Council Building utilizes porous pavement made of recycled materials to reduce runoff. This reduction in runoff allows the quality of water entering to the aquifer to be much higher and for the risk of flooding to be reduced.

Rapid City, S.D.: Western Dakota Tech uses pervious pavements on visitor paths to filter stormwater, allowing the water to absorb into the pavement instead of rushing off and collecting pollutants.
Western Dakota Tech Permeable Pavement

Fort Collins, CO: CTL Thompson created a driveway of pervious pavement.

Denver, CO: Path along the South Platte River near downtown

Fort Collins, CO: Permeable paver parking spaces drain to a rain garden at a local park.

Denver, CO: Denver Housing Authority's Mariposa redevelopment where grass and plants drain to grey infrastructure with permeable paver parking spaces.
Denver, CO: Multifunctional green alley behind food hall.
Recommended Sites

Rainwater Harvesting

Easy to do, rainwater harvesting allows residents to collect non-potable water and use it for various household purposes such as watering plants and mopping floors. Note that rainwater laws differ in the Region 8 states.

Rainwater Harvesting Rules by State
  Colorado Montana North Dakota South Dakota Utah Wyoming
Responsible Agency Colorado Division of Water Resources Montana Department of National Resources North Dakota Water Commission, State Engineer South Dakota Department of Natural Resources Utah State Engineer Wyoming State Engineer and Board of Control
Permit Required Situational; See Below No No Situational; See Below Situational; See Below Situational; See Below
REGULATORY REFERENCES CO Surface Water Rainwater Collection Montana Licenses & Permits North Dakota Century Code South Dakota Water Right Permit Utah Enacted Rainwater Harvesting SB 32 (pdf)

Utah Code 73-3-1.5 (pdf)		 Wyoming State Surface Water Division

Wyoming Water Law Summary

Unique Benefits

  • Reduces water bills by using the non-potable rainwater to water plants and for other household uses.
  • Allows more water to be available for downstream use as less treated water is withdrawn from locations upstream.

Recommended Sites

Further Reading on GI/LID

Resources for Financing GI Projects

Regionally Specific Scoping and Design Guidance for GI

Regional Case Studies and Example GI Projects

Webinars

Contact Information

Stacey Eriksen (eriksen.stacey@epa.gov)
Urban Watershed Revitalization Coordinator & Green Infrastructure Coordinator
303-312-6692

Amy Clark (clark.amy@epa.gov)
Environmental Scientist
303-312-7014

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Last updated on October 17, 2024