Water Efficiency Measures on School Campuses: A Case Study

09.21.2010

The George Washington University (GW) wanted to convert Square 80, an underutilized space, into an urban, multi-functional, sustainable plaza. STUDIO39 Landscape Architecture, PC was chosen to design and transform the site into social gathering spaces. Square 80 now serves as an urban plaza with a central open space and an outdoor classroom for the university’s Landscape Design & Sustainable Landscapes programs. STUDIO39, a landscape architecture firm based in Alexandria, VA, was perfectly suited for this project because of the firm’s focus on sustainable and green roof design.

Completed in 2010, Square 80 presented a unique opportunity to combine multiple sustainable elements into one project. The design harvests 100% of on-site rainwater for irrigation, maintenance and other amenities. Other sustainable elements of the project include biofiltration planters, pervious paving, underground cisterns, rain barrel, native plants, rain gardens and a bioswale. Interpretive signage designed by STUDIO39, made of recycled content, will be installed this month to explain how these elements work together.

Square 80 fits GW’s Sustainable Vision:

“The George Washington University envisions a future with resource systems that are healthy and thriving for all. In efforts to enhance our campus, our nation’s capital and the world at large, the GW community is building a greener campus, providing research and intellectual discourse on policies and pathways to sustainable systems, and equipping students with the skills and knowledge to contribute to a sustainable future.”

Sustainable Sites Initiative

The Sustainable Sites Initiative™ (SITES™) is a partnership of the American Society of Landscape Architects, the Lady Bird Johnson Wildflower Center at The University of Texas at Austin, and the United States Botanic Garden. The program’s objective is to transform land development practices with the first national rating system for sustainable landscapes. Square 80 is one of about 150 projects within the initiative’s pilot program and STUDIO39 has already begun SITES certification. The U.S. Green Building Council (USGBC), a stakeholder in the initiative, anticipates incorporating these guidelines into future iterations of LEED Green Building Rating System™.

The site originally functioned as a parking lot, with spaces for a pedestrian walk and trash collection for the residents of Guthridge Hall, Strong Hall and 2109 F Street. These uses resulted in a 93% impervious surface. Specific issues addressed with the redesign effort included: the existing pedestrian connection from F to G streets which was indirect, undersized, and did not meet ADA standards; the retaining walls were structurally compromised; and the existing vegetation was in decline.

Rainwater Harvesting

Rainwater harvesting benefits the natural environment by eliminating the reliance on potable water. Harvesting all the rainwater on site reduces the amount of stormwater that enters into sewer systems and contaminates the local waterways. The plaza design implements numerous Low Impact Development (LID) practices in order to clean, store and reuse the harvested rainwater. LID practices maintain and enhance the pre-development hydrologic regime of urban and developing watersheds.

Native Plants

Native plants are indigenous to a specific region. They benefit the environment because they require little to no supplemental water or fertilizer to remain healthy since they are adapted to local soils and climate. Native plants provide food and natural habitat for wildlife, including important pollinator species (insects, birds, bats), and promote wildlife habitats that support ecotourism, recreational uses and environmental education.

The majority of the plants used at Square 80 are native species. The remaining plants, with the exception of the lawn, are non-invasive, adaptive species that tolerate regional soils and climate. The planting design respects the establishment period (the first growing season). After which, the trees, shrubs, grasses and groundcover would no longer require supplemental irrigation, so harvested rainwater can be completely allocated to the open lawn.

Pervious Paving

Conventional impervious paving causes water to quickly sheet flow over the surface and into gutters and storm drains, often causing flooding during a heavy rain event. Urban runoff contains pollutants like heavy metals, oil and other hydrocarbons, which are conveyed to natural waterways, damaging ecosystems. Pervious paving allows water to move vertically through the paving material to slowly infiltrate and recharge groundwater. Water flows through the joints between pavers, filters through the gravel subbase, percolates into the native subgrade and ultimately recharges the groundwater. Naturally-occurring oil-degrading microbes within the subbase break down contaminants into less harmful forms before the water reaches the water table. Pervious paving can be designed to detain or convey water. At Square 80, excess water that does not infiltrate the soil below is collected into a pervious PVC underdrain and channeled to the underground cistern for storage and reuse on site. Including pervious paving in any urban setting creates a cleaner environment and can save on costly stormwater vaults and other filtration systems.

Roof Water Collection

Rooftops are another rainwater source that deserves attention. Utilizing existing gutter and downspout systems, rainwater can be re-routed to rain barrels and cisterns. These components allow the reuse of water that would otherwise flow into storm drains, polluting natural waterways and preventing groundwater recharge.

A rain barrel interrupts the discharge of roof water. Designed to retrofit downspouts, a typical rain barrel consists of an above-ground, opaque tank (to prevent algae), a screened inlet (to prevent mosquito breeding), a hose or spigot to reuse water, and a means of overflow relief. At Square 80, overflow from the rain barrel is piped to the underground cistern. An underground vortex fine filter separator removes debris and diverts 90% of clean rainwater to the cistern.

The downspout at 2109 F Street is connected to a 300-gallon rain barrel and is used for routine maintenance. The overflow from this source and the downspout at Guthridge Hall are connected to vortex separators. Additional vortex separators are utilized at each inlet to the cisterns.

Cisterns

Underground cisterns are waterproof tanks that provide rainwater storage for reuse and distribution on site. Each cistern has one outfall with the opportunity for multiple inlet sources. Using cisterns for rainwater harvesting makes it possible to eliminate the reliance on potable water.

In the plaza, all stormwater collection systems convey water to three underground cisterns with 8,000, 10,000, and 15,000 gallon capacities, respectively. Rainwater from the Guthridge Hall and 2109 F Street roof downspouts, the drain inlets and trench drains, the pervious paving, and the overflows from the biofiltration tree planters, rain garden and bioswale are all collected and stored in the underground cisterns. Prior to the water reaching the cisterns, it is flushed by the vortex fine filter separators, which remove small debris. The stored water is redistributed to either the irrigation system or the rainwater fountain feature at the center of the plaza.

Biofiltration planter

Biofiltration planters capture runoff from impervious surfaces like sidewalks, roads, compacted lawns and roof downspouts. They allow the water to infiltrate the amended soil into the native subgrade, recharging groundwater. The soil and plant material filter pollutants from the water, recharge groundwater system and prevent polluted water from reaching natural waterways. Runoff flows into trench drains and is conveyed to the depressed biofiltration planters where it is retained and allowed to slowly infiltrate the amended soil.

Biofiltration planters need to be planted with native species that tolerate drought, high moisture, and expected pollutant levels. Native plants are recommended because they are typically more adaptable to these conditions. ‘Wynstar’ Willow Oak (Quercus phellos ‘QPMFT’) and native grasses are planted at Square 80.

At the plaza, runoff from the paved sidewalk flows toward the linear trench drains at the edge of the walkway. The trench drains act as a water runnel, conveying water to a series of biofiltration tree planters. The soil is depressed below the paved surface to retain stormwater while it slowly infiltrates the amended soil into the native subgrade. These planters are designed to hold six inches of standing water. Additional water drains into an overflow pipe that carries the water to a vortex filter prior to entering into the underground cistern for storage and reuse on site.

Rain garden + bioswale

A rain garden is a shallow planting bed depressed six to eight inches that collects water runoff from impervious surfaces like sidewalks, roads, compacted lawns and roof downspouts. The water is filtered, retained for a short time, and released slowly through the amended soil into the native subgrade, recharging groundwater. Rain gardens capture water that would otherwise flow into storm drains, polluting our natural waterways and preventing groundwater recharge.

Similar in function to a rain garden, a bioswale is a wide, shallow, landscaped channel with a slight gradient. It captures surface water during a rain event, and allows the water to flow slowly and infiltrate the enriched soil into the native subgrade. It is used as an alternative to traditional gutters and storm drains. Like rain gardens, bioswales recharge groundwater supplies and filter pollutants from water before it reaches natural waterways. A perforated drain pipe may be incorporated to convey excess water due to oversaturated soil.

Rain gardens and bioswales need to be planted with native species that tolerate drought, high moisture and expected pollutant levels. In Square 80’s rain garden, Blue Flag Iris is planted with a Sweet Bay Magnolia, while the bioswale has a diverse planting of native grasses and groundcovers.

At Square 80, the sloped surface in the courtyard conveys rainwater to the rain garden. During heavy rain, the bioswale acts as the rain garden’s overflow, conveying water to an area drain and ultimately to the underground cisterns for storage and reuse on site.

Rainwater irrigation pump

Conventional irrigation systems source their water from municipal or other potable water sources, wasting the cost and effort of bringing that water to human-consumption standards. Instead, rainwater collected on site can bestow a naturally replenishing source of irrigation water.

Square 80 is irrigated using filtered rainwater from on-site collection. Water lines are gravity fed from underground storage cisterns to the irrigation pump, which then distributes it to the planting beds organized in zones. Ninety percent of the irrigation system is designed as drip irrigation, the most efficient way of delivering water to plants by supplying slow, steady and precise quantities of water. Flexible tubing is installed throughout the beds with a drip emitter at each plant, allowing the correct amount of water for each plant while preventing water loss through evaporation, interception from overhead foliage, and runoff. Less water is used more efficiently than traditional spray applications.

Rainwater for fountain

The rainwater fountain sources 100% of its water from on-site rainwater harvesting. A designated cistern collects and stores approximately 600 gallons of water beneath the plaza surface. If additional water is needed, a sensor in the fountain cistern activates a submersible pump in one of the larger cisterns to refill the fountain supply. In addition to the pump, the fountain system is equipped with a UV filtration unit that helps clean the rainwater by removing bacteria, algae and protozoa, making it safe for human interaction. The use of this UV filtration process reduces the amount of chemicals needed for water treatment, which benefits the surrounding natural environment.