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Experimental Rain Garden

In October 2009, EPA finished upgrading a major parking lot at its Region 2 laboratory in Edison, New Jersey, with low impact development (LID) features including a rain garden. EPA plans to use this effort as a demonstration project to study the ability of the rain garden to accept stormwater runoff.

Background

The rain garden at the Edison laboratory.

The rain garden cells shortly after construction on them was completed. Plants were introduced after six months in order to compare stormwater infiltration rates with and without vegetation.

The Region 2 laboratory needed a 110-vehicle-capacity parking lot to provide safe and secure parking. The project began as a building and facilities improvement project under the Office of Administration and Resources Management (OARM). EPA’s Office of Research and Development (ORD) recognized the project as an opportunity for research and contributed funding that helped to install instrumentation to evaluate the ability of rain gardens to accept stormwater runoff and lessen the effects of peak stormwater runoff on receiving streams, including stream bank erosion and negative effects on aquatic plant and animal life.  ORD is evaluating rain gardens as part of a long-term research project examining multiple stormwater management practices.

Rain Garden Benefits

Rain gardens provide several benefits:

Goals

The rain garden has three goals:

Design

A schematic of the Edison rain garden.

This bird’s-eye view schematic details the design of the rain garden cells located south of the laboratory’s newly constructed LID parking lot. The rain garden consists of six separate cells, represented by solid green rectangles, that are hydrologically isolated from each other using 3/8 inch-thick plastic sheeting installed to a depth of four feet, represented by yellow lines. The six cells receive stormwater runoff, represented by red arrows, from an impervious section of the parking lot and adjoining sidewalk through curb cuts at the south end of the parking lot. Stormwater runoff from the roof of the adjacent building is collected from multiple downspouts and conveyed beneath the sidewalk in an 8-inch diameter pipe, represented by a thick dashed blue line. A dedicated 4-inch diameter pipe, represented by thin dashed blue lines, distributes the roof runoff upward into each rain garden cell just south of the curb cuts.

The drainage area to all six cells is roughly equal, about 1,200 square meters, but because the rain garden cells are different sizes, they represent different percentages of their drainage areas. The smallest cells are 2 percent of their drainage areas, the medium-sized cells 4 percent, and the largest cells 8 percent. Each cell size is duplicated for statistical purposes, and both cells of each size are planted with the same plants. All cells are equipped with instrumentation for quantifying the timing and size of the depth of the stormwater as it infiltrates through the rain garden during and following storm events. Small observation wells were installed at different depths in the center of each rain garden to quantify the elevation of groundwater by infiltrating water.

EPA will first examine and document the capabilities of the garden without plants.  When plants are introduced, the Agency will be able to determine whether the plants and the plant root system have the anticipated beneficial effects on stormwater infiltration rates. A more complete understanding of how rain gardens function will enable EPA to provide national guidelines on rain garden design, construction, maintenance, and monitoring, which local organizations can use to reduce peak flows to receiving waters.

Impacts

The benefits to the area around the rain garden will include:

The successful application of bioretention and porous pavement systems at Edison’s parking lot demonstration site, as determined by the results of the research and monitoring effort, will help facilitate:

More Information

Download an informational poster showing a schematic of the rain garden (PDF) (1 pp, 716 KB).

Download a science brief describing the rain garden in detail (PDF) (3 pp, 818 KB).

Edison’s parking lot was also upgraded with several types of permeable pavement.


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