Just as Frank Lloyd Wright believed that the architecture of Chicago should reflect the flat, Midwestern prairie, a study found that native prairie plants are the most effective vegetative cover for rain gardens.
Rain gardens allow runoff from impervious areas, like roofs, driveways, or parking lots to soak into the ground while also filtering the water. This process reduces the amount of polluted runoff that flows into storm drains and surface waters, and increases the amount of groundwater. Rain gardens can be used for local flood control and to improve water quality by filtering runoff. Rain gardens are a great option for retrofitting urban areas.
A U.S. Geological Survey study undertaken in Madison, Wisconsin compared the effectiveness of rain gardens with differing soil and vegetation types. Two rain gardens, both 0.5 feet deep, were planted, one in sandy soil and one in clay soil, both with native prairie plants and turf grass. Both rain gardens received approximately equal runoff from a nearby rooftop, equivalent to approximately five times the area of the rain garden.
The rain gardens were studied over a 5-year period, from late 2003 thorough 2008. All four types of rain garden were able to store and infiltrate most of the runoff during the study period. The rain gardens with prairie vegetation had higher median infiltration rates than those planted with turf grasses, in similar soil types. In a sample year, 2005, the recharge amount was 81 to 75 of the total influent volume for the prairie- and turf-rain gardens in sand, and 87 to 78 percent for the prairie- and turf-rain gardens in clay, respectively. The rain garden planted in the prairie-clay rain garden yielded greater biological activity than the turf-clay rain garden; greater root activity allowed greater earthworm activity and more organic matter. Overall this increased soil development meant that the prairie-clay garden has a greater ability to store and infiltrate stormwater than the turf-clay combination.
Since the Chicago region is home to clay soils, this study demonstrates the effectiveness of installing a rain garden with native plants in your own backyard. Channeling water from a rooftop to a rain garden will ease flooding, help recharge the groundwater supply, and reduce the amount of pollution in our surface water, meaning cleaner and more accessible drinking water for the region!