What Is a Rain Garden?
A rain garden, also called a bioretention cell, is an engineered combination
of specially selected plants, soils and mulch designed to collect, retain and
cleanse rainwater that runs off impervious surfaces such as parking lots and
rooftops. Physical, chemical and biological processes occur on the surface, in
the root zone and throughout the soil profile. Shortly after a heavy rain, water
stands in these rain gardens for several hours. Unlike traditional curbs and
storm drains that quickly move stormwater off site, new practices, such as rain
gardens, slow down stormwater so it can percolate into the soil, naturally
filtering pollutants and recharging the groundwater. This is especially
beneficial to the health of trees and streams during dry spells.
Professor Allen P. Davis, Department of Civil and Environmental Engineering,
is conducting research to measure the effectiveness of contaminant removal by
rain gardens, focusing on lead, phosphorus, zinc, copper and suspended solids.
Several campus rain gardens have concrete channels and automated monitoring
stations that measure water flow and pollutants. Each area is lined with plastic
to ensure that all stormwater runoff can be measured. The findings of this
research are helping us design even more effective small-scale water treatment
methods. Bioretention sites were designed and installed at the campus in 2003
through a partnership with UM Facilities Management and the Prince George's
County Department of Environmental Resources under a U.S. Environmental
Protection Agency grant for experimental technologies.