Bioretention

Bioretention for Research and Education

With the support and collaboration of the Prince George's County Government, Department of Environmental Resources, two parallel bioretention cells (rain gardens) have been installed on the University of Maryland Campus.  The cells were constructed in Fall and Winter 2002 and have become operational in Spring 2003.  The bioretention system has been placed at the southeastern corner of lot 11B, near the area where Campus Creek enters into the Paint Branch. 

One of the cells contains a submerged layer with an overdrain to promote the removal of nitrate from the runoff via microbial denitrification processes.  This modification was optimized in the laboratory through previous work.  In addition, Professor Pat Kangas, coordinator for the Natural Resources Management Laboratory, is monitoring the ecology of the rain gardens, following the behavior and survival of the vegetation. 

The bioretention cells have been monitored for input and output water flow and quality to investigate long-term performance characteristics.  Pollutants monitored include suspended solids, phosphorus, nitrate-N, and several heavy metals.    

This cell was constructed using standard bioretention design criteria and specifications.  

The construction of the cells was documented over October to November 2002

Two dedication ceremonies for the bioretention cells were held in April 2003

Hydrology.  From twelve discrete rain events ranging in storm duration from eight to sixty hours, outflows typically release around 10% of the inflow by the end of the event.  The cells can take up to two weeks to release all the stored runoff.  The rain gardens were effective in moderating the flow, with a delay in peak time of about 3 to 4 and peak flow being 40-80% of input.

Water Quality.  Water quality data are available for five storm events.  Removal efficiencies based on EMC calculations for TP average 72-80%.   Lead removal rates average above 90%. TSS removal rates have varied significantly over the first year of operation, apparently due to washout of the soil media.

This cell contains a submerged layer to promote microbial denitrification processes and also contains Thlaspi plants near the inlet channel to hyperaccumulate zinc from the biorention media.

Bioretention Installations