STREAM RESTORATION BY REGENERATIVE STORMWATER CONVEYANCE TO IMPROVE WATER QUALITY IN THE CHESAPEAKE BAY

Total Maximum Daily Load (TMDL) levels set for the Chesapeake Bay have created a sense of urgency to mitigate nutrient input into the Bay. Muddy Creek, a deeply eroded tributary of the Bay, will soon be restored with a Regenerative Stormwater Conveyance (RSC) to reconnect the stream to the floodplain. The goal is to induce infiltration to remove suspended sediments, nitrogen and phosphorous from the stream water by diverting high flow over the floodplain. Flows of water, sediment and nutrients will be compared before and after the restoration to determine the effectiveness in restoring stream function. Before the restoration, groundwater quality and flow rate were measured along the restoration site’s 450 m reach. The groundwater was determined to be anoxic, with dissolved oxygen ranging from 0 to about 1 mg/L, phosphate-P up to 46 µg/L, and ammonium-N up to 450 µg/L. Groundwater nitrate concentrations were below 11 µg/L and iron concentrations exceeded 9 mg/L in some locations, suggesting denitrification and iron oxide reduction were occurring in the aquifer. Groundwater emerging along the restoration reach made up 15% of the stream flow exiting the reach, as determined on one date by dilution of bromide tracer added at the upstream end. Success of the RSC will be judged from decreases in nutrient concentration in stream water beyond the effect of mixture with emerging groundwater. If the RSC approach is successful, it could provide a guide to future stream restorations.