Wheaton Branch Dam Overtopping Project

The Wheaton Branch Regional Stormwater Management Pond was originally designed and constructed in 1979 for flood control to protect downstream properties in the Woodman Avenue and Inwood Avenue areas as well as further downstream along Wheaton Branch and Sligo Creek. The pond receives runoff from a 770-acre watershed that is comprised of just over 50% impervious land cover, including a large shopping mall and commercial complex around the Wheaton Metro Station, and other commercial and residential developments between Wheaton and Dennis Avenue along the intensively developed Georgia Avenue corridor. The pond was retrofitted to its current configuration as a three celled wet pond in 1988 to add water quality treatment in addition to flood control. Overall, the pond provides many benefits downstream in lower Wheaton Branch and Sligo Creek including; 1) reduced stream channel erosion as stormwater captured in the pond is slowly released after storms, 2) water quality treatment as sediment and pollutants settle out in the pond, and 3) flood control.

As Part of the 1988 retrofit, an approximately 500-foot spillway was added on top of the dam to help pass the Probable Maximum Flood (PMF). The PMF is a theoretical flooding event resulting from the greatest depth of precipitation for a given duration that is physically possible over a particular geographic location at a given time of year. The spillway was protected by adding grouted gabions at the top of the dam and Enkamat on the downslope side. Information obtained from a 2018 analysis found that the dam embankment is not adequately protected during a PMF event.