Role of Low Impact Development in the Attenuation of Flood Flows in Urban Areas

Rapid urbanization of relatively small watersheds is the primary reason attributed to the reduced infiltration rate, increased runoff volume and the consequent flooding in the urban areas. This study focuses on selection of different low impact development (LID) design options that can attenuate flood flows in urban areas. Watershed considered for this study is Moores Run watershed (8.8 km2) located in Baltimore, Maryland. A basin scale curve number based hydrologic model was developed in HEC-HMS with the aid of ArcGIS and HEC-GeoHMS. USGS 01585230 at Radecke Avenue gauge was used for the calibration of hydrologic model. Design storms with different return periods, developed by NOAA, were routed through the watershed to produce the peak flood scenarios for current land use conditions. Further, the hydrologic model was used in conjunction with EPA-SWMM to evaluate the applicability of various LID retrofitting to reduce flood peak and volume. LID design approach recommends the reduction of flow at its source, restoring the natural hydrology rather than controlling it through infrastructure based design. LID retrofitting technologies such as permeable pavements in parking lots, sidewalks and green roofs were evaluated for various design storms. About 2.65 % and 2.1% of the total area were subjected to permeable pavement and, green roofs, respectively under standalone conditions. Consequently, 6-11% and 2-8% of flood peak reduction was achieved using permeable pavement and green roof techniques. For small watersheds such as Moores Run, these LID retrofits are deemed effective measures for reducing flood flows.