PAIRED-WATERSHED COMPARISONS TO ASSESS EFFECTIVENESS OF TRADITIONAL STORMWATER MANAGEMENT
We compare hydrologic response variables for Scotts Level (drainage area 8.6 km2, 32.9% impervious, 10.5% watershed area draining to SWM) and Gwynns Falls near Delight (drainage area 10.5 km2, 28.5% impervious, 42.7% SWM), both located in the upstream portion of the Gwynns Falls watershed. We also compare three small headwater tributaries in the Dead Run watershed (DR1: 1.2 km2, 67% impervious, 48.1% SWM; DR2: 1.9 km2, 49.1% impervious, 30.5% SWM; DR5: 1.6 km2, 45.9% impervious, 2.9% SWM), located in an inner-ring suburb that drains to lower Gwynns Falls. We assess a population of storms for which we have bias-corrected watershed-average HydroNEXRAD radar rainfall records with 15-minute time steps and streamflow data recorded at 5 or 15-minute intervals. Response metrics assessed include Richards-Baker flashiness index, volume to peak ratio, R(t) discharge-precipitation ratio, ratio of peak runoff intensity to peak rainfall intensity, runoff ratio, centroid lag time, and lag from rainfall center of mass to peak runoff. Metrics were calculated separately for single-pulse rainfall events and for longer, more complex storms. Responses within and between watersheds were also compared for storms grouped by total rainfall accumulation. For both sets of watershed comparisons, the group of metrics assessed failed to show a clear trend demonstrating a difference in hydrologic response attributable to SWM, suggesting that other factors are as important or more important in controlling rainfall-runoff response.