Baltimore Ecosystem Study Cary Institute of Ecosystem Studies

2012 BES Annual Meeting Presentation and Poster Abstracts

Comparison of Characteristic Unit Hydrographs in the Gwynns Falls Watershed
Shamer, Sierra
Co-Authors: Sierra Shamer (UMBC) Andy Miller (UMBC)

Abstract: Eighteen stream gages in the Gwynns Falls watershed (4 on the mainstem and 14 on tributaries) drain parts of Baltimore County and Baltimore City, with varying land cover, age and pattern of development, and stormwater management practices. This study characterizes hydrologic response of selected sub-watersheds to pulse rainfall events. Unit hydrographs were developed from analysis of HydroNEXRAD rainfall data and streamflow records for ten subwatersheds. Five (Gwynns Falls at Delight, Scotts Level, Powder Mill Run, Maidens Choice Run and Dead Run) had drainage areas between 8.7 and 14.2 km2. Within the Dead Run watershed, the six gages (including one listed above) are nested at three drainage area scales (1-2 km2, 5-6 km2, and 14 km2). Storms totaling over 6 mm of total rain with the majority falling within time periods ranging from <30 minutes (smaller tributaries) to ~90 minutes (larger watersheds) were characterized as pulse rainfall events. A recursive digital filter was used to separate base flow from the corresponding storm hydrographs, from which unit hydrographs were developed. These were averaged to create characteristic pulse-event unit hydrographs for each watershed studied. Comparative analysis among watersheds shows differences in hydrograph shape and lag time between rainfall and runoff that may be related to watershed characteristics including drainage network topology, watershed shape, development patterns, and stormwater management. Among the larger watersheds, Maidens Choice and Powder Mill Run had the flashiest response. Questions remain about the relative importance of impervious cover and stormwater management as determinants of hydrologic response.