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EEWR Brown Bag Seminar with Jonghun Kam and Brianne Smith, Graduate Students

Speaker: Jonghun Kam and Brianne Smith, Graduate Students
Series: EEWR Brown Bag Seminars
Location: Engineering Quad E225
Date/Time: Friday, November 15, 2013, 12:00 p.m. - 1:30 p.m.

Abstract:

Speaker: Jonghun Kam
Title: Low flows in the northeastern U.S. and their association with local antecedent rainfall and large-scale climate indices (1962-2011)


Low flow is a seasonal hydrologic response of the land surface to climate; it is a good hydrologic indicator for assessing the risks of natural hazards including droughts and floods. In order to mitigate these hazards, it is critical to understand the driving mechanisms for low flow occurrence. In this study, we select 150 USGS stations from Hydroclimatologic Data Network (HCDN) over the northeastern U.S. (NE) and focus on annual 1-day low flow from 1962- 2011. We compare time series of annual 1-day low flows and antecedent precipitation. Over the NE, annual 1-day low flow occurs during early fall (August-October) and its interannual variability is led by antecedent precipitation one month (north) up to four month (south) ahead depending on the latitude of the station. Across the study region, low flows across also show a significant and negative correlation with the springtime Atlantic Multi-decadal Oscillation (AMO) index. However, low flows over only the southern part of the study region (below 40°N) show a significant and positive correlation with the summertime North Atlantic Oscillation (NAO) index. At last, we discuss possible mechanisms for relating low flow occurrences over the NE with physiographic factors and oceanic and atmospheric forcings.

Speaker: Brianne Smith
Title: Distributed watershed modeling for a small urban basin in Baltimore County, MD


Improvements to hydrologic modeling of urban watersheds are necessary to improve flash flood forecasting, flood hazard assessment, and urban planning. We use the Gridded Surface/Subsurface Hydrologic Analysis (GSSHA) model to represent the 14.3 square kilometer Dead Run watershed in Baltimore County Maryland. Dead Run is a flashy watershed with extremely high runoff ratios. We strive to represent the watershed with a physically-based watershed model and as little calibration as possible. GSSHA is a gridded model with 2-D overland flow and 1-D stream flow and infiltration processes. Significant efforts are made to accurately represent the effects of detention infrastructure, storm drains, and urban soils within the watershed. High resolution, spatially distributed, Hydro-NEXRAD rainfall fields are used to drive the model, and comparisons are made with a network of rain gages. We utilize USGS instantaneous streamflow data for the watershed outlet and five sub-watershed gaging sites to compare to model output. These nested gaging sites allow us to assess the model’s performance throughout the watershed and to ensure that the hydrologic processes in each of the different sub-basins are properly captured.