Hydrologic Modeling of the Lower Chesapeake Bay Watershed Using HECC-HMS with Implications for Future Coupled Coastal Modeling

This study explores the hydrological methodology for modeling a coastal watershed basin using the US Army Corps of Engineers hydrologic software, HEC-HMS with an objective of being able to create riverine boundary conditions that could be applied to a coupled compound flood model. Compound flooding is defined as high water inundation event that occurs due to the simultaneous occurrence of multiple flooding drivers. The Atlantic Seaboard and the Gulf of Mexico regions of the United States account for most of the compound events observed in the United States with a higher occurrence caused by hurricanes from July to November. In this study three events were modeled for the Lower Chesapeake Watershed in Virginia: Tropical Storm Andrea, Michael, and Zeta. Each event was modeled using Modified Clark transform, simple canopy interception and loss, Green and Ampt or deficit & constant infiltration loss, linear base flow, and Muskingum-Cunge routing. Gridded precipitation and temperature were applied as boundary conditions for each event. Results from the models indicated large differences between event model parameters with difficulties in modeling and calibrating the coastal transition zone. Calibration statistics to observed data was generally within acceptable statistical parameters using Nash Sutcliff, R-squared, and percent bias.