Compound Simulation of Riverine Freshwater and Storm Tides in the U.S. East Coast under Tropical Cyclones: Application to Hurricanes Sandy and Isabel

Tidal rivers and river-bay-ocean systems in the U.S. East Coast are highly vulnerable to flooding exposures from combined influences of river inflows and storm surges produced by tropical cyclones. Most of the people that live in these low-gradient coastal watersheds do not get a compound flood forecast. Consequently, to decrease the flood risks, an accurate flood-modeling framework based upon state-of-the-art numerical models is needed. Water dynamics in this area are controlled by multifaceted interactions of storm surges, tides, waves, riverine discharge, and atmospheric forcings. Because of these multiple influences, a complex modeling scheme is necessary to fully understand the flow behavior in the river-bay transition zone. Numerical simulations of the U.S. East Coast using a coupled ocean-hydrologic-hydrodynamic-wave framework, forced by river discharges, and atmospheric forcings are compared with an extensive set of time series and measurements over two extreme storms (i.e. Hurricanes Isabel and Sandy), with large variations in tidal forcing and freshwater discharge. The coupled model combines the Advanced Circulation Ocean Model, the WAVEWATCH III model, the National Water Model (NWM), and the D-Flow FM hydrodynamic model. In the hydrodynamic model, a 1D model is applied to the tributaries and is connected to the 2D model for estuary and ocean section. The study site covers the three important watersheds: Delaware Bay, Chesapeake Bay and Albemarle-Pamlico Sound. The model is specifically effective at reproducing the measured spatial and temporal variations in water levels, containing surge, tides and riverine discharge. The model predictions show that using 2D/1D coupled modeling system has advantages over 1D or 2D hydraulic/hydrodynamic models. Simulations show that water level simulations depend on both river discharges and elevated sea levels. These results specify the strengths of the above-mentioned modeling framework for simulations of flooding during the extreme storms.