Hydrodynamic Modeling of the Barrier Islands and Tidal Inlets of Long Beach, Long Island

This paper presents an example of the use of two-dimensional, localized, high resolution hydrodynamic models to evaluate the flood risk of the Long Island Beach and upland, backwater areas. The flood risk is characterized for several different return periods (up to 1000-year). The coastal flood hazard was determined using the empirical simulation technique (EST) using observed gage data supplemented by simulation of synthetic tropical cyclones. The EST-calculated stage-frequency curve represents the combined coastal flood hazard due to both tropical and extratropical storms. Synthetic hydrographs were developed based on the combined coastal flood hazard and used as boundary conditions to a high resolution Riverflow2D model for Long Beach, which modeled the beaches, tidal inlets, rivers, marshes, and upland areas. The results of the model simulations were highly informative as to the cause and effect of both the beach and backwater, upland flooding and indicated where flood mitigation measures would be most effective. The results were used to establish the flood design basis for the design and construction of new critical infrastructure in the area, as well as design flood mitigation measures.