Simulating the impact of sea level rise on storm surge; a case study in the northeast of the US.

Soroush Kouhi, University of Rhode Island, Department of Ocean Engineering, Narragansett, United States and M Reza Hashemi, University of Rhode Island, Department of Ocean Engineering and Graduate School of Oceanography, Narragansett, RI, United States
Storm surge models are commonly used to assess the impacts of tropical or extra-tropical storms on coastal zone .Further, evaluating the effect of the projected sea level rise (SLR) on storm surge is necessary for the safe design and risk assessment of coastal structures. While linear superposition, or adding projected SLR to simulated storm surge is a common and efficient method, it can lead to inaccuracies. Alternatively, a new model can be developed in which bathymetry and/or boundary conditions are changed due to projected SLR (i.e., nonlinear approach) which needs additional effort. Here, after a brief theoretical analysis using governing equations of storm surge, we compared the linear and nonlinear approaches in a number of idealized and realistic case studies. The idealized cases included bay, estuary, and channel geometries. Also, two realistic case studies were conducted: Narragansett Bay (RI, USA) and Long Island Sound (CT, USA). Results showed that for the idealized cases with variable depths, in general, linear superposition of SLR and storm surge was conservative compared to the nonlinear approach. The simulated surge from the Narragansett Bay simulation confirmed the outcome of idealized cases showing linear assumption was conservative up to 10%. The Long Island Sound model behavior was also consistent to the estuary idealized case with a constant depth. In general, based on the results of this research, a difference of up 10% in estimation of storm surge was predicted comparing the linear and nonlinear approaches. In conclusion, the geometry of water body (i.e., Bay vs Estuary) and the bathymetry of a region are key factors leading to discrepancies between linear and nonlinear approaches.