Relative Sea Level Rise Impacts on Storm Surge Flooding of Transportation Infrastructure

Relative sea level rise increases the vulnerability of coastal infrastructure to storm surge flooding. In this study, we develop, validate, and apply a coupled hydrodynamic and wave model to simulate storm surge inundation under different local sea level projections to quantitatively assess some of these vulnerabilities. Our study area is located in southeast Virginia, where the rate of relative sea level rise is the highest in the US East Coast. The model is developed in two levels of nesting in which a region-scale model with relatively low resolution provides boundary conditions for a high-resolution city-scale model. The model is first validated with documented water levels in water and over land during Hurricane Irene (2011). It is then applied to investigate changes in vulnerability of transportation infrastructure to relative sea level rise by quantifying changes in flood intensity and duration over access roads to critical bridges that are identified based on elevation and traffic volume. Furthermore, the length of flooded roadways as well as the extent and volume of inundation is quantified under different combinations of relative sea level rise and storm return periods. With a 1.8-m sea level rise, an upper bound of sea level projections in the study area in 2070, and under 10- and 50-year storms, collective flood intensity and duration increase by factors of 23 and 51, respectively, and the length of flooded roadways increase by factors of 9 and 7 from their present values, respectively. Variations in flood intensity, duration, area, and volume under storm and sea level rise combinations indicate that storm surge response to relative sea level rise is generally nonlinear, and linear superposition of these factors mostly overestimates inundation intensity while consistently overestimating inundation volume. Variation of rate of change in total inundation volume is more complex and suggests that the linear summation overestimates flood volume for small to moderate rates of sea level rise while it underpredicts flood volume for high sea level projections. This suggests that nonlinear effects act to intensify flood vulnerability at an accelerated rate as sea level rises.