Sensitivity considerations and the impact of spatial scaling for storm surge modeling in wetlands of the Mid-Atlantic region

Among the many activities in the recent efforts to evaluate coastal resiliency is the study of the capacity of wetlands and coastal marshes to attenuate storm surge. The development of an acceptable index or attenuation rate for coastal flooding is complicated by the many factors that contribute to maximum surge elevation, inundation extent and duration, including storm characteristics (e.g. track, size, forward speed, duration, central low pressure) and local features including topo-bathymetry, land-cover, barrier islands, channels, lagoons and inlets. For this study, we investigated the impact of spatial scaling, mesh resolution, storm characteristics and bottom friction on storm surge in wetland areas in the barrier island system of the Delmarva Peninsula using the coupled hydrodynamic-wave model (ADCIRC + SWAN). Synthetic storms derived from hindcasts of historical storms affecting this region were used for model forcing through multi resolution meshes recreating the complex wetland areas exposed to varying degrees of ocean surge through natural breaks in the barrier islands. Sensitivity to mesh resolution and bottom friction were evaluated for regional attributes and storm characteristics, confirming the results of previous studies. Results suggest inlet configuration and exposure to ocean surge are dominant factors for surge propagation through small scale wetlands and barrier island systems for weak to moderate storms. Attenuation rates observed for weaker storms, were influenced secondarily by the complex geometry of channels, lagoons and the presence and continuity of marshes. Results evaluating greater surge produced by stronger storms, even of less than a meter of storm surge increase, indicate that the mitigating impacts of local features are greatly diminished. Our results indicate that although the back bays systems in the Delmarva Peninsula and similar ecosystems in the US East Coast could provide storm surge attenuation for annual storm events, its use in coastal engineering protection may require a case by case analysis due to the high dependence on local characteristics.