Flood Modeling in Coastal Cities and Flow through Vegetated BMPs: Conceptual Design

Abstract

Undeniably, climate-change-induced sea-level rise has served as a powerful driving force for the occurrence of coastal storms more severe than ever before. Low-lying metropolitan coastal areas, in particular, have become increasingly vulnerable to coastal flooding as a result of the rapid expansion of urbanization along flood-prone areas. Safeguarding coastal communities from the repercussions of flooding through the utilization of best management practices (BMPs) is one of the most effective ways of alleviating the situation. However, solely relying on inshore BMPs might not be the best possible approach when the storm event’s intensity can be reduced before the storm reaches the shoreline through the installment of offshore BMPs. Moreover, many recent studies have confirmed the cost-effectiveness and usefulness of natural elements, especially when combined with engineering solutions. This paper assesses the overall suitability and effectiveness of various combinations of nature-based inshore and offshore BMPs for coastal flood mitigation of storms with different intensities with applications to the Southern Brooklyn area in New York City. Moreover, inevitable conditions stemming from climate variability and change have made the assumption of stationary recurrence of extreme events unreliable. Furthermore, historical events of remarkable impacts have not been considered differently in the attainment of the flood design values. Thus, as one of the main objectives of this study, and in order to consider both, a nonstationary partial frequency analysis is utilized, including the major historical storms jointly with the precipitation data in the study area to obtain 100-year flood design values. To achieve the goals of the study, first, the offshore simulation was carried out using the Delft3D hydrodynamic model, developed by Deltares, in order to find the water level hydrograph for the ungauged areas of interest, with and without offshore BMPs followed by the simulation of the flood events on the inland coastal area using gridded surface subsurface hydrologic analysis (GSSHA), a module of the watershed modeling system (WMS) developed by the USACE, to assess the effectiveness of inshore BMPs. The proposed scenarios are tested against Superstorm Sandy, Hurricane Irene, and the 100-year flood hydrographs. The results showed a remarkable coastal flood wave height and water level reduction when integrating offshore and inshore green BMPs.