The effects of coastal marsh geometry and surge scales on water level attenuation

Abstract

Coastal wetlands are an effective natural and nature-based feature to mitigate coastal flood hazards. While the sheltering and attenuation offered by wetlands are recognized, the protection level varies based on wetland and storm characteristics. Here we focus on the effects of the spatial scales of the coastal wetlands (i.e., channel geometry, marsh elevation-gradient) and the temporal scales of storm forcing (i.e., storm surge amplitude and duration) on peak water level attenuation. The study was conducted by performing hydrodynamic simulations on an idealized marsh geometry. One hundred seventy-one hydrodynamic simulations were conducted by varying wetland features under variable hydrodynamic forcing. Increased tidal channel area enhances water flow across marshes by reducing the capacity of vegetated platforms to resist propagation of a storm surge. The level of surge attenuation and channel area shows a non-linear relationship. Storm scales also affect surge attenuation for a given channel geometry. Higher amplitudes and lower surge durations provide greater attenuation of peak water levels. The level of attenuation and surge scales also show a non-linear correlation. A multivariate scaling relationship was developed that successfully integrates the combined effects of channel geometry and surge scales on water level attenuation by salt marsh. This research provides guidance to engineers and coastal managers on salt marsh's flood hazard reduction benefits.