Removal of Salt Marsh–Impairing Tidal Flow Restrictions: Impact on Upstream Flooding under the Combined Influence of Rainfall and Tide

Abstract

Restoring tidal flow to anthropogenically flow-restricted waterways provides ecological benefits while also changing the flood risk of adjacent lands. Our research evaluated the flooding risk on Tremley in Linden, New Jersey if the adjacent Marshes Creek’s tidal flow is fully restored. A hydrological/hydraulic model of Marshes Creek was used to simulate the peak water surface elevations (WSELs) generated by existing restricted and fully unrestricted conveyance options under dry and wet weather scenarios. Model results indicated that simulated peak WSELs generated by the fully unrestricted conveyance option versus the existing restricted option (1) were higher under dry weather conditions, (2) increased at a slower rate under wet conditions, (3) were equal under wet conditions at a threshold rainfall depth, and (4) were lower under wet conditions for rainfall exceeding the threshold rainfall depth. It is intuitive that if the simulated common WSEL generated by both conveyance options is lower than the adjacent minimum grade elevation, then full tidal flow restoration reduces flooding risks. Alternatively, if the simulated common WSEL was higher than the adjacent minimum grade elevation, then full tidal flow restoration will increase flooding risk. A simple procedure based on this finding is provided in this paper, which identifies the maximum tidal conveyance level that generates a common peak water surface lower than the adjacent minimum grade elevation at the threshold rainfall depth.