Influence of storm surges and sea level on shallow tidal basin erosive processes

TLDR

The WWTM finite‑element model simulates shallow‑water dynamics, wave propagation, and wind, storm surge, and sea‑level scenarios in Virginia Coast Reserve lagoons, validated against field measurements, to compute bottom shear stresses and wave energy driving marsh erosion. Wave energy at marsh boundaries is far more responsive to wind direction and rises nearly tenfold with sea‑level rise, whereas bottom shear stresses increase less, and the model predicts both positive and negative feedbacks between these processes.

Abstract

The finite‐element model WWTM is applied to a system of lagoons at the Virginia Coast Reserve, USA. The model solves the shallow water equations to compute tidal fluxes, and is equipped with a wave propagation module to calculate wave height during local wind events. The model is validated using measured water elevations, wave heights, and periods at five locations within the lagoon system. Scenarios with different wind conditions, storm surges, and relative sea level are simulated. Results are analyzed in terms of bottom shear stresses on the tidal flats, a measure of sediment resuspension potential, and total wave energy impacting the marsh boundaries, which is the chief process driving lateral marsh erosion. Results indicate that wave energy at the marsh boundaries is more sensitive to wind direction than are bottom shear stresses. Wave energy on marsh boundaries and bottom shear stresses on the tidal flats increase with sea level elevation, with the former increasing almost ten times more than the latter. Both positive and negative feedbacks between wave energy at the boundaries and bottom shear stresses are predicted, depending on the fate of the sediments eroded from the salt marsh boundaries.