Modelling Wave Attenuation by Salt Marsh

Williams, J.J.; Kumar, S.V.; Matthews, J.; Palmer, T.; Hoskins, N.; Remla, R.M.; Gibbons, A., and Tung, N., 2024. Modelling wave attenuation by salt marsh. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 594-598. Charlotte (North Carolina), ISSN 0749-0208. Coastal salt marsh vegetation is a sustainable nature-based coastal defence solution that can effectively dissipate wave energy and reduce storm impacts and coastal flooding. An important part of planning salt marsh restoration is to define, using numerical models, the optimal location for a new salt marsh area in the tidal frame and to assess how the vegetation affects incident waves throughout the growth cycle from sparse immature plants to mature salt marsh. This study uses the wave models MIKE SW and XBeach-NH-VEG to simulate interactions with vegetation at study sites in the Thames Estuary, UK. The vegetation properties, including height, drag coefficient, stem diameter, and density, are taken from the literature. The model results demonstrate unequivocally that the greatest changes in incident wave characteristics occur from the seaward edge of the vegetation over the first 10 to 50m. While re-establishing wider strips of salt marsh reduces wave energy reaching the coastline further, greater benefits accrue from maximising the lateral extent of the salt marsh along the shoreline normal to the dominant incident wave direction. The paper also discusses the advantages and disadvantages of each model tested and makes recommendations for future model development and application.