Idealized COAWST model cases for testing sensitivity of sediment transport and marsh accretion to vegetation, wave, and sediment parameters

Marshes may drown if they are unable to accrete sediment at the rate of sea level rise, but predicting the rate of sediment accretion at different marshes is challenging because many processes (e.g. tidal range, wave frequency) and conditions (e.g. available sediment, vegetation density, shape of the marsh edge) impact it. The Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST, Warner and others 2019; Warner and others 2010) model was used to simulate three-dimensional hydrodynamics, waves, and sediment transport on a marsh platform in an idealized domain. The computational grid was 400 (20) cells in the cross-shore (along-shore) directions with 10 vertical sigma layers, and a cross-shore horizontal resolution that ranged between 0.2 and 14m. The model domain was intended to mimic the China Camp marsh in San Francisco Bay, where extensive observations of flow and sediment were collected in 2016 (Lacy and others 2020, Lacy and others 2017). The model was then run across 66 different scenarios to evaluate the sensitivity of accretion on the marsh platform, wave dissipation, sediment flux, and bed shear stress to wave, vegetation, and sediment model parameters. This subset of runs was selected via the equadratures (Seshadri and others, 2021) framework, and together they enable the quantification of model sensitivity to the specified set of parameters. A modified version of the COAWST v3.7 model was used for these runs: branch v3.7-marsh. It is available at code.usgs.gov/coawstmodel/COAWST/-/tree/v3.7-marsh.