Field observations and SWAN model predictions of wave evolution in a muddy coastal environment

Abstract

It is well known that the presence of mud deposits on the continental shelf can cause dramatic damping of ocean surface wave, but quantitative field observations are very scarce. Wave prediction models currently lack a physics-based representation of the mud-induced dissipation process, and hence the accuracy of wave predictions in muddy littoral environments is unknown. This thesis presents a comprehensive field data set for comparison with the operational wave model SWAN (Simulating Waves Nearshore). During February to March 2008, an extensive array of 16 wave measuring instruments were deployed on the muddy shelf of Western Louisiana in depths ranging from 13 to 4 m. Box cores were collected at all instrument sites to characterize bottom sediment properties (Garcia-Garcia et al., 2008). Analysis of local wind sea events along two cross-shore transects shows a decay of waves from the deeper to the shallower instruments, with the strongest decay at the muddiest site. The wave spectra evolution shows strong decay of high-frequency wind sea spectral levels and weaker decay at the lower swell frequencies. The default bottom friction parameterization (the JONSWAP model with coefficient value 0.067 m²/s³) in the SWAN model generally yields reasonable estimates of nearshore wave heights that are sufficiently accurate for most operational Navy applications. However, the predicted cross-shore wave decay is more gradual than is observed and the model does not capture the spectra decay at high freq