The Impact of Waves and Tides on Residual Sand Transport on a Sediment-poor, Energetic and Macrotidal Continental Shelf

E.V. King, D.C. Conley, G. Masselink, N. Leonardi, R.J. McCarroll, T. Scott
2019 Journal of Geophysical Research - Oceans  
The energetic, macrotidal shelf off South West England was used to investigate the influence of different tide and wave conditions and their interactions on regional sand transport patterns using a coupled hydrodynamic, wave, and sediment transport model. Residual currents and sediment transport patterns are important for the transport and distribution of littoral and shelf-sea sediments, morphological evolution of the coastal and inner continental shelf zones, and coastal planning. Waves
more » ... y influence sand transport across this macrotidal environment. Median (50% exceedance) waves enhance transport in the tidal direction. Extreme (1% exceedance) waves can reverse the dominant transport path, shift the dominant transport phase from flood to ebb, and activate sand transport below 120-m depth. Wave-tide interactions (encompassing radiation stresses, Stoke's drift, enhanced bottom-friction and bed shear stress, refraction, current-induced Doppler shift, and wave blocking) significantly and nonlinearly enhance sand transport, determined by differencing transport between coupled, wave-only, and tide-only simulations. A new continental shelf classification scheme is presented based on sand transport magnitude due to wave-forcing, tide-forcing, and nonlinear wave-tide interactions. Classification changes between different wave/tide conditions have implications for sand transport direction and distribution across the shelf. Nonlinear interactions dominate sand transport during extreme waves at springs across most of this macrotidal shelf. At neaps, nonlinear interactions drive a significant proportion of sand transport under median and extreme waves despite negligible tide-induced transport. This emphasizes the critical need to consider wave-tide interactions when considering sand transport in energetic environments globally, where previously tides alone or uncoupled waves have been considered. Plain Language Summary The South West UK has a large tidal range (macrotidal) and is exposed to high-energy waves. We created a numerical model of this region, which calculates waves, tides, and sand transport over time. This was used to investigate the importance of waves, tides, and their interactions on the net movement of sand under different wave and tide states, which is important for evolution of the coastline and coastal planning. Sand transport is heavily influenced by waves. The interaction between waves and tides can contribute more to net sand transport than the summed contributions of waves and tides alone. Storm waves can cause sand movement at depths below 120 m and can reverse sand transport pathways.
doi:10.1029/2018jc014861 fatcat:6yhehtgjgrbqjjl5gtlphevlri