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

Abstract

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 heavily 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.

Multiscale Superposition and Decomposition of Field‐Measured Suspended Sediment Concentrations: Implications for Extending 1DV Models to Coastal Oceans With Advected Fine Sediments

“…The contribution of waves and tidal currents to sediment resuspension in coastal oceans is a classic topic (Ward, 1985) that still attracts substantial attention (Andutta et al., 2019; Desguée et al., 2011; Guillou et al., 2017; Heath et al., 2017). Numerical models, such as Delft3D (Lesser et al., 2004) or the Regional Ocean Modeling System (ROMS) (Shchepetkin & McWilliams, 2005), can be used to evaluate the contributions via open or closed inputs of waves or tidal currents (King et al., 2019; Mulligan et al., 2019). However, further experiments, especially those involving in‐situ observations, are required to validate the modeling results.…”

Wave, Tide and Topographical Controls on Headland Sand Bypassing

“…The North Coast model was one‐way nested within a regional fully coupled hydrodynamic, wave and sand transport model validated and presented in King et al. (2019). Grid resolution of the North Coast model was circa 50 m in the vicinity of headlands, and the model was run in 3D hydrodynamic mode with 10 sigma‐levels in the vertical.…”

“…We also aim to quantify the impact of tides and nonlinear wave‐tide interactions on headland bypassing rates. The North Coast of Cornwall presents ideal conditions for this investigation, with a wide variety of embayed beaches separated by irregular and varied rocky headlands, energetic waves, spatially variable sand coverage and macrotidal regime (King et al., 2019). We quantify headland and embayment morphologies and sediment spatial variability across this region and determine sand bypassing rates under various physical forcing conditions using a validated coupled hydrodynamic, wave and sediment transport model.…”

The Equilibrium Scour Depth around a Pier under the Action of Collinear Waves and Current

“…This loosening of sediment particles result in increased upward seepage forces on the sand bed making the particles highly vulnerable to the destabilising forces responsible for setting the particles into motion. Ultimately the loosened sediment particles are transported by the tidal current ( [35,41,42]). The velocity of the tidal currents become zero at the seabed and is maximum at or near the water surface.…”