Predicting dominance of sand transport by waves, tides and their
interactions on sandy continental shelves
Abstract
Waves and tidal currents resuspend and transport shelf sediments,
influencing sediment distributions and bedform morphology with
implications for various topics including benthic habitats, marine
operations, and marine spatial planning. Shelf-scale assessments of
wave-tide-dominance of sand transport tend not to fully include
wave-tide interactions (WTI), which non-linearly enhance bed shear
stress and apparent roughness, change the current profile, modulate wave
forcing, and can dominate net sand transport. Assessment of the relative
contribution of WTI to net sand transport requires computationally/
labour intensive coupled numerical modelling, making comparison between
regions or climate conditions challenging. Using the Northwest European
Shelf, we show the dominant forcing mode and potential magnitude of net
sand transport is predictable from readily available, uncoupled wave,
tide and morphological data in a computationally efficient manner using
a k-Nearest Neighbour algorithm. Shelf areas exhibit different dominant
forcing modes for similar wave exceedance conditions, relating to
differences in depth, grain size, tide range, and wave exposure. WTI
dominate across most areas in energetic combined conditions. Over a
statistically representative year, meso-macrotidal areas exhibit
tide-dominance, while shallow, finer grained, amphidromic regions show
wave-dominance, with WTI dominating extensively >30m depth.
Seabed morphology is strongly affected by sediment transport mode, and
sand wave geometry varies significantly between predicted dominance
classes with increased length and asymmetry, and decreased height, for
increasing wave-dominance. This approach efficiently indicates where
simple non-interactive wave and tide processes may be sufficient for
modelling sediment transport, and enables efficient inter-regional
comparisons and sensitivity testing to changing climate conditions with
applications globally.