Estimating sand wave migration from local hydrodynamics and sediment mobility

Abstract

Sand waves are large migrating seabed features that are widespread on sandy continental shelves. Their migration causes seabed level changes that can affect offshore infrastructure, motivating the need for decadal-scale predictions of migration rates. Common prediction approaches rely on extrapolation of historical observations and are therefore difficult to apply in data-scarce regions or under changing environmental conditions. To satisfy the need for quick process-based estimations of sand wave migration, we explore relations between hydrodynamic forcing, sediment mobility, and sand wave migration. We calculated and verified sand wave migration rates across the Dutch Continental Shelf, including ∼14,500 km of sand wave crests. Using hydrodynamic conditions from the Dutch Continental Shelf Model and sediment grain size and water depth measurements, we derived migration rate estimators based on driving processes. Results show that an estimator based on tidal current asymmetry provides a reasonable first-order estimate of site-specific migration rates with strong linear correlation. Including non-tidal forcing improves estimates, especially for slowly migrating sand waves. By incorporating sediment mobility through excess velocity and shear stress estimators, more consistent non-linear relations are found that better reflect sediment transport physics and reduce regional differences in predictor performance. The strongest relation is obtained using squared excess velocity, while excess shear stress proves more robust when sediment grain size is uncertain. Sensitivity analyses further show that both sediment size and bed roughness influence estimator performance. These process-based estimators enable first-order migration rate predictions in data-scarce areas and provide quantitative estimates of how environmental changes affect sand wave dynamics.