A modeling study of the impact of major storms on seabed shear stress and sediment transport on the Grand Banks of Newfoundland

Waves, current, and sediment transport processes in major storms on the Grand Banks of Newfoundland were simulated using integrated wave, three-dimensional tide and circulation, and combined-flow sediment transport models. While the tidal and nontidal currents are generally low and cause little sediment transport, storm-induced waves and currents enhance bed shear velocity by more than 5 times and cause significant sediment transport over the entire Grand Banks. The impact of storms on shear stress and transport strongly depends on water depths and the greatest impact occurs over the bathymetric highs on southeastern Grand Bank where the maximum shear velocity reaches 15 cm s−1 and the maximum transport rates are >5 kg m−1 s−1. The direction of sediment transport rotates clockwise progressively through nearly 360° during the passage of a storm. Although peak transport typically occurs on central and southeastern Grand Bank with a southeastward direction, the magnitude, direction, and timing of peak transport show strong spatial and temporal variability. The variability of the peak transport largely depends on the timing and relative intensity of the waves and the total bottom currents which in turn depends on the addition of the storm-induced and tidal currents. The calculation of the maximum transport potential suggests that sediments as coarse as small pebbles are mobile in water depths <80 m under 1:1 year storms and that medium sand is transported in water depths as deep as 200 m during major storms. Results of the sediment transport models corroborate the observed sediment erosion and accretion patterns.