Wave-induced sediment mobility on a morphologically complex continental shelf: eastern Brazilian shelf

Abstract

Wave-induced sediment mobility and transport are important issues regarding seabed stability and sediment balance on continental shelves. This study compares the near-bed velocity induced by waves with the critical orbital velocity for sediment mobility to determine the threshold exceedance for non-cohesive sediment motion on a portion of the eastern Brazilian continental shelf. Based on a 13-year wave time series, dominant wave climate has been used as boundary conditions in a wave propagation model. The region presents complex continental shelf morphology, varying north to south from a narrow shelf with coastal parallel isobaths to a wide shelf with irregular isobaths. The wave orbital velocities, which vary from 0 to 1.4 m s−1, are capable of mobilizing sediment across almost the entire continental shelf area, since the critical bottom sediment velocity required for potential sediment mobility varies from 0.11 to 0.13 m s−1 Such findings are of great relevance to gain a better understanding of the sediment dynamics in this area that hosts several reef banks, and that has been recently affected by a large environmental disaster through the failure of a tailing dam that resulted in an increase in contaminated sediments that have spread into the ocean.