Representation of Near-Bed Sediment Gravity Flows within the Regional Ocean Modeling System (ROMS)

Authors: Courtney K. Harris and Aaron J. Bever, Virginia Institute of Marine Science, Gloucester Point, VA USA



Within the past decade, data from several continental shelf and deltaic environments has shown near-bed sediment gravity flows to be an important component of across-shelf sediment transport. Both observational and theoretical work has concluded that stratification at the top of the wave-boundary layer can trap sediment within this thin layer (~10 cm thick), creating fluid muds whose density anomaly is sufficient to cause downslope transport. This transport process, however, can not be represented within standard vertical grids (z-, s-, or sigma-coordinate) used within ocean models because the thickness of the wave boundary layer typically increases as water depth decreases, and because it is usually too thin to be resolved. Additionally, standard wave-current interaction modules used within ocean models do not resolve velocities and turbulence at the vertical resolution of the wave boundary layer. These considerations motivated previous work within ECOM-SED (Estuarine and Coastal Ocean Model – SEDiment) to represent near-bed sediment gravity flows using a separate grid cell underneath of the model’s sigma-grid (Harris et al., 2004; 2005). A similar component is being implemented within the Regional Ocean Modeling System (ROMS) and being tested using an idealized continental shelf / river plume test case.