IMPROVED TECHNIQUES FOR GRAVITY CURRENT MODELING

Boundary gravity currents play a key role in circulation for estuaries, bays, lakes and the coastal ocean. Three-dimensional models of large basins using z-level coordinates tend to overestimate entrainment of boundary gravity currents as the stair-step topography leads to artificial mixing. Boundary following models using sigma-coordinates avoid the stair-step problem, but introduce difficulties for the 3D processes in the basin interior and allow artificial entrainment based on changes of the grid cell height where the density current thickness is poorly resolved. Previous researchers have proposed isolating the gravity current physics into a separate depth-averaged model that is coupled to the interior of the 3D z-level model. However, existing methods for coupling the models have adhoc features that are undesirable and, in some cases, may result in non-physical solutions. Approaches to accurately coupling gravity current and three dimensional models are explored, the problems are investigated, and possible solutions are proposed