Abstract
Anentrainment model for fluid mud is derived by integrating the equation for turbulent kinetic energy across the mixed layer and introducing some modelling assumptions. The resulting entrainment model is similar to models of mixed-layer deepening in lakes and reservoirs, but in addition accounts for the work needed to entrain bed material. Two basically different flow conditions are considered: (1) flow in the water layer but no flow in the fluid-mud layer, and (2) flow in both layers driven by a tide-induced streamwise pressure gradient. In the first case, which applies to laboratory experiments in an annular flume, for example, the water layer is the turbulent mixed layer that erodes the quiescent fluid-mud layer. In the second case the fluid-mud layer is the mixed layer, which deepens because of entrainment of water from the overlying water layer. The water layer then is the quiescent layer. The viscous drag of the quiescent layer due to the flow in the mixed layer, which effect can play a part in laboratory experiments, is accounted for. Empirical model coefficients are obtained from the literature.
