A numerical study of the scale effects affecting the evolution and sediment entrainment capacity of a gravity current, propagating over a loose bed containing large-scale roughness elements

When compositional gravity currents propagate over a loose bed, they can entrain, carry, and deposit large quantities of sediment over considerable distances from the entrainment location. The capacity of compositional gravity currents to entrain sediment of various sizes from a loose bed containing large-scale roughness elements in the form of two-dimensional (2D) ribs is investigated using high-resolution Large Eddy Simulation (LES). The compositional gravity current is produced by the instantaneous release of a large volume of heavier lock fluid in a straight open channel. The present study focuses on the influence of the Reynolds number and the presence of 2D ribs on the evolution of the lock-exchange gravity current and on the distributions of the bed friction velocity. At the higher Reynolds number considered in the present investigation, the structure of the gravity current is closer to the inviscid state often assumed in simplified models.