Sediment dynamics over a dredge pit during summer fair weather conditions: A numerical study for Sandy Point, west flank of the Mississippi River

摘要

A coupled Flow-Wave-Sediment model was used to study hydrodynamics, sedimentation, and bottom boundary layer (BBL) dynamics over the Sandy Point Dredge Pit (SPDP; a potential sand mining site in the Louisiana shelf, northern Gulf of Mexico) during fair weather summer conditions (July and August 2015). The Delft3D modeling system on a curvilinear computational grid with spatial resolution between 10 m and 2.8 km was used. The flow, wave, and sediment transport models were evaluated using water level, current speed, wave parameters, and sediment concentration. During this period, the wind over the Louisiana shelf is characterized as low energy with the prevailing direction from southeast to the southwest, which corresponds to small wave heights (H-s < 1.2 m) and small wave periods (T-m < 4 s). The relatively shorter waves resuspended sediments only in very shallow areas along the Mississippi Birdfoot Delta. Simulations with and without the SPDP showed that the presence of the pit could decrease the speed of surface currents by as much as 19%, while its effect on wave characteristics was minor. The northward current produced by the prevailing winds transported the discharged sediments from the Mississippi River contributed 60% of the sedimentation over the SPDP. Sediment re-suspension inside the BBL of the SPDP occurred during the days that more energetic waves propagated over the shelf. As a result, sediments from the Mississippi River significantly increased the sediment concentration near the bottom of and throughout the water column above the SPDP.