Numerical modeling of hydrodynamics and sediment transport in lower Mississippi at a proposed delta building diversion

SummaryThe Mississippi River Delta of south Louisiana USA is a highly engineered system with extensive levees, flood control, and diversion structures. This region is experiencing a high rate of coastal wetland loss. Solutions to divert or re-direct a portion of the River’s sediment to benefit wetlands and reduce coastal land-loss are considered. The question that must be answered, regarding the impact and feasibility of sediment diversions is: What is the sediment–water ratio at a diversion? To help answer this question a numerical model of hydrodynamics and sediment transport supported by extensive field data is used to analyze a proposed sediment diversion near Myrtle Grove, Louisiana. This location is at a River Kilometer 90 above the Head of Passes – exit of the Mississippi River to the Gulf of Mexico. The numerical model showed that the location of the diversion, the size and the alignment of the diversion channel are critical parameters affecting the sediment–water ratio captured by the diversion. The analysis shows that locating the intake near a lateral sandbar increases the sediment–water ratio in the diversion. Further, the analysis shows that a larger diversion channel with a favorable alignment orientation to the flow direction in the river results in higher sediment–water ratio.

► Three-dimensional modeling is effective in assessing the performance of diversions.
► The diversion channel alignment and orientation impact the sediment–water ratio.
► Placing the intake on top of a sand bar increases the amount of sand diverted.
► Increasing the diversion size improves the performance of a sediment diversion.