Characterization and Modeling of Sediment Settling, Consolidation and Suspension to Optimize the Retention Rate of Sediment Diversions for Coastal Restoration

Many research efforts have been made to the Mississippi coastal restoration, but long-term rheological and sedimentological experiments for sediment erosion, deposition and consolidation in diversion receiving basins are still lacking. Push cores and sediment samples were collected from West Bay, a semi-enclosed bay located on the Mississippi River Delta, and Big Mar pond, a receiving basin of the Caernarvon freshwater diversion from the Mississippi River, Louisiana. A dual-core Gust Erosion Microcosm System was used to measure time-series (0.5, 1, 2, 3, 4, 5, and 6-month after initial settling) erodibility at seven shear stress regimes (0.01-0.60 Pa) using experimental cores prepared with two initial sediment concentrations (60 and 120 kg m-3). A 230-cm tall settling column with nine sampling ports was used to measure the consolidation rates for initial sediment concentrations ranging from fluid mud (10 kg m-3) to dredge effluent (120 kg m-3) in combination with two levels of salinities (1 and 5 PSU). The erodibility of West Bay sediment decreases with increasing time of consolidation. The critical shear stress increases from 0.2 Pa after 2-month of consolidation to 0.45 Pa after 4-month of consolidation. Organic content plays a role on both sediment resuspension and consolidation, particularly for Big Mar sediment. The consolidation rates are inversely and exponentially related to initial sediment concentrations. Sediment in 1 PSU tests generally settles faster than that in 5 PSU tests. A model using a single consolidation rate was improved by adding another exponential coefficient. The improved Sanford (2008) model can better predict the consolidation profile of both rapid early settling and slow self-weight consolidation processes