Influence of Key Environmental Drivers on the Performance of Sediment Diversions

A Delft3D morphodynamic model for Barataria Bay, Louisiana, USA is used to quantify a plausible range of land change in response to a proposed sediment diversion under a range of environmental drivers. To examine the influence of environmental drivers, such as Mississippi River water hydrographs, mineral and organic sediment loading, sea level rise rates, subsidence, and a projected implementation (or operation) date, 240 multi-decadal (2020–2100) numerical experiments were used. The diversion was assumed to begin operation in 2025, 2030, or 2035. The experiments revealed persistent benefits of the sediment diversion through 2100. Start data of 2025 result in a median net positive land change of 32 km2 by 2100; whereas the 90th, and 10th percentiles are 69 and 10 km2. A delay in the operation date of the diversion to 2030 or 2035 would reduce the net positive land change by approximately 15–20% and 20–30%, respectively.

Mitigating for coastal erosion and C loss in the Mississippi Delta; do river water diversion do more harm than good?

<p>Sediment, nutrient deprivation and saltwater intrusion, among other factors, are driving widespread organic soil collapse and marsh loss in the Mississippi River Delta. Freshwater wetland diversions were designed to reintroduce Mississippi River water and sediment into the adjacent basins to manage salinity and mitigate land loss. However, there is concern that loading of excess nutrients from the Mississippi River into Barataria Basin wetlands can potentially lead to increased soil OM decomposition, less soil strength or increasing buoyancy and decreased belowground biomass. A baseline study was effected of a 3,145 km<sup>2</sup> area of wetlands and estuaries within Barataria Basin in 2007, in which the spatial variation in plant and soils were described at 140 stations before full scale diversion operations began in 2009. A subsequent spatial survey was conducted in 2018 after 11 years of diversion influence. By resampling the top 20 cm, separated into 0-10 cm and 10-20 cm layers, in 2018 provides an assessment of the status of those soils produced since 2007 and provides context for changing soil conditions. For the 2018 sampling, the soil </p>

Mississippi River and Campeche Bank (Gulf of Mexico) Episodes of Cross-Shelf Export of Coastal Waters Observed with Satellites

The cross-shelf advection of coastal waters into the deep Gulf of Mexico is important for the transport of nutrients or potential pollutants. Twenty years of ocean color satellite imagery document such cross-shelf transport events via three export pathways in the Gulf of Mexico: from the Campeche Bank toward the central Gulf, from the Campeche Bank toward the Florida Straits, and from the Mississippi Delta to the Florida Straits. A catalog of these events was created based on the visual examination of 7280 daily satellite images. Water transport from the Campeche Bank to the central Gulf occurred frequently and with no seasonal pattern. Transport from Campeche Bank to the Florida Straits occurred episodically, when the Loop Current was retracted. Four such episodes were identified, between about December and June, in 2002, 2009, 2016, and 2017, each lasting ~3 months. Movement of Mississippi River water to the Florida Straits was more frequent and showed near seasonal occurrence, when the Loop Current was extended, while the Mississippi River discharge seems to play only a secondary role. Eight such episodes were identified—in 1999, 2000, 2003, 2004, 2006, 2011, 2014, and 2015—each lasting ~3 months during summer. The 2015 episode lasted 5 months.