Exploring salt wedge dynamics and nature-inspired mitigation measures in the lower Mississippi River

A high-resolution numerical model of hydrodynamics to simulate salinity conditions in the lowermost Mississippi River was utilized to analyze the salt wedge propagation. Extensive upriver propagation occurred during 2022-2024 with discharge conditions between 5,000 and 8,500 cms, which are below long-term seasonal averages but above historically defined severe drought thresholds. Our analysis reveals that while sea level rise and deepening of the navigation channel contribute to upstream wedge movement excessive water loss through a series of lateral crevasses was a primary cause of the upriver wedge propagation distance. When the lateral crevasses (during drought events) are closed in the simulation using native sand material, it results in significant reduction of the salt wedge propagation upriver. The model also demonstrated that an underwater sand sill presently utilized in low events to limit propagation of the wedge upriver movement, if moved further downstream enhances its function and effectiveness. Overall, this model may serve as a vital tool for public risk communication and co-production, fostering informed decision-making for water management in the Lower Mississippi River. • River discharge at Head of Passes (RK0) is the primary control on salt wedge migration. • Sea level rise and channel deepening increase salt intrusion by 6.5 and 3.5 km. • Thalweg earthen sills are most effective near the river–ocean interface (e.g., RK72). • Existing earthen sills are ineffective when river discharge falls below 3.54k cms. Our study investigated how saltwater denser saltwater from the Gulf moves upstream beneath the freshwater layer in the Mississippi River, especially during droughts, using a computer model to understand causes and solutions. Among the modeled mitigation scenarios, artificial closure of eastern distributary outlets reduced wedge intrusion by up to 120 km relative to the benchmark case, exceeding the effect of sill relocation (10 km reduction) and sea level rise impacts (6.5 km increase). Earthen sills, acting as underwater speed bumps, halt the upriver movement of salt and help by mixing saltwater with freshwater. Our model not only predicts saltwater movement and evaluates solutions but also helps communicate these complex issues to the public, encouraging informed decision-making for river management.