Three-dimensional hydrodynamic modeling of saltwater intrusion and circulation in Lake Pontchartrain (Louisiana)

Saltwater intrusion has been observed in the vicinity of the Inner Harbor Navigation Canal (IHNC). Although periodic, the density gradients are sometimes strong enough to propagate the saltwater plume over a large area at the bottom of Lake Pontchartrain. During strong stratification, density gradients form a stable interface, which at low wind conditions limits water column mixing above the interface. As a result of low mixing conditions in the bottom waters, dissolved oxygen below the interface may become hypoxic. Wind waves and wind-induced circulation currents in the Lake can produce conditions that can mix or re-distribute and expand this high saline and low oxygen plume. A Freeport McMoRan and Environmental Protection Agency supported study was initiated at the University of New Orleans, to study the dynamics of saltwater intrusion from the IHNC, and investigate conditions and circulation patterns that might produce favorable conditions for mixing of this plume. A Hydrodynamic and Transport model has been developed, calibrated and verified for Lakes Pontchartrain and Maurepas. Freshwater inputs from the major tributaries, as well as saltwater inputs from the IHNC and Pass Rigolets have been included. The model predicted a two-gyre wind driven circulation pattern in Lakes Pontchartrain and Maurepas with low currents in the center of the Lake counter to the wind direction and higher currents along the Lake periphery following the direction of the wind. The model also predicted significant interaction between bottom currents and density currents.