Stratification and Circulation in Lake Pontchartrain

Abstract

A three-dimensional hydrodynamic model (Princeton Ocean Model, POM) was used to study the dynamic behavior of a saltwater plume originating from a navigation canal and advancing in the lake. The Inner Harbor Navigational Canal (IHNC) is part of the Mississippi River Gulf Outlet, which permits ships to navigate from the Gulf of Mexico to Lake Pontchartrain and the Mississippi River at New Orleans. Lake Pontchartrain is a relatively shallow, brackish estuarine lake with a mean depth of less than 4 m and a mean salinity of 7 ppt. At times, the IHNC brings highly saline water (> 20 ppt) into Lake Pontchartrain. Under certain conditions, this higher density water has been observed to form a thin layer of high salinity water over a large area near the bottom of the lake. Field data showed that the stratified zone was approximately 0.5 m deep and up to 250 km2 in area. A three-dimensional hydrodynamic model (POM) was developed for the area to study the effect of Lake circulation on the location and stability of the saltwater plume. Field and laboratory data were used for model calibration and verification. The forcing functions for the model include tide from nearby connections to the Gulf of Mexico, wind and river flows from tributaries to the north and west. The model includes 20 sigma levels with surface and bottom refinement in order to capture the momentum transfer from the wind shear and the density current near the bed. The horizontal grid resolution is 600 m.