Basin Side Hydrodynamic and Morphological Modeling for the Delta Building Diversion at Myrtle Grove

This paper presents the basin side analyses that were performed in support of the Delta Building Diversion at Myrtle Grove project on the Mississippi River in southern Louisiana. These analyses included the hydrodynamic numerical modeling of various diversion magnitudes and operational regimes to determine their potential impacts on the Basin. Additionally, morphological modeling was performed to determine the resulting sediment distribution patterns and quantities over 45 years.

The Barataria Basin covers an enormous area of approximately 1.75 million acres between the Mississippi River and Bayou Lafourche in the southern section of the State of Louisiana in the United States (see Figure 1). The system encompasses freshwater and brackish wetlands and salt marshes, as well as freshwater ponds and lakes, natural and man-made canals, and brackish and saline bays and passes. The system, though, is stressed due to a number of factors. Primarily, the flood control levees on the Mississippi River have interrupted the natural overflow of freshwater, nutrients and sediment into the wetlands. This has deprived the marshes of their ability to maintain equilibrium. In the past, this sediment influx allowed them to continue building upward in response to the land subsidence and sea level rise related to regional and global geologic processes, but this no longer happens and therefore, the marshes are slowly drowning. Furthermore, a constant flux of freshwater is needed to ward off saline intrusion into the marshes. Higher salinity levels kill the freshwater marsh vegetation, converting the wetlands to brackish, open-water habitat.