Effects of Levee Extension on Marsh Flooding

Abstract

Western Terrebonne Parish, a low‐lying coastal marsh with numerous meandering bayous and small lakes, is located in south‐central Louisiana. The area is frequently inundated by backwater, tidal, and headwater floodings. An extension of the existing Avoca Island levee is proposed for further providing flood protection to the area. This paper evaluates the potential changes in the hydrologic regime and the area's hydrodynamics caused by the proposed levee extension. The study area is modeled as a network of junctions and channels. Riverine and tidal boundary conditions are used as input to a watershed model that predicts the time history of water level, flow, and sediment of the area. The response of the marsh to flooding events is simulated with both existing and future conditions. The results in terms of surface water contours, current discharge patterns, and sediment concentration distributions are presented. The changes before and after the levee extension are discussed.