The Chenier Plain in southwestern Louisiana was built by sediment drifting westward over the last 7,000 years from the shifting deltaic lobes of the Mississippi River as well as the Atchafalaya River distributary. Cycles of shoreline erosion and sediment deposition built ridges, or cheniers, running east-west between wide expanses of marsh. Sediment transport westward along the coast from both the Atchafalaya and Mississippi rivers has been limited by coastal infrastructure.

The Chenier Plain is characterized by fresh to brackish marshes and interior lakes that are fed by the Vermilion, Mermentau, Calcasieu and Sabine rivers. But for decades, navigation features, such as the Calcasieu Ship Channel, Sabine Waterway, the Mermentau Navigation Channel and the Freshwater Bayou Canal, have allowed salt water from the Gulf to penetrate formerly freshwater marshes. Today, the Chenier Plain is being overwhelmed by saltwater intrusion, leading to widespread marsh loss, while the jetty systems of the many navigation channels have interrupted the flow of sediment from east to west.

The priority projects chosen in this basin include Calcasieu Ship Channel Salinity Control Measures Hydrologic Restoration, which focuses on increasing sustainability of the basin by reducing tidal action and interior salinity to marshes and water bodies adjacent to Calcasieu Ship Channel. In addition, Freshwater Bayou North Marsh Creation project will build land quickly, creating critical wetland habitat and maintaining hydrologic barriers between inland lakes and navigation channels.