Lessons learned from 30-years of operation of the Caernarvon Freshwater Diversion, Louisiana USA

Abstract

Wetland loss is a worldwide issue with estimates of loss ranging from 50% to 71% in the 20th century. Louisiana's coastal zone lost approximately 4,830 km2, or 25% of the land area between 1932 and 2016 due to a variety of natural and anthropogenic forces that both erode and prevent the growth or maintenance of existing land. Freshwater diversions were constructed along the Mississippi River to convey freshwater, nutrients, and sediment from the Mississippi River to Louisiana's coastal basins to combat saltwater intrusion, nourish the marshes, and stimulate fisheries. The Caernarvon Freshwater Diversion (CFD) was authorized by the Flood Control Acts of 1928 and 1965, the 1974 Water Resources Development Act, and a 1984 Environmental Impact Statement, with construction completed and operations started in 1991. The CFD has been largely successful from the standpoint of the project's authorized goals. Early on in the project, the CFD helped combat saltwater intrusion in a 2,730 km2 basin and re-established the gradient from fresh to salt marsh, by creating conditions favorable to fresh marsh species. Although not a specific project goal, the CFD also built more than 700 acres of new emergent wetland between 1991 and 2016. By critically assessing 30 years of CFD governance, operations, monitoring, and adaptive management, lessons learned are developed that provide valuable information for making the operations and governance of current and future diversions more effective, transparent, adaptive, and trusted by the basin communities. Louisiana's Coastal Master Plan pivots to the use of river diversions to focus on land building and large-scale ecosystem restoration by mimicking natural processes that originally built the Louisiana deltaic landscape, rather than the more common small-scale restoration that has occurred over the past decades. However, large-scale restoration projects, by their nature, impact a wide variety of stakeholders and tend to cross political boundaries. Lessons learned from the CDF highlight the need for flexibility in the long-term and specificity in the short term in governing the operations of a large-scale coastal project. Recommendations developed for modernizing project implementation into the future given changing estuaries and climate will help increase effective implementation of larger-capacity river sediment diversions and other ecosystem-scale projects. It is time for big and bold action to restore south Louisiana and other coastal environments worldwide, and critical to success is using results from numerous past studies, applying lessons learned from existing projects like the CFD, and projections of future conditions.