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Riverine Sediment and the Louisiana coast

Students measure river flow
Students measure river flow in LSU AgCenter research. (Photo by Y. Jun Xu)
Figure 1.
Figure 1. Major river systems supply sediments to coastal Louisiana.
Table 1.
Calcasieu River
Calcasieu River. Photo by Timothy Rosen
Vermilion River
Vermilion River. Photo by Timothy Rosen

About 40 percent of the nation’s coastal wetlands are in Louisiana and include contiguous freshwater wetlands, contiguous brackish wetlands, and low and high salt marshes. These natural ecosystems are highly productive and serve as critical nursery areas for Gulf of Mexico sea life, ensuring a thriving marine and fisheries industry. However, Louisiana coastal wetlands are disappearing at an alarming rate. Since the 1990s the land loss rate has been estimated to be between 9,884 and 13,838 acres each year, and over the previous 50 years, land loss rates have exceeded 14,826 acres per year. Total land loss since the 1930s has been more than 1.2 million acres. This loss represents 80 percent of the coastal wetland loss annually in the entire continental United States.

The factors that have contributed to the rapid wetland loss along Louisiana’s coast include land subsidence, sea level rise, coastal erosion and reduction in riverine sediment loads. Coastal Louisiana is built on sediment, and many wetlands in the region depend on sediment supplies from the inland rivers (Figure 1). Information on the quantity and distribution of the supplies is therefore important for policy makers to develop effective resource management strategies for regional sediment management.

Over the past several years, LSU AgCenter scientists have conducted studies to quantify long-term total yields of suspended solids from 10 major rivers entering the Gulf of Mexico from Louisiana (Figure 1). The rivers supply sediments to three coastal sections. From east to west these are Lake Pontchartrain fed by the Pearl, Tangipahoa, Tickfaw and Amite river systems; the Mississippi-Atchafalaya River Delta; and the Chenier Plain fed by Vermilion, Mermentau, Calcasieu and Sabine River system.

On average, these rivers deliver a total of 200 million tons of sediment to Louisiana’s coast annually while the Mississippi-Atchafalaya river system alone delivers 198 million tons of sediment (Table 1). This sediment delivery is approximately 180 times more than all other eight rivers combined. All these rivers show a seasonality of high sediment yield in the spring and low sediment yield in the summer and early fall. The sediment discharges are crucial resources, and further studies are under way to explore an environmentally sustainable, economically feasible concept of maximizing the benefits of the riverine sediments, while maintaining navigation and flood control in coastal Louisiana.
Y. Jun Xu, Associate Professor, and Timothy Rosen, Graduate Student, School of Renewable Natural Resources, LSU AgCenter, Baton Rouge, La

(This article was published in the fall 2011 issue of Louisiana Agriculture magazine.)

Last Updated: 11/29/2011 8:50:01 AM

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