The long public works legacy in Louisiana’s retreating coastline Craig Colten Carol O. Sauer Professor Louisiana State University, Baton Rouge, Louisiana Member, Public Works Historical Society Board of Trustees ouisiana has a particularly fragile coastline. Unlike the rugged fjords of Norway or the cliff-backed Oregon coast, Louisiana’s shore is made up of recently deposited delta soils. They are compressing and subsiding under their own weight and are subject to erosion by wave action and storms. Between 1978 and 2000, over 650 square miles of coastal wetland disappeared. While gravity and other natural processes are very much at work, there is an important public works component to this story that goes back several centuries. Soon after the French platted the grid street pattern that became New Orleans, settlers began calling for protective levees to fend off the annual floods delivered by the Mississippi River. The town undertook to erect modest earthen barriers along its riverfront. Over time, the colonial government passed legislation mandating that individual landowners up and down the river were responsible for building their own levees. By the midnineteenth century, parishes (counties) and then the state took on the responsibility for building and maintaining the flood protection system and it became a major public works project along the lower river. These levees were the initial factor in coastal land loss. By preventing annual floods that would rejuvenate the delta each spring, the bulwarks guided the muddy Mississippi into the Gulf of Mexico, in effect starving the coastal region of fresh sediment borne by the river that might offset natural subsidence. In the 1870s, James Eads constructed jetties near the mouth of the Mississippi River to help sustain a deep water channel for oceangoing ships. By narrowing one of the mouths, the jetties further steered sediments carried from the farmlands of the Midwest out into the deep waters of the Gulf. During the same
decade, Congress assigned the duty of building and maintaining levees along the lower river to the Mississippi River Commission. Authorized as a navigation project, they adopted a “levees only” policy that ultimately saw the erection of a more effective levee system that closed down several of the lower river’s distributaries. Better levees meant fewer failures and less chance for even occasional flooding and delivery of sediments to the delta. Even during the disastrous floods of 1927, when upstream levees failed with remarkable frequency, there were few crevasses in the area below Baton Rouge and the delta remained starved of sediment. For flood-control purposes the federal government added a series of dams along the upper Mississippi and the Ohio Rivers, and eventually built multipurpose dams on the Tennessee and the western tributaries of the Mississippi. These structures serve to capture huge quantities of sediment that erodes from the rich agricultural lands of the Midwest and Great Plains. Estimates suggest that the river carried in excess of 600 million metric tons of sediment in the 1880s. By the 1950s that total was close to 500 million metric tons and, after the completion of numerous dams in subsequent years, the sediment load dropped to below 200 million metric tons. This decline in sediment is critical to current efforts to restore the delta. The Corps of Engineers has built several “freshwater diversion” structures in the delta. These devices allow freshwater from the river to pass through control structures cut through the levees and to flow across the sediment-starved wetlands. As the sediment-laden water passes through the coastal marshes, it deposits a
portion of its load and has built marshland in Plaquemines Parish. There are other projects under discussion that will direct sediment to susceptible areas in hopes that it will fortify the unraveling coast. Of course, with less sediment in suspension, relying on the river to restore wetlands takes longer and time is not an ally of coastal Louisiana, especially when you factor in sea level rise. As the shoreline recedes, inland communities are at greater risk from tropical cyclones. After the particularly destructive Hurricane Betsy in 1965, Governor John McKeithen proposed a levee to armor the entire Louisiana coast from near New Orleans to the Texas border. This public works project never materialized, but massive barriers were erected around New Orleans and agricultural and industrial areas downstream from the state’s largest city. Additional barriers were erected on Grand Isle and along Bayou Lafourche, but the entire coastline never received fortifications. Since Hurricane Katrina, calls for a more complete levee system have reemerged. The state’s coastal plan issued in 2012 considers a set of hurricane levees that reflect McKeithen’s vision of 1965. In effect, Louisiana’s cities, farmers, and factories have benefitted from flood protection. But the state today faces huge costs to protect its larger coastline that is disappearing due in part to human actions taken in the past. Public works projects have unleashed unanticipated environmental consequences and also an ongoing series of public works remedies to the problems created by previous generations. Craig Colten can be reached at (225) 5786180 or ccolten@lsu.edu. June 2012 APWA Reporter
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