Since the 1930s, levees have been built along both sides of the river to prevent the river from 

 overflowing its banks during spring flooding, and several minor "distributaries" (alternative 

 channels that lead through the wetlands to the Gulf of Mexico) have been sealed off. Although 

 these actions have reduced the risk of river flooding in Louisiana, they also prevent sediment and 

 fresh water from reaching the wetlands. As a result, wetlands are gradually submerged, and salt 

 water is intruding farther inland, killing some cypress swamps and converting freshwater marsh 

 to brackish and saline marsh. Finally, dams and locks on the upper Mississippi, Arkansas, 

 Missouri, and Ohio Rivers (and improved soil conservation practices) have cut in half the amount 

 of sediment flowing down the river, limiting the growth of wetlands in the Atchafalaya delta, the 

 one area that has not (yet) been completely leveed and channelized. 



Canals and poor land use practices have also resulted in wetland loss (Turner, Costanza, and 

 Scaife 1982). However, levees and channels are particularly important because they disable the 

 mechanisms that could enable the wetlands to repair themselves and keep pace with sea level. 

 With almost no sediment reaching the wetlands, an accelerated rise in sea level could destroy 

 most of Louisiana's wetlands in the next century. 



Figure 1-9 illustrates the disintegration of wetlands at the mouth of the main channel of the 

 Mississippi River between 1956 and 1978. Because there are no levees this far downstream, this 

 marsh loss is attributable to navigation projects. Figure 1-10 illustrates changes in Terrebonne 

 Parish's wetiands from 1955 to 1978. Note the extensive conversion of fresh marsh to saline and 

 brackish marsh, as well as the conversion of cypress swamps to open water. Figure 1-11 shows the 

 generally expected shoreline for Louisiana in the year 2030 if current management practices and 

 sea level trends continue. Although projects to slow the rate of wetland loss may improve this 

 picture, accelerated sea level rise could worsen it. Figure 1-12 shows the loss expected if sea level 

 rises 55 cm by 2050. 



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