Figure 24. Computerized re-creation of the west side of Barataria Bay showing the 

 change in wetlands between 1945 (a) and 1980 (b). Black is open water; marshes are 

 shown as varying shades of grey (Dozier 1983). 



large a delta as it has historically. In 

 addition, channel ing and leveeing the river 

 entrains much of the sediment, preventing 

 spring overbank flooding that nourishes 

 the interdistributary marshes . 



There is now strong evidence that the 

 rate of marsh loss is being accelerated by 

 local human activities in addition to the 

 reduction in the river's sediment load. 

 Canals are the major culprit in this 

 scenario. Formerly, rain runoff from 

 adjacent uplands flowed across wetlands, 

 dropping its load of sediment and 

 nourishing the marshes. Now a network of 

 drainage canals along the marsh-upland 

 interfaces of the delta estuaries carries 

 this runoff directly into estuarine lakes 



and bays, bypassing the swamps and marshes 

 (Conner and Day 1982). If runoff flowed 

 across the wetlands, the trapped sediment 

 would help minimize wetland subsidence and 

 the quality of the runoff water would be 

 improved before it entered the lakes and 

 bays. Instead, the portions of the 

 estuaries near urban areas are becoming 

 increasingly turbid and eutrophic (Craig 

 et al. 1977). 



At the other end of the estuary, 

 navigation canals, especially those that 

 cross the barrier islands, cause major 

 disruption of circulation. The canals are 

 straight and deep in estuaries that have 

 an average depth of only 1 or 2 m. There- 

 fore they capture flow from smaller 



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