Before the emergence of the Atchafalaya delta during the floods of the I970's, 

 existing wetlands adjacent to the lower Atchafalaya River were deteriorating at a rapid 

 rate. During 1972-78, the loss rate was reversed and the wetland area grew. Baumann 

 and Adams (1982) examined quadrangle maps for the area and found a net loss during 

 1955-72 of 7,805 ha (4.88 kmVyr). The interval between 1972 and 1978, by contrast, had 

 a much reduced rate of land loss and some areas experienced wetland gain (Baumann and 

 Adams 1282). Nonflotant marsh in the examined area experienced a net gain of 1,676 ha 

 (0.28 kmVyr) during 1972-78, with 1,277 ha (0.21 kmVyr) attributable to formatiop of 

 the new delta in Atchafalaya Bay. The same area lost a total of 6,736 ha (0.42 km /yr) 

 of wetlands from 1955 ta 1972. The marshes peripheral to Atchafalaya Bay experienced 

 a reversal from 0.42 km /yr loss to a 0.07 km^/yr gain (Baumann and Adams 1982). In 

 summary, the net wetland gain in the Atchafalaya Bay area is caused by two factors: (!) 

 the creation of new land in Atchafalaya Bay in the form of the new delta and (2) the 

 reversal of land loss in deteriorating marshes adjacent to the bay by infilling with 

 riverine sediment. 



Table 1. Effects of different mitigation techniques for reducing land loss 

 (see text for derivation). 



Activity Reduction in land loss rate 



(km^/yr) 



Atchafalaya River 



New delta growth 11.9 



Reversal of chenier plain beach retreat^ 1.1 



Infilling of older marshes 4.9 



TOTAL 17.9 



Controlled diversions lower 



Mississippi River 1-3 



Regulatory control of new canals 30-40 



^This value assumes that the present net rate of shoreline retreat will be 

 arrested. The net rate of retreat was calculated as the algebraic sum of 

 shoreline changes for each interval along the chenier plain as given in 

 Adams et al . (1978). 



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