An additional impact of Atchafalaya River sediments is the reduction of beach 

 retreat along the chenier plain coast west of Atchafalaya Bay. During most of this 

 century, there has been a net shoreline retreat in this area (Adams et al. 1978). Fine- 

 grained sediments from the Atchafalaya are now being deposited along this coast, 

 however, and it is estimated that within 50 years there will be a net growth (Wells and 

 Kemp 1981). 



Future growth of the Atchafalaya delta, assuming the flow regimes of 1851-1977, 

 will take place at the rate of I 1.9 km /yr (Baumann and Adams 1982). The infilling of 

 older marshes adjacent to the Atchafalaya as previously discussed, is occurring at 4.9 

 km /yr (Baumann and Adams 1982). A reversal of the chenier plain beach retreat, which 

 will stabilize the situation and result in no net loss for that area, is occurring at a rate of 

 LI km /yr (Adams et al. 1978; Wells and Kemp 1981). Therefore, the accretion from 

 Atghafalaya River sediments is responsible for a total reduction in land loss of 17.9 

 km Vyr (Table I). 



Controlled Diversions 



As a means of introducing river water and sediment to offset wetland loss, plans 

 have been developed for controlled diversions of the Mississippi River. "Basically, it 

 would re-establish the overbank flow regime of the deltaic plain, presently disrupted by 

 flood protection levees, and restore more favorable water quality conditions to the highly 

 productive deltaic estuaries" (Gagliano and van Beek 1974). According to Gagliano et al. 

 (1971), the feasibility of controlled diversion is indicated by the relatively small input of 

 energy and materials needed to build a subdelta. Several sites for controlled diversions 

 are presently being developed along the lower Mississippi River. According to Gagliano 

 (I98IJ the potential reduction in land loss rate using controlled diversion is between I and 

 3 km /yr. 



Regulatory Control of New Canals 



The highest rates of marsh loss occur in areas with the highest density of canals. 

 Land loss rates were determined for the seven management basins in Louisiana and it was 

 estimated that when canal, spoil area and indirect Josses were included (Craig et al. 

 1979), 44% to 54% of the total annual loss of 102 km"^ (39.4 mi^) in the deltaic plain was 

 caused by canals. 



Canals contribute to wetland loss both directly and indirectly. The direct impact 

 of canals can be easily measured. For example, unpublished data from U.S. Fish and 

 Wildlife Service records show that 397 permits for dredging of Louisiana marshes were 

 granted to oil companies in 1975, with a direct loss of 772 ha (1,907 acres) of marsh; in 

 1976, 435 permits resulted in a direct loss of 981 ho (2,424 acres); and during the first 6 

 months of 1977, 206 permits were issued resulting in a direct loss of 524 ha (1,295 

 acres). Thus, in 2.5 years there was a direct loss of 2,227 ha (5,626 acres) of Louisiana 

 marsh just to the petroleum industry (Lindall et al. 1979). Spoil deposition from canal 

 construction is generally two to three times greater than the canal area itself. Craig et 

 al. (1979) estimated that the indirect impacts of canals can cause wetland loss in an area 

 three to four times the initial canal area. Therefore, the total loss of wetlands caused by 

 industrial access canals for the 2.5-year period mentioned above will ultimately be 6,000- 

 8,000 ha (15,000 to 20,000 acres). One of the mechanisms by which this additional loss 

 takes place is the widening of canals with time. Annual increases in canal widths of 2% 

 to 14% in the Barataria Basin have been documented, indicating width doubling rates of 5 



236 



