and erosion. Inland nnarsh loss is caused prinnarily by lack of sufficient sedimentation to 

 offset apparent sea level rise. Studies done by DeLaune et al. (1978) and Baumann (1980) 

 showed that only streamside marshes are accreting fast enough to offset the effects of 

 subsidence. 



Artificial Causes of Land Loss 



Flood control, navigation improvements, agricultural impoundments, and 

 canalization interact with natural geologic processes to accelerate wetland loss. Lack of 

 adequate sediment supply is caused largely by the construction of levees along the 

 Mississippi; these have almost eliminated overbank flooding and caused the closure of a 

 number of minor distributaries. The modern delta has grown out to the edge of the 

 continental shelf and most of the river's sediment load is deposited in deep Gulf of 

 Mexico waters. These flood control measures have interrupted the balance between 

 riverine and marine processes which built and stabilized marsh and swamp areas. The 

 only significant land building along the Louisiana coast is in Atchafalaya Bay where a 

 new delta is being formed (Roberts et al. 1980). 



Canals constructed for such activities as oil exploration and recovery, navigation, 

 and drainage significantly contribute to wetland loss. Aerial photography of coastal 

 Louisiana gives a stunning image of wetlands densely webbed by canals. The 



construction of canals leads directly to land loss through dredging and spoil deposition. 

 Indirect influences include such factors as changes in hydrology, saltwater intrusion, and 

 altered sedimentation patterns (Craig et al. 1979; Cleveland et al. 1981). The highest 

 rates of marsh erosion occur in areas with the highest density of dredged canals 

 (Blackmon 1979; Craig et al. 1979; Turner et al. 1982). 



MANAGEMENT OF WETLAND LOSS 



A number of management approaches have been suggested to combat the problem 

 of wetland loss. The creative use of riverine sediments to help build new wetland areas 

 or infill decaying marshes is one mitigation technique that has been suggested. This 

 could be accomplished through controlled diversions along the lower Mississippi River 

 (Gagliano and van Beek 1974), and through proper management of sediment flows into the 

 newly forming Atchafalaya delta region. Another management option is stricter 

 regulatory controls on canal construction within the coastal zone. In this paper, we will 

 assess the effectiveness of these various approaches in reducing wetland loss rates. 



Atchafalaya Delta 



The Atchafalaya River is a major distributary of the Mississippi and carries about 

 30% of the total flow. It is currently creating new wetlands in the Atchafalaya Bay 

 Delta, as well as restoring deteriorating wetlands in adjacent areas. There is also a 

 measurable accretion of sediments along the chenier plain associated with the deposition 

 of fine sediments from the Atchafalaya River. The amount of sediment required to fill 

 Atchafalaya Bay could be deposited in a 60-year period given the flood regimes of the 

 period 1851 to 1967. If abnormally high floods of 1970-77 are included in this long-term 

 average (i.e. 1951-77) the estimated time for this to occur is 42 years. The recurrence in 

 the I980's of the extremely high flood stages of 1970-77, would reduce the time needed 

 to fill the bay to less than a decade (Baumann and Adams 1982). 



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