particularly the difference in depth and cross-sectional area of natural ponds and trappers' ditches 

 in the post-canal condition versus the size of the canals. The canals provide conduits for tidal 

 action which suck the poorly consolidated organic sediments out of the protecting shells provided 

 by the mineral sediment ridges. 



The geometry of the pipeline canals and associated spoil banks has also changed during the 

 more than 30 years since its construction (Figure 11). Where the canal cuts through the natural 

 levee ridges there has been little tendency to widen, but in the areas between the ridges the canal 

 is now more than twice its original width. Spoil banks composed of mineral sediment remain 

 elevated and vegetated with small trees and shrubs, while those composed of organic materials have 

 diminished in width and elevation and support marsh vegetation. 



Under natural conditions tidal invasion of fresh marshes is slow, and mineral sediment 

 accumulation along tidal channels and lake rims protects organic soils. Canals cause rapid invasion 

 of tidal processes and massive marsh die-back followed by rapid tidal scouring of organic soils. 



The overall canal system superimposed on the Barataria Basin has created a sieve effect which 

 has completely destroyed the natural hydrology of this basin. Today, the leading edge of marine 

 tidal influence is now far into the upper end of this basin, in areas that were occupied by 

 freshwater swamps 100 years ago. 



IMPLICATIONS FOR WETLAND MANAGEMENT 



A number of conclusions that have important implications for management can be derived from 

 this study: 



1. Peats and high organic soils form, and the vegetation communities which produce them 

 persist, in fresh, nontidal, enclosed, and semi-enclosed hydrologic units with anaerobic 

 conditions. 



2. Under natural conditions in the deltaic plain, fresh and floating marshes are impounded 

 and semi-impounded and are not subjected to tidal inflow and outflow, and ingress and 

 egress of estuarine organisms. 



3. Continuous spoil banks along tidally influenced canals protect adjacent high organic 

 substrate marshes from saltwater intrusion and tidal scour. 



4. When a tidal regime is abruptly imposed on a high organic substrate marsh (that formed 

 as a freshwater swamp or marsh), the integrity of the marsh is destroyed and a high 

 percentage of the total wetland area reverts to open water. 



5. Some researchers advocate tidal inflow to maintain subdelta marshes. This position, derived 

 largely from studies of Atlantic coast tidal marshes, fails to recognize the high susceptibility 

 of peat and organic-rich marsh soils to the erosive forces of the marine tidal zone. When 

 tidal fluctuations are allowed to persist, they may increase rather than decrease marsh 

 deterioration and erosion. 



6. In deltaic marshes located away from active distributary outlets, the primary source of 

 sediment is that which is liberated by erosion. Since a high proportion of the near-surface 

 deposits consist of peats and highly organic materials, erosion produces very little mineral 

 material for accretion. 



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