The summer and winter sedimentation dominance has been related to storm events 

 (Baumann 1980). The cyclical and repetitive nature of cold front activity is responsible 

 for the comparatively high winter sedimentation rate. High winds re-entrain sediment in 

 the water column with southeasterly winds preceeding the frontal passage pushing 

 sediment-laden water over the marsh where the sediment is deposited. The reversal to 

 strong northerly winds pushes the water off the marsh and maintains high turbidity levels 

 in the lakes and bays (Cruz-Orozoco 1971) setting the stage for the cycle to be repeated. 



Sedimentation during the summers of 1975-78 was relatively low, but increased 

 dramatically in 1979 due to the large scale redistribution of sediments by Tropical Storm 

 Claudette and Hurricane Bob. Thus, sedimentation rates during the summer can be 

 expected to be normally low, but episodically high depending on tropical storm activity in 

 this area. We expect this would also characterize the fall season, however, no major 

 tropical storm activity occurred over the study area during the fall during the 

 examination period. 



Perhaps the most striking aspect is the lack of sedimentation during the spring 

 when the Mississippi River is in flood and carries peak sediment loads. Even the flood of 

 1979, which was the second largest flood since 1950 (U.S. Army Engineer District, New 

 Orleans 1980), did not directly result in substantial sedimentation on the study area 

 marshes. This lack of substantial sedimentation during the spring shows that the 

 Mississippi River is no longer a direct source of sediments to the study area. 



The final aspect addressed in the Barataria example was an attempt to directly link 

 the net sedimentation deficit to land loss rates. By combining the sedimentation and 

 sea-level rise data with marsh elevation relative to water level data a theoretical land 

 loss rate could be calculated. These calculations, which are outlined in Baumann (1980), 

 indicated that the saline marsh in the lower Barataria Basin should have a maximum life 

 expectancy of nearly a century if current sedimentation rate and sea-level trends 

 continue in the future. 



Actual land loss rates (Adams et al. 1978) indicate that maximum life expectancy is 

 much less even after considering the direct and intentional loss of marshes via man's 

 activities. This suggests that additional factors are also contributing to the land loss 

 problem in the lower Barataria basin. 



Calcasieu Site 



Both '-^'Cs profile distributions and the artificial marker techniques showed that 

 the East Cove marsh has been aggrading at an average rate of 0.7 cm/yr. Sampling 

 was not designed to compare streamside with inland accretion. The lower rate of 

 accretion at the Calcasieu site in comparison to the Barataria site was expected due to 

 the previously discussed regional differences in sediment supply and subsidence potential. 



The accretion rate of 0.7 cm/yr is not sufficient to maintain the elevation of the 

 marsh with respect to water level. Apparent sea-level rise as measured at the nearby 

 Cameron tide gauge has averaged 1.2 cm/yr from 1954-80 (Figure 5). Thus, apparent sea 

 level has been rising at nearly twice the rate of marsh aggradation during the past 

 quarter-century. 



