1984). In the Bayou l'Ours area tidal introduction of sediment was prevented by the natural levee 

 ridges, but the marsh thrived. Fresh marshes, even in locations that are remote from overbanlc 

 flooding, are able to maintain themselves through accumulation of organic material and through 

 development of floating mats. 



ABILITY OF THE LIVING SURFACE TO HEAL AND ENDURE 



Since its origin as a subdelta, and during the 250 years that it has remained in the abandoned 

 stage, the Bayou l'Ours area has been periodically subjected to natural transgressive processes. 

 The most active of these destructive processes are subsidence, hurricanes, and animal eat-outs. 



Subsidence rates during modern decades have increased dramatically. Dozier et al. (1983) 

 indicated that subsidence rates for the Barataria Basin from 1945 to 1956 were 0.29 cm/yr. From 

 1956 to 1980 they had increased to 1.27 cm/yr. The 1956-80 rate is more than 7 times the long- 

 term geological rate. 



Using 137 C dating, DeLaune and Smith (1984) determined that the annual rate of peat 

 accumulation in the Barataria Basin averaged 0.85 cm/yr for a freshwater site and 0.95 cm/yr for 

 a brackish site. Their research indicates that peat accumulation at the locales studied has been 

 able to keep pace with accelerated subsidence, which they estimated to be on the order of 0.6 to 

 1.0 cm/yr. 



The stabilizing effect of the natural levee ridges continues as long as they remain unbreached. 

 In some places, ridges have subsided so that they are at or slightly below marsh level, but the 

 firmer soils form a solid substrate. Marsh vegetation is tightly knit over the ridges and the marsh 

 floor is firm. These ridges are often the sites of the most successful invasion by brackish and saline 

 marsh vegetation species. 



During the late 19th and early 20th centuries, several ditches were dug through the marshes 

 from Little Lake to trappers' settlements of the Bayou l'Ours ridges. These were initially hand- 

 dug and only large enough for small skiffs and pirogues. They were too shallow to navigate during 

 low water and were often clogged with vegetation. They were hydrologically inefficient and had 

 little impact on the hydrology or the wetlands they traversed. 



This area has been in the path of severe hurricanes during historic times (1893, 1909, 1915, 

 1947, 1965, 1985, and others) and has been subjected to animal eat-outs from muskrat (Ondatra 

 zibethicus rivalicius) and nutria (Myocastor coypus). As long as the skeletal system of natural levee 

 ridges and firmer marshes of the lake rims remained intact, organic marsh soils stayed in place and 

 the living wetland surface had a remarkable ability to mend itself, to build up and across disturbed 

 areas, and to endure. 



POST-CANAL CONDITIONS 



Beginning in the 1940's, a system of dredged pipeline and drilling rig access canals was 

 superimposed upon the Bayou l'Ours wetlands. These canals allowed rapid drainage of the 

 impounded and semi-impounded hydrologic units. They created avenues of saltwater intrusion 

 and tidal movement into the marshes that altered vegetation and scoured out poorly consolidated 

 sediment. 



37 



