THE BAYOU L'OURS SUBDELTA 



Distributaries started building into the shallow waters of the gulf, in what is now the Bayou 

 l'Ours area, around A.D. 100 and continued until about A.D. 700 (Weinstein and Gagliano 1985; 

 Figure 2). The streams bifurcated and in some instances rejoined. A complex system of natural 

 levee ridges evolved along the distributaries through overbank sedimentation, forming enclosed and 

 semi-enclosed interdistributary basins. Hardwood forests became established on the ridges, and 

 swamps and marshes formed in intervening areas. 



By about A.D. 700, all of the distributaries except Bayou Lafourche and Bayou l'Ours were cut 

 off from their interconnection with the Mississippi River (Weinstein and Gagliano 1985). However, 

 some progradation continued on Bayou Lafourche until it was blocked from the Mississippi River 

 at Donaldsonville, LA, around the turn of the century. Bayou l'Ours also may have continued to 

 receive limited flow, but the specific date of its cutoff has not been established. 



After being deprived of Mississippi River flow and sediment supply, the channels became clogged 

 and filled. The areas remained in a low energy, very slowly changing condition for approximately 

 250 years until the advent of active canal dredging in the 1940's. During this abandoned phase of 

 the subdelta, the wetlands functioned as an integral part of the Barataria interdistributary basin. 



Environmental conditions which prevailed during this interval have been reconstructed from 

 geological, archaeological, and historic data. Forensic analysis of historic survey records, maps, 

 and aerial photographs has been particularly valuable in understanding changes that have occurred 

 during the past 100 years. 



Reconnaissance surveys conducted during 1731 to 1831 produced several important maps that 

 provide an overall impression of the landforms and configuration of the region. However, it was 

 during 1832 to 1880 that professional surveys (including hydrographic and township and range) were 

 made. The official Division of State Lands surveys of this region began around 1832 at Cutoff, 

 LA, and proceeded south along Bayou Lafourche to the gulf and eastward into the interior basin 

 marshes until this initial effort was completed around 1880. In general, the latter surveys were 

 more detailed than the earlier ones as were surveys of areas that were easy to traverse, such as 

 better-drained natural levee ridges and navigable waterways. Where waterways were meandered 

 (i.e., survey stations plotted), the bayous and lakes were so accurately depicted on these early plates 

 that they can be identified on modern aerial photography. Geographic conditions of the landscape 

 not traversed, such as trembling prairies and non-navigable streams, are either unmarked or 

 roughly sketched on the plats, often with brief comments on the condition of the terrain. 



The features depicted on these surveys assume greater significance when the plats are viewed 

 with a knowledge of survey regulations prevalent at the time. Instructions to deputy surveyors 

 stated that township plats should "exhibit a perfect delineation of the country as represented in 

 the field notes of the survey" (Moore n.d., p. 14). Areas calculated by extrapolation were to be 

 shown as dashed lines. It should also be noted that the principal modes of transportation used by 

 surveyors in this region were small boats. Any water body accessible by skiff could have been 

 surveyed. Government instructions from the Surveyor General included the requirement that 

 navigable water bodies be meandered (i.e., surveyed). 



The surveyors traversed the north-south and east-west boundaries of mile-square sections 

 recording features of the landscape chain-length by chain-length. These remarkable maps, which 



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