One canal has been chosen to illustrate the processes (Figure 6). A major north-south cut 

 through the ridge system was created by a pipeline canal dredged in 1956. The canal originated 

 in Lake Enfermer, which was tidally interconnected to Caminada Bay. There were no weirs or 

 dams placed across the canal to block the flow of water. The canal cut through three separate 

 natural levee ridges and created an avenue of tidal movement into the naturally impounded fresh 

 marshes lying between the ridges (Figure 7a). The 1987 photograph in Figure 7a shows the place 

 where the pipeline canal cuts through the natural levee ridges of the West Fork of Bayou l'Ours. 

 Note the three dead oak trees marking the crest of the natural levee ridge. The linear feature 

 trailing off to the background is an old trappers' ditch dug in the 1920's. This ditch originally had 

 a cross-sectional area of less than 1 m 2 . In contrast, the cross-sectional area of the canal, which 

 was typical of a new canal network, was more than 100 times the cross-sectional area of the 

 trappers' ditch. Unlike the shallow trappers' ditches, this deep canal completely altered the 

 hydrologic regime of the area (Figure 7b). 



An aerial photo taken in 1945, before any of the canals were dredged, shows well-defined, 

 natural levee ridges with relict channel remnants and largely unbroken marsh with a few small 

 ponds (Figure 8a). This is, in part, a floating marsh and, in part, a marsh rooted in and anchored 

 to the natural levee ridges. When mapped on a small scale map by O'Neil in the 1940's, this was 

 classified as a brackish, three-cornered grass marsh. However, early aerial photographs from the 

 1940's and 1956 clearly indicate fresh-to-intermediate vegetation in the portions of these 

 interdistributary basins and high concentrations of muskrats, as evidenced by their mounds. 



An aerial photo taken in 1959 shows the newly cut canal (Figure 8b). It was dug with a dragline 

 and was originally 21 m wide and 24 cm deep. Spoil was placed in a staggered, discontinuous 

 pattern along each side of the canal. Spoil mounds were approximately 150 m long. The canal 

 formed a continuous connection with the upper reaches of Caminada Bay. The dark pattern on 

 this photo is largely the result of a marsh burn. The marsh had been burned as a form of 

 management to enhance the growth of three-corner grass, which is favored by muskrats. 



Aerial photographs show that by 1970 small marsh ponds had become interconnected and a 

 tidal drainage network was developing (Figure 8c). The tidal network extended outward from the 

 canal into the marshes. It was probably formed through enlargement of animal trails between the 

 various ponds. Relict sections of the distributary channels had become exhumed and reactivated 

 where they were crossed by the canal. They were also interconnected with the marsh ponds. This 

 area was mapped as brackish marsh by Chabreck et al. in 1968. 



A photograph taken in 1982 shows that the tidal system had expanded and the marsh ponds 

 had enlarged (Figure 8d). Not only had the vegetation died back, but active tidal scouring had 

 occurred, removing the organic substrate. In their 1978 survey of the coastal marshes Chabreck 

 and Linscombe (1978) mapped this area as salt marsh. 



Field inspection in 1987 indicated that the marsh was in very poor condition. It had a mottled 

 appearance on current aerial photographs. There had been extensive die-back and the ponds had 

 enlarged considerably. 



Even after marsh die-back, the organic substrate remains as mud flats until it is scoured by the 

 tides. Water depths in the scour areas near the channel were found to be 1.5 m. Widespread 

 scouring to a depth of about 1 m was found in most of the open water areas, and most of the peat 

 and organic material had been removed. 



38 



