We first examine the relationship between proposed canal widths specified in 

 dredging permit applications (permitted width) and the actual wetland affected— that .o, 

 dredged or covered with spoil material. Secondly, we document the widening of canals 

 that occurs through time as their banks erode, through case studies of three old canal 

 systems. Finally, we show that boat traffic has a significant effect on the widening rate. 



METHODS 



Permit files of the U.S. Army Corps of Engineers, New Orleans District, (USACE- 

 NOD), provided a source of canal dimensions authorized in dredging permits. Oil and gas 

 well-access canals in Terrebonne and Cameron parishes, Louisiana, and the Louisiana 

 Offshore Oil Port (LOOP) pipeline system from the Southwest Louisiana Canal near 

 Leeville north to the Clovelly saltdome were evaluated. Criteria used for choosing 

 particular canals were accessibility, recent construction (within two years), and the 

 vegetation traversed. Table I summarizes canal locations, habitats, and approximate 

 construction dates. 



Site visits were made to LOOP on 25 July 1979 and from 6 to 8 August 1979; to 

 Terrebonne Parish from 31 August 1979 to 3 September 1979; and to Cameron Parish 

 from 24 to 26 September 1979. Canal widths and elevations were measured with a Lietz 

 self-leveling level equipped with top and bottom stadia hairs, and a 3.7 m stadia rod with 

 0.1 cm graduations. Measurement locations on the LOOP pipeline were randomly 

 selected. At each well-access channel, two transects were sighted perpendicularly near 

 the well head and in the access channel. 



The widths of spoil, berm, and canal were estimated. From these measurements 

 the total width modified by the construction and the actual canal width were 

 calculated. Canal depth and, where possible, canal length were measured. 



Simple linear regressions were used to relate permitted canal width to the 

 corresponding actual canal width and to the total impact width (width of both spoil banks 

 and the canal). In addition, paired t-tests were used to determine if permitted berm 

 widths, berm depths, canal widths, canal lengths, and well head slip lengths were 

 significantly different from the actual dimensions measured in the field. 



Evalutations were made of the widening rates of three canal systems: old oil field 

 navigation canals on the Rockefeller Wildlife Refuge at Grand Cheniere, Louisiana; the 

 Southwestern Louisiana Canal which connects Caminada Bay and Little Lake in southern 

 Lafourche Parish, Louisiana; and the Leeville oil field canals surrounding Leeville, 

 Louisiana. 



Using data from Nichols (1961) on selected sites in the Rockefeller Wildlife Refuge, 

 we ascertained the initial canal widths at the time of construction. Nicholls also 

 provided the canal widths as measured in May 1958 and again in March 1961. On 26 

 September 1979 we remeasured the canals at the same locations. 



An historical evaluation of the width of the Southwestern Louisiana Canal was 

 made by Doiron and Whitehurst (1974), using the original construction date and width, 

 aerial imagery made, and field measurements made in 1979. We updated these 

 measurements from Environmental Protection Agency (EPA) infared photographs made in 

 October 1978, scaled to 1:24,000 with a Bausch and Lomb Zoom Transfer Scope. 



61 



