120 -\ 



E 



X 



I- 

 o 



< 



o 



80- 



40- 



SOUTHWESTERN LOUISIANA CANAL 



1880 



1900 



1950 



— I r 



1980 



DATE 



Figure 5. Relationship between canal width and age in the Southwestern 

 Louisiana Canal, Lafourche Parish, La. See Table 5 for raw data. 



Analysis of the Rockefeller Refuge canals showed that although canals widened 

 linearly, the rate of increase and the zero age-intercept in the Humble canals were 

 different (P < 0.05) from those in the Deep Lake-Constance Bayou canals (Figures 3 and 

 4). In the Humble canal system, canals widened at 1.018 m/yr and 82.4% of the variation 

 in canal width was explained by canal age, while in the Deep Lake-Constance Bayou 

 system the canal widening rate was 0.704 m/yr and 78.5% of canal width variation was 

 explained by canal age. Widening rates for the Southwestern Louisiana Canal (Table 5 

 and Figure 5) were much higher than those for the Rockefeller Refuge canals (15 m/yr), 

 and are increasing through time. 



The amount of boat traffic greatly influenced the erosion rate in the Leeville oil 

 field. Well-access canals (Table 2) widened faster when connected to major navigation 

 waterways (2.25 m/yr) than when connected to less traveled oil field navigation canals 

 (1.12 m/yr) or to nonmajor canals well removed from boat wake exposure (0.95 m/yr) 

 (Table 4). When canals were widened for well access (Table 2) the width of the widened 

 recess was not influenced by boat traffic density (Table 4, SMNC vs. SNMC). 



DISCUSSION 



The newly dredged canals examined in this study were an average of 13 m wider 

 than the widths specified on permit applications. In no case were they narrower. This 

 was expected, since the width indicated in the permit request is the minimum width at 

 the bottom of the canal. Canal side slopes are typically about 3:1, depending on the 

 solidity of the substrate, so that the surface width is greater than the permitted width. 

 Berms are encouraged because, although they expand the total impact width, they also 

 prevent spoil from backwashing and shoaling the canal, which would then require 



67 



