of the lost area must be based on the percentage of intact levee system 

 remaining. 



The most significant impacts of a complete breaching of a levee are often 

 felt by the ecosystems admacent to the levee, rather than by the levee system 

 itself. For a complete discussion of attribute alterations and techniques 

 designed for mitigation of turbidity/erosion problems, see the section on 

 "Installation and maintenance of lines" in this section. The second category 

 includes those cases where the wellsite is located on the spoil deposit and 

 the landform is not completely breached. The following description and dis- 

 cussion are oriented primarily toward this second category. 



1. Activity sequence 



Surveyors enter the area by truck, marsh buggy, or on foot, stake 

 the wellsite location and access route, and leave the area. The 

 pathway is generally the most direct one possible. Usually there is 

 no need to clear vegetation, but vegetation may be trampled and 

 crushed in adjacent zones. 



Site location, equipment availability, spoil placement requirements, 

 and economic factors may dictate which type and size of dredge is 

 used in each phase of the operation. In a levee system, each new 

 canal is usually an extension or branch of an existing canal. There- 

 fore, a barge-mounted bucket dredge or a hydraulic dredge may be used. 

 Alternatively, a track-mounted bucket dredge may be employed. Spoil 

 is placed on both sides of the channel and completely around the well- 

 site in most cases. Canal depth must be about 3 m (8-10 ft); typical 

 widths approach 23 m (70 ft); a 10-m (30-ft) berm typically exists 

 between the canal edge and the inside foot of the continuous fresh 

 spoil banks (on both sides of the canal). 



Small vessels, crew boats, supply boats, and tugs may move to the 

 dredging site daily. Alternatively, marsh buggies may be used for 

 these various functions. After the wellsite location is dredged 

 (usually 50 by 115 m, or 150 by 350 ft), all equipment moves out of 

 the area. Redredging may be necessary once e\/ery six months to once 

 every five yr. 



2. Primary ecological alterations 



2.1 Creation of depressions in land surface by marsh vehicles 



2.2 Loss of vegetation along canal route due to excavation and 

 covering 



299 



