deep is necessary to provide access for the pipe-laying equipment. A 

 smaller, deeper ditch is dredged within the canal for actual line place- 

 ment. Spoil is placed along each side of the canal, generally 10 to 15 m 

 (30 to 50 ft) away from the edge. Gaps in the spoil levees may or may 

 not be provided. Levee dimensions depend upon canal width and depth 

 (which determine the quantity of spoil) and spoil stability; a levee may 

 be 1 to 2 m (3 to 5 ft) high and possess a base width of 17 to 28 m 

 (50 to 85 ft). Under certain site conditions, spoil disposal may be 

 entirely subaqueous, with e\ery little, if any, material becoming exposed. 

 The pipe is assembled on and laid by a floating barge which travels the 

 length of the line. In order to prevent drainage, erosion, impounding, 

 and navigation traffic, earthen plugs, dams, riprap, or bulkheads may be 

 required wherever a canal intersects another waterway. Whenever open 

 water is traversed, the same equipment is used, although only a trench 

 will be dredged. If a hydraulic dredge is used, spoils may be pumped to 

 nearby land, dispersed over the adjacent area, or piled up in a spoil 

 island. Normally, flotation canals are not backfilled due to the large 

 size. Straight open-water canals flanked by low spoil levees are the 

 firwl product of the flotation method. 



Inland marsh sites too small or shallow to facilitate use of barge- 

 mounted dredges may require the use of a tracked dragline moving over 

 wooden mats or a marsh-buggy dragline. A marsh buggy dragline consists 

 of a dragline mounted on a marsh buggy carriage smilar to that used to 

 carry seismic equipment. It is a motorized tracked vehicle equipped with 

 large flotation pontoons. A ditch is cut for floating in the pipe, 

 eliminating the necessity for dredging a full-scale canal to accommodate 

 a pipeline-laying barge. While this type of operation produces far less 

 spoil, marsh buggy tracks often may cause changes in the marsh topography. 



Once pipelines are pressure checked and operating, they are periodically 

 inspected for leaks; boats, marsh buggies, or aircraft may be employed. 

 The equipment utilized and traffic frequency depends on the nature of the 

 pipeline, its size, and the local marsh conditions. 



2. Primary ecological alterations 



2.1 Partial vegetation loss within line easement due to trampling and 

 crushing effects of construction machinery 



2.2 Complete loss of vegetation within a canal zone 10 to 100 m (30 to 

 300 ft) wide and on disjunct spoil disposal areas 



2.3 Partial or complete removal of consumer groups, depending on the type 

 of the line and placement methodology utilized 



279 



