Overhead electrical lines typically parallel existing access corridors, 

 and placement of lines requires equipment for placing support poles and 

 stringing line. A tractor or backhoe operating from a leveed road or 

 access canal may perform these activities. Holes are dug and poles are 

 placed and anchored. The site is then abandoned. 



Installation of transport lines 20 to 150 cm (8 to 60 inches) in diameter 

 requires a more complex series of activities. Lines are buried in coastal 

 fresh marshes using either the push or flotation method. Both methods 

 require a survey crew to partially clear and stake an alignment (usually 

 a small area) which typically follows the shortest straight-line route 

 between points. Access is provided by marsh buggy or boat. Pipeline 

 installation through inland fresh marshes requires a set of "jery different 

 techniques which are determined by the site characteristics. A barge- 

 mounted hydraulic or bucket dredge may be used in deepwater sites. In 

 shallow-water areas having firm soils, a dragline or marsh buggy dragline 

 is utilized. 



If the push method is utilized, which is normally the case where the 

 marsh substrate is firm enough to support the equipment, a dragline on 

 mats or a buggy-mounted backhoe follows the survey crew and excavates a 

 ditch 2 to 3 m (4 to 6 ft) deep and 3 to 4 m (8 to 10 ft) wide. Spoil is 

 piled continuously along one or both sides. A specialized stationary 

 barge, located in a dredged slip, assembles the pipe sections and pushes 

 the line down the channel; the pipe is supported by floats and guided by 

 a marsh buggy. Once positioned, the line is sunk in place by removing 

 the floats. Typically, approximately one m (four ft) of water will 

 remain above the pipe. The ditch may be left open, but it is more 

 frequently backfilled by the dragline. If backfilling is not performed, 

 an open-water canal bordered by one or two continuous spoil levees 

 remains. Backfilled routes appear as straight shallow depressions due to 

 subsequent spoil shrinkage and subsidence. When small watercourses are 

 crossed, earthen plugs are placed to prevent lateral water flow down the 

 ditch. Traversal of larger water bodies (canals, streams, rivers) 

 requires the use of dredges or jetting equipment. Easement widths range 

 from about 10 to 50 m (30 to 150 ft), depending upon the line size. 



If the flotation method of pipe laying is utilized, which is often the 

 case where the marsh substrate is too unstable to support installation 

 equipment, a barge-mounted bucket or hydraulic dredge excavates the 

 ditch. A canal 12 to 15 m (40 to 50 ft) wide and 2 to 3 m (6 to 9 ft) 

 deep is necessary to provide access for the pipelaying 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 40 ft) away from the canal 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). The pipe is assembled on and laid by the floating barge which 

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

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



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