Draglines or jetting barges are necessary for the burying proce- 

 dures. Placement of supports for elevated flowlines is accomplished 

 by marsh buggy and by hand operations. 



Overhead electrical lines typically parallel existing access corri- 

 dors and require 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 in diameter (8 to 60 

 inches) requires a more complex series of activities. Lines are 

 buried using either the push method or flotation method. Both 

 methods require a survey crew to partially clear and stake an align- 

 ment which typically follows the shortest straight-line route 

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



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 crews and 

 excavates a ditch 2 m (6 ft) deep and 3 m (10 ft) wide. Spoil is 

 piled continuously along one or both sides. A specialized station- 

 ary 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 waterwill remain above the pipe. The ditch may be left 

 open but is more frequently backfilled by the dragline. If backfill- 

 ing 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 water flow down the ditch. Traversing 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 terres- 

 trial 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 placement. Spoil is placed along each side of 

 the canal, generally 10 to 15 m (30 to 40 ft) away from the edge. 

 Gaps in the spoil levees may or may not be provided. Levee dimen- 

 sions depend upon canal width and depth (which determine the quan- 

 tity of spoil) and spoil stability. A levee may be 1 to 2 m (3 to 

 5 ft) high and have a base width of 17 to 28 m (50 to 85 ft). The 



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