On occasion, the canal is not backfilled at all. This leaves a small 

 spoil levee alongside the canal. Whether the levee remains or not, there 

 should be periodic circulation breaks in the spoil bank so that the drainage 

 patterns of the marsh are not entirely destroyed. 



The pushing may be done from a land location, or more frequently from a 

 pipeline barge that is located in a slip at the head of the push canal. A 

 channel and slip must be dredged for access of the push-barge. Methods for 

 dredging and orienting this barge are the same as those used in dredging 

 well site slips and canals. 



The sequence of activities to join the pipe sections together is the same 

 as previously described, only taking place on the barge. As each new section 

 is completed, sets of floats, often 55-gallon drums or large pieces of styro- 

 foam, are attached to the pipe and it is pushed into the canal. It is not 

 unusual to have a marsh buggy travel along with the head of the pipe to steer 

 it and keep it clear of the banks. 



When the pipe is completely strung out, floats are removed in sequence 

 and the pipe sinks into the ditch. The floats are retrieved and rafted back 

 to the push-barge or to the new push location. Depending upon the size of the 

 pipe being laid, there may be more than 600 floats per km (1,000 floats per mi) 

 to be retrieved. 



Sometimes a long push pipeline is made by pushing the pipe from the barge 

 in one direction, and then turning the barge around and pushing the pipe in 

 the opposite direction (Petroleum Extension Service, 1972). The same sequence 

 of operations is followed, but this requires less dredging of push-barge slips 

 and canals. 



Backfilling is the preferred method of completing the laying operation 

 because the spoil levee is eliminated, pipe is protected by soil, and the 

 possibility of marsh recovery is maximized. A dragline progresses along the 

 canal, filling it with the spoil. If the surface material was separated from 

 the deeper earth, it will be replaced on top. 



In some places, the canal may cross natural or man-made watercourses that 

 have water flowing through them. Here it is desirable to place a bulkhead or 

 wier across the pipeline canal to block water flow, protect the bank from 

 erosion, prevent marsh drainage or saltwater intrusion, and prohibit boat 

 traffic. This is particularly true where the normal water level is below that 

 of the marsh surface. Where backfilling is not used, pipeline canal plugs or 

 wiers are sometimes used. A wier has an advantage over an earthen plug in 

 that it will allow easy passage of water above prescribed levels and may be 

 adjustable for height. Thus, water levels in the marsh can be controlled. 

 Low wiers are often used where there is occasional tidal influence so that 



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