attached digging cups. As the wheel turns and removes the dirt, it is 

 placed beside the trench in a continuous mound. Other trenching operations 

 are also available. In most cases the trench is refilled with the soil 

 that had been removed. When pipe has been placed in the hole, more soil 

 may be available than needed and mounds which could alter local hydrology 

 may remain. In organic soil the stockpiled soil may oxidize and there 

 may be insufficient amounts of soil to refill the trench, and a depression 

 may exist after pipeline placement which may divert natural water flow and 

 provide a new route for salt water intrusion. 



For landfalls where the pipeline from offshore intercepts the shore- 

 line, a second method often used is the "pipe-pull" method. A tpench 

 traversing the beach and littoral zone is excavated (including any 

 necessary blasting). After the trench is excavated, sections of pipe are 

 assembled on the lay barge anchored offshore and pulled by winch and cable 

 through the trench toward the shore. 



The third method is the "push-ditch" or "shove" method often used 

 in wetlands. A narrow, relatively shallow ditch is excavated from the 

 bank by a dragline or clamshell digger. The ditch may be 4 to 6 feet deep 

 and 8-10 feet wide. The pipe sections are joined together at the point 

 of origin of the ditch, and the line is given temporary buoyancy by 

 strapped floats and is pushed or shoved down the ditch. After being 

 floated into place, the floats are cut loose and the line allowed to sink 

 to the bottom of the ditch. 



The fourth method of pipe laying utilizes a "floatation canal" to 

 provide access for the pipe-laying equipment. Such a canal may be 40 to 

 50 feet wide and 6 to 8 feet deep, and may have an additional trench in 

 the bottom to provide 10 to 12 feet clearance above the top of the pipe- 

 line. The pipeline is constructed on a series of lay barges and passed 

 over the stern. This type of canal is excavated by a flotation dredge, 

 which normally piles the spoils upon each side to form a low levee. 

 Characteristically, this type of dredging is conducted where the marshes 

 are soft and unstable. 



In the past, levees beside the flotation canal were characteristically 

 continuous with few or no breaks. More recently, after studies have shown 

 the impacts caused, openings are required to be cut in levees in order to 

 minimize disturbances to existing drainage and use patterns. 



Of the four methods of laying pipe (dry land, pipe-pull, push-ditch 

 and flotation), the push-ditch method results in the least amount of 

 disturbance to the terrain and biota, which effect may be further 

 minimized by backfilling and restoration. The push-ditch method causes 

 a loss of approximately one acre per mile of pipeline construction 

 (assuming a trench 8 feet wide) while the flotation method causes an 

 estimated loss of 6 acres per mile of pipeline installed (assuming a 

 trench 50 feet wide) [73]. 



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