stretch crossing a wildlife refuge. Gaps may be left between the spoil banks 

 for marsh circulation. However, even discontinuous spoil piles can cause 

 severe disruption of waterflow patterns unless carefully planned. In an 

 impact assessment statement concerning canal dredging in the Delta Refuge, the 

 USFWS recommended a final conformation of spoil to be low circular islands (30 

 to 60 m in diameter) separated by 10 to 20 m of water. The material dredged 

 is very fluid and tends to spread out, compacting the marsh soil below. 

 McGinnis et al. (1972) reported that the spoil banks from this operation are 

 typically 0.9 to 1.5 m (3 to 5 ft) high and 15 to 24 m (50 to 85 ft) wide with 

 a 9.1 to 15-m (30 to 50-ft) berm. 



The barge travels the length of the canal, laying the pipe. The opera- 

 tions involved with pipe connection are the same as those described before 

 except that no flotation devices are applied; the pipe is laid directly off 

 the barge. 



Many land owners require plugging the wide canal. Significant erosion 

 problems from boat traffic and water movement can occur if the canal is left 

 unplugged. Saltwater intrusion or major alterations in marsh drainage patterns 

 result from unplugged pipeline canals. The methods for plugging are essentially 

 the same as described before. When a wide flotation canal intersects a naviga- 

 tion canal or open-water areas, even greater strengthening of the plug is 

 required. Often concrete riprap or slabs are used to control erosion. On 

 major navigation channels, small wave diversion islands are sometimes placed 

 in front of the plug to help dissipate wave energy from passing vessels. 



In open waters, the pipeline laying technique is Mery similar to the 

 flotation method. In shallow areas, the bottom may be dredged for passage of 

 the barge and for pipe placement. When the water is deep enough for barge 

 passage, a jetting technique is sometimes used to bury the pipe, using a lay 

 barge and a jet barge. The pipe sections are assembled and laid directly on 

 the bottom by the lay barge. Then a jet barge follows the submerged pipe and 

 pumps high-velocity water immediately around and under the pipe, and the pipe 

 settles into the resulting trench; the suspended sediment falls back to the 

 bottom, partially settling in the trench. Burial by jetting may disturb an 

 area 9 m (30 ft) wide (True et al . , 1977), but there are no long piles of 

 spoil. Suspended sediments may contribute to increased water turbidity of the 

 surrounding area. The extent is dependent on water velocity, particle size, 

 and bottom morphology. Hellier and Kornicker (1962) found fine sediment 

 deposition between 0.8 and 1.6 km (0.5 and 1 mi) downstream from a dredging 

 operation. 



River and stream crossings. Over small streams that are nonnavi gable, 

 the pipe may be bent up so that it emerges from the ground along the stream 

 bank. The pipe itself may cross the stream above the water level. Usually 

 the crossing is braced so that supports can take the strains of floods or col- 

 1 isions. 



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