the marsh surface itself. It is usual to place the excavated spoil on both 

 sides of the channel, though land owners and/or permitting agencies may specify 

 modifications. Erosion from boat traffic is always a problem in the access 

 canals. Ensminger (1963) notes that dredged canals often widen, doubling in 

 width in five yr. Many dredge operators leave 9 m (30 ft) or more of berm, 

 the area between the edge of the dredged channel and the spoil pile, so that in 

 the short term, erosion occurs on the unexcavated marsh soil rather than on the 

 spoil pile. Nichols (1959) notes that the condition of the marsh surface 

 should really dictate what kind of bucket dredge is used. 



Conner et al. (1976) described the shrinkage, compaction, and water loss 

 of spoil banks. In highly organic soils, structural problems can occur in the 

 marsh foundation if spoil is heaped too high. The solid spoil bank may impede 

 local marsh drainage. Thus, some surface owners require periodic breaks in the 

 levee for drainage purposes. In areas with particularly small tidal amplitudes, 

 the height of the spoil banks is restricted so that marsh areas behind the 

 levee will be periodically flooded during times of high water. 



Other spoil disposal techniques are occasionally used. The "broadcast 

 method" refers to any procedure that distributes the spoil over a wide area. 

 This can be accomplished by mechanical or hydraulic dredges. When hydraulic 

 dredges are used, the spoil may be directed away from the immediate vicinity 

 through the long slurry pipes. On occasion, a hopper barge could be employed, 

 though this is expensive and rare. 



Contractors doing the dredging prefer to place the spoil in the most 

 convenient area possible. There are physical limits to the distance away from 

 the channel a bucket dredge can place spoil. Likewise, there are cost limits 

 to the distance hydraulic dredge spoil may be pumped. According to some esti- 

 mates, each extra mile of pumping increases the cost by an amount equal to the 

 base cost (Belaire and Alexander, 1976). However, if definite spaces between 

 spoil piles or the discontinuous borrow pits are within equipment capability, 

 and definite plans are available for the dredging contractor, cost increases 

 are minor. 



Most dredgers prefer to place spoil directly on top of old spoil piles or 

 areas without special surface preparation. If spoil is placed directly on top 

 of marsh vegetation, the matted stems, leaves, and roots can provide a more 

 porous zone within the pile through which water may pass. Thus, to create 

 levees relatively impermeable to water movement, it is sometimes desirable to 

 remove surface vegetation and even part of the root zone, and then fill the 

 area with spoil. This introduces considerably more work and expense, however. 



Bucket dredges progress up a new channel, generally placing spoil on both 

 sides. Very large dredges may work 24 hr a day, though smaller ones work 

 mostly during daylight. There may be a number of small vessels moving back and 

 forth, including crew and supply boats as well as small tugs. The dredges work 



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