Key attribute alterations 



The alteration which leads to the most significant impacts on the eco- 

 system is the creation of depressions in the land surface. Although 

 long-term effects on vegetation types may result from changes in water- 

 flow regimes, the areal extent and impact on consumers are minimal. 



Site access by canal and wellsite dredging . 

 1. Activity sequence 



Surveyors enter the marsh by vessel, marsh buggy, or on foot, stake the 

 wellsite location and access route, and leave the area. The pathway may 

 or may not be the most direct one possible. Usually there is no need to 

 clear vegetation, but vegetation may be trampled and crushed in adjacent 

 zones. 



Site location, equipment availability, spoil placement requirements, and 

 economic factors may dictate which type and size of dredge is used in 

 each phase of the operation. If the wellsite is in the distal portion of 

 the marsh, entry may be from bayside toward the marsh. A barge-mounted 

 bucket dredge or a hydraulic dredge is used to cut the channel to the 

 marsh edge. Spoil is placed on both sides of the channel and is usually 

 submergent. Maintenance dredging may eventually lead to subaerial spoil 

 levees or "islands. " 



Once the dredge reaches the marsh proper, the spoil levees will be sub- 

 aerial. If the marsh soils are firm enough to support the weight, a 

 track-mounted bucket dredge may be substituted for a hydraulic or a 

 barge-mounted dredge. Spoil is placed on both sides of the channel and 

 completely around the wellsite in most cases. Canal depths must be about 

 3 m (8-10 ft); typical widths approach 23 m (70 ft); a 10-m (30-ft) berm 

 typically exists between the canal edge and the inside foot of the con- 

 tinuous spoil banks on both sides of the canal. 



Small vessels, crew boats, supply boats, and tugs may move to the dredg- 

 ing site daily. Alternatively, marsh buggies may be used for these 

 various functions. After the wellsite location is dredged (approximately 

 50 to 115 m, or 150 by 350 ft), all equipment moves out of the area. 

 Redredging may be necessary once ewery six months to once e\ery five 

 yr. 



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