4. Key attribute alterations 



The key attribute alterations involve the digging of the borrow pit 

 and disruption of flow patterns within the marsh. The continuous 

 borrow pit provides a drainage pathway such that a significant 

 proportion of the fresh water from upland drainage normal ly contrib- 

 uting to marsh sheetflow could discharge directly to the estuarine 

 system without entering the marsh. In addition, the continuous 

 borrow pit might allow estuarine water from tidal forces to regu- 

 larly intrude into the marsh via the unobstructed drainage pathway. 

 Finally, the presence of the borrow pit allows more regular and 

 frequent mixing of estuarine and fresh water (from upland sources) 

 and more rapid drainage of mixed surface water from the marsh. The 

 area affected may range from the roadway and borrow pit to a much 

 more extensive area if major waterflow patterns are altered. 



Site access by canal and wellsite dredging. 

 1. Activity sequence 



Surveyors enter the marsh by truck, 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. In a brackish marsh, any new 

 canal is usually an extension or branch of an existing canal. 

 Therefore, a barge-mounted bucket dredge or a hydraulic dredge may 

 be used. Alternatively, a track-mounted bucket dredge may be 

 employed. Spoil is placed on both sides of the channel and com- 

 pletely around the wellsite in most cases. Canal depth 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 continuous spoil banks (on both sides of the canal). 



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

 dredging site daily. Alternatively, marsh buggies may be used for 

 these various functions. After the wellsite location is dredged 

 (usually 50 by 115 m, or 150 by 350 ft), all equipment moves out of 

 the area. Redredging may be necessary once every six months to once 

 e^ery five yr. 



214 



