Use by wading and shorebirds may increase or decrease depending upon 

 the suitability of the canal and/or impounded marsh to provide 

 habitat for small fish and invertebrates. If the marsh is impounded 

 and the salinity remains low, desirability of the area may be 

 enhanced for waterfowl. However, if the area becomes drier and 

 develops upland vegetation, it may become less desirable for water- 

 fowl use. The areal increase in favorable habitat is usually less 

 than the decrease resulting from dredging and vehicle movement, 

 unless freshwater is abundant and sound habitat management is pursued. 



Displacement due to activity and noise during construction is short 

 term since dredges may progress at rates or up to 300 m (975 ft) 

 per day. However the area affected may be considerably larger than 

 the excavation or spoil sites themselves. 



Key attribute alterations 



Key attribute alterations induced by this phase of oil and gas oper- 

 ations involve changes in land elevations. Canals and marsh vehicle 

 tracks may allow an increase in frequency and area of inundation by 

 salt water. First-order effects include removal of vegetation and 

 creation of a standing water habitat. If the saltwater flows are 

 not confined by spoil and/or natural topographic features, much 

 larger areas of marsh may be affected. Long-term changes in vegeta- 

 tion and consumer groups would occur. Long-term turbidity increases 

 would also result. 



Canal construction requires spoil placement; this results in higher 

 land elevations. Burial of flora is less significant than possible 

 alterations of waterflow regimes. Poorly planned placement of spoil 

 may result in blockage of existing upland drainage and/or runoff 

 patterns. These blockages will lead to long-standing changes in 

 types and/or amounts of vegetative cover, followed by corresponding 

 changes in consumers. 



Wellsite preparation and operation for leveed marsh-floor locations. 

 1. Activity sequence 



The equipment and techniques utilized during construction of the 

 access road are also employed during preparation of the wellsite. 

 After surveyors have staked the area, the dragline constructs a ring 

 levee around the entire site by utilizing borrow from pits located 

 exterior to the levee. Outside dimensions of the levee are usually 

 less than 120 by 120 m (400 by 400 ft). Initial levee height is 

 about two m (six ft); shrinkage occurs through time. A sump ditch 

 is excavated immediately inside and parallel to the entire levee. 



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