flowlines that are laid by hand or with the aid of a lightweight vehicle 

 which moves along the top of the levee. If the levee is extensively 

 traveled by vehicles, the lines may be buried along the roadway. A small 

 trencher or backhoe, moving along the roadway, is used. Levee vegetation 

 is seldom so dense as to require major clearing operations. Digging or 

 mowing operations are sufficient to remove grasses or small woody vegeta- 

 tion. Following line placement, the trench is backfilled, leveled, and 

 abandoned. A section of buried line may be installed in one or two days. 

 Surface lines can be placed at a faster rate. Vegetation recovery is 

 usually completed within one growing season. Pipelines are often put 

 through levees and spoil banks using either the flotation method or the 

 push method. These two common techniques are described in some detail 

 for line installation in the marsh systems. Essentially, the flotation 

 technique involves having a floating dredge bore a wide gap (up to 15 m, 

 or 50 ft, wide) through a levee as it places the pipeline. The push 

 method involves having a dragline, either track-mounted or marsh-buggy 

 mounted, excavate a narrow ditch through the levee for subsequent line 

 installation. The ditch is usually completely backfilled when the push 

 method is employed. However, in the case of the flotation method, the 

 opening may be left as is; \:]ay be dammed by wood, steel, or earthen 

 plugs; or the entire ditch may be backfilled and plugged with an effort 

 made to restore the original elevation of the spoil bank or levee at that 

 point. The push n;ethod seems to be more frequently utilized. 



If earthen plugs are required, extra fill material is typically acquired 

 from nearby narsh sediments. Water erosion, slumping, and subsidence may 

 require periodic maintenance and repair of such plugs to maintain the 

 plug at its initial height and thickness. Plugs may also be constructed 

 of steel, alumninum, creosoted wood, concrete, or shell which stabilized 

 reworked levee sites more efficiently. 



2. Primary ecological alterations 



2.1 Complete or partial vegetation removal, depending on line type (sur- 

 face flowline, buried pipeline) being installed 



2.2 Partial or complete removal of consumer groups, depending on line 

 type and installation technique 



2.3 Loss of soil structure within easement due to construction activi- 

 ties 



2.4 Introduction of toxic chemicals from line leakage and construction 

 activities 



2.5 Sediment transport 



304 



