backfilled. This results in one or two small continuous spoil 

 levees alongside the canal. When small watercourses are crossed 

 with this open-canal method, earthen plugs are placed to prevent 

 water flow down the canal. The pipeline is usually buried under 

 large watercourses (canals, streams, rivers); this burial necessi- 

 tates additional dredging or jetting activities. Bulkheading or 

 riprap is placed at the crossing to prevent erosion; pilings are 

 often necessary. 



If the situation does not allow the push method to be used, the 

 flotation method is employed. This procedure involves dredging a 

 large canal to accommodate the pi Delaying barge. The canal is 

 typically 12 to 15 m (40 to 50 ft) wide and 2 to 3 m (6 to 9 ft) 

 deep; hydraulic or bucket dredges are used. A narrower, deeper 

 ditch is dredged within the wide canal for the actual pipeline 

 placement. Since it is rare to backfill such a large canal, gaps 

 approximately ewery 150 m (450 ft) are left between spoil banks for 

 water circulation. Such spoil deposits are typically 1 to 2 m (3 to 

 6 ft) high and 15 to 30 m (50 to 85 ft) wide with a 10 to 15-m (30 

 to 50-ft) berm. The barge travels the length of the canal, assembling 

 and laying th epipe. Plugs are also used in this method to prevent 

 erosion, saltwater intrusion, or other major alterations to marsh 

 drainage patterns. 



Once they are pressure checked, Installed, and operating, all pipe- 

 lines are periodically inspected for leaks; boats, marsh buggies, or 

 aircraft may be employed. The equipment used and frequency of 

 traffic depends on the kind of pipeline, the size of pipeline, and 

 the marsh conditions. 



2. Primary ecological alterations 



2.1 Trampling and crushing of vegetation along pipeline path 



2.2 Temporary and permanent loss of consumers 



2.3 Loss of vegetation in canal zone, 10 to 100 m (30 to 300 ft) 

 wide 



2.4 Increases in concentrations of suspended sediments and dis- 

 solved nutrients 



2.5 Creation of pathways for increased saltwater inundation (buggy 

 tracks and/or backfilled canals) 



192 



