While navigation canals have a high potential for adverse eco- 

 logical effects, they preempt wetlands, increase saltwater intrusion, 

 unbalance salinity regimes in coastal waters, upset nutrient cycles, 

 and compartmentalize ecosystems. For coastal canals, the net effect 

 of alteration is usually, but not always, adverse to fish and wildlife 

 resources. The particular circumstances of each canal vary so widely 

 that they may generate different sets of effects on fish and wildlife 

 resources. 



Perhaps the most dramatic alterations caused by canal building 

 have been experienced in the oil and gas recovery operations of the 

 Louisiana lowlands and wetlands. In a 5,258 square mile area, bounded 

 by. the Mississippi River and the east levees of the Atchafalaya Floodway 

 and extending to the Gulf, 106 square miles of canals (2 percent of the 

 total area) were built. Oil and gas industries are responsible for 

 nearly 65 percent of the total, drainage canals account for almost 

 21 percent, and navigation canals for over 10 percent [42] (Figure 28). 

 Most of the canal dredging involves access to drilling locations 

 or laying of pipelines. Secondary canals for crude-oil transport 

 barges and production workboats are also common. 



In the Louisiana coastal zone, suction-dredged spoil is typically 

 deposited in small hillocks or mounds in the vicinity of the tail pipe 

 where the slurry is discharged. Sometimes in large jobs it is impounded 

 by dikes. This is done where it is desirable to build an embankment or 

 elevated area for construction, or when the material is to be used as 

 future borrow material [42]. Bucket dredges, which are the Louisiana 

 workhorses, usually leave a continuous embankment of spoil along one or 

 both sides of the canal. Spoil bank dimensions depend on the size of the 

 excavation, the length of the boom, and the stability of the canal and 

 spoil banks [42]. 



In some cases, a dragline is mounted on a marsh buggy (a motorized, 

 tracked vehicle with flotation pontoons) to lay pipelines through the 

 marsh areas by cutting a ditch for floating in the pipe, thus avoiding 

 the need for a full-size canal for a pipeline-laying barge. This type 

 of operation produces smaller canals and far less spoil, but the marsh 

 buggy tracks may have pronounced adverse effects on the marsh surface 

 [42]. 



Through these various canal building activities, the integrity of 

 the natural environment is altered. Land has been lost directly through 

 canal dredging, and natural drainage and tidal circulation have been 

 altered. Erosion rates are increased because of increased length of 

 land-water edge and the increase in the volume of water exchange. 

 Bank erosion caused by wakes of boats is a particular problem. However, 

 the spoil banks become habitat types in themselves. Raised several 

 feet above the surrounding water, they develop high-ground vegetation 

 types. Some that have been in existence for over 20 years have viable 

 stands of oak and other large trees. Their potential use by wildlife 

 and as a recreation base may be high [42], 



122 



