to a marsh also increases the sediment 

 load since rain runoff and river water are 

 both generally quite turbid. Mechanisms 

 that maintain slow, sinuous, shallow 

 natural channels and overland flow will 

 generally also reduce salt intrusion and 

 stabilize water levels. They may also 

 reduce the sediment-carrying capacity of 

 the water, but this has to be balanced 

 against the increased overland flow. 



A number of practices are already 

 being used or are potentially useful to 

 minimize marsh loss (Table 34). They can 

 be grouped as those that build new marshes 

 to replace those lost and those that 

 minimize the loss of existing marshes. 



Day and Craig (1982) assessed the 

 potential for reduction in wetland loss by 

 several mitigation techniques. They 

 concluded that diversion of fresh water to 

 baild new marshes could only create 1-3 

 km^ of marsh a year, and the Atchafalaya 

 had the potential of building about 18 

 km^/yr. The largest potential for saving 

 marshlands (30 - 40 km^/yr), therefore, was 

 by strict regulatory control of new 

 canal s. 



We have little experimental 



experience on which to outline the best 

 canal ing technology. Prohibition against 

 new canals would be the best solution, but 

 prohibition against crossing barrier 

 islands, connecting basin interiors to the 

 periphery, and creating canals that shunt 

 upland runoff around marshes would be 

 partial solutions. 



Directional drilling is a well- 

 established technology that would 

 eliminate the need to dredge canals for 

 many well heads. It has not been used 

 often in the coastal marshes, and good 

 studies comparing the extra cost of 

 directional drilling against the 



environmental cost of the canal are 

 needed. 



Another technology that needs to be 

 explored is the use of air cushion 

 vehicles to traverse the marshes. These 

 are used in the tundra and might provide a 

 way to approach well sites and even 

 transport drilling rigs without damaging 

 the marsh extensively and without the need 

 for canal dredging. 



There are also possibilities for 

 better design of canals. Where possible, 

 they should follow natural channels in 

 order to maintain natural circulation 

 patterns. Spoil deposits are usually 

 placed on both sides of the canal, 

 isolating the canal from the adjacent 

 marsh. Any design that breaks the spoil 

 barrier to allow better exchange with the 

 marsh would probably be an improvenent. 

 Unfortunately, there are no studies upon 

 which to base detailed recommendations. 



It is common practice to require that 

 when canals cross natural streams and 

 other canals, they must be blocked to mini- 

 mize the danger that the new canal will 

 capture the flow of the other channels 

 and/or allow salt intrusion. Some fairly 

 straightforward engineering work is needed 

 to improve the design of these barriers. 

 Earth fill, shell, or rock are usually 

 used. These materials have densities much 

 greater than the organic marsh, and their 

 weight tends to settle and load down the 

 adjacent marsh. As a result, the barriers 

 are constantly breaching, especially at 

 their ends. It would seem that an inert 

 plastic material of the same density as 

 the surrounding marsh, perhaps anchored 

 into place with a mininum number of pil- 

 ings, could be more effective. 



Many canals can be backfilled - cer- 

 tainly all those dredged for pipelines and 

 also many that lead to dry or depleted 

 wells. Yet we know little about the 

 relative value of backfilling compared to 

 open canals. Work in progress (Men- 

 delssohn, Sikora and Turner, Center for 

 Wetland Resources, LSU) points to the 

 effectiveness of backfilling canals 

 because the practice removes spoil banks 

 and also raises the bottom of the canal 

 (although it seldom fills it completely 

 because of the oxidation and dissipation 

 of sediments when they are exposed in 

 spoil banks) to a depth where the water 

 column does not stratify. Oxygen is then 

 available to the sediments, and a healthy 

 benthic infauna can grow. In addition, 

 there is some evidence that these shallow 

 ditches, if left open in areas where marsh 

 circulation is poor, can improve the 

 quality of adjacent marshes. Such 

 research on canals can yield major bene- 

 fits to the State by providing practical 

 means of reducing marsh degradation. 



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