The Impact and Mitigation of Man-Made Canals in Coastal Louisiana

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Abstract
Coastal landloss in the sedimentary deltaic plain of southern Louisiana is 0.8% annually and is rising geometrically with time. Landloss is directly correlated with man-made features, particularly canals. The local and indirect effects of canals are modified by the deltaic substrate, distance to the coast, and availability of new sediments. The local impacts are similar to those observed for mosquito ditching along the eastern Atlantic seaboard, even though the canals are typically 10 times larger than mosquito ditches. Some cumulative impacts of land losses are increased saltwater intrusion, loss of the capacity to buffer the impact of storms and fertilizers and diminished fisheries. The mechanism for the role of coastal engineering, particularly canal construction, probably involves an alteration in wetland hydrology, but a more complete understanding is presently lacking. Principles for modifying present canal construction projects are presented and include the rationale for: maintaining natural subsurface and overland waterflow patterns, reducing compaction by spoil banks, backfilling canals no longer needed, and the greater use of existing canal corridors in lieu of new canal construction.

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