An evaluation of the potential for infilling existing pipeline canals in Louisiana coastal marshes

Abstract

The impact of canals and their dredged-material levees on Louisiana coastal marshes has been assessed in a number of studies. The aerial coverage by canals and associated dredged-material levees has been shown to be approximately 10% of total marsh area in coastal Louisiana, which is about the same coverage as natural channels. In addition to the direct loss of marsh habitat caused by the canals, the indirect effects of dredge material placement in levees has been associated with marsh deterioration. The restoration of productive fisheries habitat by infilling pipeline canals depends upon maximizing the area of shallow water in the canals and restoring as much of the adjacent marsh habitat as possible by removing dredged-material levees. The degree to which the canal can be infilled depends upon the amount of dredged material available and the bathymetry of the canal at the time of backfilling. Geomorphic survey and analysis was used to evaluate the potential result of infilling canals and the type of habitat that may result. Comparison of data for saline and brackish canal segments indicates that for both plugged and unplugged canals, canals in brackish areas have greater potential for infilling than those in saline areas. However, older brackish canals have a greater potential for the creation of shallow water habitat than younger canals, suggesting that changes in canal cross-section may be of greater magnitude than changes in levee material. Our analysis demonstrates that simple survey techniques can be used to indicate the potential efficacy of canal infilling. We recommend that such surveys be used to evaluate both pipeline and abandoned location canals across the Louisiana coastal zone to determine the potential for increased shallow water habitat.