Now, we know that both the longshore movement of sediment and the general absence of sand-sized sediment is the principal cause of the islands' instability. The sediments underlying coastal Louisiana are made up mostly of silts and muds which do not contribute to the building of beaches, dunes, and spits-geomorphic features associated with healthy barrier islands. In addition, long-shore currents redistribute the available sand from headland areas to embayments, depriving shorelines of much needed sand. Seafloor change along the Louisiana barrier island coast from the 1930's to the 1980's shows historical patterns of seafloor erosion and accretion. This information, collected as part of the USGS's Louisiana Barrier Island Erosion Study, was instrumental in altering our understanding of the factors responsible for rapid shoreline retreat in the area.
USGS studies aid environmental managers in decisionmaking for erosion mitigation.
Experience suggests that the most cost-effective means for the preservation of Louisiana's barrier islands may be to renourish them while permitting their landward migration. Placement of hard, fixed structures appears to be a less effective strategy for preserving barrier islands in the face of historically high rates of shoreline and bathymetric change. On East Island of the Isles Dernieres chain, appropriate placement of sediment helped to preserve the island even as Hurricane Andrew passed over it. Any proposal to renourish barrier islands will need to consider where the necessary materials will be found and how naturally-occurring processes will affect the materials. Results of USGS studies are critical to managers charged with making optimal use of limited funds for erosion mitigation.