THE DEMISE OF THE CHANDELEUR ISLANDS IN SOUTH EASTERN LOUISIANA: NOT YET!

The 2005 impact of hurricane Katrina caused widespread erosion, which resulted in a large-scale reduction in the aerial and subaqueous extent of the northern Chandeleur islands. On the basis of post-storm Lidar data, overhead airborne photography, and satellite imagery, it has been suggested that such a large volume of sediment was removed from this area by the storm that recovery of this important barrier system to even modest pre-storm conditions seemed unlikely. Lidar surveys, as recent as late summer 2006, showed that remnant marsh islands of the system with no fronting sandy shoreline, continued to erode landward as much as several hundred meters well after the 2005 hurricanes. Considering the absence of sand and continued marsh island erosion, many have predicted that the barrier system will soon become entirely subtidal and transformed into a subaqueous sand shoal on the middle continental shelf.

In spite of these dooms-day scenarios, field observations made during early summer 2007 have established that a large volume of sediment is present in the nearshore and offshore zones of the marsh islands and that this sand is being transported onshore by the post-storm wave climate. Ground-based mapping, bathymetric surveying, and grab sampling show island recovery along the northern Chandeleur system because of large, shore-oblique bars that are moving onshore and contributing toward beach recovery, closure of tidal passes and storm breaches, development of spit platforms, and renewed dune formation locally. These observations form the basis for establishing the volume of sand contained in offshore reservoirs, the rate of onshore transport, and fundamental processes of barrier reconstruction following a large tropical cyclone. Considerations such as these will be an important basis for the development of any, even preliminary, efforts to manage the longer term thinning and lateral shrinking of the northern Chandeleur system.