ABSTRACT

Louisiana's rapidly changing land-water interfaces have caused both federal and state support to be focused on various strategies related to coastal restoration. Most promising of these strategies is river diversions, which introduce freshwater and sediment to river-flanking environments (lakes, bays, and associated marshlands). Two river diversions planned by Louisiana Department of Wildlife and Fisheries and U.S. Army Corps of Engineers, known as Caernarvon and Davis Pond, are designed to nourish marshes with freshwater and to a lesser extent sediment as well as to help establish ideal isohalines over historic oyster grounds. Already, pending litigation against the State related to environmental changes associated with the Caenarvon diversion amounts to tens of millions of dollars. For the first time digital high resolution acoustic instrumentation linked to state-of-the-art data acquisition and processing software is available for building a baseline of information that can be used for evaluating future changes of such shallow water bottoms. Application of digital side-scan sonar (100 and 500 kHz) and a broad-spectrum subbottom profiler (4-24 kHz) for rapidly acquiring both surficial and shallow subsurface data (average water depths 0.7 to ~ 3.0 m) has now been accomplished. These data sets "calibrated" with coring, surface sampling, and other "ground truthing" techniques have enormous potential for understanding (a) distributions of bottom sediment types, (b) locations of active and historic oyster reefs and distributions of scattered live oysters and shells, (c) fisheries habitats, (d) areas of active sedimentation and erosion, and (e) shallow subsurface configurations that influence surface conditions. A large scale pilot study verified the utility of linking high resolution acoustic data with various direct sampling techniques.