Hurricane Impact Analysis of a Louisiana Shallow Coastal Bay Bottom and Its Shallow Subsurface Geology

Angelina M. Freeman¹, Harry H. Roberts¹, and Patrick D. Banks^2
1 Coastal Studies Institute, Department of Oceanic and Coastal Sciences, Louisiana State University, Baton Rouge, Louisiana 70803
² Louisiana Department of Wildlife and Fisheries, P.O. Box 98000, Baton Rouge, Louisiana 70898

Using high-resolution acoustics, the bay bottom and shallow subsurface in Sister Lake (Terrebonne Basin) of coastal Louisiana’s deltaic plain was imaged pre- and post-hurricanes Katrina and Rita to assess the effects of these storms. The first acoustic survey was conducted in May 2005; high-resolution side-scan, chirp sonar subbottom, and echo sounder profile data were collected simultaneously for the entire bay bottom. The post-hurricanes survey was conducted in October 2005 after both hurricanes Katrina and Rita impacted the area, and included acoustic resurveying of corridors of data covering all major sectors of the lake to evaluate areas of sedimentation and erosion. Box cores were collected in critical areas of Sister Lake to further evaluate the addition or erosion of sediment over the short storm period between surveys. Standardized analysis procedures are developed to characterize the bay bottom and shallow subsurface and assess storm effects. Differences in side-scan reflectance between pre- and post-storm periods were observed, suggesting regions of both sedimentation and erosion. The chirp sonar subbottom data show regions of onlapping sedimentation in the post-storms survey, as well as zones of scour. X-ray radiographs of the box cores show clear increments of sediment 0.4-1.2 in (1.0-3.0 cm) in thickness associated with the storm period, corroborated with radionuclide dating. In addition to storm impacts, this study provides baseline data for habitat characterization, and analysis procedures for understanding Louisiana’s data-poor coastal bays.

AAPG Search and Discover Article #90069©2007 GCAGS 57th Annual Convention, Corpus Christi, Texas