Title page for ETD etd-11122007-203748


Type of Document Master's Thesis
Author Greene, Michelle
Author's Email Address mgree22@lsu.edu
URN etd-11122007-203748
Title The Anatomy of a Coastal Bay/Lake System
Degree Master of Science (M.S.)
Department Oceanography & Coastal Sciences
Advisory Committee
Advisor Name Title
Harry H. Roberts Committee Chair
Charles Wilson Committee Member
Nan D. Walker Committee Member
Keywords
  • davis pond
  • grain size
  • bathymetry
  • river diversion
  • coastal restoration
  • little lake
  • louisiana
  • geochronology
  • geophysics
  • geology
  • sedimentology
  • hurricane lili
  • sediment accumulation
  • barataria basin
  • x-radiography
  • trawl marks
  • side scan sonar
  • tropical storm isidore
Date of Defense 2007-11-09
Availability unrestricted
Abstract
A comprehensive and integrated approach involving sedimentology, shallow surface geophysics and radio-chemistry was used to understand lakebed sediment dynamics in Little Lake. This methodology attempted to (1) define the morphology and origin of the lake, (2) understand the variability in lake-bottom sediments, (3) assess short-term and long-term sediment accumulation rates, and (4) image lakebed features.

Subbottom chirp, single beam echo sounder, and side scan sonar data were collected to define hydrographic depths, lateral variability in seabed sediment type, lakebed features, and shallow subsurface structure. Sediment samples were taken at representative locations throughout the lake and particle size distributions were determined. Radionuclide dating was performed on selected samples to gain an understanding of lake sediment accumulation rates.

The results indicate the lake formed as a consequence of subsidence and the amalgamation of four sub-basins to form the current lake extent. The distribution of surface sediment is controlled by basin morphology and in situ relic channel/levee deposits. The surface sediment in Little Lake is organic rich clay near tidal channels (from erosion of tidal channel banks), silt near the perimeter of the lake (winnowing by shallow wave action), and sand in the center of the lake (erosion of relic channels).

The shallow surface sediments showed three discernable accumulation layers defined as (1) short-term, < 200 days, Be-7 in the upper few centimeters with a potential riverine source, (2) event deposition, days to weeks, constant excess Pb-210 activity up to 10 cm thick interpreted as a storm deposit (Isidore and Lili, 2002) and (3) long-term, 150 years, excess Pb 210 with classic decay, 1-5 mm/year accumulation rates.

Identified lakebed features include bottom scars, marine pipelines, channels and shell beds. Bottom scars cover approximately 25% of the lake bottom and are preserved in silts and clays whereas sands are mostly devoid of recognizable scars.

This thesis is the first comprehensive study of a coastal lake/bay and represents a baseline dataset for future studies trying to understand the affects of the Davis Pond River Diversion restoration project on lakebed sediment dynamics. Data indicate that the Davis Pond River Diversion has not significantly affected Little Lake.

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