Impacts of Winter Storms on Sediment Transport Within the Terrebonne Bay Marsh Complex

Murray, Stephen P.; Walker, Nan D.; Adams, Charles E.; ,

Impacts of Winter Storms on Sediment Transport Within the Terrebonne Bay Marsh Complex

by Stephen P. Murray, Louisiana State Univ, Baton Rouge, United States,
Nan D. Walker, Louisiana State Univ, Baton Rouge, United States,
Charles E. Adams, Jr., Louisiana State Univ, Baton Rouge, United States,

Document Type: Proceeding Paper

Part of: Coastlines of the Gulf of Mexico

Abstract:

Winter storms provide important controls on erosion and deposition in coastal Louisiana. An unanswered question of the Louisiana land loss problem is how these storms impact sediment flux within the numerous marsh-bay systems. In an attempt to improve our knowledge in this area, a major data collection exercise was launched during the 1990, 1991 and 1992 winter seasons. This paper discusses the results of two field experiments in the Bayou Chitigue/Lake Barre region, where deteriorating marshland is connected, via a major bayou, to an embayment of Terrebonne Bay. Four sites were instrumented with electromagnetic current meters and Downing OBS^tm nephelometers for measuring suspended sediment. During the first experiment in December 1990, sediment was resuspended in the bay by strong winds before, during and after a weak frontal passage, then carried into the bayou by strong flood tidal currents, yielding a net sediment import to the marsh of approx.3.6 ? 10⁶ kg. Computations with a wave-current interaction model confirmed that waves and current present in Lake Barre both prior to and during frontal passage were adequate to resuspend the entire range of sediments found there. During the November 1991 experiment, strong northerly winds from 3 successive winter storms caused erosion and resuspension of sediments in the bayou, which were transported to the bay by strong ebb tidal currents. In contrast to the first experiment, approx.3.8 ? 10⁶ kg of sediment was exported from the marsh environment into the bay. Our results demonstrate that sediment flux events in marsh-coastal bay systems are highly episodic and controlled by complex interactions between wind speed, wind direction and fetch, bathymetry, tidal currents, water level and sediment availability.

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