Identifier

etd-07022013-224213

Degree

Master of Science in Civil Engineering (MSCE)

Department

Civil and Environmental Engineering

Document Type

Thesis

Abstract

Louisiana’s saltmarshes, one of the most productive wetlands in the nation, are undergoing severe erosion due to hydrodynamic forces (storm surge) and sea level rise. The erosional behavior of coastal saltmarshes, which possess cohesive sediments as their integral components, are very difficult to analyze and understand. The erosional resistance of cohesive sediments determines the stability and sustainability of coastal wetlands. This erosional resistance is expressed as an erosion threshold or critical shear stress, which depends on various soil properties (e.g. water content, root content, organic matter content, and pore water salinity) affecting saltmarsh erodibility integratively. A cohesive strength meter was deployed to measure the critical shear stress in Bay Jimmy (Barataria Bay), an oil spill site, and Terrebonne Bay, a normal saltmarsh. Results show that erosion threshold is positively correlated with organic matter and root contents. In fact, both roots and organic matters assist with the aggregation of mineral particles through bridging effect. However, when the organic matter content exceeds 10%, the critical shear stress decreases with organic matter content, as observed for the Terrebonne Bay sediments. The erosion threshold of the sediment surface of Bay Jimmy was found to be less than that of Terrebonne Bay, which may be attributed to the lower pore water salinity and possibly reduced inter particle binding due to residual crude oil retained by the cohesive sediments. However, the higher root content at depth in Bay Jimmy ensured greater stability than that found in Terrebonne Bay. Therefore the possible critical mechanism of erosions in Bay Jimmy and Terrebonne Bay are surface erosion and undercut erosion respectively.

Date

2013

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Zhang, Guoping

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