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Evaluation of coastal wave attenuation due to viscous fluid sediment at Jefferson County, Texas
Abstract
This thesis is a two-part discussion concerning a Gulf of Mexico beach in Jefferson County, Texas. The first part involves collecting and analyzing shoreline evolution data for an ongoing Texas A&M University Ocean Engineering Program investigation. Excessive shoreline erosion exists along approximately 27 kilometers of highway in Jefferson County, Texas that has led to the subsequent destruction of State Highway 87. The hydrographic and land surveys conducted throughout the past year have quantified the volume of sand transported on the beach face. The entire survey area is receding except the eastern section where the shoreline has accreted a mean 6 meters during the investigation period. The survey confirmed the central region of the study area is the most severely eroding segment. Beach transect comparisons are presented for the Spring versus Winter walking surveys and for all offshore data. The data provide a baseline to facilitate designing a final roadway alignment for State Highway 87. The paper also investigates a natural 'fluid mud' phenomenon. A viscous seabed exists at the eastern survey area, causing water wave attenuation. The interdependent effects of seafloor mud on progressive surface waves are discussed. The reduction in wave height due to damping is quantified by data collected on a waverunner. It illustrates the wave height differential between the eastern coastline and the middle of the survey region. The thickness of fluid sediment is evaluated with a dual frequency echosounder and collected soil samples. Testing concluded that a dual frequency fathometer is employable in the surf zone, but that low frequency data must be collected in water depths greater than two meters of water. The observed wave data is employed to validate the model simulations. The finite difference model REF/DIF is implemented as a vehicle to simulate two dimensional, dual-layer viscous fluid attenuation. The analytical solution for the two-layer model consists of liquid overlying a denser fluid upon a rigid seafloor. The boundary layer approximation and the shallow water boundary layer approximation are discussed in detail. These two theories are compared for theoretical accuracy against published results for the complete model theory. The boundary layer theory agrees well except for shallow sediment beds because the mud layer becomes too thin for the model assumptions. The boundary layer theory is applied to the Jefferson County eastern seabed to compare with gathered wave data. The thinnest sediment seabed is used, 0.28cm, to satisfy the model assumptions and to simulate the actual site conditions. This is seven centimeters thicker than the value estimated with the echosounder results. This data comparison is the closest match between field conditions and model limitations. The model produces wave attenuation in excess of actual beach conditions. An empirical formula is evaluated for this region and shows good correlation. Damping varies with water depth and wave amplitude. Damping equals approximately ten times the amount of turbulent boundary layer damping associated with the same seabed and no fluid sediment. The model supports the concept that regional wave attenuation is affected more by viscous sediment than bathymetry.
Description
Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references (leaves 68-71).
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Citation
Tuttle, Meghan I (2000). Evaluation of coastal wave attenuation due to viscous fluid sediment at Jefferson County, Texas. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2000 -THESIS -T767.
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