Ship Shoal, a shore-parallel sand body, was recently recognized as having a unique physical and biological environment and also as a potential sand resource for coastal restoration in coastal Louisiana. Little is known regarding such dynamics, in concert with fluvial sediments and winter storms, influenced in unique ecosystems, and likely in future potential sand mining. This dissertation addresses such the morphodynamics and sedimentary processes and their implications for the mining from the shoal using field measurements and numerical modeling studies.
During the winter-spring season, fluvial sediment plumes shifted from the prevailing west to southeast during the post-frontal phases, resulted in accumulation of fluid mud on the eastern flank of the shoal and consequent shoal sediment heterogeneity during the spring of 2006; this fluid mud layer strongly interacted with storm waves and currents through the processes of sediment re-suspension, vertical mixing, and hindered settling and redistribution. Studies during winter 2008 represented dynamics dominated by non-cohesive bottom material and hence followed the conventional approaches.
State-of-the-art numerical models for waves, currents and transport provided reasonably well estimation for the study area and showed changes in wave transformation, current variability, and sediment transport for various hypothetical post-dredging scenarios. Sediment re-suspension intensity showed spatial differences along the shoal: high on the western flank of the shoal and a decrease toward the eastern shoal due to the change in shoal bathymetry. The results indicated a favor for the fluid mud accumulation on the eastern flank of the shoal, corroborated by in-situ measurements.
Data suggest that Ship Shoal appears to have recurring sandy and muddy bottoms depending on the amount of storm-induced sediment reworking and fluvially-derived sediments. The fluid mud on the shoal seems to be patchy and does not remain in place as permanently consolidated mud, given the frequency of winter storms and the dispersal shifts. Numerical simulations suggest that targeted small-scale mining would not significantly alter the hydrodynamics and sediment transport over the shoal. Dredging from the eastern flank of the shoal may give rise to lesser impacts than that from the middle and western flank of the shoal. This suggestion is consistent with that from our collaborative biological study.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-01222009-042457 |
| Date | 22 January 2009 |
| Creators | Kobashi, Daijiro |
| Contributors | Masamichi Inoue, S.A. Hsu, Irving Mendelssohn, Michael A. Dunn, Felix Jose, Chunyan Li, Gregory W. Stone |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-01222009-042457/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached herein a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to LSU or its agents the non-exclusive license to archive and make accessible, under the conditions specified below and in appropriate University policies, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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