Doctor of Philosophy (PhD)
Civil and Environmental Engineering
Louisiana is facing severe coastal land loss through erosion and inundation, threatening ecosystems that serve as both habitat and protective infrastructure. The Coastal Protection and Restoration Authority (CPRA) and United States Army Corps of Engineers (USACE) have implemented restoration strategies to nourish natural coastal infrastructure using dredged sediment. However, if the geotechnical properties and processes of the projects are not accounted for, the service life and efficacy of these natural infrastructure will be underpredicted. The research objectives addressed in this dissertation are as follows: (1) how does accounting for the combined and dynamic impacts of overwash and consolidation of a nourished headland compare to single force simulations, (2) how do modeling practices of a nourished site predict sediment quantities retained within the site and can they explain potential losses of dredged sediment, and (3) how does the vegetation and soil strength of a nourished wetland establish over time and what technologies can be employed to measure the wetland soil establishment? To address question (1), coupled and uncoupled consolidation and overwash simulations were performed on a recently restored low-lying headland showing that by accounting for both processes, the elevation loss of the dune crest is double that of the individual processes. To address question (2), consolidation modeling was conducted, calibrated with elevation surveys, to determine sediment volume losses attributed to consolidation and drainage via an onsite tidal creek during a beneficial use of dredged sediment nourishment of a wetland. This study found that 63% and 6% of sediment volumes were lost due to the tidal creek and consolidation, respectively. Lastly, to address the final question (3), cone penetrometer tests (CPT) quantified the establishment of wetland soil strength of a site 3.5 years post sediment nourishment and found that the nourished site exhibited weaker shear strength within the vegetated mat when compared to the reference area, suggesting the soil strength of the nourished site is still establishing, while providing a methodology for using CPT as a rapid, accurate means to measure wetland establishment post nourishment. This dissertation provides examples of how wetland surface elevation, dictated by geotechnical properties, serves as a main determinant on the performance of natural infrastructure. Accurately quantifying the existing and expected geotechnical components to better inform elevation predictions is a vital step in planning and implementing a successful natural infrastructure nourishment project, furthering the state of the practice within the field.
Harris, Brian D., "Geotechnical Properties, Design, and Performance of Natural Infrastructure" (2020). LSU Doctoral Dissertations. 5399.
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