Date of Award
Engineering and Applied Science
Earth and Environmental Sciences
McCorquodale, J. Alex
Barrier islands are widespread and typically enclose landward basins connected to the ocean through tidal inlets. Low energy in the basin enables fine sediment accumulation and salt marsh formation. Sea Level Rise (SLR) causes loss of marshes due to their low elevations and inundation sensitivity. Both long-term trends in sediment supply due to SLR and episodic transfers of sediment due to storms are important to the sustainability of marshes and tidal basins. The trajectory of deltas, including the Mississippi River Delta (MRD), are also impacted by sediment supply. The redistribution of sediments (autogenic reorganization) within transgressive systems will determine their survival under projected SLR regimes (allogenic forcing). In this research, I investigate the processes driving sediment exchange and morphologic evolution on multiple timescales with process-based numerical models.
Chapter 2 focuses on the long-term response of tidal basin systems to SLR. With SLR, hydrodynamics shift to flood- dominant while the ebb-delta expands. Despite the shift to residual sand import, fine sediment continues to be exported. In Chapter 3, net sediment fluxes due to storms at a conceptual basin are analyzed to determine the influence of relative phasing of tides and surges and storm characteristics. In Chapter 4, this work is extended by applying similar storms to a model of Plum Island Sound (PIS) in Massachusetts. Each of these models applies a unique approach to bed sediment partitioning to determine imported sediment provenance. Results show that surge/tidal phasing has a high influence on sediment fluxes. For the conceptual basin, storms were found to generally import sediment, while the influence of SLR on sediment flux depends on surge/tidal phasing. For the PIS model, storms are an important source of sand for the sediment-starved basin, though on net storms are unable to counteract the ebb-dominance that exports muddy sediments. Chapter 5 investigates the efficacy of enhanced sediment supply for land-building sediment diversions in the MRD. Results show that augmenting sand supplied to the delta during low flows is effective in increasing land building. Greater sediment supply encourages more-frequent autogenic reorganization of the distributary channel network, with wider distribution of sediments and greater reworking
Hanegan, Kevin C., "Morphodynamics of transgressive coastal systems: Modeling allogenic and autogenic response to sea level rise, storms, and changes in sediment supply" (2020). University of New Orleans Theses and Dissertations. 2808.