Semester of Graduation

Summer

Degree

Master of Oceanography and Coastal Sciences (SOCS)

Department

Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Coastal river deltas possess substantial socioeconomic and ecological importance and are expected to encounter increasing risks because of global climate change. The long-term sustainability of many deltaic systems is at risk due to a mix of natural and human-induced factors. Deltas are characterized by their continuous reconfiguration of channels and floodplains due to allogenic and autogenic processes. Sediment supply and composition, sea level rise, vegetation, river discharge, and human development may affect the morphological evolution of river deltas. The timescales and patterns of hydrological transport within a river delta are important indicators of ecological function. One such metric, the water residence time, quantifies how long water takes to flow through a system, which should be modulated by morphology. However, there is no systematic investigation of how the factors controlling the morphology of a delta influence short-term hydrological transport time. Thus, this research aims to understand how different input sand fractions, sea level rise rates, and vegetation affect water residence times in river deltas. This research used pyDeltaRCM, a reduced-complexity hydro-morphodynamic model, to analyze water transport timescales during morphological changes of river deltas over 150 years. Stochastic parcel-based cellular routing algorithms model water and sediment movement in the pyDeltaRCM model, which applies phenomenological criteria to accurately reflect sediment deposition and erosion. Under each set of boundary conditions, delta morphologies, and flow fields were generated across five realizations to account for the inherent stochasticity in the pyDeltaRCM modeling scheme. Delta shorelines were delineated and a Lagrangian particle tracking strategy was used to measure the residence time distribution. This study expected that greater sea level rise rates and input sand fractions dominate water residence times while vegetation has significant effects on system scale water residence time in low to moderate input sand fractions and lower sea level rise realizations. Results indicate that input sand fraction and rate of sea level rise hold inverse relationships with system-scale residence time as varying delta sizes result in different transport distances under different rates of sea level rise. The relationship between the presence of vegetation and water residence time is secondary and acts to both increase and decrease residence times across the model run. This thesis holds implications for understanding the impacts of various forcing mechanisms on the hydrology of deltas formed naturally and through river diversions in the face of climate change.

Date

7-15-2024

Committee Chair

Hiatt, Matthew.

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Available for download on Tuesday, July 15, 2025

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