Monday, October 25, 2021, 12:00PM - 1:00PM
Due to an abundance of natural resources, many of the world's large deltas are densely populated. However, these populations are at risk due to land submergence caused by rising sea-level rates, anthropogenically-enhanced sediment compaction driven by ground fluid extraction, and reduced sediment supply caused by river engineering practices (e.g., damming).
This talk is motivated by a need to promote resiliency of highly coupled human-natural delta systems. Naturally, distributary channels on deltas relocate through a process called avulsion, and this disperses sediment and water along coastlines. Mimicking avulsions with engineered diversions of sediment and water is a tool to nourish drowning deltaic landscape and combat landloss. Land-building as a result of sediment and water diversions has been extensively studied. However, the factors that control the stability of land abandoned by avulsion or diversion are unclear. Throughout this talk, I will evaluate the sediment transport processes that control the growth and decay of deltaic land in order to optimize land-building. The Yellow River (Huanghe) delta of China and the Stikine River delta of Alaska will be used as case studies. Both systems possess high sediment loads which drive rapid delta dynamics, resulting in regular channel migration and abandonment of the subaerial delta surface. Using remote sensing and field data from these systems, I will ask the following questions: 1) how do abandoned deltaic distributary channels evolve in response to cutoff of upstream sediment and water, 2) how is the shoreline stability of abandoned delta lobes impacted by topography, vegetation abundance and distribution, and fresh water supply, 3) how do changes in sediment load impact delta-front sediment transport processes? Broadly, we find that for abandoned delta lobes, shoreline retreat is influenced by vegetation present at the shoreline, marine sediment delivery, and inherited lobe topography. Using bathymetry data, we find that failures can extensively rework the delta-front at the active channel mouth and abandoned delta lobes. These observations inform land loss on deltas globally.
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