Doctoral Dissertation Research: Geomorphology and Sediment Dynamics of a Tropical Montane River

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This doctoral dissertation research project will examine bedload sediment transport of tropical montane rivers and estimate the potential impact of predicted climate change and dam development scenarios on their geomorphology. Tropical montane rivers are geomorphically dynamic and complex. They convey large-magnitude floods with the capacity to mobilize coarse bedload (gravels to large boulders) multiple times during a single rainy season. This doctoral dissertation research project will examine bedload distribution and flux, which play an important role in defining channel form in these systems and therefore are a proxy of system sensitivity. The doctoral student will pursue answers to the following research questions through an analysis of the Rio Pacuare, Costa Rica: (1) How does channel geomorphology vary going downstream in relation to local geology and sediment sources? (2) What are the sediment transport rates and annual yields of each reach? (3) Does downstream flux of bedload express local, reach, or system-wide geomorphic connectivity? (4) How will sediment flux change in response to predicted future climate change and impoundment (dam) scenarios? The Rio Pacuare is an appropriate stream for these kinds of analyses because it is free-flowing, relatively accessible, and is representative of other tropical montane rivers. The student will use innovative field techniques to map and characterize sediment and to create reach-scale sediment budgets. In addition to traditional survey methods, the Structure from Motion approach, which derives topographic data from multiple photographs, will be adapted for grain-size analysis and identification of grain mobilization to validate sediment transport estimates. Hydraulic and sediment transport models will quantify sediment flux to characterize system sensitivity to projected climate change and impoundment scenarios. Research on tropical rivers is particularly important because demands on their resources (freshwater supply, hydroelectricity, ecology, and agriculture) continue to increase steadily, but relatively little research has been done on the geomorphology of these systems. The distinctive mix of field and remote sensing techniques used in this research will overcome some of the noted challenges of tropical river research, including difficult access, high sediment flux, rapidly fluctuating flows, and large-grain mobilization. Beyond expanding basic understanding of the dynamics of fluvial geomorphology, and especially the dynamics of tropical river morphology, this project may assist in the sustainable development, management, and conservation of tropical rivers by offering fundamental information that is usable by the public, scientists, resource managers, and policy makers. As a Doctoral Dissertation Research Improvement award, this project will provide support to enable a promising student to establish an independent research career.