Collaborative Research: Role of lithologic variability in controlling downstream channel response to sediment pulses

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Landslides in mountainous regions produce large volumes of debris that are eroded by rivers and travel downstream to populated lowland areas. The gravel-size components of these landslides can accumulate on the streambed and increase the frequency of flooding in downstream communities. The resultant changes in the rock sizes in the riverbed can alter habitat for fish and insects that live there. Alternatively, if the sediment in the landslide is smaller than sand, it can result in cloudier water that requires costly filtration for drinking water or irrigation and is often harmful to the fish, insects, and other animals living in the river. The downstream effects of different river and landslide sediment characteristics are important as climate change threatens to increase landslides and the amount of sediment moving within affected rivers. This project will determine the degree to which the rock type (density and durability) of the sediment controls the timing and magnitude of sediment accumulation and size composition on the riverbed, with specific attention to those rivers in the volcanic terrain of the Pacific Northwest. The project will introduce new students to the Earth Sciences through short overnight field excursions to participate in the research and share results with regional flood managers.In the Pacific Northwest, a disproportionate number of major mass-wasting events occur in volcanic terrain, producing sediment pulses of variable density and abrasion rate. This project will use field observations and modeling to characterize river channel sensitivity to these large sediment pulses. The research focuses on how the lithologic characteristics of sediment pulses control the timing and magnitude of downstream channel response. This question will be addressed by: quantifying the variability in the sedimentary characteristics of mass-wasting deposits in several basins; modeling the downstream fate of a specific mass-wasting event in a river for which there are good field constraints on downstream abrasion and channel response; and determining the sensitivity of the river system to observed ranges of sediment pulse and channel characteristics using the model, which is based on Lagrangian tracking of individual sediment “parcels” that have unique characteristics such as abrasion rate and density.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.