Project Abstract Broad Explanation. In order to better understand deposition, retention, and evacuation mechanisms and the sediment budget in valleys strongly affected by debris-flow deposition, the proposed research will characterize volumes, ages, and sedimentology of sediment storage and their relationships to contributing drainage basin and local valley characteristics in headwater streams of the Oregon Coast Range. This project will address a key interface in the source-to-sink flow of sediment off landscapes. An important goal in modern geomorphology is to determine the first-order rate laws that govern fluxes in geomorphic systems, and this projectl specifically addresses this issue. To reach an informed compromise in mountainous areas between exploitation and conservation, it is vital to understand the natural mechanisms mediating downstream effects of episodic disturbances such as forest fires and associated debris flows. The research will contribute to the scientific and political debate around forest practices and habitat in the Pacific Northwest and elsewhere by elucidating the downstream attenuation of debris-flow-derived sediment pulses and presenting that information to managers and policy-makers.
What are the mechanisms, rates, and volumes of sediment deposition, retention, and evacuation in mountain streams, and how do these mechanisms, rates, and volumes change downstream? How are they related? How are they affected by climate change? Investigations will encompass streams at varying positions along the transition between debris-flow and fluvial processes, from valleys where both debris-flow scour and deposition are important, through valleys where debris-flow scour appears unimportant but debris-flow deposits predominate, to valleys where debris-flow deposition from tributaries merely punctuates otherwise fluvial deposits. Specific research activities will include (1) mapping and measurement of sediment volumes throughout headwater networks with airborne laser swath mapping (ALSM) and ground-based mapping and testing of the method with ground-based surveying; (2) characterization and mapping of deposit sedimentology and stratigraphy, deposit radiocarbon age distributions, and strath terraces to elucidate retention and evacuation mechanisms, evacuation times, and changes due to climate change; and (3) analysis of digital elevation models (DEMs) to find the dependence of deposit volumes and characteristics and valley morphology (e.g., strath terraces) on network structure and topography. Field sites will be in parts of the Oregon Coast Range (OCR) underlain by an Eocene sandstone formation (Tyee) because prior studies provide knowledge of geomorphic processes and paleoclimate; debris flows dominate sediment delivery to storage in headwater valleys; Quaternary climate change has not changed the dominant geomorphic processes; the OCR is the focus of debate between advocates of exploitation and conservation, respectively; and this area is readily accessible.
