This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 11-5).
Most of the rivers in hilly and mountainous landscapes have small, steep channels, which are typically mantled by boulders that rarely move. In these channels, boulders moderate the rate of river incision, roughen the flow creating local patches of gravel , and provide crucial habitat for a variety of organisms such as salmon and steelhead spawning. Coarse sediment can also become entrained by river floods, which rush down slope with considerable destructive consequences. No current theory or empirical model exists that successfully predicts the threshold of movement of boulders or their organization by river processes. This research project addresses this fundamental gap in basic knowledge through a combined theoretical, experimental and field-based approach. A semi-empirical theory for boulder mobility and step-pool formation will be developed and tested using a newly constructed state-of-the-art laboratory flume at the California Institute of Technology. The flume experiments will allow exploration of channel slopes (up to 30%) and grain sizes (up to 10 cm) that have been severely limited in past studies. Experiments will be designed to investigate the conditions under which boulders move and the mechanisms responsible for boulder organization into steps and pools. Data from these experiments will be used to test and validate predictive models for boulder transport and step-pool formation. The experimental and theoretical findings will be compared to observed flow conditions during boulder movement events in tributaries of the South Fork Eel River in the University of California Angelo Coast Range Reserve. The result will be a robust method for calculating boulder transport dynamics in steep mountain streams, with implications for predicting landscape evolution, the rate of movement of sediment through steep channels, critical habitat conditions, and the beneficial use of boulders in restoration projects.
The results from this research project will have significant implications for basic science and a number of practical concerns of societal relevance. Results from this project will aid in restoration and hazard mitigation efforts where assessing boulder mobility is needed for restoring stream habitat (e.g., salmon spawning) and functionality, as well as mitigating flood and debris flow hazards in steep urban areas. This research project includes mentoring undergraduates, a PhD student, and a post-doctoral researcher in experimental, field and theoretical science. Research from this study will be uswd to design a 1-day workshop for area high-school teachers. The goal will be to give teachers the necessary skills to teach their students simple ways to assess flood and debris flow hazards that can result in loss of life and property in the Los Angeles area.
