Developing Mechanistic Models for Bedrock Erosion at Waterfalls.

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The upstream movement of waterfalls controls the shape of many landscapes and sets the rate by which landscapes respond to changes in climate and tectonics. However, we currently lack mechanistic models for waterfall erosion which inhibits our ability to predict landscape response to environmental perturbations. The goal of this project is to fill this knowledge gap through a combination of experiments in an indoor waterfall laboratory and monitoring waterfall processes in nature. The waterfall experiments will be completed in a new state-of-the-art hydraulic and sediment flume at the California Institute of Technology. This work will lead to mathematical theories for the sediment transport capacity and erosion of waterfall plunge pools. The models developed from flume experiments will be tested against sediment transport data that we will collect at an active waterfall in the San Gabriel Mountains, CA, and over longer timescales against a new database of waterfall retreat rates compiled from previous studies. In addition to deriving and testing models for waterfall retreat, our work will aid understanding sediment routing and storage in mountain streams because waterfall plunge pools are natural temporary sediment sinks, with importance for mitigating river flood hazards and understanding habitats of aquatic organisms that depend on pools in summer months. A focus of this proposal is an integrated research and education program. Waterfalls are ubiquitous and awe-inspiring landforms in the natural landscape; they provide a great medium through which to interest students and the public in issues of erosion and sedimentation, as well as landscape evolution. The proposed educational program includes mentoring summer undergraduate research fellows and PhD students who will be directly involved with the research. Through the Caltech Summer Undergraduate Research Fellowship program, undergraduate students will define and develop a project, write research proposals, carry out subsets of the laboratory and field work, submit a technical paper, and give an oral presentation at a symposium modeled on a professional technical meeting. Outreach events will be focused on tours, classroom visits, and field excursions for students and teachers in the Pasadena Unified School District (P.U.S.D.), a district where the majority of students are from groups under-represented in geosciences.