International Research Fellowship Program: Modeling the Morphodynamics of Bedrock Meandering

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0965064NelsonThe International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support an eighteen-month research fellowship by Dr. Peter A. Nelson to work with Dr. Giovanni Seminara at the University of Genoa in Italy.Meandering bedrock rivers are visually spectacular examples of nature?s ability to form patterns. The origin and behavior of bedrock meanders have been debated for over a century, yet today we are still unable to answer very basic questions about them; for instance, how do meanders form in bedrock, and what determines the selection of a meander wavelength? The aim of this project is to develop a theoretical morphodynamic model for bedrock meandering as an important step toward being able to answer these questions. The host and PI are using available studies in the literature and available topographic datasets to develop a comprehensive description of bedrock meanders in nature, and, building upon existing theory for alluvial meandering and recent advances in our understanding of the mechanics of bedrock erosion, these observations are used to develop a theory for bedrock meander formation. Theory development includes the following: 1) new approaches to estimate local vertical and lateral erosion due to abrasion from saltating bed load and suspended load, and bedrock breakdown due to weathering; 2) a linear stability analysis of a basic state to ascertain whether lateral erosion may provide a mechanism for bend growth; 3) the development of a 3D model for flow in a curved channel whose axis may display both bending and torsion; and 4) the development of a 3D planform evolution equation for the channel centerline to illustrate predicted channel behavior. This project promotes cooperation between geomorphologists and theoretical morphodynamicists. Since so little is known about the behavior of bedrock rivers, this project has the potential to dramatically broaden our basic understanding of bedrock systems. Our proposed work will combine the state-of-the-art in theoretical morphodynamics of alluvial meandering and bedrock incision, and the theoretical framework we develop will be the first of its kind to employ a purely erosive mechanism, to include the effects of sediment supply, and to be intrinsically 3D. The novel aspects of this work, particularly the incorporation of sediment supply-limited effects, should be applicable to a broad range of geomorphic problems, including possible anthropogenic or climatic effects on river behavior. We expect this project will provide opportunities for continual international collaboration between theoreticians and geomorphologists now and in the future.