Graduate Thesis Or Dissertation
 

Modeling sediment transport, channel morphology and gravel mining in river bends

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/4m90dx86j

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  • A technique is developed and tested to analyze the interaction of flowing water, bed topography, and bedload sediment transport in meandering channels where gravel bars are removed. The method relates the local velocity distribution, bed shear stress and sediment transport conditions to the local bed configuration in river bends before and after gravel bar removal. Specific attention is given to pool-depth changes as an immediate result of gravel removal, the residual effects of boundary shear stress changes, and the potential long-term consequences from subsequent runoff events with brief periods of increased streamflow and sediment transport. The most significant new aspect of this work is the ability to predict whether or not periodic gravel "mining" by means of bar scalping has a residual or cumulative effect on channel morphology and pool depth, particularly in bends. This application is tested against field data collected for the Chetco River and South Santiam River in Oregon, the East Fork River in Wyoming, and the upper Rhone River in France. Some of these sites have been partially subjected to gravel mining; others offer contrasting circumstances to allow comparisons of effects. The study suggests that the maximum velocity distribution shifts inward toward the convex bank of a channel bend at high water levels after gravel removal from a point bar, assuming that sediment transport rates and resupply from upstream are the same as before bar scalping. The inward shift of the maximum velocity distribution causes changes of boundary shear stress distribution in pool zones. Weaker boundary shear stresses are expected in pool zones after bar scalping. This will result in fewer incipient motion events in pool zones over each runoff season. As a result, the pool will experience net sediment deposition as a long-term effect of sediment transport events separated by periods of bed stability.
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