Hydraulic Jump Mechanics and Channel Interactions in Mountain Rivers

University Of California-Davis, Davis CA

Investigators

Abstract

0207713 Pasternack Hydraulic jumps in mountain rivers are turbulent mixtures of air and water that produce significant kinetic energy dissipation, air entertainment, surface waves, and spray. Despite their prevalence, the role of natural hydraulic jumps on river flow mechanics, sediment transport, channel change, and basin evolution is unknown primarily because of adverse site conditions that previously limited field data collection. The overall goal of this project is to overcome past constraints on investigating hydraulic jump fluid mechanics in the natural setting and its relevance to fluvial geomorphology with the aid of new technologies that enable precise in situ measurement for the first time. New technologies developed and tested at UC Davis include a River Truss, an air content sensor, and large-scale particle image velocimetry. The new technologies will be used to address three hypotheses that predict how systematic changes in the external controls of channel geometry and discharge directly affect the response variables of water surface topography, velocity, pressure, air content, air entertainment, and energy dissipation. The role of response variables in sediment transport, channel change, and basin evolution will follow from a thorough investigation of the response variables themselves, especially when addressing conditions near the bed. Observing 13 natural hydraulic jumps in the American River basin over a 3-year period will test hypotheses. Results will be compared between jumps and against results from engineering flume-based studies using theoretical and empirical equations. A better understanding of the role of natural jumps in channel change is very important to science because it would improve the physics of landscape evolution models, provide needed guidance for including in-stream features in river restoration and rehabilitation, and make interdisciplinary contributions to ecology and aquatic geochemistry. In future research, other scientists will be able to apply the newly proven field technologies and resulting models to better understand the complex flow mechanics and channels interactions occurring in mountain rivers.