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Raphelt, N.K., 1996

An examination of gravel bedload functions applied to observed gravel bedload discharge measurements of selected streams

Bibliographic Reference

Raphelt, N.K., 1996, An examination of gravel bedload functions applied to observed gravel bedload discharge measurements of selected streams: Fort Collins, Colorado, Colorado State University, Ph.D. dissertation, 135 p.


This research investigates aspects of gravel load transport measurements in selected streams. A transport function that predicts total gravel load transport was developed. Total gravel load transport is determined by summing the gravel load transport computed for six gravel size classes from a comprehensive data set of observed gravel transport measurements. The data set is a compilation of observed gravel load transport from ten gravel bed streams, which range in size from very small streams, less than 12 feet wide, to the large rivers such as the Susitna River near Talkeetna, Alaska, more than a 1000 feet wide during high flow conditions. The results of six existing gravel load transport equations are compared to the observed gravel load. Analysis of the results of the application of the six existing equations showed a number of deficiencies exist in the prediction gravel transport. To develop a new gravel load transport equation, three concepts are studied: (1) incipient motion; (2) probability of grains to remain in place; and (3) the effects of hiding of smaller gravel particles by larger particles. This research proposes a modification to the work of Van Rijn for the initiation of motion in gravel bed streams with non-uniform sediment. Additional consideration of Gessler's procedure to determine the probability of grains to remain in place is also proposed. This research develops a hiding factor using the D$\sb{84}$ of the bed material. A relationship between the hiding factor and the critical shear stress divided by applied shear stress ratio indicates that three distinct zones exist. These zones represent the areas where movement of material is assured, a zone where movement is probabilistic, and a zone where no movement is expected.

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