Stream Channel Stability. Appendix N. Alluvial Channel Flow Resistance: Stochastic Properties

摘要

This report describes a series of experiments that were performed in a laboratory flume that was adapted to allow computer control of the independent experimental variables, and computer acquisition of data during experiments. The object of the study was to relate the Darcy-Weisbach resistance coefficient of an alluvial channel flow to the bed roughness as expressed by the standard deviation of bed elevation records (a measure of the dune and antidune roughness height). Since the Darcy-Weisbach coefficient in an alluvial channel shows considerable time variation even in supposedly steady uniform flows, and since the bed roughness, as measured from the time records of the bed elevation, is a stochastic quantity; time records of the Darcy-Weisbach coefficient and of the bed elevation were analyzed to obtain probability density functions, which were typified by means values and standard deviations of the relevant quantities. Autocorrelation functions of the time records were also computed and plotted. From these functions, time constants for variation of the resistance coefficient and for the propagation of bed forms were obtained. The Darcy-Weisbach resistance coefficient is of importance in the development of mathematical models of streamflow for predicting floodwave propagation, channel bed and bank modification, and the intensity of fluvial attack on channel protection or river training structures.