Prediction of bedload discharge for alluvial channels

Abstract

The problem of defining sediment supply conditions is of fundamental importance in the prediction of bedload discharge in alluvial channels, because most bedload equations were developed based on the general assumption that the rates at which sediment becomes available for transport equal the sediment-transport capacity of the flow. The classification of availability of sediment on the accuracy and applicability of seven bedload equations in alluvial channels is described and discussed in this dissertation. Historical hydraulic and sedimentological data from 22 alluvial channels of the United States are used to define the sediment-transport regimes and to compare predicted and measured bedload discharges. Exponential relations between sediment supply end energy are used to show if at a reach scale a channel has supply-limited or non-supply limited regime based on the statistical variations of bedload-transport rates with stream power. The root-mean-square error and the inequality coefficients are use to assess the bedload equation's ability to reproduce the trend of the measured values, whereas the discrepancy ratio is used to evaluate the equation's ability to reproduce individual measured data. Relations between the median particle-size ratio, which quantifies the coarseness or fineness of the channel bed, and the discrepancy ratio are used to illustrate process controlling the accuracy of bedload equations. Information presented here shows that an understanding of channel's sediment regime in the process of bedload prediction improves the applicability of bedload equations in alluvial channels.