Predicting Coarse Sediment Transport from Patchy Beds in Ephemeral Channels

Abstract

Seven 1-D sediment transport formulae are employed to predict coarse sediment transport in a low-order, ephemeral channel with patchy bed material. Sediment transport is modeled through two different methods to characterize the sediment supply: by using a channel-averaged grain-size distribution (GSD) and by using the mean GSDs from the relatively coarse and fine textured patches that compose the channel bed.Modeling results show that the two different characterizations of the sediment supply produce significantly different values of predicted coarse sediment yield. The relative differences in the predicted yield values are dependent on the assumptions of each formula, including how the sediment supply is parameterized within the model. Modeled sediment yield values are contrasted to observed values for seven flashflood-type runoff events. The formulae accuracies typically are comparable to past analyses in fluvial systems more reminiscent of the hydraulic environments in which the models were derived (perennial flow, gravel-bed material).Study results reaffirm that the method by which sediment supply is characterized significantly impacts the performance of sediment transport formulae and that a single GSD might not adequately describe the sediment supply originating from patchy beds.