The Effect of Sediment Supply on Pool‐Riffle Morphology

Abstract

Downstream width variations can generate pool‐riffle morphology under experimental conditions, in numerical simulations and natural river channels. The present understanding of how pool‐riffle morphology varies with sediment supply and caliber, however, is insufficient due to the limited range of sediment supply rates explored in previous experiments and the little attention paid to sand supply and sediment size distribution in the laboratory and in the field. We present a model of river morphodynamics that can account for the spatial variability of channel width, and we validate the model with experimental data. Model validation shows how this one‐dimensional model can capture pool‐riffle formation, growth, and equilibration with errors that are comparable with those of other 1D models of river morphodynamics. We then apply the validated model to study the effects of sediment supply rate and caliber on pool‐riffle morphology. Model results show that pool‐riffle morphology is resilient to the range of tested sediment supply (i.e., five‐fold the sediment amount, 41‐fold the sand amount and coarsening the gravel supply). Bed and water surface slopes are sensitive to all types of change of sediment supply, whereas the sensitivity of bed surface sediment grain size varies with the type of change. These findings support prior research emphasizing the role of downstream width variations for the development/maintenance of pool‐riffle morphology and can help in the restoration and recovery of pool‐riffle gravel‐bed rivers.