Effects of sediment supply on surface textures of gravel-bed rivers

Using previously published data from flume studies, we test a new approach for quantifying the effects of sediment supply (i.e., bed material supply) on surface grain size of equilibrium gravel channels. Textural response to sediment supply is evaluated relative to a theoretical prediction of compet ent median grain size (D-50'). We find that surface median grain size (D-50 ') varies inversely with sediment supply rate and systematically approaches the competent value (D-50') at low equilibrium transport rates. Furthermor e, equilibrium transport rate is a power function of the difference between applied and critical shear stresses and is therefore a power function of t he difference between competent and observed median grain sizes (D-50' and D-50'). Consequently, we propose that the difference between predicted and observed median grain sizes can be used to determine sediment supply rate i n equilibrium channels. Our analysis framework collapses data from differen t studies toward a single relationship between sediment supply rate and sur face grain size. While the approach appears promising, we caution that it h as been tested only on a limited set of laboratory data and a narrow range of channel conditions.