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.