Understanding the influence of slope on the threshold of coarse grain motion: Revisiting critical stream power

Multimode Morphodynamic Model for Sediment-Laden Flows and Geomorphic Impacts

“…A number of studies have highlighted that the variation in channel gradient has an influence over the mean bed shear stress at which sediment is entrained (Lamb, et al, 2008, Parker, et al, 2011. For the threshold of sediment motion, the empirical Eqn.…”

Zinc, copper, nickel, and arsenic monitoring in natural streams using in-situ iron–manganese oxide coated stream pebbles

“…While both pebble-sized and sand-siltsized grains have been successfully used as geochemical tracers (Huelin et al, 2006;Whitney, 1975), pebble and cobble-sized grains are stable at higher discharges, which allow precipitation of iron and manganese oxide coatings and metal sorption to continue for longer periods of time. One way to explore bedload stability is to estimate the critical shear stress needed to move a pebble, which can be estimated using the Shield's criterion (Parker et al, 2011) parameterized with channel metrics derived from Lidar data, and discharge characterized by USGS gaging stations. These calculations can identify that portion of the bedload grain size distribution that likely stay in place for long periods of time, more than minutes or days, and permit iron and manganese coatings to accumulate.…”

“…where τ c is the critical shear stress, τ* is shield's criterion, taken to be 0.045 for gravel, ρ p is the density of the quartz pebble (2600 kg/m 3 ), ρ w is the density of water (1000 kg/m 3 ), D 50 is the intermediate axis grain size (5 cm) used for all sites, and g is the gravity (Parker et al, 2011).…”

Discussion of “Understanding the influence of slope on the threshold of coarse grain motion: Revisiting critical stream power” by C. Parker, N.J. Clifford, and C.R. Thorne Geomorphology, Volume 126, March 2011, Pages 51-65

“…A serious question for the work by Parker et al, (2011) is about the estimation of the mean bed shear stress over the section τ. As presented by Parker et al, (2011), geomorphologists generally used an approximation of the bed shear stress (and stream power ω) by assimilating the hydraulic radius R h to the mean water depth h. However, to be more rigorous, especially in the of laboratory measurements, one should be careful about the computation of τ and ω:…”

“…In the case of the laboratory channel used by Parker et al, (2011), one should also use wall corrections such as suggested by Vanoni and Brooks, (1957). In Fig.…”