Hyperconcentrated Flow and Sediment Transport at Steep Slopes

In order to simulate a fine‐material slurry of a debris flow, a clay suspension of various concentrations was recirculated in a steep flume. The effect of an increasing fluid density and viscosity on the flow behavior and the bed‐load transport capacity of the flow was examined. Viscous effects were found to become important below a limiting particle Reynolds number of about 10. Above this limiting value, density effects cause an increase in the bed‐load transport rates as compared to similar conditions with clear water as transporting fluid. The experimental data in this range can be described with conventional (Newtonian) formulas and is analyzed together with other bed‐load transport data. Two different calculation schemes are proposed for the steep slope range (S>≈10%) where the bed‐load concentration is significant with respect to the total flow depth. Below the critical particle Reynolds number of 10, the bed‐load transport rates decreased strongly.