Spatial Variability of Channel Erosion by Debris-Flows (Field Observations in the French Alps)

Debris-flows are known to have important volume growth from channel erosion on steep slopes. However, it is still difficult to quantify the relationship of debris-flow scouring and slope. High densities of multi-date cross-sections in both the Manival and Real debris-flow catchments (French Alps) have clearly shown that debris-flows have significant scouring with large spatial variability. Bedload transport was observed to be at equilibrium with little variability. Field observations of channel deformations show that debris-flow scouring is strongly controlled by upstream slope and storage conditions. A logarithmic relationship is proposed as an empirical fit for the prediction of channel erosion. Since the important volumes of debris-flows are composed of scoured material, this empirical model provides a basis for estimating potential magnitudes using simple channel profile and active channel width.