Debris Flows and Landslides - River Dynamics and Integrated River Management - page 237

(a)
(b)
Fig. 4.56 Comparison of the bed surfaces before (a) and after (b) the bed paving process. The bed surface is much
smoother after the bed paving process and the resistance is, therefore, reduced (See color figure at the end of this topic)
Fig. 4.57 The holes left by air bubbles in a debris flow deposit in a debris flow gully in the Bailong River basin in
Wudu County, Gansu Province, in west China
Figure 4.58 shows the relation of the ratio of drag reduction with the concentration of air bubbles, in
which the concentration of air bubbles, C g , is the ratio of the volume of air bubbles to the total volume of
the mixture. The ratio of drag reduction is defined as
R D = ( n w - n d )/ n w (4.12)
where n d is the roughness of debris flow calculated with Eq. (4.8) and n w is the roughness of water flow.