If the critical shear stress for entrainment of grains from the slope is 0.7 Pa, how far from the divide must one go to find entrainment in the case shown in Figure 11.17? This is Horton’s Xc. Verify that the calculation of basal shear stress is done correctly by using the flow thickness at that location, the slope, and the acceleration due to gravity to calculate the basal shear stress.

Figure 11.17

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(a) Flow thickness (mm) @ Flow thickness (mm) 2.5 2 1.5 1 0.5 0 0 20 15 10 50 0 0 20 R=8 mm/hr h 5 10 15 20 25 30 35 40 45 50 Distance downslope (m) 0.004 slope at 100m, n=0.04, R=0.005, 1=0.002 R=6mm/hr 40 60 Distance downslope (m) R=4 mm/hr R=2mm/hr 80 1.5 0.5 0 100 Basal shear stress (Pa)