Mountain Rivers and Incised Channels - River Dynamics and Integrated River Management - page 148

Creek has the best developed step-pool system and has the largest bed roughness. Fork Gully is
developing a step-pool system and the bed roughness is between that of the Jiangjia Ravine and Shengou
Creek. The Jiangjia Ravine has no step-pool system and the roughness and resistance are small. Field
investigations found that the height of steps depends on the size of the largest particles (Wohl et al.,
1997). In general both the height and the number of steps per length increase with the bed slope. Closer
spacing of steps often occurs with steeper slopes in response to an increase in the number of large
particles. If sufficient time is given for a step-pool system to develop, the S P value increases with the
average bed slope.

Fig. 3.28 (a) Instrument for measuring the development degree of step-pool system; (b) Measurement of the S P
value on the Yigong Tsangbu landslide dam

Fig. 3.29 Thalweg profiles of Shengou Creek, Fork Gully, and the Jiangjia Ravine

Figure 3.30 shows the S P value as a function of average bed slope, s , in which the triangles are
measured in mountain streams including Shengou Creek, the Jiangjia and Xiaobani ravines, and Fork
Gully, and the black points are the results from a laboratory experiment, which is discussed in the
following section. In general, the development degree of a step-pool system increases with the average
bed slope. Two straight lines are shown in the figure roughly describing the trends for the mountain