Integrated River Management - River Dynamics and Integrated River Management - page 751

bed load transport increased about 100 times for the Hunshui and Xiaobaini ravines and about 10 times
for the Diaoga River. The results prove that the effect of bed structures on the bed load transportation is
reversible. In other words, the development of bed structures results in reduction in bed load motion and
destruction of bed structure results in an increase of bed load motion. For a given stream power the
functions of bed structures and bed load motion are mutually replaceable.
Fig. 11.38 Change of the rate of bed load transport g b and the development degree of bed structures S p due to
destruction of the bed structures on the Diaoga, Xiaobaini and Hunshui rivers
11.2.2.5 Bed Structures Control Bed Load Motion
The Yalutsangbu Grand Canyon has the highest stream power p and strongest step-pool system. The
step-pool system consumes most of the flow energy, therefore, there is no intensive bed load motion in
the canyon. Figure 11.39 shows the bed profile of the Yalutsangbu River, in which five knickpoints are
marked with numbers. The fourth and fifth knickpoints are the Grand Canyon, which is the deepest gorge
in the world. Huge stones with diameter of 5-15 m overlapped and form huge step-pool systems.
Fig. 11.39 Longitudinal bed profile of the Yalutsangbu River, in which numbers are knickpoints and Knickpoints 4
and 5 are the upper part of the Grand Canyon
The step-pool systems create high resistance to the flow and resulted in waves of height of several
meters, as shown in Fig. 11.40(a). The waves consume a lot of energy and make great noise. The bed
gradient is as high as 0.04-0.06, but the average velocity is only 3-4 m/s. Sand is carried by the flow as
suspended load. Because the step-pool system balances the stream power there is no intensive bed load
transportation. Therefore, no gravel and cobbles are transported through the grand canyon.
The plane view of the Yalutsangbu River upstream of the Grand Canyon looks like a lotus root, as
shown in Fig. 11.40(b). Each narrow section is a gorge with high gradient bed consisting of step-pools.