Integrated River Management - River Dynamics and Integrated River Management - page 749

measured at 0.11. No bed incision occurred in this case (profile marked with “Bed structure”). The bed
profile with bed structure and the profile with bed load were almost the same, which implies that the bed
structure played a similar role as bed load in affecting river morphology. Nevertheless, the artificial bed
structure had different effects on cross sections compared with the effects that the bed load motion had
on the cross sections. In the experiment with bed load motion the channel was not very stable and
migrated slowly with moving meanders, but the experiment with artificial structures had relatively stable
meanders.

Fig. 11.36 Final bed profiles of the three experiments in the Jiangjia Ravine

In all three experiments, the suspended load was not controlled because it has little effect on the stream
morphology. The concentration of suspended load at the beginning of the experiment was 16.7 kg/m 3 at the
inlet of the experimental channel and 48.3 kg/m 3 at the outlet of the experimental channel, which implies
that a lot of fine sediment was scoured and became suspended load during the channel development
process. After the channel reached equilibrium the concentration was 22 kg/m 3 at the inlet and 25 kg/m 3
at the outlet, which implies that there was no intensive scouring in the experimental section.

11.2.2.4 Experiment of Destruction of Bed Structures
Development of bed structures, by nature or by humans, may control riverbed incision and reduce bed
load transportation. Will the destruction of bed structures result in riverbed incision or intensive bed load
motion? The second kind of experiment, conducted on the Diaoga River, Xiaobaini and Hunshui ravines,
was designed to answer this question. It was very dry from January to May in 2010 and there was almost
no rainfall in the Xiaojiang River basin. All flowing water in the streams was from ground water and
spring water. There was no sediment supply from upstream reaches and tributaries because there had
been no rain. The flow had to scour the bed and initiate bed load, or develop bed structures, to match the
stream power. In April and May, bed structures, although not strong, have developed in all the streams
and the bed load motion reduced to the minimum.
Before the second kind of experiment the Sp value of the bed structures, the stream power, the rate of bed
load transportation and the size distributions of sediment were measured. Then, for each stream a 30 m-long
section with a relatively regular structure and a generally low strength step-pool system, was selected. A few
key stones for each step were removed and the structure was then destroyed. The flow velocity increased
because of reduction in resistance. The bed sediment was scoured and the rate of bed load transport sharply
increased. The diameter of the bed load particles also increased. The bed load motion and the bed structures
were measured to compare with the values before the experiment. During the experiment the flow discharge