130
8 Sediment-Storage Effects of Check-Dam …
built in the 1960s, such as the Kanghegou check-dam system in Shanxi Province
and the Wangmaogou dam system in Shannxi Province, are also typical projects
attaining good relative stabilities, and have retained enormous amounts of sediments
and yielded plentiful crops. Hence, it is most evident that the attaining of relative
stability should be the ultimate goal to build check-dam systems.
8.4.2 Further Research on the Theory of Relative Stability
The amount of dam-land increase per year. It is supposed that floodwater was evenly
spread on the dam-land in the initial hypothesis on the relative stability of checkdams. In fact, the water depth near the dam is larger than that far from the dam,
due to the longitudinal deposition profile existing in the upper reach of the checkdam, and the wallop of the floodwater pouring into the reservoir. According to the
field investigation, the average longitudinal slope gradient of the check-dam lands in
Shannxi Province is 0.2–0.5%, which makes an obvious impact on the distribution of
the impounded floodwater, especially that on the check-dam land with large reservoir
capacity (Tian et al. 2004). The phenomenon mentioned above was also widely found
in the rainfall simulation experiments. Figure 8.9a shows the slope gradient of the
check-dam land gradually became small in the runoff experiments of the single
check-dam. Figure 8.9b shows the change of the gully bed after 9 events of rainfalls.
Both figures illustrate that the longitudinal slope gradient of the check-dam land was
larger before the reservoir filled, and it became smaller after the reservoir filled, but
the gradient never be equal to 0.
Consequently, the annual increment of the check-dam height in the connotation of
relative stability should be the spatial mean value of the dam-land increase per year
(Fang 1995). Experimental data related to the amount in this chapter had been also
processed according to the above method. Clarification of the definition is helpful to
construction of the check-dam systems in the practice of erosion control.
The relationship between the construction of the check-dam system and the control
of the slope erosion. From the previous experimental data it could be found that the
main function of the check-dam system is to control soil and water loss in the gullies,
other than directly alleviate soil and water loss on the slope. Thus comprehensive
treatment including tree planting, terrace constructing and pit digging should be
implemented order to improve the eco-environment of the Loess Plateau.
Actually, the relative stability of the check-dam system and the control of the
slope erosion may be mutually promoted. Gully is usually the influx of the runoffs,
which is also the channel of surface runoffs, therefore, the water resources are comparatively centralized. With the reservoir of the check dam system in the gully, the
water resources could be fully impounded to irrigate the plant on the check-dam
and the slope, and indirectly reduce soil and water loss on the slope. At the same
time, the control of slope erosion could reduce the flood peak to a certain extent,
which favors the flood control of the check-dam system. Besides, the control of the
slope erosion decreases the amount of soil flowing to the reservoir. Consequently the
8 Sediment-Storage Effects of Check-Dam …
built in the 1960s, such as the Kanghegou check-dam system in Shanxi Province
and the Wangmaogou dam system in Shannxi Province, are also typical projects
attaining good relative stabilities, and have retained enormous amounts of sediments
and yielded plentiful crops. Hence, it is most evident that the attaining of relative
stability should be the ultimate goal to build check-dam systems.
8.4.2 Further Research on the Theory of Relative Stability
The amount of dam-land increase per year. It is supposed that floodwater was evenly
spread on the dam-land in the initial hypothesis on the relative stability of checkdams. In fact, the water depth near the dam is larger than that far from the dam,
due to the longitudinal deposition profile existing in the upper reach of the checkdam, and the wallop of the floodwater pouring into the reservoir. According to the
field investigation, the average longitudinal slope gradient of the check-dam lands in
Shannxi Province is 0.2–0.5%, which makes an obvious impact on the distribution of
the impounded floodwater, especially that on the check-dam land with large reservoir
capacity (Tian et al. 2004). The phenomenon mentioned above was also widely found
in the rainfall simulation experiments. Figure 8.9a shows the slope gradient of the
check-dam land gradually became small in the runoff experiments of the single
check-dam. Figure 8.9b shows the change of the gully bed after 9 events of rainfalls.
Both figures illustrate that the longitudinal slope gradient of the check-dam land was
larger before the reservoir filled, and it became smaller after the reservoir filled, but
the gradient never be equal to 0.
Consequently, the annual increment of the check-dam height in the connotation of
relative stability should be the spatial mean value of the dam-land increase per year
(Fang 1995). Experimental data related to the amount in this chapter had been also
processed according to the above method. Clarification of the definition is helpful to
construction of the check-dam systems in the practice of erosion control.
The relationship between the construction of the check-dam system and the control
of the slope erosion. From the previous experimental data it could be found that the
main function of the check-dam system is to control soil and water loss in the gullies,
other than directly alleviate soil and water loss on the slope. Thus comprehensive
treatment including tree planting, terrace constructing and pit digging should be
implemented order to improve the eco-environment of the Loess Plateau.
Actually, the relative stability of the check-dam system and the control of the
slope erosion may be mutually promoted. Gully is usually the influx of the runoffs,
which is also the channel of surface runoffs, therefore, the water resources are comparatively centralized. With the reservoir of the check dam system in the gully, the
water resources could be fully impounded to irrigate the plant on the check-dam
and the slope, and indirectly reduce soil and water loss on the slope. At the same
time, the control of slope erosion could reduce the flood peak to a certain extent,
which favors the flood control of the check-dam system. Besides, the control of the
slope erosion decreases the amount of soil flowing to the reservoir. Consequently the