Experimental Erosion by Xiangzhou Xu & Tongxin Zhu & Hongwu Zhang & Lu Gao

Author:Xiangzhou Xu & Tongxin Zhu & Hongwu Zhang & Lu Gao
Language: eng
Format: epub
ISBN: 9789811538018
Publisher: Springer Singapore

(8.1)

where Wp is the amount of impounded floodwater (m3) when the flood frequency f is 2%; δ is the design depth of water for the dam farmland (m); and F is the area of controlled watershed by the check-dam (km2) (Zeng et al. 1999).

Zeng et al. (1995) has confirmed the feasibility of maintaining the relative stability of the check-dams by comparing the relationship between the dam height and the retention area in the Wangjiagou watershed of China. Fang et al. (1998), Fang (1995) and Zeng et al. (1999) have studied the condition, criterion and mechanism for the maintaining of the relative stability by investigating hundreds of typical check-dams on the Loess Plateau. Empirically, in small watersheds of the Loess Plateau, the check-dam systems will remain relatively stable when the ratio of the dam-land area to the area of the controlled watershed is between 1/25 and 1/15. When the impounded water depth is less than 0.8 m and the storage time is shorter than 3–7 days, a dam designed for withstanding a rainstorm occurring once in a hundred year has been found to be relatively stable (Zeng et al. 1995). Lei and Zhu (2002) have developed a mathematical model for optimizing the layout of the dams in a small watershed according to the principle of relative stability. Nevertheless, dissensions still exist on the theory of relative stability of check-dams. Li (2004) expressed the idea that no check-dam would be stable if sediment has to be detained in the reservoir when soil and water is inputted continuously from the upper reaches.

Alternatively, scaled model laboratory experiments may be a useful method that produces results that can be employed to design check dam systems. The use of physical models to test or predict the performance of full-scale prototype behavior has several inherent advantages such as (a) to give insight into problems which cannot be solved theoretically or numerically; (b) to get better control of boundary conditions; and (c) to save time and money (Timmons 1984). The accuracy of such predictions depends on the similarity between model and prototype in three principal characteristics: (a) geometric similitude; (b) kinematic similitude; and (c) dynamic similitude. While some similarity requirements appear to have been firmly established, others have not been fixed (Zhang et al. 1994; Timmons 1984).

Scaled modeling has been widely used for a long time in the field of hydraulics and river engineering (e.g., Zhang et al. 1994). However, few studies simulated the process of soil loss using a scaled model experiment, as such simulation is quite complicated in that rainfall, soil surface crusting, land-use and vegetation cover, etc., should be considered. Hancock and Willgoose (2004) investigated the effect of erosion on a back-filled and capped earthen dam wall by constructing an experimental model landscape simulator in a laboratory. The design of the rainfall simulator was difficult to directly scale the rainfall runoff processes to the field conditions. Consequently, no attempt was made to match the rate of gully development on the tailings dam to field-scale processes.

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