118
8 Sediment-Storage Effects of Check-Dam …
covered with the Lishi loess and the Malan loess (Cai et al. 1998). The precipitation
in this area can be found in the general condition of the Loess Plateau mentioned
above. In the 1960s, no dams had been built in this region, so that the average annual
runoff rate was 36,700 m
3 /km
2 , and the average annual soil loss rate was 20,811
t/km
2 (Zhang et al. 1995). Therefore, annual soil loss, namely, the soil loss of the
conceptual prototype in a rainfall event, S p , could be obtained by the multiplying
the watershed area by annual soil erosion rate, which is 4.29 × 10
6 kg/a. As in
engineering practices, the annual erosion rate is adopted as an index when planning
the check dam system, and a rainfall event in the recapitulated prototype watershed
accounts for soil loss in one year in the prototype watershed.
The prototype catchment of the rainfall experiments is abstracted according to the
common erosion characteristics of the Loess Plateau. The conceptual watershed is
also located in the Loess Hill Ravine Region, but it covers an area of 3.32 km
2 . The
total length of the gullies is 3 km, and 694 m of which are from the outlet, with a
“U”-shaped gradient of 2.3%. Soil of the ground surface, the average annual runoff
rate, and average annual soil loss rate in this small watershed are all correspondingly
same to those in the Yangdaogou Catchment. The soil loss of the conceptual prototype
catchment in a rainfall event, S p , is 6.87 × 10
7 kg/a.
8.3 Experimental Methods
Scaled-down models are scale models of a general class that possess geomorphic
features, which can be regarded as the replica of a natural landform, but scaled down in
such a way that ratios of significant dimensions and forces are equal to those in nature
(Timmons 1984). Three conditions should be satisfied to ensure physical similarity:
(a) geometric similitude; (b) kinematic similitude; and (c) dynamic similitude. While
some similarity requirements seemed to have been firmly established, others have not
been fixed so far (Timmons 1984; Albertson et al. 1960). Scale modeling has been
widely used and has a long history in the field of hydraulics and river engineering
(Zhang 1994). However, few researchers have published data on the simulating of
the process of soil loss by scale model experiments, as it is very complicated with
respect to rainfall, soil surface crusting, land-use and vegetated cover, etc. Hancock
and Willgoose (2004) have examined the effect of erosion on a back-filled and capped
earthen dam wall by constructing an experimental model landscape simulator in the
laboratory. However, the designing of a rainfall simulator for directly scaling the
processes of rainfall runoff to the fields is rather difficult. Consequently, no attempts
have been made to match the rate of gully development on the tailings dam to the
field-scale processes. Recently, scale model experiments on soil and water erosion
in small watersheds have been performed, and progress has been made in similitude
methodologies. Shi et al. (1997a, b) have observed quantitative erosions in gullies and
on slopes of a small watershed model shrunk from the landform of the Xiaofanjiagou
Gully of the Shaanxi Province in China (the length scale was 75). Jiang et al. (1994)
and Yuan et al (2000a, b) have carried out a series of scale-down model experiments
8 Sediment-Storage Effects of Check-Dam …
covered with the Lishi loess and the Malan loess (Cai et al. 1998). The precipitation
in this area can be found in the general condition of the Loess Plateau mentioned
above. In the 1960s, no dams had been built in this region, so that the average annual
runoff rate was 36,700 m
3 /km
2 , and the average annual soil loss rate was 20,811
t/km
2 (Zhang et al. 1995). Therefore, annual soil loss, namely, the soil loss of the
conceptual prototype in a rainfall event, S p , could be obtained by the multiplying
the watershed area by annual soil erosion rate, which is 4.29 × 10
6 kg/a. As in
engineering practices, the annual erosion rate is adopted as an index when planning
the check dam system, and a rainfall event in the recapitulated prototype watershed
accounts for soil loss in one year in the prototype watershed.
The prototype catchment of the rainfall experiments is abstracted according to the
common erosion characteristics of the Loess Plateau. The conceptual watershed is
also located in the Loess Hill Ravine Region, but it covers an area of 3.32 km
2 . The
total length of the gullies is 3 km, and 694 m of which are from the outlet, with a
“U”-shaped gradient of 2.3%. Soil of the ground surface, the average annual runoff
rate, and average annual soil loss rate in this small watershed are all correspondingly
same to those in the Yangdaogou Catchment. The soil loss of the conceptual prototype
catchment in a rainfall event, S p , is 6.87 × 10
7 kg/a.
8.3 Experimental Methods
Scaled-down models are scale models of a general class that possess geomorphic
features, which can be regarded as the replica of a natural landform, but scaled down in
such a way that ratios of significant dimensions and forces are equal to those in nature
(Timmons 1984). Three conditions should be satisfied to ensure physical similarity:
(a) geometric similitude; (b) kinematic similitude; and (c) dynamic similitude. While
some similarity requirements seemed to have been firmly established, others have not
been fixed so far (Timmons 1984; Albertson et al. 1960). Scale modeling has been
widely used and has a long history in the field of hydraulics and river engineering
(Zhang 1994). However, few researchers have published data on the simulating of
the process of soil loss by scale model experiments, as it is very complicated with
respect to rainfall, soil surface crusting, land-use and vegetated cover, etc. Hancock
and Willgoose (2004) have examined the effect of erosion on a back-filled and capped
earthen dam wall by constructing an experimental model landscape simulator in the
laboratory. However, the designing of a rainfall simulator for directly scaling the
processes of rainfall runoff to the fields is rather difficult. Consequently, no attempts
have been made to match the rate of gully development on the tailings dam to the
field-scale processes. Recently, scale model experiments on soil and water erosion
in small watersheds have been performed, and progress has been made in similitude
methodologies. Shi et al. (1997a, b) have observed quantitative erosions in gullies and
on slopes of a small watershed model shrunk from the landform of the Xiaofanjiagou
Gully of the Shaanxi Province in China (the length scale was 75). Jiang et al. (1994)
and Yuan et al (2000a, b) have carried out a series of scale-down model experiments