8.4 Results and Discussion
127
6
7
8
9
10
11
0
5
10
15
Slope , SL
m (%)
Runoff , N m
10
15
20
25
30
0
2
4
6
8
1 0
Slope , SL
m (%)
Rainfall , N m
(a)
(b)
Fig. 8.6 Variation of the mean slope with runoff/rainfall. a Single check-dam; b Check-dam system
However, if the runoff experiments were continued, the increasing rate in damland elevation would become much slower. It was really difficult to provide strict
threshold values for gully slopes and dam-land elevations only by model experiments.
In practice, the threshold value of dam-land increase per year which could be borne
by the local peasants is decided by the local social and economic conditions (Li
2004), and generally amounts to 0.3 m/a (Zheng 2004; Wang and Ma 2003).
In fact, from our experimental results, the increase rate of the dam-land altitude
was evidently shrinking as the runoff was carrying on, and the trend was exhibiting
a relative stability in the gully in respect of the hydro-sedimentologic balance.
8.4.1 Mechanism of the Relative Stability Development
Figure 8.7 shows the variation in composition of the sediment on the surface of the
gully bed after 18 runs of model runoff. Just like any other water-blocking structure
Fig. 8.7 Coarsening of the
gully bed after runoffs
0
20
40
60
0
200
400
600
Diameter , D
50 /(10 m)
Thalweg distance from outlet , L m (cm)
After constructing dam
Before constructing dam
127
6
7
8
9
10
11
0
5
10
15
Slope , SL
m (%)
Runoff , N m
10
15
20
25
30
0
2
4
6
8
1 0
Slope , SL
m (%)
Rainfall , N m
(a)
(b)
Fig. 8.6 Variation of the mean slope with runoff/rainfall. a Single check-dam; b Check-dam system
However, if the runoff experiments were continued, the increasing rate in damland elevation would become much slower. It was really difficult to provide strict
threshold values for gully slopes and dam-land elevations only by model experiments.
In practice, the threshold value of dam-land increase per year which could be borne
by the local peasants is decided by the local social and economic conditions (Li
2004), and generally amounts to 0.3 m/a (Zheng 2004; Wang and Ma 2003).
In fact, from our experimental results, the increase rate of the dam-land altitude
was evidently shrinking as the runoff was carrying on, and the trend was exhibiting
a relative stability in the gully in respect of the hydro-sedimentologic balance.
8.4.1 Mechanism of the Relative Stability Development
Figure 8.7 shows the variation in composition of the sediment on the surface of the
gully bed after 18 runs of model runoff. Just like any other water-blocking structure
Fig. 8.7 Coarsening of the
gully bed after runoffs
0
20
40
60
0
200
400
600
Diameter , D
50 /(10 m)
Thalweg distance from outlet , L m (cm)
After constructing dam
Before constructing dam