2.5 Results and Discussion
23
Table 2.5 Data from rainfall experiments conducted on the Model Da with the same initial landform
but different rainfall intensities before the dam system was constructed
Sequence
number
Experiment
Rainfall intensity,
I D (mm/min)
Soil loss,
S D (kg)
Regression
analysis
1
C2-04-11-02-01(0.046) 2.24
4.66
S D =
0.993I 1.98
D
r 2 = 0.94
2
C2-04-10-26-01(0.044) 2.48
6.03
3
C2-04-10-24-01(0.042) 2.07
2.93
4
C2-04-10-23-01(0.040) 0.94
1.17
5
C2-04-11-07-01(0.040) 1.71
2.99
6
C2-04-11-22-01(0.038) 1.26
2.26
7
C2-04-11-28-01(0.037) 0.54
0.21
where S
∗
D is the amount of soil loss free from the influence of the difference in
rainfall intensities, and ¯
I D is the expected rainfall intensity. In this study, ¯
I D is the
mean rainfall intensity in a group of rainfall experiments.
2.5.2 Calculation of Soil Loss Scale Number and Relative
Ratio
Seven rainfall events were applied to the initial ground cover of the Model B without
check dams. The rainfall-erosion in the fifth rainfall event (I B = 1.53 mm/min, S B =
121.53 kg), in which the initial soil density and moisture, and rainfall intensity were
close to the condition in the experiments with check dams, was adopted as the index
to calculate soil loss scale number of the Model B. In the same way, the amount of
soil loss was 4.76 kg when the rainfall intensity was 1.65 mm/min in the Model Da.
Let R DB , the relative ratio of erosion extent between the Model Db and Model B,
be equal to 1.0. Then the amount of soil loss for the Model Db without any dams is
shown as follows:
S D =
S p
λ
3
LD
=
S B × λ
3
LB
λ
3
LD
=
121.53 × 60
3
240 3
= 1.90(kg)
(2.7)
where λ LD is the length scale number of the Model Db, and λ LB is the length scale
number of the Model B. After implementing a series of practices before the check
dams were constructed, including increasing rainfall intensity, mixing fine sand as
the land cover, and cultivating rills on slopes, the amount of soil loss in the Model
Db was approximately 1.90 kg, 2.20 kg in practice, when the rainfall intensity was
2.45 mm/min.
The soil loss scale number of the Model B was calculated as follows according
to its definition:
23
Table 2.5 Data from rainfall experiments conducted on the Model Da with the same initial landform
but different rainfall intensities before the dam system was constructed
Sequence
number
Experiment
Rainfall intensity,
I D (mm/min)
Soil loss,
S D (kg)
Regression
analysis
1
C2-04-11-02-01(0.046) 2.24
4.66
S D =
0.993I 1.98
D
r 2 = 0.94
2
C2-04-10-26-01(0.044) 2.48
6.03
3
C2-04-10-24-01(0.042) 2.07
2.93
4
C2-04-10-23-01(0.040) 0.94
1.17
5
C2-04-11-07-01(0.040) 1.71
2.99
6
C2-04-11-22-01(0.038) 1.26
2.26
7
C2-04-11-28-01(0.037) 0.54
0.21
where S
∗
D is the amount of soil loss free from the influence of the difference in
rainfall intensities, and ¯
I D is the expected rainfall intensity. In this study, ¯
I D is the
mean rainfall intensity in a group of rainfall experiments.
2.5.2 Calculation of Soil Loss Scale Number and Relative
Ratio
Seven rainfall events were applied to the initial ground cover of the Model B without
check dams. The rainfall-erosion in the fifth rainfall event (I B = 1.53 mm/min, S B =
121.53 kg), in which the initial soil density and moisture, and rainfall intensity were
close to the condition in the experiments with check dams, was adopted as the index
to calculate soil loss scale number of the Model B. In the same way, the amount of
soil loss was 4.76 kg when the rainfall intensity was 1.65 mm/min in the Model Da.
Let R DB , the relative ratio of erosion extent between the Model Db and Model B,
be equal to 1.0. Then the amount of soil loss for the Model Db without any dams is
shown as follows:
S D =
S p
λ
3
LD
=
S B × λ
3
LB
λ
3
LD
=
121.53 × 60
3
240 3
= 1.90(kg)
(2.7)
where λ LD is the length scale number of the Model Db, and λ LB is the length scale
number of the Model B. After implementing a series of practices before the check
dams were constructed, including increasing rainfall intensity, mixing fine sand as
the land cover, and cultivating rills on slopes, the amount of soil loss in the Model
Db was approximately 1.90 kg, 2.20 kg in practice, when the rainfall intensity was
2.45 mm/min.
The soil loss scale number of the Model B was calculated as follows according
to its definition: