6.4 Results and Discussion
89
Table 6.2 The role of landslide erosion in the upper and middle reaches of the Yellow River
Catchment/watershed Reference
Statistical
time
Area
(km 2 )
Landslide
volume
(10 3 t)
*R
(%)
Averaged
R (%)
Qiaogou Catchment
Yang et al.
(2014)
2009–2011
0.45
0.65
42
39
Luoyugou Watershed TSSWS
(2004)
1987
73
446
12
Lv’er Catchment
TSSWS
(2004)
1961
12
100
50
Nanxiaohegou
Catchment
Jiang et al.
(1966)
1954–1960
31
86
72
Jiuyuangou
Catchment
Jiang et al.
(1966)
1954–1960
70
241
20
Chabagou Watershed Li et al.
(2009),
Wang and
Li (2009)
1967
205
467
21
17
Wudinghe Watershed Wang and
Li (2009)
1977
29,600
5230
12
*R is expressed as the ratio in percentage between the sediment discharge from landslides and the
total soil loss of a catchment
in the small watershed and then estimated the amount of the landslide erosion by
measuring the volume of soil loss from the failure surface and the landslide deposit;
for example, TSSWS (2004) reported the contribution of landslide erosion to the total
sediment discharge with this method in the Lv’ergou Catchment and the Luoyugou
Catchment. In fact, the upstream sediment-laden runoff might take away part of the
landslide deposit or result in a large quantity of sediment deposition. Hence, errors
existed as the landslide volume was calculated in such a way according to the state
of failure scar after rainfall.
All in all, landslide erosion accounts for a considerable proportion of soil erosion
in the middle reaches of the Yellow River, and it is also an important contributor
to sediment input to the Yellow River. Table 6.2 shows that the proportion of landslide erosion to total erosion generally decreased, while the area of the watershed
increased. In fact, the detached soil from gully banks could enter the gully runoff
directly, because the landslide erosion was mainly distributed in the gully-head and
branch gully. However, for large-scale channels, the ratio of width to depth was relatively large, so that detached soil could not directly get into runoff even if landslide
erosion occurred. On the other hand, as runoff grew with increased spatial scale,
the detached soil in a single landslide event could not significantly affect the total
sediment concentration (Li et al. 2009). In Table 6.2, the landslide erosion accounted
for 39% of the total erosion at the catchment scale with an area less than 100 km
2 .
However, the average ratio of landslide erosion to the total erosion was only 17%
89
Table 6.2 The role of landslide erosion in the upper and middle reaches of the Yellow River
Catchment/watershed Reference
Statistical
time
Area
(km 2 )
Landslide
volume
(10 3 t)
*R
(%)
Averaged
R (%)
Qiaogou Catchment
Yang et al.
(2014)
2009–2011
0.45
0.65
42
39
Luoyugou Watershed TSSWS
(2004)
1987
73
446
12
Lv’er Catchment
TSSWS
(2004)
1961
12
100
50
Nanxiaohegou
Catchment
Jiang et al.
(1966)
1954–1960
31
86
72
Jiuyuangou
Catchment
Jiang et al.
(1966)
1954–1960
70
241
20
Chabagou Watershed Li et al.
(2009),
Wang and
Li (2009)
1967
205
467
21
17
Wudinghe Watershed Wang and
Li (2009)
1977
29,600
5230
12
*R is expressed as the ratio in percentage between the sediment discharge from landslides and the
total soil loss of a catchment
in the small watershed and then estimated the amount of the landslide erosion by
measuring the volume of soil loss from the failure surface and the landslide deposit;
for example, TSSWS (2004) reported the contribution of landslide erosion to the total
sediment discharge with this method in the Lv’ergou Catchment and the Luoyugou
Catchment. In fact, the upstream sediment-laden runoff might take away part of the
landslide deposit or result in a large quantity of sediment deposition. Hence, errors
existed as the landslide volume was calculated in such a way according to the state
of failure scar after rainfall.
All in all, landslide erosion accounts for a considerable proportion of soil erosion
in the middle reaches of the Yellow River, and it is also an important contributor
to sediment input to the Yellow River. Table 6.2 shows that the proportion of landslide erosion to total erosion generally decreased, while the area of the watershed
increased. In fact, the detached soil from gully banks could enter the gully runoff
directly, because the landslide erosion was mainly distributed in the gully-head and
branch gully. However, for large-scale channels, the ratio of width to depth was relatively large, so that detached soil could not directly get into runoff even if landslide
erosion occurred. On the other hand, as runoff grew with increased spatial scale,
the detached soil in a single landslide event could not significantly affect the total
sediment concentration (Li et al. 2009). In Table 6.2, the landslide erosion accounted
for 39% of the total erosion at the catchment scale with an area less than 100 km
2 .
However, the average ratio of landslide erosion to the total erosion was only 17%