December, 2011
Journal of Resources and Ecology
J. Resour. Ecol. 2011 2(4) 289-297
Vol.2 No.4
Article
DOI:10.3969/j.issn.1674-764x.2011.04.001
www.jorae.cn
Soil Erosion and Sediment Control Effects in the Three Gorges
Reservoir Region, China
CUI Peng1*, GE Yonggang1 and LIN Yongming2
1 Key Laboratory of Mountain Hazards and Earth Surface Processes/ Institute of Mountain Hazards and Environment, CAS, Chengdu 610041, China;
2 College of Forestry, Fujian Agriculture and Forestry University, Fuzhou 350002, China
Abstract: The Three Gorges Reservoir, the world’s largest hydropower reservoir, receives a significant
sediment yield from soil erosion. Sloping farmland is the main source, exacerbated by changes in land
use from relocating the inhabitants, and from engineering projects related to dam construction. Related
geo-hazards, including landsliding of valley-side slopes, will further increase the sediment yield to the
completed reservoir. Integrated watershed management, begun extensively in 1989, has effectively
controlled soil erosion and sediment delivery to date. What is described here as the Taipinxi Mode of
integrated watershed management, based on its application in the 26.14 km2 watershed of that name in
Yiling District, has been successful and is recommended for the entire region. The effects of this set of
erosion-mitigation measures are assessed, using experienced formulas for soil and water conservation and
information from remote sensing. The amount of soil erosion, and of sediment delivery to the reservoir
were reduced by 43.75–45.94 × 106 t y-1, and by 12.25–12.86 × 106 t y-1, respectively, by 2005, by which
time the project had been operative for 16 years.
Key words: soil erosion; sediment yield; sediment delivery; soil and water conservation; watershed
management; Three Gorges Reservoir Region
1 Introduction
The Three Gorges Reservoir, the largest hydroelectric
project in the world, is threatened by landslides and high
rates of sedimentation. Sedimentation, mainly from soil
erosion, is the most important factor imperiling efficient
operation of the project, and has been studied as a key
engineering problem since the project was first discussed
in the 1950’s (Yangtze River Water Resources Commission
of Water Resources Ministry 1997). Soil erosion and
sediment delivery have been intensively studied in recent
years (Cai et al. 2005; He et al. 2004; Wang et al. 2003;
Zhan and Wan 2001; Lu and Higgitt 2001, 2000; Yangtze
River Water Resources Commission 1997; Du et al. 1994;
Shi et al. 1992; Shi et al. 1987). Most research has been
concentrated on management practices in small watersheds,
and on a single aspect of soil and water conservation (Bu
et al. 2006; Tian et al. 2005; Shen et al. 2005; Zhang et al.
2004; Shi 2002; Yin and Yin 2002; Shen 1998; Qin and
Yin 1998), but not with an integrated approach to large
portions of the entire region. This research is an integrated
evaluation of a significant part of the region based on data
from field observations and remote sensing. Moreover,
we have not corrected rates and quantities of material
delivered for the differing sizes of the watersheds and
regions we have considered. For the regions with gentle
slope and homogeneous environment, delivery and erosion
rates per unit area differ with watershed size by a power
function, for example, drainage area to the power of –0.11
in North America (USDA 1983) and of –0.158 in hills of
Sichuan, near the Three Gorges Reservoir Region occupied
by purple soil (Gao et al. 2007). However, for much of
the Three Gorges Reservoir Region with steep slopes and
various environments, sediment yields are complex and
are not reduced per unit area with increase in watershed
size. Readers will note that our comparisons of rates per
unit area differ only in the time period of data collection.
Received: 2011-10-19 Accepted: 2011-11-22
Foundation: State Key Project of 2006BAC10B04, China and CAS Knowledge Innovation Project of KZCX2-YW-302.
* Corresponding author: CUI Peng. Email: [email protected].
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Journal of Resources and Ecology Vol.2 No.4, 2011
2 Study area
3 Impacts of soil erosion
The part of the drainage basin of the Three Gorges
Reservoir reported on here is an area of 5.80 × 104 km2,
between 29°16′–31°25′ N and 106°50′–110°50′ E. It is
located in the eastern part of the upper reaches of the
Yangtze River basin and includes 21 counties / districts
in Chongqing City and in Hubei Province (Fig. 1). It
has a population of 19.99 million, 342 persons km -2.
Mountainous terrain occupies over 90% of the total.
Highly erodible bedrock, including purple sandstone and
shale, crops out throughout much of the area. Erodible
purple soil is the dominant soil type, interspersed with
areas of yellow, yellow-brown, and brown soil (Major soil
types are commonly distinguished in China by color). A
subtropical humid climate dominates the region, the effect
of the east-Asian monsoon. Annual precipitation is in the
range of 1010–1385 mm.
Eroded land made up a total of 38.8×103 km2, 66.8%
of the total study area, in mid-1980’s (Water Resources
Ministry 2003). Severe soil erosion has resulted in
high rates of alluvial sedimentation, rises in streambed
elevation, frequent geo-hazards, and environment
deterioration. Farmland destruction by soil erosion has
reduced agricultural production, impoverished the local
people, and increased already high rates of sedimentation,
thus imperiling the operation of the Three Gorges
Reservoir. Consequently, in 1989 this area was selected
for the testing of measures designed for soil erosion
control, and it has in subsequent years been the subject of
a succession of conservation projects.
(1) Intense soil erosion and high rates of sediment
delivery are resulting in severe eco-environmental
degradation to the point that, if allowed to continue
unabated, will endanger the usefulness and efficiency
of the Three Gorges Reservoir. Soil erosion exceeded
157×106 t y-1 by 1990 (Shi et al. 1991), with an average of
3000 t km-2 y-1 in the entire region (Yangtze River Water
Resources Commission of Water Resources Ministry 1997;
Shi et al. 1991, 1992), and over 4500 t km-2 y-1 in the
eroded region. Over 40×106 t of sediment was delivered to
the Yangtze River per year, resulting in channel blocking
and shortening as well as a rise in riverbed elevation.
After completion of the Three Gorges Dam construction,
increases in alluvial sedimentation occurred due to the
decrease in flow velocity (from 2.66 to 0.38 m s -1 at
Chongqing) and the rise of water level. In addition, soil
erosion caused heavy deposition in lakes, ponds, small
reservoirs, etc.
(2) Geo-hazards, including landslides, rock avalanches
and debris flows, occur frequently and each of these
processes delivers large amounts of sediment into the
channels and into the reservoir. There are 4683 sites
of potential geo-hazards, including 4663 that involve
rock avalanches and landslides, with a total potential
volume of 13.3 ×109 m3 (Zhou et al. 2005). In addition,
272 debris flow valleys discharge to the reservoir (Du et
al. 1990), and frequent flash floods transport significant
amounts of sediment within them. Since 1982, over 70
geo-hazard events have occurred in the valley-side slopes
Yangtze River Basin and Three Gorges Reservoir Region
N
N
Legend
City
River
Three Gorges Reservoir Region
Yangtze River Basin
Legend
City
Boundary of basin
Administrative area
National boundary
First class river
Second class river
Third class river
Four class river
N
Three Gorges Dam
Legend
Yangtze River
County or district
Fig. 1 Location of the region studied in this paper.
Three Gorges Reservoir Region
CUI Peng, et al.: Soil Erosion and Sediment Control Effects in the Three Gorges Reservoir Region, China
along the Yangtze River, aggravating soil erosion and
increasing sediment delivery. The big landslides at Xintan
and Qianjiangping delivered over 30 and 15 million
m 3 sediment to the Yangtze River in 1985 and 2003,
respectively (Huang and Xu 2008).
(3) Sloping farmland is highly eroded, which not only
decreases the productivity of the farmland, but also reduces
its area. Sloping farmland occupies 74% of the total
farmland in the region; 1.408×106 ha of sloping farmland
occurs in Chongqing city; and sloping farmland accounts
for 18.39% of the upper reaches of the Yangtze River.
Serious soil erosion causes heavy losses of surface material
and soil nutrients, decreases in farmland productivity,
degradation of farmland and even soil desertification
and litho-desertification in some areas. The area of bare
rock expanded by 900 km2 between 1950 and 1990 in the
Wanzhou District, and the area of litho-desertification was
increased by 4 km2 per year in Zigui County.
(4) Soil erosion also contributes to contaminated water
in rivers and reservoirs by transportation of pollutants.
Significant quantities of soil nutrients, heavy metals and
fertilizers are delivered to rivers with the eroded sediment,
and result in serious deterioration of the aquatic ecosystem.
In purple soil watersheds, the NO3-N concentration of
surface runoff varies from 0.08–3.15 mg L -1, with an
average of 1.2 mg L-1. The loss modulus of nitrogen and
phosphorus is 38.9 and 42.5 kg hm -2 y -1 in residential
areas, respectively. Moreover, intensive soil erosion from
sloping farmland generally delivers sediment, pesticides
and fertilizers to surface runoff and rivers, resulting in the
severe pollution because of high concentrations of N and
P. Farmland runoff supplies 90% of the suspended material
as well as significant amounts of fertilizer to the reservoir,
which constitutes most of the non-point source pollution
by agriculture. It was established with investigational data
that agricultural non-point source pollution accounted for
60% of the water pollution in the reservoir.
4 Causes of soil erosion
4.1 Natural factors
Natural environmental factors, including abundant
precipitation, fractured and erodible rocks, steep slopes,
low vegetation coverage, and frequent geo-hazards, result
in serious soil erosion.
Fractured, erodible rocks are developed as a result of
active tectonism, thus increasing the ease with which they
are eroded. Purple soil, yellow-brown soil and brown
soil are also easily eroded. Moreover, steep terrain with
a relief difference of 1000 m to 2500 m and an average
slope of 20° creates conditions for higher erodibility. The
intense rainfall occurs due to the impacts of the east-Asian
monsoon. About 60%–80% of the annual precipitation
is concentrated in the rainy season (May to September).
Rainstorms, source of most precipitation, often generate
291
rapid and intensive erosion. Low vegetation coverage
facilitates local soil erosion. Forests cover only 19.5%
of the entire region, and as little as 5% in areas marginal
to the Yangtze River. Pure Masson’s pine forest with a
majority of young trees and little land surface coverage is
extensive but does little to retard runoff.
With the completion of the Three Gorges Reservoir,
rock avalanches and landslides will increase in frequency
and accelerate soil erosion. Since the reservoir began water
storage in 2003, earthquakes with a magnitude less than
Ms 3.0 occur frequently. Two earthquakes of M 3.2 and 4.1
occurred in Zigui County on Sept. 27 and Nov. 22, 2008,
respectively (China Earthquake Network Center 2008).
Moreover, after the reservoir stored water at a high level
(175m), the water level change of about 30m between
the dry and rainy seasons resulted in unstable slopes,
which failed in the rainy season and delivered sediment
directly to the Yangtze River. Stable slopes will decrease
by 37.8% and potential unstable terrains will increase by
51.7%. Since the reservoir stored water at a level of 175m
in Sept., 2008, 166 geo-hazards occurred in 14 cities and
counties of the Chongqing Reservoir Region by March 18,
2009. The large Liangshuijing landslide of 3.6 × 106 m3 in
Yunyang County poses a significant threat to the Yangtze
River channel. Geo-hazards will supply an increasing
quantity of sediment into the Reservoir and become the
major factor in the total sediment increase with time.
4.2 Human activities
Human activities, including cultivation on steep slopes,
people relocation and engineering construction, also result
in intensive soil erosion.
Sloping farmland is the predominant source of sediment
delivered to the reservoir. Sloping farmland is 74% of
the total farmland. Steeply sloping farmland of over 25°
is highly erodible and accounts for 14.8% of the total,
especially constitutes up to 76% in Yunyang County and
28.6% in Badong County (Chen 1999). In addition, poor
farming practices, including down-slope tillage, single
crop cultivation, and farming during the rainfall season,
further facilitate soil erosion. The soil erosion modulus
of regional average and sloping farmland is 4484 and
6699 t km-2 y-1, respectively, and is even in excess of 10
×103 t km-2 y-1 in some sloping farmland. It was estimated
that the soil erosion of sloping farmland produced about
94.5×106 t y-1, accounting for 60%–65% of the total (Shi et
al. 1991, 1992), and providing 46% of the total sediment
that was delivered to the reservoir. Soil erosion generally
facilitates geo-hazards occurrence, which in turn result in
more serious soil erosion. Soil erosion induced by forestry
destruction and human activities aggravated the losses
with the huge 1998 flood and triggered many geo-hazards.
Inhabitant Relocation Projects and engineering
construction further accelerate soil erosion. The Three
292
Gorges Reservoir construction caused the relocation of 1.03
million inhabitants to higher areas, which generated new
sloping farmland reclamation and mountain exploitation,
and increased soil erosion by at least 10–12×106 t y-1 (Shi
et al. 1991). Relocation projects created 29.99 km 2 of
eroded land and produced 34.19×106 m3 of waste residue
in only the Wanzhou District, which in turn created about
25.5×103 t y-1 of soil erosion, with a modulus up to 8500 t
km-2 y-1. In addition, engineering construction also created
24.82 km2 of eroded land and 80×106 m3 of soil loss in
only Zigui County. However, soil erosion from Inhabitant
Relocation Projects and engineering construction was
difficult to evaluate accurately because of their inherent
uncertainty.
5 Soil and water conservation measures
The Soil Erosion Control Project of the Middle and Upper
Yangtze River (SECPYR) began in 1989. In this project,
engineering measures, botanical measures and farming
measures are integrated to control soil erosion and reduce
sediment yield.
5.1 Engineering measures
Engineering measures include terracing of sloping
farmland and slope contour-irrigation, and sedimentstorage dams also play important roles in soil erosion
control.
Terracing of sloping farmland is performed as a key
engineering measure. It can not only increase agricultural
product yields, but can substantially control soil erosion
and sediment yield. Observations indicate that terraced
sloping farmland can control the total surface runoff from
a rainfall event of 150 mm in paddy terraces, and one of
70–100 mm with dry-farming terraces, thereby reducing
soil erosion by over 90%. By 2005, 135.7×10 3 ha of
sloping farmlands had been converted into terraces (The
Central People‘s Government of the People’s Republic of
China 2006).
Slope-irrigation engineering, including ponds, pools,
sediment storage dikes, check dams, irrigation channels,
drainage channels, etc., are constructed to collect surface
runoff, impound sediment and facilitate agriculture. By
2005, 20.7×103 check dams and sediment storage dikes,
54×103 ponds and pools, and 46.9×103 km of irrigation
channel and drainage channel had been constructed in this
region (The Central People’s Government of the People’s
Republic of China 2006).
Sediment storage dams, large impoundments designed
to impound significant quantities of sediment, are generally
constructed in valleys to retain the sediment delivered by
flash floods, landslides and debris flows and to generally
mitigate sediment hazards. Sediment storage dams could
be constructed at 145 sites and will store up to about
20×106 t sediment per year (Tang 2005).
Journal of Resources and Ecology Vol.2 No.4, 2011
5.2 Botanical measures
Botanical measures can effectively control soil erosion
and sediment yield. They increase vegetation coverage,
enhance soil water infiltration and reduce surface runoff
so that soil erosion is reduced. Presently, soil and water
conservation forestry, fruit forestry, and recovering forest
and grass in denuded farmland, and similar practices have
been extensively implemented. Moreover, these measures
increased the income of peasants, which inspired them
to expand the areas of botanical measures and devote
more energy to controlling soil erosion. According to
governmental statistic data, 516.7×10 3 ha of soil and
water conservation forest, 182.7×103 ha of fruit forest,
and 470.3×103 ha of grassland had been planted by 2005.
Meanwhile, 486.1×103 ha of land had been prohibited from
farming (The Central People’s Government of the People’s
Republic of China 2006).
5.3 Farming measures
Improvements in farming measures also benefit erosion
control. Soil conservation farming, transverse-slope
farming and contour farming can effectively reduce the
erosion capability of rainfall and control soil erosion.
Contoured hedgerows are being extensively recommended
and adopted throughout the region. Data from Zigui
County showed that it reduced sediment yields by 89.8%–
91.2% (State Environmental Protection Administration
of China 2005). Soil conservation farming is also broadly
used to control soil erosion, which had been applied to
341.8×103 ha of farmland by 2005 (The Central People’s
Government of the People’s Republic of China 2006).
Moreover, crop rotation, intercropping, inter-planting, and
mixed cropping are utilized to assist soil erosion control.
Optimizing the spatial distribution of plants increases
vegetation coverage rate, thereby reducing surface runoff
and decreasing soil erosion.
Generally, engineering measures, botanical measures
and farming measures are integrated in order to maximize
the control of soil erosion.
6 Mode and effects of soil and water
conservation
Watershed integrated management, the major mode of
SECPYR, has been extensively carried out since 1989
and has effectively controlled soil erosion and reduced
sediment yield.
6.1 Watershed integrated management: the case in
Taipingxi watershed
Taipingxi watershed, with an area of about 26.14 km2, is
located in Yiling District, Yichang City. Mountains and
gorges dominate this watershed. Easily eroded yellow soil
predominates. Before watershed integrated management,
the forest coverage was only 23.3%, and 13.6 km2 of the
CUI Peng, et al.: Soil Erosion and Sediment Control Effects in the Three Gorges Reservoir Region, China
293
Fig. 2 Taipingxi watershed after integrated management.
Fig. 3 Water-quality comparison between Three Gorges
Reservoir and Taipingxi watershed.
land was eroded intensively, with an erosion modulus
up to 6037 t km-2 y-1. Soil erosion reached 82.1×103 t y-1,
and 27.81×103 t of sediment was delivered to the Yangtze
River per year (Qin and Yin 1998).
Watershed integrated management began in 1982 and
has been successful. The following measures have been
conducted continuously:
(1) Engineering, botanical and farming measures were
selectively integrated with the object of erosion control.
Ponds, pools, desilting works, irrigation channels and
drainage channels were constructed to collect surface
runoff and sediment, and to prevent sediment transport
out of the watershed. Terracing of sloping farmland, fruit
forestry, and soil and water conservation forestry were
applied to reduce surface runoff and control soil erosion.
Farming measures were improved to further reduce soil
erosion.
(2) The integrated management system, including
engineering, botanical, and other sub-systems, was
established to guarantee the effects of soil erosion control.
As for the botanical subsystem, 745.2 ha of soil and water
conservation forest and 368.8 ha of fruit forest were
planted; 89.4 ha of sloping farmland was reconverted
into forest, and 262.4 ha was prohibited from farming.
The ponds, pools, sediment storage dikes, check dams,
irrigation channels and drainage channels were constructed
in appropriate locations to prevent gully erosion and
control soil erosion and sediment delivery, and also to
improve farming conditions.
(3) Terracing of sloping farmland was implemented
as the keystone of watershed integrated management,
and 108.4 ha of sloping farmland was converted to
terraces. As a result, farmland area increased 60%, and
the average farmland of each person rose from 0.034 to
0.053 ha, which successfully resolved the conflict between
watershed management and any consequent shortage of
farmland.
(4) A mode of “enterprises, farmers and crop bases”
was set up to plant, process and sell fruit crops such as tea,
which increased the income of local peasants, improved
the local economy and provided the necessary financial
support for watershed integrated management.
The observation showed that the eco-environment,
farming conditions and the economic level of this
watershed were significantly promoted after watershed
integrated management of over 20 years (Figs.2 and 3).
Vegetation coverage rose to 72%. The runoff coefficient
dropped from 0.78 to 0.40. The sediment directly delivered
into Yangtze River was reduced on average by 15.3×103 t
y-1 and the modulus of sediment delivery decreased about
81.2%. The efficiency of sediment reduction by soil and
water conservation measures reached 77.2%. 93.5% of
tillage land was utilized economically and scientifically.
The income of crops was improved by 63 times. Due to
the outstanding ecological, economic and social effects,
the Taipingxi watershed was selected as a national
demonstration area of watershed integrated management
and recommended for widespread application in the region
of the Three Gorges Reservoir.
6.2 Results of soil and water conservation
The soil and water conservation project achieved a
notable success in the region. Soil erosion on 21.4×10 3
km2 of land had been controlled by 2005 (The Central
People’s Government of the People’s Republic of China
2006). By 2000, the area of eroded land was 29.56×103
km 2 and occupied 50.9% of the total area, which was
reduced by 15.9% compared to the situation in the mid1980’s (Yangtze Water Resources Commission of Water
Resources Ministry 2007). Paddy farmland, terraced
farmland, fruit farmland and forest increased by 143×103,
104×10 3, 286×10 3 and 204×10 3 ha, respectively. Slope
farmland and grass-shrub land decreased by 76×103 and
55×103 ha, respectively.
Soil erosion data of the Chongqing Reservoir Region
in 1995, 2000 and 2005 in Fig. 4 show that soil erosion
294
Journal of Resources and Ecology Vol.2 No.4, 2011
km2
32000
1995
28000
2000
2005
24000
20000
16000
12000
8000
4000
0
≤500
500–2500
2500–5000 5000–8000 8000–15000
Total
t km-2 y-1
Fig. 4 Change of soil erosion in Three Gorges Reservoir
Region of Chongqing City from 1995 to 2005.
intensity was reduced and that soil erosion was controlled.
The amount of eroded land dropped continuously, the
land with a soil erosion modulus of over 2500 t km -2
y-1 decreased gradually, and the land with a soil erosion
modulus of less 500 t km-2 y-1 increased continually.
7 Sediment-reduction analysis
Based on a few field observations in the entire area,
sediment reduction can be estimated by integrating
experiential formula for soil and water conservation with
data from remote sensing investigations.
7.1 Analysis using the experiential formula
When using the soil and water conservation methodology,
the average modulus of soil erosion reduction was first
calculated according to the reduction modulus and area
percentage of the various measures in practice, and then
the amount of soil erosion reduction was computed.
The average modulus of soil erosion reduction by
watershed integrated management is calculated by the
formula:
s=
n
∑s x
i
(1)
i
i =1
where, S stands for the average modulus of soil erosion
reduction, Si denotes the reduction modulus of soil erosion
by a special measure, and Xi indicates the area percentage
that the measure occupied.
Different soil and water conservation measures
produced various effects on soil erosion control. The
research and observational data in the Three Gorges
Reservoir Region and the nearby areas showed that the
terraced sloping farmland generally reduces soil erosion by
80%–90% and by 85% on average, and by even over 90%
in some watersheds (Cai and Wu 1998). As for botanical
measures, the higher the vegetation coverage rate, the more
that soil erosion is reduced. It was proved that soil erosion
would be reduced by 91.2 t km-2 y-1 in Zuigui County when
the forest cover ratio was increased by 1% (Zheng and
Li 2006), and the transition to forest on sloping farmland
would reduce soil erosion by 85.4%–95.6% (Wang et al.
2007). Pinus forest and conifer and broadleaf mixed forest
could decrease soil erosion by 75.25%–85.21% when
the vegetation coverage reached 70%–80% (Zhang et al.
2007), with a reduction of 80% on average. Fruit forest
could reduce soil erosion by 80% and by 60% under the
conditions of slope irrigation construction and non-slope
irrigation construction, respectively, with a reduction of
70% on average (Tang 2002). The observational data from
runoff plots showed that the soil erosion modulus of shrub
and grassland was only 28.5% that of sloping farmland,
and that grassland with perennial grass species could
reduce soil erosion by 65%, and that planting grass could
decrease soil erosion by 60% on average (Tang 2002).
The efficiency of soil conservation farming on soil erosion
control varies with the different measures applied. Contour
farming and non-furrowing could reduce soil erosion by
66.50%–87.92% and 81.49%, respectively (Li and Zhang
2000). Contour hedgerows could reduce soil erosion by
18.4%–70.0 %, and by 60.8% on average 4 years after
planting (Bu et al. 2008). The investigational data showed
that soil conservation farming reduced soil erosion by 60%
on average, equal to 2700 t km-2 y-1, which was identical
to that of purple soil watersheds in the Jianglinjiang River
basin (Lei et al. 2003). Moreover, prohibiting farming can
decrease soil erosion by 60% with a soil erosion modulus
of less 2500t y-1 (Tang 2002). Data in the Fuling District
proved that prohibiting farming reduced soil erosion by
1250 t km-2 y-1 (Zhou and He 2006), which was close to
that (1 250 t km-2 y-1) in similar areas in the Jianglinjiang
River basin (Lei et al. 2003). Additionally, small
engineering measures, including ponds, pools, sediment
storage dikes, and check dams, could prevent sediment
transport and reduce sediment delivery.
According to the above analysis, the reduction modulus
of soil erosion by soil and water conservation measures is
calculated in Table 1.
With the above analysis, the average modulus of
soil erosion reduction by 2005 was calculated using the
experiential formula and is shown in Table 2.
Table 1 Efficiency of soil erosion reduction by soil and water conservation measures.
Terraced
farmland
Soil and water conservation measures
Efficiency of soil erosion reduction (%)
Reduction standard of soil erosion (t km-2 y-1)
-2
-1
Reduction modulus of soil erosion (t km y )
Soil and water
conservation forest
Fruit
forest
Planting Soil conservation
grass
farming
Prohibiting
farming
85
80
70
60
60
6699
4500
4500
4500
4500
60 (conditional)
–
5695
3600
3150
2700
2700
1250
295
CUI Peng, et al.: Soil Erosion and Sediment Control Effects in the Three Gorges Reservoir Region, China
Table 2 Average modulus of soil erosion reduction by soil and water conservation measures.
Terraced Soil and water
Fruit
farmland conservation forest forest
Soil and water conservation measures
Area (103 ha)
2036
Percentage (Xi) (%)
7751
Planting Soil conservation Prohibiting
grass
farming
farming
2740.7
7094.5
5126.9
Total
7290.8
21 359.6
6.4
24.1
8.6
22.1
16
22.8
100
Soil erosion reduction modulus (Si) (t km-2 y-1)
5695
3600
3150
2700
2700
1250
–
Si Xi
361.8
870.9
269.5
432
341.3
285
2560.5
Table 3 Soil erosion change of the Chongqing section of the reservoir region in 1995 and 2005
(afforded by Professor Wen Anbang and Fan Jianrong).
Soil erosion modulus
(t km-2 y-1)
Mean value
(t km-2 y-1)
1995
Soil erosion (106 t y-1)
8.99
500–2500
1500
2500–5000
3750
15.79
59.21
11.03
41.37
6.4
41.58
5.88
38.22
2.23
25.59
1.01
11.6
5000–8000
6500
8000–15 000
11 500
>15 000
15 000
Total
–
0.2
30.61
Area (103 km2)
5.82
2005
Soil erosion (106 t y-1)
8.73
Area (103 km2)
5.99
3.04
0.13
1.96
138.41
23.87
101.88
Table 2 shows that the average modulus of soil erosion
reduction is 2560.5 t km-2 y-1, accounting for 56.9% of the
average soil erosion modulus of the eroded area (4500 t
km-2 y-1). The investigational data from the soil and water
conservation projects carried out from 1989–1996 showed
that the efficiency of soil erosion reduction by watershed
integrated management generally varied by 43%–72%
(Liao 2009), and was 57.5% on average, and as much as
in excess of 80%. The efficiency that estimated by the
experiential formula was consistent with the investigational
data.
Accordingly, the soil erosion amount was reduced by
54.69×106 t y-1 by 2005. However, the efficiency of soil
and water conservation measures gradually decreases with
time because of the unsustainability of the maintenance
and related reasons. Investigation data showed that soil
and water measures produced about 90% efficiency in the
initial 4–5 years after they were completed and then kept
about 80% efficiency. Therefore, the soil erosion amount
was reduced by 43.75–54.69×106 t y-1 by 2005 because soil
and water measures were completed in succession.
obtained by means of manual identification and computer
auto-identification according to the national standards of
classification of soil erosion intensity (Water Resources
Ministry 2008). This work used the data of TM images of
1995 and 2005 and a 1:50 000 DEM to get the related data
and results, as shown in Table 3.
In calculating the soil erosion amount, the erosion
amount of every intensity was calculated by using the
mean soil erosion modulus for this intensity, and then the
total amount was obtained.
Table 3 shows that the soil erosion amount of the
Chongqing section in 1995 and 2005 was 138.41×10 6
and 101.88×106 t y-1, respectively. Comparing data for
1995 and 2005, the soil erosion amount was reduced by
36.54×10 6 t y -1. Consequently, by extrapolation it was
estimated that the soil erosion amount was reduced by
about 45.94×10 6 t y -1 by 2005 in the whole reservoir
region, because the Chongqing Reservoir Region occupies
about 79.54% of the entire region with similar soil erosion
characteristics and to which the watershed integrated
management mode was applied.
7.2 Remote sensing investigation
7.3 Result analysis
Soil erosion amounts can be calculated on the basis of data
on soil erosion intensity and the area obtained by remotesensing image identification. Furthermore, the change
in soil erosion amount can be assessed with data from
different periods. In this methodology, the corresponding
relationship between remote sensing images and the soil
erosion rate is established and the identification marks
of remote sense images are confirmed based on the
former land use data and field investigation. Then, threedimensional images integrating DEM’s and remote sensing
images are made. Finally, soil erosion information is
The results for soil erosion reduction induced by soil and
conservation measures differed with the methodologies.
The experiential formula indicated that the soil erosion
amount was reduced by 43.75–54.69×106 t y-1 by 2005. The
lower value was calculated on the basis of the influences
of the disadvantageous factors, which was close to the
actual value, and the higher value indicated the effects
under the conditions that all soil and water conservation
measures were applied well, which probably overestimated
the amount.
The remote sensing investigation showed that soil
296
erosion had been reduced by 45.94×10 6 t y -1 by 2005
and that the modulus of soil erosion reduction was 2150
t km -2 y -1. This modulus was very close to that of the
Yichang Reservoir Region. According to hydrologic and
sediment data, it was calculated that soil erosion had been
reduced by 5.22×106 t when 2400 km2 of eroded land was
effectively controlled (Yin and Yin 2002), and the modulus
of soil erosion reduction was 2175 t km-2 y-1. The result
generated by the remote sensing investigation approached
the actual amount and fell in the range obtained from
experimental formulae. Both results appear reasonable.
In term of the above analysis, soil erosion should
be reduced by 43.75–45.94×10 6 t y-1. Additionally, the
sediment delivery rates are variable, from 0.10 to 0.45
in watersheds due to the differences in geographical
environment, with an average of 0.28 in the region (Yang
et al. 1991). Consequently, the sediment delivered to the
Yangtze River was reduced by 12.25–12.86×106 t y-1 by
2005.
8 Conclusions
This study documents that intensive soil erosion is
environmentally and ecologically destructive, and
that in addition it aggravates natural hazards in the
area surrounding the Three Gorges Reservoir. Sloping
farmland was the dominant source of soil erosion and of
sediment delivered to the reservoir. Inhabitant relocation,
mountain exploitation in response to resettlement at
higher elevations, and engineering construction further
aggravate soil erosion and increase sediment yield.
Geo-hazards, including collapses and landslides, will
further exacerbate soil erosion and increase the sediment
yield to the reservoir after completion. The watershed
integrated management, integrating engineering, and
botanical and farming measures, were notably successful
in erosion control, ecological improvement and local
agricultural development. The combination of measures is
designated as the Taipingxi Mode of integrated watershed
management, based on its application in that drainage,
and it is recommended for extension to the entire region.
By 2005, about 21.36×103 km2 of eroded land had been
improved in this way, resulting in notable improvement in
the area, intensity and amount of soil erosion and sediment
yield. Based on analysis of the experiential formula and
remote sensing investigation, it was estimated that soil
erosion was reduced by 43.75–45.94×106 t y-1 and that the
quantity of sediment delivered to the reservoir was reduced
by 12.25 –12.86 ×106 t y-1.
Acknowledgments
This research was jointly supported by State Key Project of
2006BAC10B04, China and CAS Knowledge Innovation Project
of KZCX2-YW-302. The authors are grateful to Professor FAN
Jianrong and WEN Anbang for providing remote sensing data, and
Professor Kevin SCOTT for his good revision in English.
Journal of Resources and Ecology Vol.2 No.4, 2011
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中国三峡库区土壤侵蚀及泥沙控制
崔 鹏1，葛永刚1，林勇明2
1 中国科学院山地灾害与地表过程重点实验室/ 中国科学院/水利部成都山地灾害与环境研究所，成都 610041；
2 福建农林大学林学院，福州 350002
摘要：三峡库区严重的土壤侵蚀与泥沙输移是三峡库区泥沙重要的来源之一，威胁三峡工程安全。坡耕地是三峡库区泥沙主
要源地，占入库泥沙的46%；大规模的库区后靠移民工程引起的土地利用变化与山区开发及三峡工程建设过程的工程扰动加剧了土
壤侵蚀与产沙。三峡工程建设及运行后引发的滑坡、泥石流等地质灾害将进一步增加入库泥沙量。为了有效控制三峡库区土壤侵
蚀，减少水土流失，保护库区环境，从1989年开始以小流域综合治理为典型模式的水土保持工程在三峡库区广泛开展，有效控制
了库区土壤侵蚀与泥沙输移。宜昌市夷陵区太平溪小流域综合治理模式是三峡库区小流域综合治理的成功模式，文章分析了其治
理模式与水土保持及泥沙控制效益。应用水保法评价了三峡库区水土保持与小流域综合治理的减沙效益，并把评价结果与遥感监
测分析法进行了对比分析，认为两种评价结果均在可接受范围。结果表明经过16年的水土保持与小流域综合治理，截至2005年三
峡库区年均减少土壤侵蚀43.75–45.94×106 t ，减少入库泥沙12.25–12.86×106 t 。
关键词：土壤侵蚀；产沙量；泥沙输移；水土保持；小流域综合治理；三峡库区