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Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
669
DOI: 10.4408/IJEGE.2011-03.B-073
DEBRIS FLOW DISASTER IN THE UPPER REACHES
OF THE CHANGJIANG RIVER, CHINA
Xie HONG
(*,**)
, y
onG
li
(*,**)
, Zhong DUNLUN
(**)
& f
anQianG
w
ei
(*,**)
(*)
Key Laboratory of Mountain Hazards and Earth Surface Processes, Chinese Academy of Sciences - Chengdu 610041, China
(**)
Institute of Mountain Hazards and Environment, Chinese Academy of Sciences & Minister of Water Resources
Chengdu 610041, China
the total length, 4500km upper to Yichang, the Up-
per Reaches of the river. The Upper Reaches is lo-
cate in 24°28′ - 35°50′ N, 90°30′ - 111°20′ E and its
drainage area is 100.5×10
4
km
2
.
Debris flows in the areas are severely active,
chiefly due to the complexity of geology, abun-
dance of faults, recurrences of earthquakes, dete-
rioration of eco-environment; and more directly, to
the concentrated precipitation of typical mason cli-
mate as well as to the irrational activities of human
in constructions (e.g. wanton clearance of forest
and cultivation on precipitous slope) (t
anG
et alii,
1993; C
HenG
1999; s
Hi
et alii, 1999).
DISASTERS OF DEBRIS FLOWS
In the last decade, debris flows have caused loss
of 120-180 million dollars in the area, killed tens or
hundreds each year. Historic record indicates that
there were 17 events that killed more than one hun-
dred persons between 1753-1997 (Figure 1). Damages
are mainly caused to towns and villages, to factories
and mines, and to other constructions.
DAMAGE TO TOwNS AND VILLAGES
Towns and villages are commonly located on
debris-flow fans in mountains because of the scarcity
of land (Photo 1). About 50 counties are under the
menace of debris flow, distributing in Sichuan, Yun-
nan, Qinghai, Gansu, Hubei, and Chongqing, and most
counties had suffered from the disasters. For instance,
ABSTRACT
The upper reaches of Changjiang River are the most
serious regions of debris flow disasters. Nearly 50 coun-
ties and cities as well as hundreds of towns are under
menaces of 6 800 gullies of debris flow. Every year de-
bris flow claims deaths of tens to hundred and causes
economic loss amounting to 120-180 million US dollars,
which has lagged and limited the development in the
areas. Debris flow gullies are widely distributed in the
Upper Changjiang, which stretches eastwards across two
geomorphologic transition zones in China: 1) the tran-
sition zone from the Qinghai-Xizang Plateau, down to
the Yunnan-Guizhou Plateau, where develop rainy and
glacial debris flows; and 2) the transition zone from the
Yunnan-Guizhou Plateau to the area of middle moun-
tains and hills, where dominate the rainy debris flows.
The concentration in the first zone mainly depends on
the more favorable conditions compared to the second:
such as the higher altitude, greater relief, and more con-
centrated precipitation. Hundreds or thousands of debris
flows occur here each year. Coarse grains are playing the
dominating roles, e.g. pebbles of more than 20 mm in
diameter counts for 49.8% (weight percent) in average.
K
ey
words
: debris flow; debris-flow disasters and features;
the upper reaches of Changjiang; China
INTRODUCTION
Changjiang (Yangtze) has a drainage area of
18×10
5
km
2
, 56% of which expands over 71% of
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X. HONG, Y. LI, Z. DUNLUN & F. wEI
670
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
There are 511 debris-flow gullies along the CK line.
Since July 1, 1970 when the whole line joined up,
there have been 18 stations buried by debris flows
that overturned 3 trains, washed out 2 bridges, and
killed more than 370 persons. Along the 627km of
Chengdu-Baoji railroad there are 159 debris flow
gullies, and 134 debris flows occurred in 1981, which
buried seven station and blocked the traffic for more
than 60 days. To be compounded, the Dongchuan
branch railway has 86 debris flow gullies within 50
km in the south, which have frequently destructed
bridges and tunnels since it operated in 1964 and fi-
nally broken the line in late 1980s (Photo 3).
Highways are also often blocked in rainy seasons
by debris flows in the area. For example, debris flow
in the Harmu gully in Lixian, Sichuan caused a month
of suspension of the No. 213 national line from Lix-
ian to Wenchuan in 1989 (x
ie
et alii, 1994). Recent-
ly, a 400m road in Songpan was inundated by water
a debris flow hit Badong County, Hubei, on August 8,
1991, killed and injured 58 persons, destroyed 1 394
houses, buried 70 warehouses, closed 43 factories and
110 shops. It brought about 6 million dollars of loss.
In each county of Wudu, Xichang, Hanyuan, and Nan-
ping, more than 10 debris flows occurred in the last 200
years. As to the villages and towns, they are more fre-
quent victims. From 1950-1990, in 7 counties (Yibin,
Pingshan, Leibo, Jinyang, Ningnan, Huidong, and Hu-
ili) of Sichuan, there had been fifty-two sites of severe
disaster where debris flows caused death of 171 and
loss of 5 million dollars (z
HanG
et alii, 1995). On July
12, 2003, debris flow in Qiongshangou gully in the up-
per Dadu, Danba county, caused 51 death and missing,
and brought damage to more than 5000 people.
DAMAGE TO FACTORIES AND MINES
There are 20 large and medium mine fields under
the threat of debris flows in Sichuan, Yunnan, and
Guizhou. On May 27, 1984, a debris flow hit Yinmin
copper mine, killed 120 people, destroyed almost
all the facilities, closed the mine, the school and the
market for half a month, resulted in a loss of 1.5 mil-
lion dollars (t
ian
, 1986). As another case, 34 deaths
and 29 injuries were claimed by a debris flow in Yi-
men mine, Huili, Sichuan, on May 31, 1990, which
devastatingly destroyed the factories and buildings
and caused a loss of 500 thousand dollars.
Railway lines in the area, especially the major
Chengdu-Kunming line (the CK line), Chengdu-
Baoji line, and the branch Kunming-Dongchuan
line are famous for their disasters of debris flows.
Fig. 1 - Map
of
hazard
points of more than
killed >100 people
in one debris flow
occurrence in the
upper reaches of
Changjiang River
Fig. 3 - Debris flow blocks river course, harm traffic and
farmland in Dongchuan, Yunnan
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DEBRIS FLOW DISASTER IN THE UPPER REACHES OF THE CHANGJIANG RIVER, CHINA
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
671
DAMAGE TO RIVERS
Debris flows carry large quantity of sediment
into main streams lift the water level and enforce the
destructive power. The Xiaojiang basin is one of the
most serious areas of debris flow, it extends 139 km
northwards and has 123 tributaries along both sides, of
which 107 gullies are concentrated within 90km and
form 78 fans in the lower river (d
u
et alii, 1987) .Some
gullies are active in their fans making at the mouths as
typically shown by the Dabaini gully who had in the
past 30 years extended its fan area from 0.52 km
2
to
1.43 km
2
, lifted depth of 20.7 m, accumulated volume
of 2.4×107 m
3
. Another case is the famous Jiangjia
gully, having its fan area up to 2.6 km
2
with radius of
1.6km on average, top depth of 100m, and volume of
7.4×10
7
m
3
(w
u
et alii, 1990) .As a result, the Xiao-
jiang is constantly in course of bed uprising and stream
winding, compounded by flood inundating in rainy
season and sand devastating in drought (Photo 3).
CHARACTERISTICS OF DEBRIS FLOW
QUANTITY AND TYPE
There have been 6 800 gullies of debris flow re-
corded in the upper Changjiang; and the special physical
location and great relief and differentiation in rocks de-
termine the diversity and intensity of debris flows (x
ie
et alii, 1994), Table 1 indicates a complete set of debris
flow type only with the exception of volcanic case.
DISTRIBUTION
The upper Changjiang transverses two geomorpho-
logic zones: 1. transition zone from the Qinghai-Tibet
Plateau of more than 4 000m a.l.t. down to the Yunnan-
Guizhou Plateau of 1000-2000 m a.l.t, including re-
gions of Hengduan Mountains, mountain areas around
the Sichuan Basin and in the south of Gansu, where de-
velop rainy and glacial debris flows that are especially
active in northeastern Yunnan, western Sichuan, and
southern Gansu; and 2. transition zone from the second
terrace to the areas east to the Wu Mountains of 500m
a.l.t., covering regions of Mts. Dalou, Wu, and Daba,
where develop debris flows in 920 gullies and slopes.
Great relief is responsible for the distribution. In par-
ticular, the concentration of debris flow in the first zone
is mainly dependent upon the facilitating conditions.
The area is near the collision zones of Indian and
Ore-Asian plates where the tectonic actions are strong
with deep and large faults and frequent earthquakes.
dammed by debris flow in Minjiang River. Statistics
indicates that some 2 000 thousand dollars had been
cost in reconstructing the destroyed lines only in 1986.
Navigation is also blocked by debris flows. For
instance, 99 debris flows have formed beaches in
the center of the river, which have so far suspended
the navigation in the upper stream from the Xinshi
town (near the county of Leibo).
DAMAGE TO AGRICULTURE
Debris flows destroy agriculture generally by in-
undation, washing, siltation and impact. For example,
in Qiaojia, Yunnan, 171 ha farmlands were buried by
a debris flow on August 24, 1980, lost ripening rice
and sugar-cane of about 2800 t. Moreover, an event
on May 6, 1989 buried 134 ha lands of sugar-cane,
destroyed water-conservancy systems including 13
drainage channels and a 1800 m dam, and brought
about damages in monetary of 200 thousand dollars to
17 villages with more than 4 000 habitants.
DAMAGE TO LIVING CONDITIONS
The high mountains and precipitous slopes in the
upper Changjiang and at the same time threatened by
debris flows that would once and forever destroy the
cultivated lands and limit cultivation of land. For in-
stance, in June and July in 1981, debris flows in La-
oshugou of Qiaojia washed and buried farmlands of
24 ha, and forced 14 families to relocate.
DAMAGE TO HYDROPOwER ENGINEERING
Water power available in the upper Changjiang
amounts to 1.7×10
8
kw, 45% the total in China. But
the utilization is constantly under the menace of de-
bris flows. There are 146 and 271 debris-flow gullies
in the area of Ertan Hydroelectric Power Station and
the Three Gorges. Debris flows reduce the reservoir
capacity and adjustability of power production due
to siltation of sediments. For example, the Gongzui
Power Station in the lower Daduhe River had an
average sediments yield of 3.5 ×10
7
t/yr in 1971-
1990, but an annual yield of 10
8
t in 1989 when the
summer witnessed debris flows on the eastern slope
of Mt. Gongga. Entrance of sediments cut operat-
ing life of station, as confirmed by so many small
scale stations. For examples, 23 out of 32 stations
in Maoxian County of Sichuan were devastatingly
destroyed by debris flows in July, 1981.
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X. HONG, Y. LI, Z. DUNLUN & F. wEI
672
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
tween 1965-1994 (with a data loss of 1986), Jiangjia-
gou gully had a record of 362 occurrences (w
u
et
alii, 1990; z
HanG
& x
ionG
1997), especially with the
extreme recurrences of 28 in a year (Rapp, a et alii,
1991). Liuwangou gully has 11 occurrences in annual
average, and Huoshaogou, 3-4(Lanzhou Institute of
Glaciology and Ggocryology, CAS, and Institute of
Communication Science, Gansu 1982).
TRANSPORTATION CAPACITY
Debris flows are of great power in carrying large
quantity of sediment and blocks from the source ar-
eas to the deposition areas or into the main rivers
(Table 2). Deposits of debris flows are characterized
by the poor-sorted and large-ranged particles, cover-
ing a radius domain of magnitude 10
7
. The biggest
boulder measured in debris flows in the area of Dadu
river is of 10 m×6 m×4 m. Coarse grains are playing
the dominating roles, e.g. pebbles of more than 20
mm in diameter counts for 49.8% (weight percent)
in average, as confirmed by 69 samples chosen out
from Niurihe (a tributary of Dadu River), Anninghe
and the tributary Sunshuihe, and Yalongjiang, as well
as other tributaries of Jinsha (Table 3).
SCOUR AND SILT
Intensive scour and silt are major effects of de-
bris flows and also the most active agents sculpturing
landform. A debris flow in August 1981 scoured the
This results in slope instability and erosion as the
causes of debris flows. Along the faults develop riv-
ers of Baqu-Benzilan of Jinshajiang, Anninghe, Xi-
anshuihe, Longchuanjiang, Zemuhe, Xiaojiang, and
Bailongjiang, where debris flows are concentrated with
12 gullies per 10km, and occur in frequency as high as
6-28 cases a year in Jiangjiagou gully (d
u
et alii, 1987).
Most debris flows develop in valleys smaller than
4 km
2
, counting for 72.7% of the total, as revealed by a
statistic conducted in the CK line with 366 debris flows
within the Sichuan (Chengdu Institute of Mountain
CAS 1990). And in 6 counties in the lower Jinsha, gul-
lies smaller than 10 km
2
count for 67.3% out of 346;
and for the Reservoir of Sanxia, 70.1% out of 271 gul-
lies are smaller than 5 km
2
(d
u
et alii, 1990) Along the
Chengdu-Baoji railroad, 74% gullies are below 2 km
2
.
The upper Changjiang spans 11º22' of latitude and
has a relief between 2 500-3 500 m, accompanied by
the striking horizontal and vertical zonality of alpine
climate which are not concerned with the develop-
ment of debris flows.
FREQUENCY
Debris flow is frequent in the study area. In every
year occur hundreds or thousands of occurrences.
Some are recurrent, such as Daqiaohe, Dabaini, Xi-
aobaini, Jiangjiagou, in Dongchuan, Yunnan, and
Huishaogou, Beiyugou, Liuwangou, in Wudu, Gansu,
and Xiahuangtian in Miyi, Sichuan. For instance, be-
Tab. 1 - Debris flow types in the upper Changjiang
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DEBRIS FLOW DISASTER IN THE UPPER REACHES OF THE CHANGJIANG RIVER, CHINA
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
673
Debris flow is one of the most vital agents of geol-
ogy, especially in destroying environment and accel-
erating landform change as well as affecting human
activities through erosion, siltation, scouring, trans-
portation and deposition. Debris flows in this area
present a variety of appearances and provide a stage
for practice of various control measurements.
CONCLUSION AND ACKNOWLEDGMENTS
This study is supported by Chinese Ministry of
Water Conservation Special Fund for Public Welfare
Industry Project.
The monitoring and prevention for dam-break flood
by landslide and debris flow in the upper Minjiang River.
channel down to 7-13 m. And a landslide-turned debris
flow on September 14, 1974 in Baimeiya, Nanjiang,
Sichuan, swept its way of 4 900 m from the landslide
( in volume of 7×10
6
m
3
) to deposit ( in a fan of 107
m
3
) in less than 5 minutes. It eroded the bedrock chan-
nel up to more than 10m, formed a fan of 2.5×10
5
m
2
,
caused a 50-60 m thick siltation in the base of Qipingsi
gully. Besides, it blocked Banqiao gully and dammed
1.3×10
5
m
3
of water. An action in several minutes, and
an effect of great change, one can feel with it at this
case. As for Jangjiagou, debris flows had blocked Xi-
aojiang 16 times from 1919 to 1968. The 1968 block-
age lasted as long as 3 months, lifting water level by
10m, inundating farm lands and villages along.
CONTROL OF DEBRIS FLOW
Since 1949, measures preventing and control-
ling of debris flow have been adopted in the upper
reaches of Changjiang. Measures including engi-
neering structures, plantation, prediction and warn-
ing, as well as danger degree division have reduced
losses to a certain extent (Photo 4).
Debris flow lags and limits economic develop-
ment in mountainous areas in the upper reaches of
Changjiang. Further studies on theory and control
measurements are urgent.
Tab. 2 - Sediment transportation of several debris flows
Tab. 3 - Grains consists in debris-flow samples (in percentage of weight)
Fig. 4 - Check dam for prevention debris flow in Heishui,
Sichuan
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X. HONG, Y. LI, Z. DUNLUN & F. wEI
674
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
REFERENCES
C
HenG
G. (1999) - Forest change: hydrological effects in the upper Yangtze River Valley. AMBIO, 28: 383-386.
C
HenGdu
i
nstitute
of
m
ountain
H
azaRds
and
e
nviRonment
, Cas. (1989) - Research and prevention of debris flows. China:
Sichuan Science and Technology Publishing House,Chengdu. (In Chinese)
d
u
R
onGHuan
, k
anG
z
HiCHenG
, C
Hen
x
unian
,
et
Alii
(1987) - Survey and prevention of debris flows in the Xiaojiang area,
Yunnan. Science and Technology Literature Press, Chongqing. (In Chinese)
d
u
R., l
iu
x., y
uan
J.,
et
Alii
(1990) - Research of landslides and debris flows in the Three Gorges Project area. Sichuan Science
and Technology Publishing House, Chengdu: 177-183.
l
anzHou
i
nstitute
of
G
laCioloGy
and
G
eoCRyoloGy
(Cas) & i
nstitute
of
C
ommuniCation
s
CienCe
, G
ansu
. (1982) - Debris flow
in Gansu.The People’s Communication Press, Beijing. (In Chinese)
R
aPP
a., l
i
. J. & n
ybeRG
R. (1991) - Mudflow disasters in mountainous areas. AMBIO, 20: 210-218.
s
Hi
P. & l
i
w. (1999) - Rehabilitation of degraded mountain ecosystems in southwestern China: an integrated approach.
AMBIO, 28: 390-397.
t
anG
R. & H
an
w. (1993) - Active faults and earthquakes in Sichuan. Seismology Press, Beijing. (In Chinese)
t
ian
l. (1986) - Reports on debris flows of Heisha gully in Yinmen Mine in Dongchuan, Yunnan. Debris flow, 3: 52-57. (In
Chinese)
w
u
J., k
anG
z., t
ian
l.
et
Alii
(1990) - Observatory researches on debris flows of Jiangjiagou Gully, Dongchuan, Yunnan.
Science Press, Beijing. (In Chinese)
x
ie
H., z
HonG
d. & w
ei
f. (1994) - Distributions and hazards of debris flow in the upper reaches of Changjiang. Journal of
Mountain Research, 12 (2): 71-77.
z
HanG
J. & x
ionG
G. (1997) - Dynamic observatory data of debris flows of Jiangjiagou Gully, Yunnan. Science Press, Beijing.
(In Chinese)
z
HonG
d., l
iu
s. & x
ie
H. (1995) - Status of debris flows in Sichuan in the lower Jinsha. Debris flow, 4: 20-29. (In Chinese)
Statistics