Land Subsidence in China
QIAN
ZHANG
MAAD
QZHANG2@SHEFFIELD.AC.UK
Abstract: Land subsidence has already become one of the most common geologic
hazards over the world. With accelerating of industrialization, urbanization and worldwide
climate change, Land subsidence obstructs the process of sustainable development. The
problem of Land subsidence also affects all aspects in China. This essay is going to explore
the phenomenon and provide some tangible proposal for the future.
Key Words: Land Subsidence; Climate Change; Sustainable Development
Introduction:
Land subsidence is a phenomenon that the earth sinks down gradually, which usually
caused by human activities and natural reasons. It is a global problem that had occurred in
more than 50 counties, for instance, United State, Japan, Italian, United Kingdom, India,
China ect. Most of these countries have a rapid speed development on industry and urban
construct. Therefore, the U.N pay a high attention on this problem. In 1964, the IHD (IHP) put
the Land subsidence problem into their research field. The UNESCO also established a
professional workshop and organized international conference to discusses this topic in
Tokyo (1969), Venice (1984), Houston (1991), Shanghai (2005) (Shiliang Gong, 2008).
In U.S.A, the subsidence area has reached to 4.4×100000 km2 and become the most
serious country for the problem of Land Subsidence. The subsidence speed in Houston
reached to 73cm/a and the land had subsidenced about 3 meters from 1906 to 2000(R. K.
Gabrysch，2005). At the same time, the hazard is also very striking in some Asia countries.
The first time of the subsidence had recorded in Japan was in 1898 in Niigata, the speed
reached to 57cm/a. Now, there are about 59 districts and regions had occurred the Land
Subsidence; because of rapid increasing of population in India, the require of underground
water has risen correspondingly, which led to water lever had drop down. Between August
and September in 1986, there were a few of potholes turned up on the road near Gangers
river. Until August in 2003, the road collapse caused by land subsidence, and resulted in
overload truck got into it and multiple-storey apartments occurred titled. (Shiliang Gong, 2008).
In China, the
earliest record can go
back to 20s, 30s in 20
century in the city of
Shanghai and Tianjin. The
Land subsidence had
already quite severe in
1960s. When in 70s,
some primary cities in the
coastal area, like Jiangsu,
Wuxi,
Changzhou,
happened
subsidence
one after another, while
other districts produce oil
in northeast also been
found this problem to
some extent. Today, there
are more than 90 cities
suffered the disaster, and
most of them distributed
at east-coaster cities.
The geologic hazards happened in 2006
(http://www.mlr.gov.cn/zt/2006dizhihuanjinggongbao/ Accessed in 23/04/2012)
This essay is going to elaborate the reasons of Land subsidence from both internal
and external aspects and illustrate effects on all social fields in China. Finally, some proposal
will be given out.
Reasons:
The reasons of Land subsidence can be various, but generally it can be classified
into two categories: human activities and natural interrupts.
Firstly, the Land subsidence caused by natural force can also be divided into 3
possibilities: 1）when loose or semi-loose surface layer forced by the gravity into dense and
hard layer, the land would occur subsidence because of decreasing thickness of the layer; 2)
the sunken caused by the geological process would push the happen of Land Subsidence; 3)
earthquake is another possibility.
Secondly, with the economic development of human society, diversity of irrational
human economic activities, production activities, and human engineering construction lead to
degradation of urban ecosystem, growing rate and area of land subsidence. In densely
populated cities, land subsidence phenomenon is particularly serious, man-made factors
have greatly exceeded the natural factors. Recent decades, in order to meet the needs of
Chinese over speed development, human over-exploitation of underground resources, like oil,
gas, solid minerals, groundwater, made reduce of pore pressure in sedimentary layer, where
in the storage of these solids, liquids and gases. The change results in a direct result of land
subsidence in China even globally today. Besides, as the city expanded, tall buildings stand
up, railways, bridges and other transportation facilities load on land, surface load increase,
and also to accelerate the Land Subsidence.
The causes of Land Subsidence
(http://www.globaltimes.cn/NEWS/tabid/99/ID/696841/Govt-shores-up-sinking-land.aspx Access in 23/04/2012)
Effects:
Serious land subsidence and the disaster it had caused have a great impact on
national economic construction in Chinese eastern region and the ecological environment
over there. As a result of the low sea lever in coastal area, Land subsidence will be further
loss of ground elevation, ground subsidence also affect on land crack, deformation of
underground well pipe, decreased flood control function, failure of national survey mark,
sewer drainage, reduced the gap between bridge and ground, the deterioration of water
quality; ground construction such as skyscrapers, highways, railways, docks, airports are also
subject to suffer to some extent: the coastal region due to the greenhouse effect has led to
rising sea levels, and if land subsidence overlay the rising sea levers, a large amount of the
coastal lowland will be submerged by sea.
1, The loss of ground elevation lead to accumulation of surface water, decreased
capacity of flood control and flood discharge in rainy season, reduced ability to resist storm
surges in coastal. In coastal areas, the subsidence of land is equal with rise of sea lever and
resulting in invasion of seawater and storm surge disasters exacerbate. At the same time, the
embankments not only have a significant substantial, but also create a partial cracking and
reduced defense capability.
2. Urban pipe network damaged. Urban water and gas supply pipeline bended with
uneven ground subsidence and deformation, leading to leaking of these urban pipeline, and
then brought about a direct impact on public life and industrial production. In Shanghai, it had
taken place Land Subsidence that break the large-diameter (300 am) gas pipes and lead to
gas leakage (Shiliang Gong, 2008).
3, Railway safety is threatened. Due to uneven sinking of railway embankment that
caused by Land Subsidence, railway safety is threatened. For example, the Beijing-Shanghai
Railway goes through the subsidence area in Cangzhou City Centre. Because of the railway
embankment subsidence, roadbed gravel cushion in Cangzhou City Center had been
thickened 500 nl, it does not only cause economic losses but also affect the railway safe
operation (Shiliang Gong, 2008).
4, Relatively shallow groundwater has caused a series of environmental problems
and urban construction problems. In coastal areas, the decline in land-based ground
elevation，relative rise in sea levels, seawater intrusion, shallow groundwater table become
more shallow, deterioration of water quality, these environmental problems are all caused by
Land Subsidence. Besides, the damage also reflects on urban construction: first, the
foundation bearing capacity of the urban buildings decline, which result in the destruction of
the foundations of buildings; secondly, the disaster accelerates the corrosion of concrete and
metal pipe, the erosion enhanced; Thirdly, it reduces the intensity of transportation routes
subgrade, shorten the service life; Fourthly, it effect on urban greening, the survival rate of
trees becomes lower; Fifth, it increases the cost of urban construction; Finally, it stresses on
land salinization, industrial and agricultural using of water.
5, Frequent ground crack
endanger the urban and rural safety.
Land Subsidence and ground crack
have internal relationship: uneven Land
Subsidence induced ground crack.
Ground crack can mainly harm for
housing cracking, destruction of ground
facilities, and farmland leakage.
(http://www.nmgcb.com.cn/html/201111/18/content_77714.htm Accessed in 23/04/2012)
Proposal:
Because of land subsidence is a continuous, gradual and cumulative geological
disasters, what human now and even the future can do is only slowing down or controlling the
momentum of the sinking, but not to recover and restore to the original condition, but if left the
land subsidence to develop, it will be disastrous. Therefore, develop and implement a rational,
comprehensive system of land subsidence control strategy system is imperative, it can
include the following aspects:
1),
To strengthening the monitoring of ground subsidence. Investigation and long-term
monitoring is the only viable methods to study the incident and the development process. The
practical data and information collected by monitoring the land subsidence can be used for
the future planning and policymaking.
At the same time, because groundwater level changes in land subsidence is the most
direct and effective factor to reflect ground condition, therefore, to strengthen the monitoring
of groundwater level can not only control the surface subsidence development trend and
possible trend, but also understand the change situation of the exploitation and recharge
groundwater level at the real-time. So it also becomes important test of the indicators for land
subsidence control measures. As to the monitor technology, groundwater should take
monthly monitoring as period, and take use of automated monitoring technology to observe
the implementation of each aquifer. Meanwhile, drawing the regional groundwater level
changes graph in time to keep the informed of groundwater level changes and water level,
and to track and evaluate the role of impact of groundwater extraction and recharge, to adjust,
and improve the pattern of groundwater extraction and filling.
2),
To control groundwater exploitation. Excessive extraction of groundwater is the main
reason and the most direct and continuous factors for land subsidence, so strictly limit the
exploitation of groundwater, to control the amount of groundwater mining and strength of
exploitation are the fundamental measure to effectively prohibit the further deterioration of
land subsidence. Only effectively reduce the amount of groundwater exploitation of the deep
aquifer that would guarantee the natural recovery of the aquifer system and reduce the
additional load of the aquifer and its adjacent strata, thereby slowing down the developmental
speed of land subsidence.
Historically, in the '50s and '60s of the last century in China, the concentrative of
exploitation at the shallow aquifer lead to serious land subsidence; in the mid-1960s the way
of exploitation was adjusted to be "scattered mining” and “ explore from shallow to deep
system”; and then 40 years later, it had returned into new way of concentrative exploitation.
All of these methods were provide to be failure. Therefore, how can we avoid these mistakes?
Now, it is suggested that greatly reduce groundwater mining of the deep aquifer in areas near
and outer suburb areas to avoid the ground subsidence (Shiliang Gong, 2008).
Strictly limit the exploitation of groundwater, can be implemented in three ways:
Firstly, to control the total annual mining will quickly reduce the overall level of exploitation. It
is recommended that the
annual extraction volume
should gradually reach and
does not exceed the 5000X
104m3 /a, the out of city area
should stop the non-drinkable
groundwater exploitation.
(http://www.chinanews.com/n
/2003-07-02/26/319986.html
Accessed in 23/04/2012)
Secondly, control the intensity of exploitation and avoid over long time exploitation.
The best way to provide a natural and necessary recovery for groundwater is to take the way
of intermittent mining. The time gap is quite important and necessary for the groundwater
level to recovery. Thirdly, "reasonably and specifically use of groundwater”. Put the valuable,
the quality of groundwater resources into the mainly use of people's lives for drinking and part
of the food, fine chemical water industry to meet special requirements on the water quality. To
eliminate the other industrial ways use of groundwater, and gradually to adopt the surface
water and the tap water network system to meet the needs of industry and other enterprises,
so that the total level of groundwater extraction can be reduced effectively.
Therefore, to reduce the over exploitation of groundwater extraction is the most
important measures to avoid ground subsidence. Practically it has already been applied in
many cities in China and has been proven to be effective measures. Issued the "Shanghai
deep Interim Measures, for instance, Shanghai had clearly defined the management
approach of the various types of wells in the issue of <Shanghai Interim Measures for the
administration of deep well>, and strictly controlled the city's groundwater extraction. Mining
amount from more than 30 million m3 a day in 1950s, to reduce to 40000 m3 a day in the
1980s, and the groundwater level get picked up. Land Subsidence from annually 22mm
reduced to 5mm and surface subsidence essentially was eased (Shiliang Gong, 2008).
3)
Artificial recharge of underground aquifers. Recharge of groundwater is to use
artificial irrigation methods to improve the water table in order to ease the effects of
sedimentation rate. To use of mathematical models of groundwater mining not only can
reasonable develop and utilize groundwater, but also to achieve the purpose to control land
subsidence. In this respect, Shanghai is the pioneer over the world. The use of artificial
recharge methods that “winter irrigation in summer and summer irrigation in winter” had
controlled surface subsidence. Since 1996, land subsidence in Shanghai has basically been
alleviated. Thus, it is worth to be learned for each settlement area.
Strengthen the artificial groundwater recharge work should involve the participation of
government, because on one hand, through government can get the sufficient investment and
drill specialized wells for artificial groundwater recharge. The government will take the
responsibility of operational fees, like drill, equipment maintenance and daily running cost and
it will be powerful enough to ensure the recharge volume increases gradually; on the other
hand, government have enough resource to strengthen scientific research, improve the
recharge layout and make scientific and reasonable technical scheme; in another aspect, it
can help the establishment and improvement of mutual coordination and management
between different monitor authorities, and effectively improve the recharge effect, avoid
personnel material waste in recirculation process, and raise scientific utilization.
4)
To strengthen scientific research. It should include carried out to reduce the
exploitation of groundwater water and recharge groundwater mitigation quantitative study of
the practical effect of land subsidence; promote the use of land subsidence in the threedimensional visualization technology; rely on high-tech to strengthen monitoring, the
establishment of unified GPS monitoring network, universal automatic monitoring of
groundwater technology development and research interference in synthetic aperture radar
technology, land subsidence monitoring.
“Many international scholars proposed many approaches to predict land subsidence due to
groundwater withdrawal according to different geological condition and ground water
withdrawal practice. There are so many approaches to predict and calculate land
subsidence. … the prediction methods are summarized into five categories: statistical model ,
numerical analysis in early stage, quisi-3D analysis, and 3D analysis.”
5)
Management and legislation. Land subsidence monitoring and prevention measures
should be developed under the principle of optimized cost-effectiveness, but in this process, it
will not only involve technical measures, but more important is that each of the land
subsidence monitoring and control measures leads to a series of social economic issues.
Only under the premise of the strict laws and regulations, and with the support form
government with economic guarantee, all sectors of society can cooperate for the common
interests (the main social benefits) in order to obtain the effectiveness treatment for land
subsidence monitoring.
Conclution:
Land subsidence as an extensive geological disaster, it has a closed relationship
between urbanization and the balance between economic development and natural resource.
Under the principal of sustainable development, it is necessary to consider the fundamental
reasons and look for an effective and sustainable way to solve this problem with a critical
thinking.
Scenario:
12/09/2020 cloudy
It is a normal day in Shanghai, hurry and busy people walk on the Nanjing Road with
their big steps and intensive face. The cloud floats in the low air like an inspector. The air is
flooding with damp drops that mixed with redundant carbon dioxide. Although Shanghai had
been identified by IPCC as a city that not long suitable for living as a result of the nature of
soft land and the factor that over-exploration of underground water had make the city like a
hollow funnel. People still keep their own pace to develop this city. So many more NO1.highrise building that reach 1000 meters had been built up after the Shanghai World Financial
Center to make Shanghai became an advanced modern city over the world. Millions and
thousands of travellers came from the world arrived here to visit these buildings and
experience this city, which push the further development of the city as well as increase the
load for the ground. However, some problems had already turned up as a warning for human.
More and more news about the land subsidence in Shanghai city had been reported on the
newspaper. Last year, at the most flourishing cross of Nanjing Road, it had happened a big
incidence, hundreds of passages died. Too many cases of unpredictable subsidence had
happened surrounding living communities, gardens and other public areas, which lead to a
serious economic loss. Importantly, some times of underground collapse caused a fatal strike
to the transportation system. There are totally 30 routes in Shanghai now, which is most in
the world. The space under the ground seems nearly to be occupied by those routes. Since
the no4 underground accidence in 01/07/2003, there were several more serious underground
collapse had caused a big scale land collapse and influenced the land building surrounding.
Last week, a big hole turned up in ground floor of a new living community. At the same time,
the Oriental Pearl TV Tower had been detected as a small margin of tilt because of the
uneven subsidence of the land. It earned its new name as “Shanghai Leaning Tower”. The
underground water and heating support system also had suffered. Because of the uneven
land subsidence, the pipes to provide water and heat under the ground were blend and
broken in a big scale. People’s normal life was interrupted. The need for drink water are
increasing, now almost all of the drinking water were transformed from other cities, which
means the exploration amount of underground water in other cities are also rising. More
worse, the ever risen sea lever pose a big threaten to this city. Every time with the hide tidy of
Huangpu River, the flooding run into the city, ruined the social facilities, destroyed green area
and disturb social order. The sea lever of Shanghai is just 4 meters in 2012 in average, now it
had sunk into 3 meters, while the highest height of tide can reach to 5 meters, if the
subsidence is continued, the whole city would become a city under water.
Reference:
1, Shiliang Gong, The Comprehensive Analysis of The Impact Factors for Land Subsidence in
Shanghai and Land Subsidence Control Countermeasures, PhD dissertation, East China
Normal University, 2008
2, Ye-shuang XU, Shu-guo2 YU, Shui-long SHEN, State-of-the-art of Approaches of
Predicting Land Subsidence due to Groundwater Withdrawal, Journal of Disaster Prevent ion
and Mitigat ion Engineering, Vol. 26 No. 03 Aug. 2006
3, http://www.mlr.gov.cn/zt/2006dizhihuanjinggongbao/ Accessed in 23/04/2012
4,http://www.globaltimes.cn/NEWS/tabid/99/ID/696841/Govt-shores-up-sinking-land.aspx
Accessed in 23/04/2012
5, http://www.nmgcb.com.cn/html/2011-11/18/content_77714.htm Accessed in 23/04/2012
6, http://www.chinanews.com/n/2003-07-02/26/319986.html Accessed in 23/04/2012