GIS-based spatial and temporal prediction system development for regional land subsidence hazard mitigation

An integrated GIS-based approach for establishing a spatial and temporal prediction system for groundwater flow and land subsidence is proposed and applied to a subsidence-progressed Japanese coastal plain. Various kinds of fundamental data relating to groundwater flow and land subsidence are digitized and entered into a GIS database. A surface water hydrological cycle simulation is performed using a GIS spatial data operation for the entire plain, and the spatial and temporal groundwater infiltration quantity is hereby obtained. Through the data transformation from the GIS database to a groundwater flow code (MODFLOW), a 3D groundwater flow model is established and unsteady groundwater flow simulation for the past 21 years is conducted with results which compare satisfactorily with observed results. Finally, a Visual Basic code is developed for land subsidence calculations considering aquifer and aquitard deformation. Future land subsidence in the plain is predicted assuming different water pumping scenarios, and the results provide important information for land subsidence mitigation decision-making.     

Three-dimensional numerical modeling of land subsidence in Shanghai,China

Shanghai, in China, has experienced two periods of rapid land subsidence mainly caused by groundwater exploitation related to economic and population growth. The first period occurred during 1956–1965 and was characterized by an average land subsidence rate of 83 mm/yr, and the second period occurred during 1990–1998 with an average subsidence rate of 16 mm/yr. Owing to the establishment of monitoring networks for groundwater levels and land subsidence, a valuable dataset has been collected since the 1960s and used to develop regional land subsidence models applied to manage groundwater resources and mitigate land subsidence. The previous geomechanical modeling approaches to simulate land subsidence were based on one-dimensional (1D) vertical stress and deformation. In this study, a numerical model of land subsidence is developed to simulate explicitly coupled three-dimensional (3D) groundwater flow and 3D aquifer-system displacements in downtown Shanghai from 30 December 1979 to 30 December 1995. The model is calibrated using piezometric, geodetic-leveling, and borehole extensometer measurements made during the 16-year simulation period. The 3D model satisfactorily reproduces the measured piezometric and deformation observations. For the first time, the capability exists to provide some preliminary estimations on the horizontal displacement field associated with the well-known land subsidence in Shanghai and for which no measurements are available. The simulated horizontal displacements peak at 11 mm, i.e. less than 10 % of the simulated maximum land subsidence, and seems too small to seriously damage infrastructure such as the subways (metro lines) in the center area of Shanghai.     

Large differential land subsidence and earth fissures in Jiangyin,China

Jiangyin County is in the infamous Su–Xi–Chang land subsidence area caused by excessive groundwater withdrawal in Jiangsu province, China. The maximum accumulated land subsidence reached 1,310 mm near the centre of the subsiding trough in 2006 in southern Jiangyin, and earth fissures of significant vertical offsets have been observed at Changjing, Hetang and Wenlin which form an arc towards the subsidence trough. An ancient Yangtze River course is found underlying and passing through the depression in southern Jiangyin, forming a local basin surrounded by outcropped bedrock ridges in the north and south. The Quaternary stratigraphy demonstrates significant heterogeneities in the basin; the second confined aquifer is much thicker and deeper and encapsulated inside the basin and absent above the ridges. The development of earth fissures along the Changjing–Hetang–Wenlin arc might be a combination of an inward rotation of sediments due to a large differential subsidence, an inward movement driven by seepage force and a steeper slope along the south-eastern shoulder of the basin that facilitates the development of horizontal tensile strain and/or shear strain necessary for fissuring. The land subsidence has slowed down and no new earth fissure zone has occurred in the area after the banning of deep groundwater extraction was enacted in 2001.     

Long-term groundwater level changes and land subsidence in Tianjin,China

Acta Geotechnica - A large volume of groundwater is withdrawn annually in Tianjin Municipality, China, to meet agricultural, industrial, and municipal water uses. Groundwater overdraft in the urban...     

Point-line-area-volume index system of land subsidence and application in Ningbo,China

Natural Hazards - Traditional land subsidence indices primarily describe the characteristics of land subsidence at a given site, but such indicators cannot satisfy the requirements for effective...     

Risk assessment of land subsidence at Tianjin coastal area in China

Risk assessment and zoning are very important to risk management. In this study, a land subsidence risk assessment index was proposed based on the Disaster Risk Index. The cumulative subsidence volume, the land subsidence velocity, and the groundwater exploitation intensity were collected, analyzed, and put together to create a land subsidence hazard evaluation map in Tianjin coastal area. The population density, Gross Domestic Product per square kilometer, and construction land proportion were adopted as indexes to create the vulnerability map. In addition, the capability of land subsidence prevention and reduction was also assessed. Finally, the land subsidence risk map was created by combing the hazard, vulnerability, and the capability of land subsidence prevention and reduction map. Specifically, the land subsidence risk was classified into five levels, i.e., very high, high, medium, low, and very low. The result of this research could provide a solid basis for the sustainable development as well as disaster prevention policy-making of Tianjin city.     

Regional land subsidence simulation in Su-Xi-Chang area and Shanghai City, China

Su-Xi-Chang area and Shanghai City, located in the south of Yangtze Delta, China, has subsided due to groundwater overpumping. Because of the regional scale of the groundwater exploitation, cone of depression and land subsidence at present, Su-Xi-Chang area and Shanghai City are treated as a single area for land subsidence study to avoid the uncertainty of boundary condition due to the regionalism. The characteristics of aquifer system compaction are complex because of the difference in the types, compositions and structures of the soils that the hydrostratigraphic units are composed of, and in the histories of groundwater level change the hydrostratigraphic units have experienced. Considering the fact that different hydrostratigraphic units have different kinds of deformation and that an identical unit may also present different deformation characteristics, such as elasticity, elasto-plasticity, and visco-elasto-plasticity, at different sites of the cone of depression or in different periods, corresponding constitutive laws have been adopted. This avoids the shortcomings of the previous research that the same constitutive law was adopted in all the hydrostratigraphic units during the entire time period. A coupled flow and subsidence model, which includes a three-dimensional flow model with variable coefficients and a one-dimensional (vertical) subsidence model, is built according to the complicated hydrological condition in the region. The simulation model is calibrated using observed data, which include compression of individual strata from groups of extensometers and groundwater levels from observation wells from 1995 to 2002. The model reproduced that the primary subsidence layer in Shanghai shifts from the shallow aquitard to the fourth confined aquifer because of the groundwater yield variations and the change of exploitation aquifers. However the third aquitard was the primary subsidence layer in Su-Xi-Chang area and the compaction deformation of the sandy aquifers was remarkable. The simulation results could provide some reasonable advice about groundwater exploitation in the future.     

我国地面沉降模拟现状及需要解决的问题

我国现有模型有下列特点:水流模型都是准三维模型,模型中的参数都是常数,沉降模型采用线弹性模型,水流模型和沉降模型的耦合分二步进行.因此,模型还存在难以精确刻画由弱透水层释水引起的地面沉降,不符合准三维模型的应用条件.水流方程应是一个变系数的动态水流方程,渗透系数、贮水率不应视为常数.土层压缩非线性,有蠕变、塑性变形存在,沉降模型采用线弹性模型不适合,对土层厚度变化大的地区沉降模型必须是三维的,滞后现象必须克服.如何描述引起地裂缝的水平位移,分两步进行的耦合不合适,要做到水流模型与沉降模型的真正耦合等八个方面的步骤.本文提出分三步进行的解决方案:首先采用三维水流模型,以便不仅给弱透水层建立方程,还能考虑它的各向异性,参数值能随着土层的变形沉降而不断改变.沉降模型为能考虑蠕变、塑性变形的非线性模型;水流模型和沉降模型要做到能真正耦合.其次,解决滞后问题.最后,建立三维沉降模型,考虑水平位移和地裂缝问题.     

Excessive groundwater withdrawal and resultant land subsidence in the Su-Xi-Chang area,China

Excessive groundwater withdrawal has caused severe land subsidence in the Su-Xi-Chang (SXC) area, China. The restriction and prohibition on groundwater pumping have been carried out since the late 1990s. Based on the latest updated field data, the changing pattern of groundwater level and the distribution of land subsidence are analyzed. The distribution of land subsidence in SXC is closely related to that of the cone of depression in the second confined aquifer in time and space. But land subsidence is not in synchronization with the changing groundwater level. Both aquitards and aquifers compacted continuously in the early period of groundwater level rising and behaved as creep materials. A series of laboratory tests were conducted on aquifer sands, which indicated that the creep deformation under virgin compression is much greater than that under recompression and unloading, and that the creep of sands decreases rapidly with the cycles of repeating load. The test results reveal the mechanism of sand creep under the condition of long-term groundwater pumpage. As a consequence of the restriction and prohibition on groundwater pumping, groundwater level has obviously recovered in the vast majority of the SXC area, and land subsidence has slowed down and even a little rebound has occurred in some sites in Suzhou and Changzhou. If the pumpage is strictly limited continuously, the groundwater level will not decline below the historical lowest value but fluctuate within a certain range. In such a case, land subsidence in SXC will no longer develop obviously.     

Characterization and mechanism of regional land subsidence in the Yellow River Delta, China

In this paper, we discuss historical and recent land subsidence in the Modern Yellow River Delta. Integrated analysis of leveling and relevant background data, including groundwater level, oil extraction, and geological structure, has revealed that land displacement is driven by natural and induced components acting at various depths. Since the 1950s, intense settlements occurred in the modern estuary delta lobes. Between 2002 and 2008, the subsidence center of Dongying and Guangrao exhibited a typical subsidence area with subsidence rates of 28.2 and 64.7 mm/years, respectively. Higher magnitudes are associated with groundwater withdrawals and oil–gas field exploitations, which induce the compaction of a deep clayey layer. There existed a significant linear positive correlation between groundwater level and elevation in the center of the deep groundwater depression cone. The major contributor of natural subsidence is tectonic movements, while moderate sinking due to the natural consolidation of the recent delta subsoil is still acting.     

Sustainable development and utilization of groundwater resources considering land subsidence in Suzhou,China

Suzhou is located at the lower reaches of the Yangtze River in southeastern Jiangsu, China. It is part of the Su-Xi-Chang area including Suzhou, Wuxi and Changzhou. As one of the most developed areas in China, this region has suffered from severe land subsidence caused by extensive groundwater exploitation since 1980s. The land subsidence was controlled by prohibition of groundwater exploration in the past several years. However, the surface water pollution prompted a new task of how to sustainably utilize the groundwater resource, especially to satisfy the emergency demands of water supply. In this paper, we took Suzhou as a representative case to discuss how to develop groundwater resources while controlling the land subsidence. The relationship between the deformation and the groundwater level was analyzed, with focus on the deformation features after the period of groundwater exploitation ban. The results confirmed the conclusion by Shi et al. (2007, 2008a): even in the period of rising groundwater level, same units may manifest different deformation characteristics, such as elasticity, elasto-plasticity, and visco-elasto-plasticity, at different locations of the cone of depression. A land subsidence model that couples a 3-D groundwater model and a 1-D deformation model was developed to simulate the groundwater level and deformation. A high-resolution local grid (child model) for Suzhou was built based on the regional land subsidence model of Su-Xi-Chang area by Wu et al. (2009). The model was used for a number of predictive scenarios up to the year of 2012 to examine how to develop sustainable use of groundwater resources under the conditions of land subsidence control. Our results indicated that about 3.08 × 10⁷ m³/a groundwater could be provided as emergency and standby water source while meeting the land subsidence control target of 10 mm/a.     

中国沿海地区可持续发展战略与地面沉降系统防治

沿海地区为我国社会经济发展战略的中心，地面沉降和海平面上升已成为其实现可持续发展战略面临的重大环境问题。地面沉降由于区域性和不可逆性，其危害是永久的；并由此将派生一系列相关的地质灾害及环境、社会问题。地势低平、地质环境脆弱的沿海地区，地面沉降系统防治具有重大的战略意义。本文根据可持续发展理论，运用系统工程原理，对地面沉降进行了系统分析，全面提出了水资源管理和地面沉降系统防治的技术性对策和政策性意见。     

The development and control of the land subsidence in the Yangtze Delta,China

Land subsidence in China occurs predominantly in 17 provinces (cities) situated in the eastern and middle regions of the country, including Shanghai, Tianjin and Jiangsu, and Hebei provinces. It is primarily caused by groundwater overpumping. One of the areas most severely affected by land subsidence is the Yangtze Delta, most of which consists of Shanghai City, the Su-Xi-Chang area (Suzhou, Wuxi and Changzhou cities) of Jiangsu Province, and the Hang-Jia-Hu area (Hangzhou, Jiaxing and Huzhou cities) of Zhejiang Province. The excessive exploitation of groundwater forms in a large regional cone of depression and, consequently, land subsidence is also regional, currently centered in the Shanghai and Su-Xi-Chang areas. In 2002, the maximum cumulative subsidence of Shanghai, Su-Xi-Chang and Hang-Jia-Hu were 2.63 m, 2.00 and 1.06 m, respectively. The land subsidence area is continuing to expand throughout the Yangtze Delta. To study the characteristics and the pattern of this land subsidence, the government has implemented a monitoring system involving the placement of 37 groups of extensometers (layers marks) and drilling of more than 1000 observation wells. These provide an invaluable historical record of deformation and pore water pressure and facilitate studies on the special features of soil deformation when the groundwater level changes due to pumping. Several measures have been taken in recent years to control the development of the land subsidence in the different areas; these include groundwater injection, prohibition of pumping deep confined groundwater, and an adjustment of the pumping depth and magnitude of the groundwater withdrawn. At present, although the subsidence area is still increasing slowly, the subsidence rate is controlled.     

The state of land subsidence and prediction approaches due to groundwater withdrawal in China

This article gives a general introduction to land subsidence with the prediction approaches due to withdrawal of groundwater in three subsided/subsiding regions in China: the deltaic plain of Yangtse River (YRDP), North China Plain (NCP), and Fenwei Plain (FP). On YRDP, Shanghai is the typical subsided/subsiding city; on NCP Tianjin is the typical subsided/subsiding city, and on FP Taiyuan is the typical subsided/subsiding city. The subsided area with subsidence over 200 mm on YRDP is about 10,000 km² and the maximum subsided value reached 2.9 m at Shanghai; on NCP the subsided area reached 60,000 km² with the maximum subsidence of 3.9 m at Tianjing; on FP the subsided area is relatively smaller than that on the other two plains and is about 1,135 km² with maximum subsidence of 3.7 m at Taiyuan city. In order to protect the civil and industrial facilities, it is necessary to predict the future development of land subsidence based on present state. Many researchers proposed several approaches to predict the land subsidence due to groundwater withdrawal according to different geological conditions and groundwater withdrawal practice. This article classifies these approaches into five categories: (i) statistical methods; (ii) 1D numerical method; (iii) quasi-3D seepage model; (iv) 3D seepage model; (v) fully coupled 3D model. In China, the former four categories are presently employed in the prediction practice and their merits and demerits are discussed. According to the prediction practice, 3D seepage model is the best method presently.     

Characterization of land subsidence induced by groundwater withdrawals in Su-Xi-Chang area, China

Su-Xi-Chang area is one of the typical regions in China which suffers from severe land subsidence. Various tools of field monitoring were integrated to study the characteristics and mechanisms of land subsidence in this region. The occurrence and the development of the land subsidence in this region are strongly related to the groundwater pumping both in time and space. The main consolidation layers are the soft mud layers; however, the compressibility of the confined sandy layers should not be ignored. The second and third confined aquifers contributed more than 30% of total subsidence. Meanwhile, irrecoverable deformations were also observed in the sandy layers. Different sandy layers deform diversely under different stress conditions. Some have the elastic feature. But the soil strata, including both sandy layers and clayey layers, located in the center of the groundwater level depression cone exhibited obvious viscous mechanical behavior which caused the common lag phenomenon. The sand composition (mingled with small clay particles or interbeds) and sand rheology are the two main reasons for the lag phenomena in sandy layers. A series of laboratory tests for modeling the effective stress changes due to groundwater withdrawals, were conducted to investigate the mechanism of the lag phenomenon. Based on the test results, the relationship of stress–strain–time for saturated sands is obtained; and it could be expressed as power functions. The results also showed that the compression of the sandy layers was time dependent, and its deformation could be remarkable. When establishing land subsidence model, the deformation for the similar soil formation could be elastic, visco-elastic and even visco-elastic–plastic, because of the different groundwater level fluctuation experienced.     

Finite-difference model of land subsidence caused by cluster loads in Zhengzhou,China

Groundwater exploitation has been regarded as the main reason for land subsidence in China and thus receives considerable attention from the government and the academic community.Recently,building loads have been identified as another important factor of land subsidence,but researches in this sector have lagged.The effect of a single building load on land subsidence was neglected in many cases owing to the narrow scope and the limited depth of the additional stress in stratum.However,due to the superposition of stresses between buildings,the additional stress of cluster loads is greater than that of a single building load under the same condition,so that the land subsidence caused by cluster loads cannot be neglected.Taking Shamen village in the north of Zhengzhou,China,as an example,a finite-difference model based on the Biot consolidation theory to calculate the land subsidence caused by cluster loads was established in this paper.Cluster loads present the characteristics of large-area loads,and the land subsidence caused by cluster loads can have multiple primary consolidation processes due to the stress superposition of different buildings was shown by the simulation results.Pore water migration distances are longer when the cluster loads with high plot ratio are imposed,so that consolidation takes longer time.The higher the plot ratio is,the deeper the effective deformation is,and thus the greater the land subsidence is.A higher plot ratio also increases the contribution that the deeper stratigraphic layers make to land subsidence.Contrary to the calculated results of land subsidence caused by cluster loads and groundwater recession,the percentage of settlement caused by cluster loads in the total settlement was 49.43%and 55.06%at two simulated monitoring points,respectively.These data suggest that the cluster loads can be one of the main causes of land subsidence.     

Analysis of urbanisation-induced land subsidence in Shanghai

Since 1980, land subsidence has accelerated and groundwater levels have decreased in the centre of Shanghai, although the net withdrawn volume of groundwater has not increased. Theoretical analysis of the monitored data shows that the decrease in the groundwater level is the primary reason for the observed land subsidence. Meanwhile, the net withdrawn volume of groundwater in the urban centre of Shanghai has not increased during this period. Many underground structures have been constructed in the multi-aquifer-aquitard system of Shanghai since 1980. This paper discusses the factors related to the development of land subsidence during the process of urbanisation in Shanghai during the past 30?years. These factors include additional load during and after structure construction, the cut-off and/or partial cut-off effect of underground structures in aquifers, the decrease in the groundwater level due to leakage of underground structures and the reduction in recharge of groundwater from the surroundings.     

Monitoring land subsidence in Semarang,Indonesia

Semarang is one of the biggest cities in Indonesia and nowadays suffering from extended land subsidence, which is due to groundwater withdrawal, to natural consolidation of alluvium soil and to the load of constructions. Land subsidence causes damages to infrastructure, buildings, and results in tides moving into low-lying areas. Up to the present, there has been no comprehensive information about the land subsidence and its monitoring in Semarang. This paper examines digital elevation model (DEM) and benchmark data in Geographic Information System (GIS) raster operation for the monitoring of the land subsidence in Semarang. This method will predict and quantify the extent of subsidence in future years. The future land subsidence prediction is generated from the expected future DEM in GIS environment using ILWIS package. The procedure is useful especially in areas with scarce data. The resulting maps designate the area of land subsidence that increases rapidly and it is predicted that in 2020, an area of 27.5 ha will be situated 1.5–2.0 m below sea level. This calculation is based on the assumption that the rate of land subsidence is linear and no action is taken to protect the area from subsidence.     

天津新生界固结特征与地面沉降

本文通过对大量的室内试验和大港油田测井资料的分析和总结,从地层的固结状态和固结阶段两个方面系统分析了天津地区新生界固结特征与地面沉降的关系,认为:天津新生界地层在原始应力状态下,除滨海地区第一海相地层和坳陷区局部2500m以下地层为欠固结状态外,其余基本为正常固结;但在地下水长期超采区,长期超采的含水组地层为超固结状态。1000m以浅的地层处于初期压实阶段,仍会有较多的孔隙水被排除,而导致比较明显的地面沉降。