Land subsidence and earth fissures due to groundwater withdrawal in the Southern Yangtse Delta,China

Excessive extraction of groundwater has caused severe land subsidence and earth fissures in the Southern Yangtse Delta, China. Based on field data, the temporal and spatial distribution of land subsidence is investigated and the causes for earth fissures are analyzed. The areal distribution of the land subsidence is closely related to the cones of depression in the main exploited aquifers. The compaction of a hydrostratigraphic unit depends on its mechanical behavior, thickness, compressibility, and the piezometric level changing. The primary subsidence layers in Shanghai have been the first aquitard before 1990 and the third confined aquifer since then. But the second aquitard unit was the primary subsidence layer in Changzhou. Earth fissures, trending in several directions, occurred in the Husu tectonic zone. They were mainly caused by differential subsidence and horizontal displacement that resulted from tensile stress and shear stress in units. The majority of fissures in the study area are tensile.     

Sea level rise and impacts on nearshore sedimentation: an overview

 Impacts on nearshore sedimentation arising from potential sea level change of the magnitude predicted in Intergovernmental Panel on Climatic Change scenarios associated with global warming are reviewed. For sandy duned coasts, the obvious sedimentation impacts include potential erosion of coastal dunes with implied deposition of the eroded material in the nearshore, possible deepening of embayments, and flooding of wetlands. For the sandy coasts a number of two-dimensional models are available for predicting shoreline change, but there are significant difficulties in applying Bruun-type models for dune erosion and assessment of sediment redistribution over the inner shelf, and for predicting the amount of shoreline retreat for a given rate of sea level rise. If the beach profile contains excessive sand relative to its equilibrium profile, sensu Dean (1991), then shoreline retreat may not occur upon sea level rise. From the evidence of Kiel Bay, at least in these semi-enclosed basin types, it is during major transgressions that maximum deposition in adjacent basins occurs, due to the sea eroding weakly consolidated and weathered surface regolith. But at the same time climatic patterns were re-adjusting and probably contributed to maximum deposition in adjacent shelf and basins below wave base. Received: 16 June 1995 / Accepted: 29 January 1996     

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.     

江阴南部地区建筑荷载和地下水开采与 地面沉降耦合研究

针对江阴南部地面沉降问题,结合地下水开发利用现状和城市建设规划,根据比奥固结理论,引入黏性土流变理论,将土体本构关系拓展至黏弹塑性,并考虑土体的土力学参数和水力学参数随应力场的动态变化,建立江阴南部地区建筑荷载、地下水开采与地面沉降三维全耦合数值模型,分别模拟预测了江阴南部地区2015年12月31日至2030年12月31日建筑荷载、地下水开采单独作用及二者叠加作用三种情况下地面沉降发展趋势。模拟结果显示,建筑荷载为引起江阴南部地区地面沉降的主因,其次是地下水开采,二者的主压缩层分别为第Ⅰ黏性土弱含水层和第Ⅱ黏性土弱含水层,分别占总压缩量的42.94%和62.60%;建筑荷载和地下水开采叠加作用下引发的地面沉降具有耦合效应,二者叠加量小于单独作用引发量的线性叠加。     

Land subsidence due to groundwater withdrawal in Arak plain,Markazi province,Iran

With current trends of groundwater exploitation, the plains of Iran have been facing numerous problems, where subsidence is considered as the foremost obstacle. In the present study, the principle aim was to analyze the level of groundwater and induced subsidence effects in different regions of Arak plain from 2002 to 2008. Arak plain located in Meyghan Lake basin is subjected to subsidence process as a result of the declining groundwater levels. Monthly variations of groundwater levels were plotted using ArcGIS software. The results indicated declining water levels especially in Meyghan Lake than the Arak plains, resulting up to 36 m of drop in the groundwater levels of marginal areas in the plains during these years.     

Sulfate transport in a Coastal Plain confining unit, New Jersey, USA

 A transient 1-D, two-pathway non-equilibrium deterministic advective dispersion model was used to examine the distribution of chloride (43–100 mg/L) and sulfate (57–894 mg/L) concentrations in the 35-m-thick section of the Lower confining unit, Atlantic Coastal Plain, New Jersey, USA. The model was used to constrain hypotheses about how pore-water chemistry changed over time. Explanations of the solute concentrations were explored by inverse and direct methods given a few known constraints, including concentrations of pore-water constituents from 12 core samples, reported simulated flow rates, and estimated hydrogeologic properties. The hypothesis that is best supported by the model results is that the distribution of chloride and sulfate concentrations in the confining unit reflect the history of the aquifer system since it was filled with seawater at the last eustatic high, about 84×10³yr BP. The model simulates fresh-water flushing of the seawater-permeated silts at a steady upward pore-water flow velocity of 8.8×10^–6 m/d, with a dispersion coefficient of 9.2×10^–7 m²/d, a dimensionless partition expression for chloride, β_Cl=0.981, and a dimensionless exchange coefficient, ω_Cl=0.31×10^–2. Sulfate concentrations were simulated over the flow path using flow and dispersion values calculated for chloride transport plus a retardation term. Parameters for sulfate transport include retardation coefficient=4.51, β_SO4=0.994, and ω_SO4=0.31×10^–2. Sensitivity analysis indicates that the model is most sensitive to flow velocity, and that fresh-water flushing of the confining unit is best simulated by having seawater concentration levels at the inflow boundary of the confining unit exponentially decrease with a concentration half-life rate of 825 yr. Received, January 1997 / Revised, April 1998, October 1998, January 1999 / Accepted, January 1999     

末次间冰期ENSO对全球海平面上升响应的模拟研究

末次间冰期的全球年平均地表气温比现今高0~2 ℃, 这一增温幅度与未来预估的增温幅度相当。因此, 末次间冰期气候往往被认为是未来气候的一个类比。本研究利用挪威地球系统模式(NorESM1-F)开展末次间冰期模拟, 并进一步讨论全球平均海平面上升5 m和10 m时末次间冰期的ENSO海温变率。模拟结果表明: 模拟的末次间冰期热带太平洋年平均海表面温度较工业革命前普遍偏低, 这与地质记录重建基本一致。与工业革命前相比, 模拟的末次间冰期El Niño事件强度偏弱, 极端El Niño事件偏少; 而La Niña事件强度偏强, 极端La Niña事件偏多; 随着全球平均海平面的上升, 海表温度异常出现变化, 表现为小于0.5 ℃的海温异常出现的频率减少, 而大于0.5 ℃的海温异常出现频率增加, 表明全球平均海平面的上升会使海温的异常更加明显, 但全球平均海平面的上升对模拟的末次间冰期ENSO事件的频次及平均强度影响并不显著。

     

Nitrogen isotope indicators of seasonal source variability to groundwater

 A nitrogen isotope study of soil water and groundwater in southern Indiana, USA, in 1991–1992 demonstrated considerable variations in nitrate degradation processes compared to an earlier investigation in 1986–1987. Although N-fertilizers were applied in May 1991, the δ¹⁵N values in soil water decreased in February 1992, indicating its delayed release into the system after substantial rainfall. The δ¹⁵N values of groundwater decreased from +12.3‰ in November 1991 to +11.3‰ in February 1992, and to +7.5‰ in March 1992. The increased residence time of nitrate in the soil resulted in increased denitrification, ammonia volatilization and plant uptake, and reduced threat to the groundwater quality. The 1986–1987 study in the area reported that excessive rainfall during the summer rapidly transported the nitrate to deeper horizons and drastically reduced volatilization and microbial reduction of nitrate, thus increasing the immediate threat to the groundwater quality in the area. The present study demonstrated that nitrogen isotopic signatures can be used to determine the effects of local soil type, rainfall, and land-use practices on the fate of nitrate in the subsurface. Received: 18 February 1997 · Accepted: 17 June 1997     

Groundwater pollution due to sugar-mill effluent, at Sonai, Maharashtra, India

 Analyses of 126 samples collected from 18 dug wells in the shallow basaltic aquifer over a period of 7 months have revealed spatial as well as temporal changes in the chemical properties of groundwater. While the temporal changes have been attributed to dilution and concentration phenomena governed by climatic factors, the spatial variations in the geochemical characteristics of groundwater appeared to be related to pollution due to effluents from the Mula Sugar Factory. The cause of groundwater pollution is the effluent carried by a stream flowing through the area. Fluctuations in the groundwater table, influent water quality character of the stream, less capacity to accommodate large volume of effluent and occurrence of zero base flow (under natural conditions) in the stream are the factors favoring infiltration of constituents of waste water into the underlying weathered basaltic aquifer. Pollutants have entered into the shallow aquifer by downward percolation through the zone of aeration to form a recharge mound at the water table and, further, lateral movement below the water table. The plume of polluted groundwater has a lateral extent of a few meters in the upstream area and more than 400 m on either side of the stream in the downstream part. The zone of polluted groundwater has an areal extent of more than 3.5 km². Groundwater is the only source available for drinking and agricultural purposes. It is recommended that the base of the lagoons and the stream used for release of plant effluent should be waterproofed for the protection of groundwater in the Sonai area. Received: 30 April 1997 · Accepted: 23 September 1997     

Groundwater level and chemistry changes resulting from tunnel construction near Matsumoto City, Japan

 Before tunnel construction began, the groundwater chemical compositions and levels around the tunnel were studied to determine if water compositions could predict whether surface water will be influenced by tunnel construction. When the chemical composition of the well and springwater was similar to that of the tunnel seepage water, and the altitude of the well and spring was above the tunnel level, the groundwater level in the well and spring was influenced by draining tunnel seepage water. Therefore, comparing the chemical compositions of surface water and groundwater may be used for predictive purposes. However, the results of this study showed there was no noticeable chemical composition change in springwater prior to changes in groundwater level at a particular site. The changes in the hydrology of the plateau caused by tunnel construction were also studied, using measurements of the changes in groundwater chemistry as well as changes in groundwater levels. Prior to tunnel construction, river discharge was greater. Following tunnel construction, some river discharge decreased because springwater was drained as tunnel seepage water and the spring in the catchment dried up. Tritium concentration indicated that 3 years after tunnel construction, surface water did not reach tunnel levels in spite of groundwater level lowering and remaining unconfined groundwater being drained. Received: 17 January 1996 · Accepted: 10 July 1996     

Hydrochemistry of aquifers in the southern Dead Sea area,southern Jordan

 The demand for water resources in the area south of the Dead Sea due to continued development, especially at the Arab Potash Company (APC) works necessitates that water quality in the area be monitored and evaluated based on the local geology and hydrogeology. The objective of this paper is to provide information on the past and present status of the main aquifers under exploitation or planned for future development. Two main aquifers are discussed: the Safi water field, presently being operated, and the Dhiraa water field, which is being developed. The aquifer developed in the Safi water field is shallow and fed by the Hasa fault system, which drains a significant portion of the Karak mountains. This aquifer seems to be well replenished within the core, where no obvious long-term degradation in water quality can be identified. However, in the low recharge areas within the distal portions of the alluvial fan, there has been a degradation in water quality with time. The degradation is caused by the dissolution of the Lisan Marl, which is present at the outskirts of the fan system, based on hydrochemistry of water in the wells. The Dhiraa field is a deep (800–950 m) aquifer drilled specifically for the extraction of brackish water present in the Kurnub aquifer. Available data indicate that there are at least three distinct water types within this field. These water types are variable in quality, and there may be potential for mixing of these waters, thus affecting the quality of the freshest waters presently available. Tritium and oxygen isotope analysis indicate that the water is old and possibly nonrenewable. Received: 24 July 1995 · Accepted: 26 September 1995     

未来上海地区海平面上升对土压缩模量的影响分析

未来上海地区海平面上升将引起地下水位抬升,将会对土压缩模量E产生影响。E是土的最重要的物理力学参数指标之一,尤其在地基沉降计算中具有重要意义。本文主要针对土压缩模量Es的预测分析工作,进行了地基变形的探讨研究,供交流参考。     

Investigation of groundwater flow in karst areas using component separation of natural potential measurements

 The natural (electrical) potential (NP) method – also known as self-potential, spontaneous potential and streaming potential (SP) – has been used to locate areas of groundwater flow in karst terrane. NP is the naturally occurring voltage at the ground surface resulting from ambient electrical currents within the earth. The measurement of NP can be used to characterize groundwater flow in karst terrane because electrical potential gradients are generated by the horizontal flow of water along fractures or conduits and the vertical infiltration of water into fractures or shafts. NP data from a site on the Mitchell Plain of southern Indiana, USA, revealed that NP data can be decomposed into three components: topographic effect, residual NP and noise. At this site, NP was inversely proportional to elevation, but the correlation varied with time. The topographic correction factor varied from –2.5 to –1.2 mV/m (NP change per unit elevation increase), with an average linear correlation coefficient (R) of 0.95. Because the site slopes toward an adjacent creek that is the local groundwater discharge zone, one possible explanation for this effect is a streaming-potential mechanism generated by groundwater movement toward the creek. The residual NP data revealed three negative anomalies at the survey area. Two of them coincide with sinkholes. A part of the third anomaly is coincident with a small valley, and concentrated infiltration does occur at this elevation in other valleys at the site, as evidenced by the existence of sinkholes. However, the dispersed, low-magnitude nature of the third anomaly does not prove the existence of concentrated groundwater recharge activity. Received: 18 March 1998 · Accepted: 27 April 1998     

Yangtze Delta, China: Taihu lake-level variation since the 1950s, response to sea-level rise and human impact

 Hydrological records collected from water gauge stations since the 1950s demonstrate that the Taihu lake level is rising. The average rate of the lake-level rise is 0.4–1.1 mm/year during the non-flood season, resulting directly from a rise in sea level. High rates of 3.0–5.0 mm/year of rise are even recorded during the wet season. This indicates increasing human activities such as reclamation, sluicing and embanking, which significantly hinder the expulsion of extra lake water to the coast shortly after a rainfall. Generally, the lake level of the western inlet is higher than that of the eastern outlet. However, the lake-level difference between the west and east has been diminished annually from ∼10–15 cm in the 1950s to <3 cm at the present time. During non-flood seasons, the lake-level difference even appears to be reversed, indicating a retrogression of the lake flow from east to west. It is predicted that the Taihu drainage basin will lose much of its natural water-expelling ability in the next 50 years as the sea level continues to rise, and retrogression will likely occur during the flood season in the near future. Received: 13 March 1998 · Accepted: 21 July 1998     

Groundwater pollution due to discharge of industrial effluents in Venkatapuram area, Visakhapatnam, Andhra Pradesh, India

 Hindustan Polymers Limited was established in the Venkatapuram area in the northwestern part of Visakhapatnam urban agglomeration. Untreated industrial effluent from the plant is discharged with total dissolved solids concentrations reaching up to 6500 mg/l. The groundwater pollution was identified as early as 1981 and a hydrogeologic and water-quality database is available from 1981. The groundwater quality in the plant environs is found to be in the range of 3500–4500 mg/l. Major chemical constituents of industrial-waste waters consist of Na, Cl, and SO₄. Some characteristic parameters of the aquifer were estimated. The available hydrogeologic and hydrologic data was analyzed to conceptualize the groundwater regime. A mathematical groundwater flow model was constructed to compute the hydraulic head at the center of finite-difference grid. The computed head distribution and effective porosity of the formations were used to calculate the groundwater flow velocity. The computed velocity field was ultimately used to prognose the pollutant migration in groundwater accounting for the advection and dispersion processes in the mass transport model and for determining the time-dependent pathlines of pollutant. Areal migration of pollutants from the source was predicted up to year 2002. Received: 23 December 1996 · Accepted: 9 September 1997     

中国近海潮汐变化对外海海平面上升的响应

针对外海海平面上升对中国沿海潮波系统和潮汐水位可能带来的影响,通过西北太平洋潮波数学模型对边界海平面上升后潮波变化进行了数值模拟。研究发现边界海平面上升后,在无潮点附近东侧迟角增加,西侧迟角减小;无潮点北侧振幅增加,南侧振幅减小;辽东湾、渤海湾顶、辽东半岛东海域、海州湾至鲁南沿海、苏北沿海、台湾海峡至浙东沿海和南海平均潮差增加,海平面上升0.90 m后潮差最大增幅达0.40 m;长江口、杭州湾至对马海峡、朝鲜西海岸和莱州湾海域潮差减小。随着海平面上升量值的增加,渤海、台湾海峡潮差变化速率相对稳定,黄海、东海和南海站位变化速率有所变动;平均高水位的变化趋势与潮差一致;潮差增加的区域,高水位抬升幅度超过边界海平面上升幅度。海平面上升引起的高水位超幅变化,增加了沿海地区对风暴潮和其他灾害防护的风险。     

Land subsidence due to water withdrawal in the vicinity of Pecos, Texas

Analysis of repeated levelings conducted by the National Geodetic Survey indicates a zone of anomalous relative subsidence in the vicinity of Pecos, Texas. The subsidence appears to have resulted from the decline of water level due to pumping from unconsolidated stream-deposited alluvium of Cenozoic age. Maximum observed vertical ground movement relative to benchmarks outside the zone of pronounced subsidence exceeded 200 mm between 1934 and 1956. The decline in the water table was as much as 60 m during approximately the same period. The subsiding region is about 30 km wide and 50 km long.     

Stable-isotopes of groundwaters from the Albuquerque, New Mexico, basin: one decade later

In the spring of 1995, 24 samples were collected from a widely distributed system of municipal water wells in Albuquerque, N.M., and analyzed for hydrogen (δD) and oxygen (δ¹⁸O) isotopic compositions. δD values for 15 of these samples are largely similar to those reported by Yapp in 1985, but have locally become more negative by as much as 5 per mil (ö). δD–δ¹⁸O data define two endmembers that are well aligned along the familiar meteoric water line (MWL): (1) the eastern domain (mountain precipitation runoff), having δD>–86ö (similar to the criteria of Yapp) and δ¹⁸O>–12.1ö (this work); and (2) a central basin domain, which may be in part derived from water seepage from the Rio Grande, having δD<–95ö and δ¹⁸O<–13.2ö. Only a few wells across the basin have δD values near the "baseline" value of the Rio Grande, defined by Yapp as –92ö. The proximity of these wells to the Rio Grande is consistent with recharge by seepage from the river bed under baseline conditions. Extensive pumping in the eastern domain and West Mesa areas may be partly responsible for an apparent expansion of the central-basin regime of water more depleted in δD, much as a plume migrating in response to transient perturbations in original hydraulic gradients. Vertically stacked groundwater occurrences having limited interconnection are inferred from the significant differences in isotopic compositions of samples from two wells screened at multiple depths. The central and western parts of the basin are little influenced by contributions from the eastern domain. Some groundwaters from the western part of the basin plot below the MWL and clearly cannot be mixtures solely of the eastern domain and central basin endmembers. The origins of these western groundwaters and the most depleted central basin groundwaters are as yet unknown, but we speculate they may have received recharge under climatic conditions different from the present.     

基坑抽水引起周围地面沉降机理及防治措施

抽水引起周围地面沉降和构筑物地基沉降已成为工程建设中的一个环境灾害问题。根据抽水引起周围地面沉降的机理分析,提出了由抽水引起地下水水头压力变化、含水层颗粒迁移、含水层压缩和水体的膨胀的更具普遍意义的地下水运动方程,该方程可以简化成Biot和Helm的地下水运动方程。在此基础上,通过实例分析和方案对比,提出了抽水引起周围地面沉降的防治措施,并分析了各种措施的适用范围及优缺点。