Land subsidence caused by ground water withdrawal in urban areas

At least eight urban areas in the world have encountered significant economic impact from land subsidence caused by pumping of ground water from unconsolidated sediment. The areas, most of which are coastal, include Bangkok, Houston, Mexico City, Osaka, San Jose, Shanghai, Tokyo, and Venice. Flooding related to decreased ground elevation is the principal adverse effect of the subsidence. Lesser effects include regional tilting, well-casing failures, rising buildings, and ground failure or rupture. Subsidence of most of these urban areas began before the phenomenon was discovered and understood. Thus, the subsidence problems were unanticipated. Methods to arrest subsidence typically have included control of ground water pumping and development of surface water to offset the reductions of ground water pumping. Ground water recharge has also been practiced. Areas threatened by flooding have been protected by extensive networks of dikes and sea walls, locks, and pumping stations to remove storm runoff.     

An assessment of the risk associated with urban development in the Thiaroye area (Senegal)

Water quality data from 56 wells, aquifer characteristics, soil types and land use in the city suburb of Dakar were compared to assess the effects of land use on the Thiaroye groundwater quality. The study area encompassed an unsewered densely populated zone, agricultural land, low density villages, and undeveloped land located in the sand dunes. A method similar to GIS technologies was applied to evaluate the degree of vulnerability of the different parts of the aquifer in relation to urban development, land use and aquifer characteristics. The aquifer parameters (hydraulic conductivity, groundwater level depth, recharge, soil type) were re-evaluated qualitatively into three class rankings (high, moderate and low), depending on the likelihood for contaminants reaching the water table, then combined using the two matrix Boolean logic based approaches to identify the nine classes of vulnerability assessed in the aquifer domain. An attempt was made to explain the distribution of nitrate concentration with the assessed vulnerability. In the area assessed, in the densely populated zone running from Pikine, to Thiaroye and Yeumbeul, very high nitrate concentrations correspond with the highest vulnerability index (H1). Nitrate contamination in this area is a consequence of point-source seepage from individual septic systems improperly built in this area. In the eastern part of the aquifer, high nitrate concentrations at Deni B. Ndao, Mbawane and Golam localities coincide with a moderate vulnerability assessment. The major source of nitrate in these areas is induced by agricultural activities.     

Impacts of at-site wastewater disposal systems on the groundwater aquifer in arid regions: case of Sfax City, Southern Tunisia

Groundwater in Sfax City (Tunisia) has been known since the beginning of the century for its deterioration in quality, as a result of wastewater recharge into the aquifer. An average value of 12 × 10⁶ m³ of untreated wastewater reaches the groundwater aquifer each year. This would result not only in a chemical and biological contamination of the groundwater, but also in an increase of the aquifer piezometric level. Quantitative impacts were evaluated by examining the groundwater piezometric level at 57 surface wells and piezometers. The survey showed that, during the last two decades, the groundwater level was ever increasing in the urban area with values reaching 7 m in part; and decreasing in Sidi Abid (agricultural area) with values exceeding −3 m. Groundwater samples for chemical and microbial analysis were collected from 41 wells spread throughout the study area. Results showed significantly elevated levels of sodium, chlorides, nitrates and coliform bacteria all over the urban area. High levels (NO₃: 56–254 mg/l; Na >1,500 mg/l; Coliforms >30/100 ml) can be related to more densely populated areas with a higher density of pit latrine and recharge wells. Alternatively results showed a very variable chemical composition of groundwater, e.g. electrical conductivity ranges from 4,040 to19,620 μs/cm and the dry residual varies between 1.4 and 14 g/l with concentrations increasing downstream. Furthermore a softening of groundwater in Set Ezzit (highly populated sector) was observed.     

Aquifer contamination by chlorinated-VOCs: the case of an urban metropolis megasite overlying the Coastal Plain aquifer in Israel

The Tel Aviv metropolitan region (200 km²), located on the sandy and phreatic Mediterranean Coastal Plain aquifer in Israel, is an example of a contaminated megasite that is additionally complicated by being part of a densely populated urban environment. Despite being a major source of fresh potable water, no dedicated aquifer monitoring systems exist. The vast majority of tested water supply wells (82% of 90 wells) were found to be contaminated with one or more chlorinated volatile organic compounds (Cl-VOCs) such as trichloroethene and tetrachloroethene, originating from multiple sources, including former industrial sites. Temporal variations in Cl-VOC concentrations in water supply wells were large and unpredictable. Such aquifer contamination requires immediate action in terms of aquifer management and municipal water distribution. To cope with temporal and spatial variations in contaminant concentrations in water supply wells in an area where monitoring wells are absent, aquifer impact areas were defined based on the concentration of the Cl-VOC contaminant in pumping wells that was greatest in relation to its drinking water standard over a 3-year period. Such a map can be used to define water supply treatment and municipal well monitoring requirements, until an adequate monitoring system is established.     

Geochemistry,isotopic composition (δO, δH,Sr/Sr,Nd/Nd) in the groundwater of French Guiana as indicators of their origin,interrelations

The current use of untreated river water for drinking purposes by the population of French Guiana has important impacts on public health. Consequently, groundwater is of major importance as a possible alternative drinking water supply to reduce these impacts. Since French Guiana belongs to the Guyana Shield, sustainable water management can be expected to depend increasingly on water from fissured aquifers in hard rocks. Groundwater samples were collected from shallow drill holes in the densely populated coastal area, and deeper wells in the basement (around Cayenne and along the Maroni and Oyapock rivers). This study reports on major and trace elements for which Na⁺ and Ca²⁺ excess with regard to Cl reflect the role of water-rock interaction, as well as Sr and Nd isotopes that reflect the role of the different lithologies. δ¹⁸O and δD in waters give constraints on the water cycle (recharge and evaporation processes).     

基于环境控制的深基坑工程管井回灌设计分析

为探讨管井回灌在深基坑工程中的设计及应用,分析了基于环境控制的深基坑工程管井回灌设计的特殊性,开展了悬挂式帷幕下不同回灌滤管类型的降水回灌渗流分析及对比,探讨了影响回灌管井平面布设以及管井滤管设计的关键因素,同时针对深基坑工程回灌的特殊性,提出了“双点位流态”控制设计原则、回扬控制措施的确定方法以及回灌水质应满足的3项原则。     

Assessment of flood mitigation through riparian detention in response to a changing climate – a case study

Considering that urban areas may suffer more substantial losses than riparian farmlands during floods, diverting floodwater into riparian areas for temporal detention is expected to mitigate flood damage in downstream urban areas. In this study, an assessment has been conducted to evaluate the effect of flood mitigation through riparian detention in response to a changing climate in the Tou-Chien River basin of Taiwan. An integrated 1D–2D flow model was used to simulate the movement of flood wave in the main stream and the overbank flow inundating into the nearby lowlands. Based on the numerical simulation results, the flooding extents in the basin corresponding to different return periods of flood using existing flood prevention infrastructures were investigated. A detention strategy by lowering the levee along the riparian farmlands was proposed to avoid severe flooding in the densely populated urban areas of the basin. Research findings showed that the proposed detention measure can completely protect the downstream areas from overbank flooding when a flood having 20-yr period occurs, and can effectively alleviate the downstream flooding area from 27.4 to \(7.6\,\hbox {km}^{2}\) for a flood possessing 200-yr period.     

Potential impacts of extreme storm surges on a low-lying densely populated coastline: the case of Dunkirk area, Northern France

Along the southern coast of the North Sea, a large proportion of the Flemish coastal plain consists of densely populated reclaimed land, much of which lying below mean high tide level. This is particularly the case along the northern coast of France, from Dunkirk to the Belgium border, where the shoreline consists of coastal dunes that protect low-lying reclaimed lands from marine flooding. This area is vulnerable and subject to several risks. Extreme weather conditions could induce strong surges that could cause (1) a shoreline retreat, (2) marine submersion and (3) land and/or urban flooding due to drainage problems of the polders. Highly energetic events such as the November 2007 storm could have had much more severe consequences especially if they occurred at high tide and/or during a spring tide. In the current context of global change and projected sea-level rise, it is then important for the local authorities to take into account the potential impacts and return periods of such events, in order to implement coastal risk policies prevention and management, to reinforce sea defense, increase pumping station efficiency and plan warning systems against marine submersion and polder flooding, which is not the case yet in Northern France.     

Aquifer system response to intensive pumping in urban areas of the Gangetic plains,India: the case study of Patna

A significant component of domestic demand for water of urban areas located in the Gangetic plains is met by heavy pumping of groundwater. The present study is focused on the Patna municipal area, inhabited by 17 million people and spanning over 134 km², where entire urban water demand is catered from pumping by wells of various capacities and designs. The present study examines the nature of the aquifer system within the urban area, the temporal changes in the water/piezometric level and the recharge mechanism of the deeper aquifers. The aquifer system is made up of medium-to-coarse unconsolidated sand, lying under a ~40-m-thick predominantly argillaceous unit holding 8- to 13-m-thick localised sand layers and continues up to 220 m below ground. Groundwater occurs under semi-confined condition, with transmissivity of aquifers in 5,500–9,200 m² day^?1 range. Hydraulic head of the deeper aquifer remains in 9–19 m range below ground, in contrast to 1–9 m range of that of the upper aquitard zone. The estimated annual groundwater extraction from the deeper aquifer is ~212.0 million m³, which has created a decline of 3.9 m in the piezometric level of the deeper aquifer during the past 30 years. Unregulated construction of deep tube wells with mushrooming of apartment culture may further exacerbate the problem. The sand layers within the aquitard zone are experiencing an annual extraction of 14.5 million m³ and have exhibited stable water level trend for past one and half decades. This unit is recharged from monsoon rainfall, besides contribution from water supply pipe line leakage and seepage from unlined storm water drains.     

A comparison of the geochemical response to different managed aquifer recharge operations for injection of urban stormwater in a carbonate aquifer

Managed aquifer recharge (MAR) is increasingly being considered as a means of reusing urban stormwater and wastewater to supplement the available water resources. Subsurface storage is advantageous as it does not impact on the area available for urban development, while the aquifer also provides natural treatment. However, subsurface storage can also have deleterious effects on the recovered water quality through water–rock interactions which can also impact on the integrity of the aquifer matrix. A recent investigation into the potential for stormwater recycling via Aquifer Storage Transfer and Recovery (ASTR) in a carbonate aquifer is used to determine the important hydrogeochemical processes that impact on the recovered water quality. An extensive period of aquifer flushing allows observation of water quality changes under two operating scenarios: (1) separate wells for injection and recovery, representing ASTR; and (2) a single well for injection and recovery, representing Aquifer Storage and Recovery (ASR).     

Origin of flooding water through hydrogeochemical identification,the Buenos Aires plain,Argentina

Hydrogeochemical behaviour of samples of surface and groundwater collected on a cross-section from Mendoza to the Buenos Aires provinces was studied based on chemical trends, mass balance and water mixing. Hydrogeochemical modelling included major, minor elements as well as stable isotopes (deuterium and 18-O). The area investigated is located in the “Médanos Longitudinales” (longitudinal dunes) of the northwest of Buenos Aires province, Argentina. The study area is subject to alternating flooding and drought. Rainfall and surface water subsequently transferred by rivers, canals and lagoons have been usually considered responsible for local flooding. For this study, origins of excess water were investigated using physical and chemical characteristics of the water involved. The prevalence of groundwater inflow to rainfall events was proposed based on data interpretation. Groundwater influence of flows of local and intermediate nature were defined and the importance of recharge, transit and discharge zones was highlighted. Lagoon floodwater, as well as groundwater from observation wells and production boreholes, show components of intermediate origin. Regional recharge water was identified in Mendoza and San Luis provinces. Their discharge zone was inferred to be located beyond the Buenos Aires province.     

地下水地源热泵系统应用对地温场的影响

通过建立地下水地源热泵系统试验场,运行热泵系统,并进行地下水温度连续监测,分析应用地下水地源热泵系统对地温场的影响。抽水井与回灌井之间以及回灌井附近的地下水温度随系统运行明显变化。系统运行后,回灌水体将以不规则边缘的透镜体贮存于含水层中,以回灌井为中心向外围扩展,水温最低或最高点位于含水层中部。粘性土相对隔水层的温度变化幅度、影响范围均小于含水层。由于热量的累积效应,即使是冷热负荷均衡的热泵系统,运行一个采暖、制冷周期后也将在热源井附近的抽、灌水含水层以及相邻的隔水层中形成冷量或热量的小范围聚积。     

煤矿矿井水净化处理与回灌治理技术

煤矿在开采煤炭的同时,会有大量的矿井污水排到地面,造成环境污染。为解决矿井水排放的污染问题,施工大口径回灌井和建造地面水净化处理厂,矿井水经处理后部分用于煤矿生产,多余部分通过回灌井注入地下,实现水资源循环利用和节能减排。通过梧桐庄矿工程实例,介绍了煤矿矿井水净化处理与回灌治理技术。     

特低渗油藏多段压裂水平井注水可行性分析

摘要：针对特低渗油藏中多段压裂水平井注水开发的可行性问题,论文采用流线模拟方法,研究了多段压裂水平井在一注一采下的生产动态特征,探讨了影响压裂水平井注水开发的主控因素。模拟结果表明：在不发生水窜的情况下,压裂水平井注水能增大单井注入量,提高采油速度和阶段采出程度。同时,交错部署裂缝,裂缝穿透比为02~04时利于注水开发。裂缝水窜增大压裂水平井注水风险,边部水窜、多条裂缝水窜,加速油井水淹,从而丧失压裂水平井注水的优势。在地质条件稳定,裂缝规模可控的条件下,可以尝试开展多段压裂水平井注水实验。研究结果可为特低渗油藏中多段压裂水平井注水提供理论支持。     

Estimating groundwater recharge induced by engineering systems in a semiarid area (southeastern Spain)

The scarcity of water resources in semiarid regions is usually accompanied by brief periods of quite intense precipitation that can generate potentially catastrophic floods. In such regions, the use of runoff water for aquifer recharge can contribute to both flooding prevention and effective management of water resources. This paper presents the results of a study undertaken in southeastern Spain focusing on the recharge induced by a number of engineering structures (check dams) and gravel pits. The current network of check dams consists of 107 dams, of which 64 are located over permeable substrates and so we can induce recharge of the storm runoff retained therein. The hydrological model was performed using the curve number method (CN) of the Service for the Conservation of Soils, utilizing code HEC-HMS. Results indicate that the proportion of runoff infiltrated through the check dams varies from 3% to more than 50%, according to the effective volume of water dammed and the substrate. In addition, hydrological modelling was carried out in a subbasin taking advantage of the presence of one of a number of gravel pits. The gravel pits are situated in the apical sectors of alluvial fans that overlie hydrogeological units that are widely overexploited, and so they are well positioned for use for artificial recharge. In this case, we conclude that a pit is capable of retaining and infiltrating the combined runoff volumes for various return periods (5, 25, 50, and 100 years). Furthermore, the simulation carried out suggests that the recharge processes in these environments are intimately linked to episodic storm events. The incorporation of hydrogeological criteria in the design and construction of check dams could therefore be very useful for the optimum management of water resources in semiarid zones.     

基于TOUGH2数值模拟软件的延津地区热储采灌研究

本文采用TOUGH2数值模拟软件,根据研究区对井在预设情景下运转30年的模拟结果,对河南省延津县下新近系热储层压力场、温度场进行模拟,在模型验证的基础上,对不同回灌率及不同采灌井间距工况进行模拟研究,结果显示:回灌井的回灌过程会使地下水水温降低,回灌时间越长水温降低幅度越大,影响范围也越大,根据模拟抽水井和回灌井不同间距条件下(55 m、150 m、250 m、300 m)温度场变化情况,建议区域下新近系地层地热回灌项目抽水井和回灌井间距应大于等于250m,以保证抽水井出水温度;而不同回灌率工况下分析化学场和压力场的模拟数据可以看出,回灌率越大,地热水水质、压力影响越大,基本呈线性关系。为区域地热资源回灌-开采提供示范和指导。     

低渗透油藏菱形反九点井网不等缝长优化研究

在低渗透油藏开发中广泛使用菱形反九点井网,但针对不同位置生产井及注水井的裂缝缝长配比关系还缺少广泛深入的研究。基于长庆油田某低渗透油藏参数,建立了数值模拟模型,在菱形反九点井网中分别设置不同的边井、角井和注水井裂缝穿透比,研究不同裂缝配置模式对水驱开发效果的影响。流线模拟及数值模拟计算结果表明,在注水开发中,注水井缝长是影响油田产液量及水驱效果的关键因素;边井裂缝较角井裂缝更易见水,对油田综合含水影响较大,在菱形反九点井网中需要进行不等缝长优化设计;边井裂缝缝长对水驱效果的影响分为早、中、晚期(Ⅰ、Ⅱ、Ⅲ)曲线段,随着注水井裂缝穿透比增加,早期(Ⅰ)曲线段增长,中期(Ⅱ)曲线段缩短,而晚期(Ⅲ)曲线段变化较小;随着角井裂缝穿透比增加,采出程度逐渐增大,当角井裂缝穿透比较大时,存在“反转”现象;随着注水井裂缝穿透比增加,角井裂缝优化穿透比减小,而边井裂缝优化穿透比增加。该研究成果对于指导低渗透油藏菱形反九点井网裂缝优化设计,提高波及系数和开发效果具有重要的指导意义。     

北京市深井人工回灌现状调查与前景分析

北京市地下水人工回灌研究始于1965年。1981年开始生产性深井人工回灌。由于种种原因，至1999年底实际回灌单位由64个缩减至13个。其间累计回灌量为10734.37×104t。据调查，停灌原因主要有回灌单位停产、转产、回灌井被占，回灌井阻塞，泵改调频，单位搬迁和改换制冷设备等。本文通过对北京市三十几年来地下水人工回灌工作的总结，分析了人工回灌在近年来发展停滞的原因，并对其在城市可持续发展建设中的节水潜力和今后的发展前景作出了论述。     

Ion exchange and trace element surface complexation reactions associated with applied recharge of low-TDS water in the San Joaquin Valley,California

Stable isotope data, a dissolved gas tracer study, groundwater age dating, and geochemical modeling were used to identify and characterize the effects of introducing low-TDS recharge water in a shallow aerobic aquifer affected by a managed aquifer recharge project in California’s San Joaquin Valley. The data all consistently point to a substantial degree of mixing of recharge water from surface ponds with ambient groundwater in a number of nearby wells screened at depths above 60 m below ground surface. Groundwater age data indicate that the wells near the recharge ponds sample recently recharged water, as delineated by stable O and C isotope data as well as total dissolved solids, in addition to much older groundwater in various mixing proportions. Where the recharge water signature is present, the specific geochemical interactions between the recharge water and the aquifer material appear to include ion exchange reactions (comparative enrichment of affected groundwater with Na and K at the expense of Ca and Mg) and the desorption of oxyanion-forming trace elements (As, V, and Mo), possibly in response to the elevated pH of the recharge water.     

细颗粒沉积物分布区地下水源热泵抽灌井施工工艺探讨

郑州市广泛分布着第四系松散堆积物,其特点是颗粒细,厚度大,含水介质主要为细颗粒的砂层。由于地下水富水性好,目前郑州市浅层地温能开发利用主要以地下水地源热泵工程为主。传统正循环泥浆钻探工艺施工的地温空调井,普遍存在洗井困难、涌水量和回灌量偏小的问题,在很大程度上限制了地下水地源热泵工程的推广使用。针对这一问题,本次采用泵吸反循环工艺施工地温空调井。施工过程及试验数据对比分析表明,在细颗粒松散沉积物分布区,采用泵吸反循环钻探工艺施工地温空调井,对提高施工进度、增大出水量和回灌量等方面具有显著优势,可以为类似地区地温空调井的施工提供借鉴。