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.     

Groundwater drawdown at Nankou site of Beijing Plain: model development and calibration

Water shortage and groundwater pollution have become two primary environmental concerns to Beijing since the 1990s. The local aquifers, as the dominant sources for domestic and agricultural water supply, are depleting due to groundwater abstraction and continuous drought in recent years with rapid urbanization and increasing water consumption. Therefore, understanding the hydrogeological system is fundamental for a sustainable water resources management. In this article, the numerical analysis of a 3-D regional groundwater flow model for the Nankou area is presented. The hydrogeological system is reproduced according to sparsely distributed boreholes data. The numerical analysis is carried out using the scientific software OpenGeoSys, which is based on the finite element method. The model calibration and sensitivity analysis are accomplished with inverse methods by applying a model independent parameter estimation system (PEST). The results of the calibrated model show reasonable agreements with observed water levels. The transient groundwater flow simulations reflect the observed drawdown of the last 9 years and show the formation of a depression cone in an intensively pumped area.     

黑河中游盆地南部山区地下水对平原区侧向径流补给量的估算

山区地下水对平原区的侧向径流补给量是一个长期争议且悬而未决的难题,这个量在西北内陆干旱盆地,被估算得或很小或很大。在总结前人研究的基础上,采用地质水文地质调查、物探、钻探、抽水试验、地下水动态观测、水化学测试、盆地地下水水位统测和综合研究等技术方法,查明了黑河中游盆地南部山盆交接带的地质构造接触关系、地层岩性接触关系及梨园河口白垩系风化壳含水层结构和水文地质参数。通过山区不同流域等级的地表水与地下水转化关系分析,将山区地下水对平原区侧向径流补给带划分为大中型河流河谷补给段和小微型河流或冲沟群流域构成的浅山带补给段。河谷补给段勘探资料较为丰富,多用达西断面流方法计算;针对浅山带补给段极为缺乏勘探资料的实际,以梨园河口断面径流量为参照,构建了浅山带岩性、汇水区面积、降水量等3 个变量的山区地下水对平原区侧向径流补给量的估算方法。估算出黑河中游盆地南部山区浅山带地下水对平原的侧向径流补给量为0.40×108 m3/a,河谷段基岩侧向补给量为0.07×108 m3/a;推算出河谷段第四系地下水补给量为0.30×108 m3/a;3 项补给量之和为0.77×108 m3/a,占盆地地下水资源量的3.0%。该研究为西北内陆干旱盆地山区地下水对平原区侧向径流补给量的估算提供了一个可供借鉴的实例。     

Numerical simulation of groundwater flow for a coastal plain in Japan: data collection and model calibration

Using a three-dimensional finite element model, this study characterizes groundwater flow in a costal plain of the Seto Inland Sea, Japan. The model characterization involved taking field data describing the aquifer system and translating this information into input variables that the model code uses to solve governing equations of flow. Geological geometry and the number of aquifers have been analyzed based on a large amount of geological, hydrogeological and topographical data. Results of study demonstrate a high correlation between the ground surface elevation and the groundwater level in the shallow coastal aquifer. For calibrating the numerical groundwater model, the groundwater flow was simulated in steady state. In addition, the groundwater level and trend in the transient state has also been elucidated. The numerical result provides excellent visual representations of groundwater flow, presenting resource managers and decision makers with a clear understanding of the nature of the types of groundwater flow pathways. Results build a base for further analysis under different future scenarios.     

Numerical modeling of the transient hydrogeological response produced by tunnel construction in fractured bedrocks

Groundwater inflows into tunnels constructed in fractured bedrocks not only constitute an important factor controlling the rate of advancement in driving the tunnel but may pose potential hazards. Drawdowns caused by tunnel construction may also induce geotechnical and environmental impacts. Here we present a numerical methodology for the dynamic simulation of the hydrogeological transient conditions induced by the tunnel front advance. The methodology is based on the use of a Cauchy boundary condition at the points lying along the tunnel according to which water discharge, Q, is computed as the product of a leakage coefficient, , and the head difference, (H−h), where H is the prescribed head at the tunnel wall and h is the hydraulic head in the fractured rock in the close vicinity of the tunnel. At a given position of the tunnel, is zero until the tunnel reaches such position when it is assigned a positive value. The use of step-wise time functions for allows an efficient and accurate simulation of the transient hydrogeological conditions at and around the tunnel during the excavation process. The methodology has been implemented in TRANMEF-3, a finite element computer code for groundwater flow in 3D fractured media developed at the University of A Coruña, Spain, and has been used to simulate the impact of a tunnel on the groundwater system at the Äspö island (Sweden). This tunnel was constructed to access an underground laboratory for research on radioactive waste disposal. The large amount of available data at this site provides a unique opportunity to test the performance of the numerical model and the proposed methodology for tunnel advance. With just minor calibration, the numerical model is able to reproduce accurately the measurements of inflows into the tunnel at several reaches and hydraulic heads at surface-drilled boreholes. These results obtained at the Äspö site lead us to conclude that accurate predictions of the transient hydrogeological responses induced by tunneling works in fractured bedrocks, can be achieved provided that a sound hydrogeological characterization of large-scale fracture zones is available.     

The impact of tunneling construction on the hydrogeological environment of “Tseng-Wen Reservoir Transbasin Diversion Project” in Taiwan

Groundwater flow and the associated surface water flow are potential negative factors on underground tunnels. Early detection of environmental impacts on water resources is of significant importance to planning, design and construction of tunnel projects, as early detection can minimize accidents and project delays during construction. The groundwater modeling software package Groundwater Modeling System (GMS), which supports the groundwater numerical codes MODFLOW and FEMWATER, was utilized to determine the impact of tunneling excavation on the hydrogeological environment in a regional area around the tunnel and a local hot springs area, at the “Tseng-Wen Reservoir Transbasin Diversion Project”, in Taiwan. A hydrogeological conceptual model was first developed to simplify structures related to the site topography, geology and geological structure. The MODFLOW code was then applied to simulate groundwater flow pattern for the hydrogeological conceptual model in the tunnel area. The automated parameter estimation method was applied to calibrate groundwater level fluctuation and hydrogeological parameters in the region. Calibration of the model demonstrated that errors between simulated and monitored results are smaller than allowable errors. The study also observed that tunneling excavation caused groundwater to flow toward the tunnel. No obvious changes in the groundwater flow field due to tunnel construction were observed far away in the surrounding regions. Furthermore, the FEMWATER code for solving 3-D groundwater flow problems, in which hydrogeological characteristics are integrated into a geographic information system (GIS), is applied to evaluate the impact of tunnel construction on an adjacent hot spring. Simulation results indicated that the groundwater drawdown rate is less than the groundwater recharge rate, and the change to the groundwater table after tunnel construction was insignificant for the hot spring area. Finally, the groundwater flow obtained via the GMS indicated that the hydrogeological conceptual model can estimate the possible quantity of tunnel inflow and the impact of tunnel construction on the regional and local groundwater resources regime of the transbasin diversion project.     

A conceptual and numerical model for groundwater management: a case study on a coastal aquifer in southern Tuscany, Italy

Ongoing hydrogeological research aims to develop a correct management model for the Plio-Pleistocene multi-aquifer system of the Albegna River coastal plain (southern Tuscany, Italy); overexploitation of this aquifer for irrigation and tourism has caused seawater intrusion. The conceptual model is based on field and laboratory data collected during the 1995–2003 period. Meteoric infiltration and flows from the adjoining carbonate aquifer recharge the aquifer. Natural outflow occurs through a diffuse flow into the sea and river; artificial outflow occurs through intensive extraction of groundwater from wells. Water exchanges in the aquifer occur naturally (leakage, closing of aquitard) and artificially (multiscreened wells). The aquifer was represented by a three-dimensional finite element model using the FEFLOW numerical code. The model was calibrated for steady-state and transient conditions by matching computed and measured piezometric levels (February 1995–February 1996). The model helped establish that seawater intrusion is essentially due to withdrawals near the coast during the irrigation season and that it occurs above all in the Osa-Albegna sector, as well as along the river that at times feeds the aquifer. The effects of hypothetical aquifer exploitation were assessed in terms of water budget and hydraulic head evolution.     

基岩岛屿地下水流场数值模拟研究

岛屿是我国领土的重要组成部分,对国家安全和国防军事意义非凡。岛屿的地下水资源尤为珍贵,地下水流场模拟是研究地下水分布规律的重要手段。水文地质条件复杂、可利用的观测井较少等原因,造成了基岩岛屿水文地质模型概化精度不高、初始条件难以获取等问题。为克服基岩岛屿地下水流场模拟的诸多困难,将珠海外伶仃岛作为研究区,利用数字高程模型数据开展地质地貌建模; 利用探地雷达法、直流电法与地质分析对岛屿进行探测,获取了地层数据; 采用地下水遥感评估法,利用实测井位数据,确定了地下水的初始水位,进而对基岩岛屿地下水流场进行建模; 最终,通过对外伶仃岛地下水流场的数值模拟得出地下水模拟流场图。岛上多个测点的探测水位值与模拟水位相关性较好,其拟合优度R²为0.872 2。由此可见,综合遥感、物探、水文地质手段等技术方法获取的数据,采用地下水模拟软件或程序实现基岩岛屿地下水流场的数值模拟,是基岩岛屿地下水资源研究的一个有效方法。     

Groundwater flow model of the Pipiripau watershed, Federal District of Brazil

In order to understand the groundwater dynamics and to improve the management of water resources in the Federal District of Brazil, this research proposes a 3D groundwater flow model to represent the groundwater level and flow system. The selected test site was the Pipiripau catchment. The development of the model was based on available geological, hydrogeological, geomorphological, climatological and pedological data. Geological and hydrogeological data were used to generate the 3D groundwater flow model. The 3D mesh elements of the domain were generated through the Groundwater Modeling System software, based on the logs of the well materials. The numerical simulation of the finite element method was implemented in the framework of the scientific software OpenGeoSys. With the 3D mesh-appropriated boundary conditions, annual average infiltration data and hydrogeological parameters were incorporated. Afterwards, the steady-state model was calibrated by the PEST software using available data of the water level from wells. The results showed the distribution of the steady-state hydraulic heads in the model domain, where the highest values occurred in the east and west recharge areas and the lowest values were found in the southwest of the basin. The results of this study can be a used as initial condition for the transient groundwater flow simulation and to provide a scientific basis for water resource management.     

天津市地下水流-地面沉降耦合模型

天津市平原区地面沉降主要由地下水大量开采引起,影响范围广、危害大,已成为天津市主要的环境地质问题。分析了研究区的水文地质条件,结合地下水开发利用状况,将研究区概化为6个含水层组,地下水流考虑三维非稳定流,地面沉降选用一维固结压缩模型,运用地下水流模型Modflow 2005和地面沉降模拟模块 Sub,建立了天津市平原区地下水流-地面沉降数值耦合模型,模型面积为1.1×10⁴ km²,利用1998-2008年地下水位等值线、过程线、地面沉降过程线等资料对模型进行了识别。模拟期的地下水均衡分析表明,在多年开采条件下,越流补给、压缩释水、侧向边界流入分别占深层含水层补给量的41.84％、32.15％和24.17％。将调试后的模型应用于南水北调实施后地下水控采条件下的地面沉降趋势预测,显示出停采或减少地下水的开采,有利于减缓地面沉降下降速度,且表现出开采层位越往下,地面沉降恢复难度越大的变化趋势。     

A synthetic study of geophysics-based modelling of groundwater flow in catchments with a buried valley

Groundwater models simulating flow in buried valleys interacting with regional aquifers are often based on hydrogeological models interpreted from dense geophysical datasets and scarce borehole data. For three simple synthetic cases, it is demonstrated that alternative methods of inversion of transient electro-magnetic (TEM) data can lead to very different interpretations of the hydrogeology inside and surrounding a buried valley. The alternative interpreted hydrogeological models are used in numerical modelling of groundwater flow to a pumping well. It is demonstrated that the alternative models result in quite different groundwater-model predictions of capture zone, recharge area, and groundwater age for the pumping well. It is briefly demonstrated that model calibration against hydraulic head data is not likely to improve the predictions or to identify the structural error of the interpreted hydrogeological models. It is therefore concluded that when TEM-based resistivity models are interpreted to construct the hydrogeological framework of a groundwater model, it must be done cautiously with support from deep borehole information. Too much reliance on geophysical mapping can lead to seriously wrong hydrogeological models and correspondingly wrong groundwater-model predictions.     

Modeling of an MTBE plume at Pascoag, Rhode Island

A numerical groundwater flow and mass transport model was developed to predict the extent of impact from methyl tertiary butyl ether (MTBE) release on a down-gradient drinking water well field. An MTBE incident in Pascoag, Rhode Island, was used as a case study and the plume’s past and future development was simulated using scenario analysis. The numerical code used was GeoSys/Rockflow, which permits a coupled flow and transport simulation as one object, thus alleviating the need for simulating the MTBE fate with separate flow and transport codes. The numerical model was built on available hydrogeological and chemical data as well as on GIS information of the site. By comparing the simulated results with observed field data, it was found that the model could provide reliable results even when the simulated aquifer was simplified to a two-dimensional flow and transport domain. Finally, the calibrated model was used for exploring a location that may be suitable for a new well field. Despite the model limitations associated with uncertainties of data and simplifying assumptions, numerical modeling of this MTBE contaminated site proved a useful tool and provided guidance for future municipal well field operation strategies and aquifer remediation alternatives.     

Evaluation of alternative conceptual models for groundwater modelling

This study evaluates the alternative conceptual models for groundwater modelling. A true model was created with a synthetic alluvial fan-plain hydrogeological framework. Various alternative conceptual models were evaluated for groundwater flow simulations. The first alternative model is a single aquifer layer model; the second alternative model is a 3-layer aquifer model; and the third model is a 5-layer model consisting of 3 aquifers separated by 2 aquitards. All models could fit very well to the observations with optimized values of hydraulic conductivities. However, the single aquifer layer model can only compute water balance components with good accuracy. The 3-layer aquifer model can be used for water balance computation and groundwater head simulation with small errors. The 5-layer model is capable of simulating water budget, groundwater head distribution and travel times with high accuracy. Multi-model analysis found only the 3rd alternative model superior.     

Groundwater head uncertainty analysis in unsteady-state water flow models using the interval and perturbation methods

In the numerical simulation of groundwater flow, uncertainties often affect the precision of the simulation results. Stochastic and statistical approaches such as the Monte Carlo method, the Neumann expansion method and the Taylor series expansion, are commonly employed to estimate uncertainty in the final output. Based on the first-order interval perturbation method, a combination of the interval and perturbation methods is proposed as a viable alternative and compared to the well-known equal interval continuous sampling method (EICSM). The approach was realized using the GFModel (an unsaturated-saturated groundwater flow simulation model) program. This study exemplifies scenarios of three distinct interval parameters, namely, the hydraulic conductivities of six equal parts of the aquifer, their boundary head conditions, and several hydrogeological parameters (e.g. specific storativity and extraction rate of wells). The results show that the relative errors of deviation of the groundwater head extremums (RDGE) in the late stage of simulation are controlled within approximately ±5% when the changing rate of the hydrogeological parameter is no more than 0.2. From the viewpoint of the groundwater head extremums, the relative errors can be controlled within ±1.5%. The relative errors of the groundwater head variation are within approximately ±5% when the changing rate is no more than 0.2. The proposed method of this study is applicable to unsteady-state confined water flow systems.

     

山东淄博市地下水资源评价及其合理开发利用研究

本文采用有限单元法进行地下水资源评价以解决评价区供水面积大、精度要求高的矛盾。首先根据实际的开采量和长期观测孔的水位资料,校正数学模型,反求有关参数;然后给定开采方案进行未来水头的预测;最后研究地下水资源的合理开发利用问题。利用有限单元法进行水源地或单一含水层的地下水资源评价已被证明是先进的、有效的。本文是对水文地质条件非常复杂的大面积的区域,用有限单元法进行地下水资源评价的一种尝试,可供类似地区参考。     

乌鲁木齐河流域北部平原地下水流模拟

本文运用数字水文地质概念模型的方法建立了乌鲁木齐河流域北部平原的地下水流模型,并用流量边界与柴窝堡盆地和河谷区的地下水流模型相接,构成一个统一的流域地下水模型,为乌鲁木齐河流域水资源整体规划利用提供了模拟分析工具。北部平原的南部倾斜平原为砂卵砾石组成的大厚度潜水含水层,北部细土平原为多层结构。地下水总体上由南向北径流,天然状态下在交界地带溢出成泉或流入沙漠。目前,地下水循环基本上由人为控制。农田灌溉回归补给量与河流和山前侧向补给量持平;而开采量已是绝对的排泄量。季节性开采造成地下水位季节性大幅度变化。水位的下降使蒸发蒸腾量减少,减轻了由于灌溉造成的土壤盐碱化问题。     

Climate and irrigation scenario analyses using three-dimensional numerical modelling: a case study of the Nasia sub-basin in the White Volta Basin,Ghana

A groundwater resource characterisation and assessment model was developed for Nasia river sub-basin in the White Volta Basin, Ghana. The model is useful to policymakers for planning and sustainable management of groundwater resources in the basin for domestic and irrigation purposes. A conceptual model was constructed that characterized boundary conditions and hydrostratigraphy, and estimated recharge rates and hydraulic and storage parameters. From current understanding of the hydrogeological dynamics, three hydrostratigraphic layers were delineated. The conceptual model was converted to a three-dimensional steady-state groundwater flow model using MODFLOW. Recharge rates estimated from the base model indicate a minimum of 1.1% and maximum of 6.2% of the total rainfall. The hydraulic conductivity ranged between 0.20 and 15 m/day. Four possible scenarios were simulated: (1) increased population, (2) climate variations (reduced recharge), (3) increased abstraction for irrigation, and (4) worst-case scenario which is a combination of the first three scenarios. Results from scenarios 1 and 2 indicated that, under such conditions, the groundwater resources could be sustained and no significant effect on any of the water budget indicators was observed. For scenario 3, there was significant drop in hydraulic head in the central portions of the study area. The scenario 4 simulation indicated that there was significant reduction in groundwater levels and groundwater discharge into streams under these stressors. Such reduction can affect stream levels in the basin and, subsequently, the ecosystem. These findings are valid within the limits of uncertainty in the hydrogeological data that were used in this study.

     

基于水化学和同位素特征的新乡某地下水污染场地水文地质概念模型细化

构建合理的水文地质概念模型对于地下水数值模拟至关重要,概念模型如果确定不合理,整个数值模拟将毫无意义。通常水文地质调查可以大致确定水文地质概念模型,然而对于一些不易被发现的补给源,通过水文地质调查也无法确定。水化学和同位素特征对地下水的补给源及水流路径有很好的指示作用,可以根据这些信息对水文地质概念模型进行细化。文章通过对研究区地下水取样,分析地下水水化学和同位素特征,确定出研究区内不易识别的地下水补给源及顶层黏土-粉质黏土的透水性,最终细化了水文地质概念模型边界条件。这对于后期得到正确的地下水流和溶质运移模拟结果具有重要意义。     

基于MODFLOW参数不确定性的地下水水流数值模拟方法

考虑到模型不确定性引起的地下水数值模拟不确定性对模拟过程的影响,在简要介绍含水层水文地质参数变异性研究进展和地质统计学的基础上,基于常用的确定性地下水流数值模拟软件MODFLOW开发了MODFLOW-Gslib软件,相较于传统的数值模拟方法,将地质统计学与数值模拟结合的方法能够模拟非均质含水层中的参数变异性问题。将MODFLOW-Gslib软件运用于模拟实例中,选择常见的不确定性因素进行模拟,并对其模拟产生的数据进行统计分析,结果表明,软件转化后的参数符合水文地质参数不确定性的相关特征;与原模拟结果进行对比,该软件能够更加真实地刻画含水层参数变异性特征。     

Numerical simulation of sea water intrusion near Beihai, China

 A leaky aquifer system occurs in the coastal plain near Beihai, China. Seawater intrusion into the confined aquifer took place along the northern coast. Chloride concentrations at some observation wells increased steadily from 1988 and were at their peak in 1993. A quasi-three-dimensional element model has been developed to simulate the spatial and temporal evolution of hydraulic heads and chloride concentrations of the groundwater near the northern coast. The simulation model was based on the transition zone approach, which requires simultaneous solution of the governing water flow and solute transport equations. An irregular grid of a quadrangle was used to discretize the flow domain. Various aquifer parameters were verified with the numerical model in order to obtain satisfactory matches between computed values and observed data from an investigation. Three pumpage schemes were designed to use the calibrated model for prediction of future changes in water levels and chloride concentrations in groundwater in the study area. Results show that seawater intrusion would worsen in the confined aquifer if the current rates of groundwater pumpage continue. The alternative, to eliminate pumpage in the intruded area and to moderate pumpage rates from water supply wells far from the seashore, may limit seawater intrusion significantly and is considered attractive in the area. Received: 27 September 1999 · Accepted: 27 December 1999