鄂尔多斯白垩系地下水盆地水文地质概念模型

水文地质概念模型是地下水模拟与水资源评价的基础。为了构建地下水数值模拟模型,以鄂尔多斯白垩系地下水盆地为研究对象,以丰富翔实的勘查资料为依据,从白垩系地下水系统边界条件、水文地质结构、水流系统、水文地质参数、源汇项等方面进行概化,联合采用ArcGIS、RS、GMS同位素、基流分割、地质统计学、随机模拟等技术方法,建立了一组水文地质概念模型及其相应的空间离散表达,并讨论了地下水模拟面临的问题与发展趋势。     

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.

     

Reconstruction of natural groundwater flow paths in the multiple aquifer system of the northern Negev (Israel), based on lithological and structural evidence

 The Judea Group, a limestone and dolomite karstic aquifer of late Albian–Turonian age, is one of the most important sources of water in Israel. In the western part of the country, the Judea Group aquifer is also known as the Yarkon–Taninim basin. In the northern Negev, the Judea Group is a recipient for fresh water flowing southward from the Hebron Mountains and of brackish paleowater flowing northward from Sinai. Very little is known of the hydraulic properties of this aquifer. In order to outline assumed natural flow paths that existed in this karstic environment prior to groundwater exploitation, use was made of lithological, structural, and paleomorphological features. A detailed hydrogeological conceptual model of the Judea Group aquifer in northern Negev was established by the geological interpretation of high-resolution seismic reflection and by analysis of lithological evidence from boreholes. Isopach, isolith-contour, and isolith-ratio maps were compiled for the main lithological components. Increase in transmissivity values is inversely proportional with the cumulative thickness of argillaceous components. The lithological and hydraulic evidence provides the basis for subdividing the subsurface into distinctive permeability zones for the upper and lower sections of the aquifer; for outlining possible preferential groundwater flow paths for both subaquifers; and for improving understanding of groundwater-salinty variations that result from lithological variability, direction of groundwater flow paths, groundwater flow rates, and the duration of rock/water interactions. In an earlier conceptual model of the basin, the Judea Group aquifer was regarded as a continuous and undisturbed entity. The present study reveals an intricate groundwater flow pattern that is controlled by lithological and structural factors that create zones of preferential flow. This interpretation bears on the overall evaluation of groundwater resources and their management and exploitation. Received, December 1996 · Revised, October 1997, June 1998 · Accepted, July 1998     

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。     

含水岩组概化的累积导水系数法

地下水流系统理论和数值模拟技术分别是水文地质学的基本理论和技术方法,含水岩组的概化是地下水流系统分析和地下水数值模拟的重要基础,直接影响着数值模拟和水流系统分析的精度和可信度.为提高含水岩组概化的精度和可信度,提出一种含水岩组概化的新方法,即累积导水系数法.依据岩层厚度与渗透系数乘积累积值随深度的变化,以及水文地质剖面岩性分布的整体特征,概化含水介质结构.以玛纳斯河流域为例,应用该方法概化流域内的岩性剖面,结合GMS软件中TINS模块构建水文地质结构模型.结果表明,应用该方法概化后的含水层结构具有较好的合理性和仿真性,建立的三维模型很好地显示了研究区含水介质的空间展布特征,为建立地下水流模型奠定了良好的基础.      

Multi-scale aquifer characterization and groundwater flow model parameterization using direct push technologies

Direct push (DP) technologies are typically used for cost-effective geotechnical characterization of unconsolidated soils and sediments. In more recent developments, DP technologies have been used for efficient hydraulic conductivity (K) characterization along vertical profiles with sampling resolutions of up to a few centimetres. Until date, however, only a limited number of studies document high-resolution in situ DP data for three-dimensional conceptual hydrogeological model development and groundwater flow model parameterization. This study demonstrates how DP technologies improve building of a conceptual hydrogeological model. We further evaluate the degree to which the DP-derived hydrogeological parameter K, measured across different spatial scales, improves performance of a regional groundwater flow model. The study area covers an area of ~60 km² with two overlying, mainly unconsolidated sand aquifers separated by a 5–7 m thick highly heterogeneous clay layer (in north-eastern Belgium). The hydrostratigraphy was obtained from an analysis of cored boreholes and about 265 cone penetration tests (CPTs). The hydrogeological parameter K was derived from a combined analysis of core and CPT data and also from hydraulic direct push tests. A total of 50 three-dimensional realizations of K were generated using a non-stationary multivariate geostatistical approach. To preserve the measured K values in the stochastic realizations, the groundwater model K realizations were conditioned on the borehole and direct push data. Optimization was performed to select the best performing model parameterization out of the 50 realizations. This model outperformed a previously developed reference model with homogeneous K fields for all hydrogeological layers. Comparison of particle tracking simulations, based either on the optimal heterogeneous or reference homogeneous groundwater model flow fields, demonstrate the impact DP-derived subsurface heterogeneity in K can have on groundwater flow and solute transport. We demonstrated that DP technologies, especially when calibrated with site-specific data, provide high-resolution 3D subsurface data for building more reliable conceptual models and increasing groundwater flow model performance.     

Coupled hydrogeological and reactive transport modelling of the Simpevarp area (Sweden)

The Simpevarp area is one of the alternative sites being considered for the deep geological disposal of high level radioactive waste in Sweden. In this paper, a coupled regional groundwater flow and reactive solute transport model of the Simpevarp area is presented that integrates current hydrogeological and hydrochemical data of the area. The model simulates the current hydrochemical pattern of the groundwater system in the area. To that aim, a conceptual hydrochemical model was developed in order to represent the dominant chemical processes. Groundwater flow conditions were reproduced by taking into account fluid-density-dependent groundwater flow and regional hydrogeologic boundary conditions. Reactive solute transport calculations were performed on the basis of the velocity field so obtained. The model was calibrated and sensitivity analyses were carried out in order to investigate the effects of heterogeneities of hydraulic conductivity in the subsurface medium. Results provided by the reactive transport model are in good agreement with much of the measured hydrochemical data. This paper emphasizes the appropriateness of the use of reactive solute transport models when water-rock interaction reactions are involved, and demonstrates what powerful tools they are for the interpretation of hydrogeological and hydrochemical data from site geological repository characterization programs, by providing a qualitative framework for data analysis and testing of conceptual assumptions in a process-oriented approach.     

Development and parameterisation of a complex hydrogeological model based on high-resolution direct-push data

Ongoing developments in geological and hydrogeological investigation techniques, especially direct-push methods, have led to an increase in the quality, density and spatial resolution of data available from such investigations. This has created new challenges in the development of numerical models in terms of accurately and efficiently translating detailed and complex conceptual models into effective numerical models. Suitable geometrical and numerical modelling tools are essential in order to meet these challenges. This paper describes the development of a three-dimensional hydrogeological flow model for a contaminated site near Berlin, Germany, based on high-resolution geological data obtained principally using direct-push methods. The available data were first interpreted to construct a detailed GIS-based geological model, which formed the basis of the conceptual site model. The conceptual model was then translated into a geometrical model, which was used to create a finite element numerical model. An innovative geometry object-based approach enabled the complex structural details of the conceptual model to be accurately reproduced in the numerical model domain. The resulting three-dimensional steady-state unconfined flow model was successfully calibrated using external automated calibration software, whereby parameter values for groundwater recharge and hydraulic conductivity were determined.     

Numerical groundwater-flow modeling to evaluate potential effects of pumping and recharge: implications for sustainable groundwater management in the Mahanadi delta region,India

Process-based groundwater models are useful to understand complex aquifer systems and make predictions about their response to hydrological changes. A conceptual model for evaluating responses to environmental changes is presented, considering the hydrogeologic framework, flow processes, aquifer hydraulic properties, boundary conditions, and sources and sinks of the groundwater system. Based on this conceptual model, a quasi-three-dimensional transient groundwater flow model was designed using MODFLOW to simulate the groundwater system of Mahanadi River delta, eastern India. The model was constructed in the context of an upper unconfined aquifer and lower confined aquifer, separated by an aquitard. Hydraulic heads of 13 shallow wells and 11 deep wells were used to calibrate transient groundwater conditions during 1997–2006, followed by validation (2007–2011). The aquifer and aquitard hydraulic properties were obtained by pumping tests and were calibrated along with the rainfall recharge. The statistical and graphical performance indicators suggested a reasonably good simulation of groundwater flow over the study area. Sensitivity analysis revealed that groundwater level is most sensitive to the hydraulic conductivities of both the aquifers, followed by vertical hydraulic conductivity of the confining layer. The calibrated model was then employed to explore groundwater-flow dynamics in response to changes in pumping and recharge conditions. The simulation results indicate that pumping has a substantial effect on the confined aquifer flow regime as compared to the unconfined aquifer. The results and insights from this study have important implications for other regional groundwater modeling studies, especially in multi-layered aquifer systems.     

Numerical simulation and evaluation of groundwater resources in a fractured chalk aquifer: a case study in Zinder well field,Niger

Groundwater is often a unique water source for agriculture, industry and domestic use for local inhabitants in semi-arid African continent owing to shortage of surface water and rainfall. It is of significance to quantify and assess the groundwater resources for local sustainable development in order to correctly evaluate groundwater resources of Zinder well field with fractured media in Zinder, Niger. A conceptual model of hydrogeology was set up by a geological and hydrogeological survey. For simulating the real conditions, a large multi-well pumping test with designed pumping rate was conducted. In addition, a two-dimensional finite-element transient flow model was developed to simulate groundwater flow at the site. Results show that generally good agreements have been found between the simulated and observed hydrogeology heads for the test. The hydraulic parameters were obtained from the pumping test. A 11-year prediction of groundwater resources has been made under three exploitation schemes, respectively, and it indicates that the well field can offer 7,000 m³/day when the aquifer remains confined. An optimal scheme of exploitation is provided.     

Impact of groundwater withdrawals on the interaction of multi-layered aquifers in the Viterbo geothermal area (central Italy)

The impact of groundwater withdrawals on the interaction between multi-layered aquifers with different water qualities in the Viterbo geothermal area (central Italy) was studied. In this area, deep thermal waters are used to supply thermal spas and public pools. A shallow overlying aquifer carries cold and fresh water, used for irrigation and the local drinking-water supply. Starting with a conceptual hydrogeological model, two simplified numerical models were implemented: a steady-state flow model of the entire groundwater system, and a steady-state flow and heat transport model of a representative area, which included complex interactions between the aquifers. The impact of increased withdrawals associated with potential future development of the thermal aquifer must be considered in terms of the water temperature of the existing thermal sources. However, withdrawals from the shallow aquifer might also influence the discharge of thermal sources and quality of the water withdrawn from the shallow wells. The exploitation of the two aquifers is dependent on the hydraulic conductivity and thickness of the intervening aquitard, which maintains the delicate hydrogeological equilibrium. Effective methods to control this equilibrium include monitoring the vertical gradient between the two aquifers and the residual discharge of natural thermal springs.     

High‐resolution conceptual hydrogeological model of complex basaltic volcanic islands: a Mayotte,Comoros, case study

We present a high‐resolution conceptual hydrogeological model for complex basaltic volcanic islands based on Mayotte Island in the Comoros. Its geological structure and hydrogeological functioning are deduced from a large dataset: geological mapping, geophysics, some forty new boreholes, piezometric data, hydraulic conductivity, hydrochemical data, etc. We describe previously unknown deep cut‐and‐fill palaeovalleys. The resulting conceptual geological and hydrogeological model of the island is very different from the Hawaiian model, in that it lacks a low‐elevation basal aquifer and dyke‐impounded high‐level aquifers. It is closer to the Canary Islands model, which has, however, not yet been described at a high‐resolution scale. It does not have a continuous aquifer, but rather a discontinuous succession of perched aquifers separated by aquicludes and aquitards. This results more from the complex geological structure of the island, which has experienced several phases of volcanism, erosion and weathering, than from its age, but is also a result of the high‐resolution scale of the model. High‐resolution conceptual modelling is now necessary to solve problems of applied geology and hydrogeology.     

Estimation of fault-zone conductance by calibration of a regional groundwater flow model: Desert Hot Springs,California

The hydraulic conductance of a large fault zone has been estimated by calibrating a regional groundwater flow model. Drops in groundwater elevations of over 80 m have been observed along a 15-km length of the Mission Creek fault, California, USA. The large drops in elevation are attributed to the reduced hydraulic conductivity of the fault materials. A conceptual and numerical model of the two hydrologic subbasins in Desert Hot Springs, separated by the Mission Creek fault, was developed. The model was used to estimate the hydraulic conductance along the fault. The parameter estimation involved calibrating the model with observed groundwater elevations from over 40 locations over a 60-year period. The fault hydraulic conductances were estimated assuming a linear trend in the fault length, yielding variations in the fault hydraulic conductance of about an order of magnitude along the fault length (2?×?10^?11–4?×?10^?10 1/s). When an average fault thickness of 35 m is assumed, the fault hydraulic conductivity values are estimated to be from three to five orders of magnitude lower than the surrounding materials. A sensitivity analysis indicated that assumptions made in the conceptual model do not significantly affect estimated fault hydraulic conductances.     

Review: Hydrogeology of weathered crystalline/hard-rock aquifers—guidelines for the operational survey and management of their groundwater resources

Hard rocks or crystalline rocks (i.e., plutonic and metamorphic rocks) constitute the basement of all continents, and are particularly exposed at the surface in the large shields of Africa, India, North and South America, Australia and Europe. They were, and are still in some cases, exposed to deep weathering processes. The storativity and hydraulic conductivity of hard rocks, and thus their groundwater resources, are controlled by these weathering processes, which created weathering profiles. Hard-rock aquifers then develop mainly within the first 100 m below ground surface, within these weathering profiles. Where partially or noneroded, these weathering profiles comprise: (1) a capacitive but generally low-permeability unconsolidated layer (the saprolite), located immediately above (2) the permeable stratiform fractured layer (SFL). The development of the SFL’s fracture network is the consequence of the stress induced by the swelling of some minerals, notably biotite. To a much lesser extent, further weathering, and thus hydraulic conductivity, also develops deeper below the SFL, at the periphery of or within preexisting geological discontinuities (joints, dykes, veins, lithological contacts, etc.). The demonstration and recognition of this conceptual model have enabled understanding of the functioning of such aquifers. Moreover, this conceptual model has facilitated a comprehensive corpus of applied methodologies in hydrogeology and geology, which are described in this review paper such as water-well siting, mapping hydrogeological potentialities from local to country scale, quantitative management, hydrodynamical modeling, protection of hard-rock groundwater resources (even in thermal and mineral aquifers), computing the drainage discharge of tunnels, quarrying, etc.

     

地下水机器学习方法研究

随着我国地下水监测工作的高速发展,高频率高密度水位监测数据的出现催生了对其进行深入信息挖掘的需求。在传统地下水模型研究中,地下水水位监测值常位于模型构建过程的下游,当水位监测的时空密度逐渐增大时,新增信息无法有效传导至模型的规划阶段并指导概念模型的修订。文章提出了一种地下水系统补排边界的识别方法,在不建立地下水数值模型的前提下,以监测井空间位置为节点,按照德劳内原则建立三角网格。在此网格系统中,首先定义一个水力梯度变换函数gradF,以求取网格中任意位置的水力梯度;借鉴机器学习领域的优化算法,使用水力梯度场驱动含水层中随机分布质点的运行轨迹,并以此推断和识别区域内地下水补给和排泄边界。在环境地学计算平台EnviFusion-CGS中实现,并构建了详细工作流程。以山东省青岛市大沽河中下游含水层为示范区,对含水系统的补给区和排泄区的空间分布及其动态变化进行了分析,取得了良好效果。本研究为构建和修订已有含水层概念模型提供了新思路。     

西北某干旱区多级储水洼地地下水数值模拟

西北某放射性废物处置场预选区,区域地下水系统包含多级独立第四系储水洼地,洼地出口以泉水排泄地下水,继而回渗补给下级洼地。根据含水层底板起伏特征,利用GMS模拟软件中的排水沟模块与溪流模块概化了泉水,通过泉流量校准与监测孔水位拟合,校正了研究区渗透系数、给水度、和储水率等水文地质参数,计算了地下水流速、流向以及地下水资源量。结果显示,研究区地下水由南向北东径流,东北部为最终排泄洼地,地下水流速缓慢,水资源相对匮乏,有利于放射性废物处置的安全。     

Hydrogeological characterization of a carbonate aquifer using geophysical and geochemical approach: case of the Krachoua Formation in Tataouine area,Southern Tunisia

An integrated hydrogeological investigation involving geological surface data, well data (lithostratigraphical and piezometric data) and the vertical electrical sounding (VES) method was carried out in Tataouine area, Southern Tunisia to characterize the hydrogeology and the geochemistry of the Krachoua Formation aquifer. The electrical data were used to differentiate lithostratigraphic units and characterize their hydrogeological potentialities. Major elements contents within groundwater samples were assessed and some plots and diagrams have been established in order to investigate the hydrochemical properties of this aquifer and the origin of its mineralization. The Krachoua aquifer exhibits a general drawdown of the piezometric level from 2004 to 2015 reflecting a dramatic decrease in groundwater resources due to increased groundwater abstraction during the last decades. Flow directions shows that the recharge of this aquifer considered as a free aquifer is directly ensured by rainfalls over the outcropping fractured limestones. The geometry of the Krachoua Formation aquifer is tectonically controlled and structured in horst and graben features that impacted greatly the hydrogeology and the hydrodynamics of the area. Subsequent thickness and facies variations within this aquifer influenced the reservoir quality and the groundwater flows. The increased values of salinity to the northwest of the study area seems to be mainly related to the dissolution of the Upper Liassic gypsum of Mestaoua Formation which outcrops widely and can be dissolute easily by meteoric water and contaminate the Krachoua aquifer. This fact is also supported by the sulfated and calci-magnesian chloride facies of this aquifer related to the dissolution of evaporitic rocks (gypsum, anhydrite, and halite). However low salinity values are recorded within the zone where these evaporitic rocks are relatively deep.     

Stochastic groundwater modeling of a sedimentary aquifer: evaluation of the impacts of abstraction scenarios under conditions of reduced recharge

A transient finite difference groundwater flow model has been calibrated for the Nasia sub-catchment of the White Volta Basin. This model has been validated through a stochastic parameter randomization process and used to evaluate the impacts of groundwater abstraction scenarios on resource sustainability in the basin. A total of 1500 equally likely model realizations of the same terrain based on 1500 equally likely combinations of the data of the key aquifer input parameters were calibrated and used for the scenario analysis. This was done to evaluate model non-uniqueness arising from uncertainties in the key aquifer parameters especially hydraulic conductivity and recharge by comparing the realizations and statistically determining the degree to which they differ from each other. Parameter standard deviations, computed from the calibrated data of the key parameters of hydraulic conductivity and recharge, were used as a yardstick for evaluating model non-uniqueness. All model realizations suggest horizontal hydraulic conductivity estimates in the range of 0.03–78.4 m/day, although over 70 % of the area has values in the range of 0.03–14 m/day. Low standard deviations of the horizontal hydraulic conductivity estimates from the 1500 solutions suggest that this range adequately reflects the properties of the material in the terrain. Lateral groundwater inflows and outflows appear to constitute significant components of the groundwater budgets in the terrain, although estimated direct vertical recharge from precipitation amounts to about 7 % of annual precipitation. High potential for groundwater development has been suggested in the simulations, corroborating earlier estimates of groundwater recharge. Simulation of groundwater abstraction scenarios suggests that the domain can sustain abstraction rates of up to 200 % of the current estimated abstraction rates of 12,960 m³/day under the current recharge rates. Decreasing groundwater recharge by 10 % over a 20-year period will not significantly alter the results of this abstraction scenario. However, increasing abstraction rates by 300 % over the period with decreasing recharge by 10 % will lead to drastic drawdowns in the hydraulic head over the entire terrain by up to 6 m and could cause reversals of flow in most parts of the terrain.     

淮河流域平原区地下水资源合理开发利用模式研究

以中国地质调查局资助的《淮河流域环境地质调查》项目为依托,对收集到的区域基础地质和水文地质资料进行了二次开发利用,对淮河流域平原区地下水资源赋存条件、开发利用历史及现状进行了调查,对淮河流域平原区地下水资源开发利用环境效应及开采潜力进行了分析,从浅层水、深层水、微咸水三个方面说明了淮河流域平原区地下水资源合理开发利用模式.