Development of a numerical groundwater flow model using SRTM elevations

Remotely-sensed elevation data are potentially useful for constructing regional scale groundwater models, particularly in regions where ground-based data are poor or sparse. Surface-water elevations measured by the Shuttle Radar Topography Mission (SRTM) were used to develop a regional-groundwater flow model by assuming that frozen surface waters reflect local hydraulic head (or groundwater potential). Drainage lakes (fed primarily by surface water) are designated as boundary conditions and seepage lakes and isolated wetlands (fed primarily by groundwater) are used as observation points to calibrate a numerical flow model of the 900 km² study area in the Northern Highland Lakes Region of Wisconsin, USA. Elevation data were utilized in a geographic information system (GIS) based groundwater-modeling package that employs the analytic element method (AEM). Calibration statistics indicate that lakes and wetlands had similar influence on the parameter estimation, suggesting that wetlands might be used as observations where open water elevations are unreliable or not available. Open water elevations are often difficult to resolve in radar interferometry because unfrozen water does not return off-nadir radar signals.     

北京市平谷盆地地下水三维数值模拟及管理应用

为缓解北京城区的用水紧张问题,平谷区建立了王都庄和中桥两个应急水源地。持续过量的开采导致盆地内水位急剧下降。为研究大规模开采对平谷盆地地下水系统的影响,并分析不同地区的开采潜力,本文建立了合理刻画三维地下水流动特征的数值模型,对五种不同的开采方案进行模拟。模拟结果表明,丰水条件下地下水位回升明显,王都庄水源地补给条件优越,尤其是盆地上游地区,具有更大的开采潜力;而盆地中下部应适当限制开采,避免水位下降过快。高仿真的数值模型可作为强有力的管理辅助工具,为地下水资源分析及合理利用提供科学的技术支持。     

Evaluating groundwater resource of an urban alluvial area through the development of a numerical model

As established in the European Water Framework Directive, the development of groundwater numerical models is fundamental for adopting water management plans aimed at preserving the water resource and reducing environmental risks. In this paper, authors present a methodology for the estimation of groundwater resource of an alluvial valley, in an urban area characterized by a complex hydrostratigraphic setting and scarcity of hydrogeological data; the study area is the urban and sub-urban area of Rome (Italy). A previous, elaborated hydrostratigraphic model set the base for the development of 3D, steady state, sub-basin scale numerical model, implemented by the finite-difference code MODFLOW 2000^®; the water system components were derived by elaboration of available data. The alluvial aquifer of the Tiber River Valley, which runs in the middle of the City in a NNW–SE direction, has been analyzed in detail, since it is covered by a densely populated area hosting most of Rome’s historical heritage, and it is characterized by low quality geotechnical parameters. Results suggest that in areas with high hydrostratigraphic complexity and scarcity of hydrogeological data, a sub-basin scale, and steady-state numerical model can be very helpful to verify the conceptual model and reduce the uncertainty on the water budget components. The proposed steady-state model constitutes the base for future applications of transient state and local scale models, required for sustainable water management.     

绕坝渗流地下水位的时空分布模型研究

许多大坝的失事是由于高地下水位引起坝肩失稳所致。绕坝渗流是影响坝肩高地下水位的主要因素。为此通常将大坝基础防渗帷幕延伸到坝肩岸坡内一定距离,以减小绕坝渗流影响。而防渗帷幕运行性态随时间变化,为了评价坝肩防渗帷幕和地下水位的运行性态,首先分析了地下水位观测资料和水位、降水、温度、时效等时空影响因素及其表达式,随后基于岸坡地下水位观测资料,利用最小二乘法建立了大坝岸坡地下水位的时空分布模型。通过比较模型剩余标准差和测点的剩余标准差,可以确定坝肩地下水位的异常测点,分析岸坡防渗薄弱部位,掌握坝肩岸坡渗流场时空分布规律,监控绕坝渗流的性态。     

Assessment of water seepage through a geologic barrier surrounding a large reservoir using groundwater levels, soil condition, and a numerical model

Though the geologic barrier surrounding a dam reservoir plays an important role in preventing water seepage to the outside of a reservoir, a detailed survey to assess bedrock conditions of the whole reservoir boundary is seldom performed when designing a dam. In this study, a variety of investigations and analyses have been conducted to reveal a seepage phenomenon through a reservoir boundary composed of highly fractured metamorphic rocks at the Daechung multipurpose dam. At the study site, groundwater levels at monitoring wells located close to a reservoir tend to change proportionally to reservoir water levels, usually with a rapid response time of 1 day or less. Soil moisture content also changes with respect to the reservoir water level, and the area where seepage from the reservoir is a possibility has a relatively high soil moisture content. The similarity of measured seepage rates at the outflow site and the seepage rate estimated by Darcy’s law suggests strong connectivity and high density of the fractures. The estimated seepage rate using a numerical model for the northernmost valley (Zone 1) is approximately 127.2 m³/day in the case of high reservoir water level and 24.3 m³/day in the case of low water level. Continuous monitoring to obtain time series data for water levels, quality, and bedrock displacement is recommended to assess the sustainable stability of this geologic barrier.     

Evaluation of change in subsurface thermal environment due to groundwater flow in the Tokyo Lowland,Japan

Information on the distribution of subsurface temperature and hydraulic heads at 24 observation wells in and around the Tokyo Lowland, the eastern part of the Tokyo Metropolitan area, were examined to make clear the relationship between groundwater and the subsurface thermal environment in the urban area. Minimums in temperature–depth logs due to subsurface temperature increasing at shallow parts were recognized in 21 wells. This fact shows subsurface temperature is affected by ground surface warming in almost all of this area. Deeper than minimums, where the effects of surface warming became relatively small, regional variation is observed as follows: high temperatures are shown in the central part to the southern part, and low temperatures shown in the inland to eastern part. The high temperature area corresponds to an area where the lower boundary of groundwater flow is relatively shallow. This area corresponds also to an area with severe land subsidence resulting from excessive groundwater pumping. It is considered that this high temperature area is formed by the effects of upward groundwater flow affected by hydrogeological conditions and pumping. On the other hand, a comparison between past data (1956–1967) and present data (2001–2003) revealed widespread decreasing temperature in the inland area. This is explained by downward groundwater flow based on an analysis of temperature–depth logs. This fact suggests that subsurface temperature is not only increasing from the effects of surface warming but also decreasing from the effects of groundwater environment change due to pumping.     

河流型水库垂向二维水沙数学模型

在垂向二维水动力模型的基础上,叠加了泥沙模型,建立了垂向二维泥沙模型,该模型的主要特点是水动力模型采用斜压模式,可以模拟由于水库水温度分布时空变化对其水动力结构及泥沙沉降速度的影响;泥沙模型采用分步法求解,简化了计算;独立求解粘性泥沙及非粘性泥沙的沉降速度及水土界面交换通量;运用经验公式估算泥沙及水动力模型参数,弥补了资料不足的缺点。最后运用实测资料对所建泥沙模型进行了有效性验证,结果表明:悬沙模拟值与实测值相对误差较小,时空分布特征相似;同时,模型能较为准确反映由于水库出入流引起的库首与库尾水温及泥沙分布特征。     

Conceptual and numerical models for sustainable groundwater management in the Thaphra area, Chi River Basin, Thailand

Sustainable management of groundwater resources is vital for development of areas at risk from water-resource over-exploitation. In northeast Thailand, the Phu Thok aquifer is an important water source, particularly in the Thaphra area, where increased groundwater withdrawals may result in water-level decline and saline-water upconing. Three-dimensional finite-difference flow models were developed with MODFLOW to predict the impacts of future pumping on hydraulic heads. Four scenarios of pumping and recharge were defined to evaluate the system response to future usage and climate conditions. Primary model simulations show that groundwater heads will continue to decrease by 4–12?m by the year 2040 at the center of the highly exploited area, under conditions of both increasing pumping and drought. To quantify predictive uncertainty in these estimates, in addition to the primary conceptual model, three alternative conceptual models were used in the simulation of sustainable yields. These alternative models show that, for this case study, a reasonable degree of uncertainty in hydrostratigraphic interpretation is more impactful than uncertainty in recharge distribution or boundary conditions. The uncertainty-analysis results strongly support addressing conceptual-model uncertainty in the practice of groundwater-management modeling. Doing so will better assist decision makers in selecting and implementing robust sustainable strategies.     

Robust numerical implementation of a 3D rate-dependent model for reservoir geomechanical simulations

A 3D elasto-plastic rate-dependent model for rock mechanics is formulated and implemented into a Finite Element (FE) numerical code. The model is based on the approach proposed by Vermeer and Neher (A soft soil model that accounts for creep. In: Proceedings of the International Symposium “Beyond 2000 in Computational Geotechnics,” pages 249-261, 1999). An original strain-driven algorithm with an Inexact Newton iterative scheme is used to compute the state variables for a given strain increment.The model is validated against laboratory measurements, checked on a simplified test case, and used to simulate land subsidence due to groundwater and hydrocarbon production. The numerical results prove computationally effective and robust, thus allowing for the use of the model on real complex geological settings.     

Spatial characteristics of groundwater temperature in the Ishikari Lowland, Hokkaido, northern Japan: analytical and numerical applications

In porous sediments of the Ishikari Lowland, there is a gradual increase in the background geothermal gradient from the Ishikari River (3–4 °C 100 m^–1) to the southwest highland area (10 °C 100 m^–1). However, the geothermal gradient at shallow depths differs in detail from the background distribution. In spite of convective heat-flow loss generally associated with groundwater flow, heat flow remains high (100 mW m^–2) in the recharge area in the southwestern part of the Ishikari basin, which is part of an active geothermal field. In the northeastern part of the lowland, heat flow locally reaches 140 mW m^–2, probably due to upward water flow from the deep geothermal field. Between the two areas the heat flow is much lower. To examine the role of hydraulic flow in the distortion of the isotherms in this area, thermal gradient vs. temperature analyses were made, and they helped to define the major components of the groundwater-flow system of the region. Two-dimensional simulation modeling aided in understanding not only the cause of horizontal heat-flow variations in this field but also the contrast between thermal properties of shallow and deep groundwater reservoirs. Electronic Publication     

Malibogazi groundwater dam: an alternative model for semi-arid regions of Turkey to store and save groundwater

In central Turkey, there are serious groundwater quality problems in the main river valleys and plains, and even in the lower parts of the secondary basins due to the underlying evaporitic geological formations. Groundwater quality improves towards the upstreams in the alluvium aquifers in most secondary valleys; however, groundwater potential decreases as well due to the reduced basin area, areal extent and thickness of the aquifers. The Malibogazi valley is situated to some 100 km north of Ankara. The dam constructed in the narrowest section of the valley has an average storage coefficient of 0.2 and the total and active storage capacities of 110,000 and 55,000 m³, respectively. The 20-m-thick aquifer extends for 6–7 km till the dam site within valley with an average width of 50–70 m. It mostly comprises sandy–gravely alluvial deposits. Malibogazi groundwater dam is a valve-controlled gravity flow dam. When the valves are opened, the water from the aquifer reservoir flows by gravity through supply pipe to the main irrigation channel, but when the valves are closed the water is stored in the aquifer and groundwater level begins to rise. Average groundwater discharge was about 20 l/s in 2005–2006 irrigation period. In this period, groundwater levels were about 2 m higher compared to the groundwater levels in the same seasons before the construction of the groundwater dam. Because the dam is of gravity flow type, it means an important contribution to the farmers since the operation cost is quite low. Malibogazi groundwater dam represents one of the first experiences of Turkey in the field of groundwater storage. Although the dam has small storage capacity, it may be a model for Turkey from the viewpoints of investigation, construction, dam wall, intake facility and measurements etc.     

大区域地下水流数值模拟研究现状及存在问题

在分析大区域地下水流数值模型构建缘起的前提下,系统论述了近年来地下水流数值模拟在大区域地下水资源评价、水文地质参数确定、地面沉降、溶质运移、海水入侵、盐渍化、风险评估、地下水管理及地表水与地下水的联合开发利用等方面的国内外研究应用现状;归纳、总结了目前大区域地下水流数值模型在灵敏度分析、裂隙和岩溶介质中模型建立、基于地下水流数值模拟的溶质运移模型建立、地下水流数值模型构建所需工作量等理论和方法研究及实际建模过程中存在的一些问题;展望了今后大区域地下水流数值拟在研究范围、模拟技术与方法以及与其它模型耦合等方面的发展趋势。     

Magnetic and DC resistivity investigation for groundwater in a complex subsurface terrain

Subsurface structures associated with hard rocks are very important for groundwater. Wadi Fatima runs through the volcanic and metamorphic rocks of the Arabian Shield which are characterized by higher magnetization than the overlaying alluvium sediments. Magnetic and direct current (DC) resistivity methods have been used for groundwater exploration in the northern part of Wadi Fatima. The magnetic survey was used mainly to map the subsurface structures, using analytic signal algorithm, of the study area. The DC resistivity method was applied to describe the lithologic domain as a function of depth, depending on their electrical property contrasts where it provided a good indication for water bearing formations. The magnetic and DC resistivity interpretations were confirmed by drilling which have provided a clear idea about the hydrogeological regime of the study area. The selected drilled well is successfully productive and it produces 30 m³/h.     

A simplified mathematical model for the dam-breach hydrograph for three reservoir geometries following a sudden full dam break

Natural Hazards - The prediction of dam-break water flow at dam site is essential to reduce the potential for loss of damage in the downstream floodplain. In this study, the influence of reservoir...     

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.     

Estimating groundwater vulnerability to pollution using a modified DRASTIC model in the Kerman agricultural area,Iran

Groundwater contamination from intensive fertilizer application affects conservation areas in a plain. The DRASTIC model can be applied in the evaluation of groundwater vulnerability to such pollution. The main purpose of using the DRASTIC model is to map groundwater susceptibility to pollution in different areas. However, this method has been used in various areas without modification, thereby disregarding the effects of pollution types and their characteristics. Thus, this technique must be standardized and be approved for applications in aquifers and particular types of pollution. In this study, the potential for the more accurate assessment of vulnerability to pollution is achieved by correcting the rates of the DRASTIC parameters. The new rates were calculated by identifying the relationships among the parameters with respect to the nitrate concentration in groundwater. The methodology was implemented in the Kerman plain in the southeastern region of Iran. The nitrate concentration in water from underground wells was tested and analyzed in 27 different locations. The measured nitrate concentrations were used to associate and correlate the pollution in the aquifer to the DRASTIC index. The Wilcoxon rank-sum nonparametric statistical test was applied to determine the relationship between the index and the measured pollution in Kerman plain. Also, the weights of the DRASTIC parameters were modified through the sensitivity analysis. Subsequently, the rates and weights were computed. The results of the study revealed that the modified DRASTIC model performs more efficiently than the traditional method for nonpoint source pollution, particularly in agricultural areas. The regression coefficients showed that the relationship between the vulnerability index and the nitrate concentration was 82 % after modification and 44 % before modification. This comparison indicated that the results of the modified DRASTIC of this region are better than those of the original method.     

广西隆安县地下水储水构造的地质-地球物理模型及其地球物理响应特征分析

通过物探勘查并结合水文地质资料分析,研究了广西隆安县岩溶石山区断裂带、溶洞、岩溶管道三种储水构造的地质-地球物理模型及其电性响应特征。受构造控制或侵蚀基准面变化的影响,广西隆安岩溶石山区形成多层溶洞及岩溶管道系统,地下水主要赋存于溶洞、管道和构造裂隙中。地球物理上,断裂带及多层洞道系统均表现为纵向低阻条带的电性特征,但储水构造充填物或是水或是泥,难以用电阻率参数加以区分。为提高解译精度,结合工作区的水文地质条件,对物探资料进行细致入微的分析,并在勘察工作中采用在高阻中找低阻、低阻中找高阻的找水定井方法,基本避开了泥质充填的难题,提高了成井率。      

Development of a coupled surface-groundwater-pipe network model for the sustainable management of karstic groundwater

This paper considers the hydrogeological simulation of groundwater movement in karstic regions using a hydrological modelling system (SHETRAN) which has been adapted for modelling flow in karstic aquifers. Flow and transport through karstic aquifers remains poorly understood, yet quantitative hydrogeological models are essential for developing and implementing groundwater protection policies. The new model has been developed and used within the STALAGMITE (Sustainable Management of Groundwater in Karstic Environments) project, funded by the European Commission. The SHETRAN model is physically based insofar as most of the parameters have some physical meaning. The SHETRAN model represents all of the key processes in the hydrological cycle, including subsurface flow in the saturated and unsaturated zones, surface flow over the ground surface and in channels, rainfall interception by vegetation canopies, evapotranspiration, snow-pack development and snowmelt. The modifications made to SHETRAN to simulate karstic aquifers are (1) the coupling of a pipe network model to a variably saturated, three-dimensional groundwater component (the VSS-NET component), to simulate flow under pressure in saturated conduits; (2) the coupling of surface water features (e.g. sinking streams or "ponors", and spring discharges) to the conduit system; (3) the addition of a preferential "bypass" flow mechanism to represent vertical infiltration through a high-conductivity epikarst zone. Lastly, a forward particle tracking routine has been developed to trace the path of hypothetical particles with matrix and pipe flow to springs or other discharge points. This component allows the definition of groundwater protection zones around a source for areas of the catchment (watershed) which are vulnerable to pollution from non-point sources (agriculture and forestry).