基于砂槽模型研究不同水流密度下盆地地下水流系统

在干旱半干旱地区,沉积盆地是人类生产、生活用水的主要载体,为查明在水流自身密度改变条件下盆地地下水流系统的变化特征,需在变密度条件下对盆地地下水流系统进行模拟研究。本文采用砂槽物理模型,在改变区域性水流密度条件下模拟研究地下水流系统的变化规律。试验结果显示:随着区域性水流密度的增加,区域水流系统的渗流速度和循环量均减少,且流线径流距离和径流深度也随之减小;而局部水流系统的渗流速度和循环量均增加。结果表明区域性水流密度的增加会抑制区域水流系统的发育,对局部水流系统有一定增强作用。本研究着重强调了区域性水流自身密度变化对盆地地下水流系统所产生的影响,并通过物理试验模拟得出在改变区域性水流密度条件下盆地地下水流系统的变化规律。     

http://www.sciencedirect.com/science/article/pii/S167498711100020X

Significant advances in regional groundwater flow modeling have been driven by the demand to predict regional impacts of human inferences on groundwater systems and associated environment.The wide availability of powerful computers,user friendly modeling systems and GIS stimulates an exponential growth of regional groundwater modeling.Large scale transient groundwater models have been built to analyze regional flow systems,to simulate water budget components changes,and to optimize groundwater developmen...     

氢氧同位素在地下水流系统的重分布：从高程效应到深度效应

大气降水的氢氧同位素含量具有高程效应,降水入渗后参与地下水循环,其高程效应如何受地下水流系统的影响转化为地下水氢氧同位素的深度效应？现有研究对于这个问题缺少定量认识。文章构建单向倾斜盆地和双峰波状盆地的稳态地下水循环理论模型,采用MODFLOW模拟剖面二维地下水流场、采用MT3DMS模拟重同位素分子的对流-弥散过程,得到地下水D和¹⁸O含量的空间分布,探讨了氢氧同位素高程效应在地下水流系统转化为深度效应的机理。结果表明：在单斜盆地,补给区大气降水D和¹⁸O含量的高程效应转化为排泄区地下水δD和δ¹⁸O值随埋深增大而指数型衰减的深度效应;在双峰波状盆地,当含水层渗透性相对入渗强度较大时(K₀/w=1 000),仅发育一个区域地下水流系统,在区域地下水的排泄区δD和δ¹⁸O随埋深增大呈现S形曲线分布;当含水层渗透性相对入渗强度较小时(K0/w=250),双峰波状盆地发育多个局部地下水流系统,区域地下水的排泄区δD和δ¹⁸O随埋深增大呈现S形曲线,而局部地下水排...     

Theis不稳定潜水井流模型的改进——具入渗补给

地下水的补排主要包括垂向的地面入渗补给、蒸发排泄（蒸发可视为入渗的负值）及侧向的地表水补给、排泄。水文地质学最基本的问题之一——地下水可持续开釆量的评价准则,涉及补给的增量与排泄的减量,因此地下水开采的预测模型必须包含上述两类的补给、排泄因素,否则不能满足要求。然而,经典的Theis不稳定井流模型,即使在傍河抽水,也只有侧边界的补给、排泄作用,而不涉及上边界的地面入渗补给。这样一来,这个解析模型基本上不能够用于预测,而只能在旱季用于井流试验求取含水系统的参数。为此,文章的目标是发展具地面入渗补给的Theis不稳定潜水井流模型。对于潜水流问题,不能再用承压水流的以水头为应变量的方程来建立,应采用第二类线性化方法的势函数来建立潜水流问题。对于既有降雨入渗补给,又有抽水井作用的复杂的水文地质问题所概化数学模型的求解,采取的方法是把它分解成若干个简单的子模型问题求解,然后将其合成为原来复杂数学模型的解。基于质量守恒原理,假定渗流服从Darcy定律并满足Dupuit徦定建立了水流基本微分方程。然后对于两平行河流及一河流平行一隔水边界形成的两类条形区域,具地面均匀稳定入渗补给的井流问题,获得通用水位方程和几类常见的特定条件水位方程及其流量方程。此外,提出并采用“边界对边界的反映法”用以求解一河流平行一隔水边界条形区域的同一问题,减少了许多推导过程。最后,作为上述理论成果的初步应用,也是一个重要的应用,即在河水水质不能满足要求的河流附近,设有一口抽水井,计算该抽水井在不汲取河水的前提下的临界流量方程,获得具重要意义的结构简洁的关系式。该方程也可以用于滨海区的抽水井,在不发生海水入侵前提下的临界抽水流量计算。给出了上述条件不稳定井流过程某时刻的地下水流网图,其流网与文献中常见的傍河井流的流网相比,具显明的特征。     

Geothermal heat extraction by water circulation through a large crack in dry hot rock mass

One proposed geothermal heat extraction scheme relies on water circulation in a large vertical crack created by hydraulic fracturing in a hot dry impermeable rock mass. Water flow, heat convection and crack opening widths are analysed by finite elements. Governing field equations of the problem are first set up rigorously and then various small terms are identified and neglected, retaining the effects of pressure gradient, buoyancy, velocity head (kinetic energy) and head loss due to viscous friction in the water flow equation, and the effects of heat convection in water and heat conduction in rock in the heat transfer equation. The finite element scheme for water flow is based on a variational principle that is typical for diffusion problems, and for heat transfer it is based on the method of least-square residuals. The system of differential equations is highly non-linear. The non-linear terms and coefficients are treated in the fiaite element analysis as constant; the finite element analysisof, the steady-state pressures, fluxes and temperatures is then iterated, evaluating all non-linear terms and coefficients on the basis of the solution obtained in the previous iteration. Numerically calculated fields at various times after the start ofcooling are presented. They indicate some features favourable for the geothermal scheme, such as formation of eddy currents, and downward flux of water toward hotter rock. However, other important questions would have to be solved to gain full understanding, of this proposed geothermal scheme.     

潜流交换温度示踪方法研究进展

潜流带是河流生态系统中活跃的生态群落交错区,是地表水和地下水相互作用的重要界面。研究潜流带内存在的潜流交换机制对评估水资源的开发利用以及维持和修复河流生态系统健康有着重要意义。系统介绍了温度示踪方法的一维垂向稳态和瞬态热运移解析模型,梳理归纳了基于温度示踪的时序数据采集方法、信号分析方法和数值方法的相关研究进展,最后对比论述了温度示踪方法的优势和存在的主要问题,同时指出了地下水的多维流动、温度测量的不确定性以及非理想条件对解析模型的影响仍是未来温度示踪方法需要进一步研究的重点。     

层流—紊流共存流场中岩溶裂隙网络演化过程的数值模拟方法

研究岩溶水系统的演化过程对许多资源与环境问题有着重要意义。岩溶地区水资源、油气资源的预测与开发、水土流失成因及防治等课题都与此密切相关。岩溶管道是地下水对裂隙的逐渐溶蚀扩展形成的,岩溶演化初期,所有裂隙宽度不大,流场整体成层流状态。随着溶蚀的进行,一部分裂隙优先扩大使其中的水流进入紊流状态,而另一部分裂隙中水流仍呈层流状态。文章提出一种数值方法,能够模拟层流-紊流共存流场的岩溶演化过程。利用蒙特卡洛(Monte-Carlo)方法模拟初始裂隙网络,通过非连续介质方法模拟裂隙网络中的渗流。裂隙扩展的速度通过岩石表面溶蚀速度经验公式计算,使用迭代方法求解层流-紊流共存条件下的水头非线性方程。构建了能够利用解析法求解的模型,把数值解和解析解的结果进行对比,验证了本研究的数值法及软件的可行性。      

区域地下水流模拟

人类活动对地下水流系统及其周围环境已经产生区域性影响,对区域性影响的预测需求促进了区域地下水流模型的重大发展。功能强大的计算机的普及、用户界面友好的模拟系统及GIS软件的广泛应用使得区域地下水流模拟呈指数增长。大尺度的地下水非稳定流模型已经用于分析区域水流系统、模拟水均衡各要素随时间的变化及优化地下水管理方案。本文简述了区域地下水流模拟的发展历史,介绍了美国死谷和澳大利亚大自流盆地两个大区域地下水流模型实例。此外,文中亦介绍了区域地下水流模拟的方法,讨论了区域地下水流模拟中遇到的特殊议题。 更多还原     

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.     

Application of Numerical Modeling for Groundwater Flow System Analysis in the Akaki Catchment,Central Ethiopia

A three dimensional steady-state finite difference groundwater flow model is used to quantify the groundwater fluxes and analyze the subsurface hydrodynamics in the Akaki catchment by giving particular emphasis to the well field that supplies water to the city of Addis Ababa. The area is characterized by Tertiary volcanics covered with thick residual and alluvial soils. The model is calibrated using head observations from 131 wells. The simulation is made in a two layer unconfined aquifer with spatially variable recharge and hydraulic conductivities under well-defined boundary conditions. The calibrated model is used to forecast groundwater flow pattern, the interaction of groundwater and surface water, and the effect of pumping on the well field under different scenarios. The result indicates that the groundwater flows regionally to the south converging to the major well field. Reservoirs and rivers play an important role in recharging the aquifer. Simulations made under different pumping rate indicate that an increase in pumping rate results in substantial regional groundwater level decline, which will lead to the drying of springs and shallow hand dug wells. Also, it has implications of reversal of flow from contaminated rivers into productive aquifers close to main river courses. The scenario analysis shows that the groundwater potential is not enough to sustain the ever-growing water demand of the city of Addis Ababa. The sensitivity and scenario analysis provided important information on the data gaps and the specific sites to be selected for monitoring, and may be of great help for transient model development. This study has laid the foundation for developing detailed predictive groundwater model, which can be readily used for groundwater management practices.     

Simulation of horizontal well performance using Visual MODFLOW

A proposed horizontal well or radial collector well installation in shallow aquifers to enhance water withdrawal rates in Pintu Geng well field in Kelantan, Malaysia was simulated using the Drainage Package of MODFLOW groundwater model. The modelling exercise aimed at identifying an optimum pumping rate that would safely achieve the desired drawdown of less than 2 m in an area of 300 m radius surrounding the Pintu Geng horizontal collector well. The model also would serve as a basis for the design of the horizontal well components. High degree of grid refinement for the well location is needed to simulate the real field installation. However, for the purpose of designing water withdrawal systems, it is important to obtain the correct production rate of these wells for a given drawdown. A transient groundwater flow model was calibrated and validated with few assumptions of the horizontal well hydraulic properties. The model demonstrates that under natural flow condition at ?3 m depth, the six collectors (drains) tap a volume of 19,200–43,700 m³/day. A steady-state model was also developed to predict the capture zone delineation. Attention is also given to the impact of the well installation to the surrounding 300 m radius by inspecting the degree of the drawdown.     

陈崇希教授的学术思想和成就综述

在地下水资源评价理论方面, 陈崇希教授分析了"平均布井法"不符合质量守衡原理的实质, 纠正了以"地下水补给量计算可持续开采量"的错误, 提出了基于"质量守衡"的地下水资源评价原则, 强调分析"补给的增加量与排泄的减少量"在评价地下水可持续开采量时的重要意义.在地下水动力学领域, 陈崇希教授纠正了稳定井流"影响半径"模型的错误, 恢复了Dupuit"圆岛模型"的原貌, 拓展了Theis公式和Hantush公式的应用条件, 改进了地下水非稳定井流理论, 完善了其中的某些基本概念.在水文地质模拟仿真技术方面, 陈崇希教授提出确定滨海承压含水层海底边界的理论和方法; 提出地下水混合井流的模型和模拟方法, 解决了混合抽水试验确定分层水文地质参数的难题; 提出岩溶管道-裂隙-孔隙三重介质的地下水线性-非线性流动的模型; 建立了考虑井管水流雷诺数对滤管入流量分布的水平井-含水层系统的地下水流模型; 完成了"渗流-管流耦合模型"的砂槽物理模拟, 并用数值方法仿真了地下水流的规律; 最近向观测孔水位形成的传统观念———常规观测孔中的水头降深反映该孔滤水管中各点的平均降深———提出质疑.陈崇希教授建立的"渗流-管流耦合模型"使传统的基于线汇/线源的井孔-含水系统模型提高到新的水平.陈崇希教授积极倡导"防止模拟失真, 提高仿真性", 强调精细地分析水文地质条件、合理地概化模型和采用正确的仿真技术的重要性.      

基于数值模拟的区域性地下水补给过程实例研究

研究主要目的是以数值模拟的方法,再现选定的研究区域20世纪70~90年代地下水位处于较低水平的过程并推求地下水的补给过程。研究区为某流域入海口前10×12km2的矩形区域,基于研究区土层纵断面的物理条件,在平面二维的基础上,考虑含水层垂向水收支成分,利用地下水计算的基本方程式开发地下水准三维数值计算模型,以数值模拟的方法验证模型效率。对地下水位数值模拟的结果表明,模型效率可以达到80%以上。基于1966~2005年的数值计算结果,推求了研究区各含水层的补给过程。研究结果可为区域性地下水数值模拟技术及地下水资源量的评估等研究提供方法上的借鉴。     

Fourier’s heat conduction equation: History, influence, and connections

The equation describing the conduction of heat in solids has, over the past two centuries, proved to be a powerful tool for analyzing the dynamic motion of heat as well as for solving an enormous array of diffusion-type problems in physical sciences, biological sciences, earth sciences, and social sciences. This equation was formulated at the beginning of the nineteenth century by one of the most gifted scholars of modern science, Joseph Fourier of France. A study of the historical context in which Fourier made his remarkable contribution and the subsequent impact his work has had on the development of modern science is as fascinating as it is educational. This paper is an attempt to present a picture of how certain ideas initially led to Fourier’s development of the heat equation and how, subsequently, Fourier’s work directly influenced and inspired others to use the heat diffusion model to describe other dynamic physical systems. Conversely, others concerned with the study of random processes found that the equations governing such random processes reduced, in the limit, to Fourier’s equation of heat diffusion. In the process of developing the flow of ideas, the paper also presents, to the extent possible, an account of the history and personalities involved. Reprinted by permission from theAmerican Geophysical Union, @ 1999. Originally published inReviews of Geophysics as “Fourier’s Heat Conduction Equation: History, Influence and Connections,” Vol. 37, issue 1, pages 151–172, February 1999. Appended here are eight figures of historical importance.     

基于GSFLOW的镜湖湿地地表水与地下水耦合数值模拟

湿地地表径流包括明渠流和片流等多种形式,且存在海绵状土壤层,其地表水-地下水耦合模拟困难。针对湿地片流和海绵层模拟不准确的问题,以绍兴镜湖国家城市湿地公园为研究对象,考虑湿地多年植物生长沉积形成的独特海绵层,基于GSFLOW模型构建湿地地表水与地下水耦合数值模型,通过二维扩散方程模拟湿地片流、一维圣维南方程模拟湿地明渠流,使用竖管法测量湿地海绵层渗透系数,利用模拟区水文站的监测数据率定模型参数并对模拟结果进行验证,应用校正后模型模拟湿地地表水与地下水的水量交互过程,并对研究区进行水均衡分析。研究结果表明:考虑湿地海绵层的湿地地表水与地下水耦合模型能较为真实地反映湿地水文特性,湿地以地表水补给地下水为主,补给量随降雨量变化。研究建立的湿地地表水与地下水耦合模型合理可靠,对湿地水文分析有良好的应用价值。     

生态输水条件下塔里木河下游断面尺度地下水流数值模拟

由于中国西北地区地表水资源有限,地下水则成为重要的备用水资源,而地表水和地下水转化过程及其耦合模拟是水资源开发利用和科学评价的基础,因此,为了准确反映塔里木河下游间歇性生态输水后地下水的动态变化,以塔里木河下游英苏断面为例,基于Boussinesq方程建立了改进的地下水动力学(GH-D2)模型,模拟了塔里木河下游绿色走廊典型断面地下水对全时段(2000-2015年)间歇性生态输水的响应过程。结果表明,尽管Boussinesq方程的GH解能较好地模拟地下水位的瞬态变化,但模拟地下水位多年变化的结果并不理想,而改进的GH-D2模型考虑了间歇性生态输水对地下水位变化的滞后效应,对长时间尺度地下水位变化的模拟具有较好的效果。与GH和GH-D1模型相比,GH-D2模型模拟的地下水位值更接近于观测值,这将对塔里木河下游实施科学合理的生态输水计划以及生态恢复和重建策略提供关键的技术支撑。     

Modelling surface–groundwater interaction in the Ruataniwha basin, Hawke’s Bay, New Zealand

Modelling groundwater and surface water is important for integrated water resources management, especially when interaction between the river and the aquifer is high. A transient groundwater and surface water flow model was built for Ruataniwha basin, New Zealand. The model covers a long-time period; starting in 1990, when water resources development in the area started, to present date. For a better resolution, the simulation period was divided into 59 stress periods, and each stress period was divided to 10 time steps. The model uses data obtained from surface water, and groundwater collected over the last 20 years. Rivers and streams were divided into 28 segments and flow and streambed data at the beginning and end of each segment was used. Parameter estimation and optimisation ‘PEST’ was used for automatic calibration of hydraulic conductivity, groundwater recharge and storativity; whereas riverbed conductance was manually calibrated. Model results show that the rivers gain from the aquifer considerably more than the river losses. The cumulative groundwater abstraction over the last 20 years is approximately 210 million m³. This amount is very low compared to other water budget components; however, the effect of groundwater abstraction on storage is significant. Based on the results of this study, it was found that the loss of storage over the last 20 years is more than 66 million m³. Results also reveal that the effect of groundwater abstraction on rivers and springs flow is significant. The rivers gain from the groundwater system, and the springs flow have been decreasing.     

Estimation of unrecorded groundwater abstractions in Jordan through regional groundwater modelling

Jordan suffers from water scarcity and groundwater covers the majority of Jordan’s water supply. Therefore, there is an urgent need to manage this resource conscientiously. A regional numerical groundwater flow model, developed as part of a decision support system for the country of Jordan, allows for quantification of the overexploitation of groundwater resources and enables determination of the extent of unrecorded agricultural groundwater abstraction. Groundwater in Jordan is abstracted from three main aquifers partly separated by aquitards. With updated geological, structural, and hydrogeological data available in the country, a regional numerical groundwater flow model for the whole of Jordan and the southernmost part of Syria was developed using MODFLOW. It was first calibrated for a steady-state condition using data from the 1960s, when groundwater abstraction was negligible. After transient calibration using groundwater level measurements from all aquifers, model results reproduce the large groundwater-level declines experienced in the last decades, which have led to the drying out of numerous springs. They show a reversal of groundwater flow directions in some regions, due to over-abstraction, and demonstrate that documented abstractions are not sufficient to cause the observed groundwater-level decline. Only after considering irrigation water demand derived from remote sensing data, the model is able to simulate these declines. Illegal abstractions can be quantified and predictive scenarios show the potential impact of different management strategies on future groundwater resources.

     

Dupuit模型的改进——具入渗补给

Dupuit（1863年）提出的模型是“圆岛状含水层稳定井流模型”,这个模型只有侧向湖海边界条件,而不涉及上边界降水入渗补给条件。因此,Dupuit模型只能在旱季用于地下水井流试验求取含水系统的参数,而不能够用于预测。文章发展Dupuit潜水井流模型,考虑地面均匀稳定入渗补给（蒸发排泄示为其负值）作用。以质量守衡原理为基础,假定渗流服从Darcy定律并满足Dupuit徦定,建立极坐标下的地下水流微分方程,再依边界条件建立相应的流量方程和水位方程。这些方程为具地面入渗补给条件下井流试验求取水文地质参数以及预测相应条件下地下水抽水的效果,提供了基础条件。讨论了引入Dupuit假定对本问题解析研究可以降维（略去z变量）带来好处的同时,在地下水分水岭附近及抽水井附近可能出现偏离Dupuit假定,建议在抽水试验求取含水层参数时,观测孔的部署要尽量回避这些区段。