Application of MODFLOW for simulating groundwater flow in the Trifilia karst aquifer, Greece

Karst aquifers can have a complex flow as a result of the formation of large conduits from dissolution features. As a result, a three-dimensional finite-difference groundwater flow model (equivalent porous media) may not apply as the dual porosity nature of karst features and the effects of turbulent flow cannot be directly simulated. Statistical analysis of karst hydrographs of the Trifilia aquifer in Greece showed the existence of a slightly karstified mass with high primary porosity that regulates the flow. An equivalent porous media model was developed to simulate the Trifilia karst aquifer using MODFLOW. Steady state and transient state calibration gave encouraging results for the equivalent porous media approach, which does not consider pipe flow or turbulence. Detailed hydrogeological research conducted in the area helped define the aquifer hydraulic conductivity zones and extent; and flux to/from the aquifer. Only hydraulic conductivity and specific yield were adjusted during calibration, as the flux to/from the system was considered known and applied as boundary conditions. Small mean absolute and RMS piezometric head error of the model under both steady and transient state conditions were achieved.     

MODFLOW中两种模拟混合井流问题方法的耦合

对于无(弱)水力联系的多含水层,混合井改变了含水层的结构,通过井筒将无(弱)水力联系的含水层联通。对于大区域井流问题数值模拟,MODFLOW中显式流量分配法和"High Kv in Wellblock"法的假设条件都很难得到满足,将两者耦合起来拓展其适用范围。采用质量守恒定理和Darcy定律计算井网格的平均等效渗透系数,结合显式流量分配法模拟混合井流问题。最后,通过两个典型算例来验证该方法的合理性,其中一个算例是非完整井穿透相邻的两个含水层,另一个算例是完整井穿透两个含水层,且中间有隔水层。将耦合法的计算结果与显式流量分配法对比,结果表明:只有在第一个例子中当水流达到稳定时,两种方法的计算结果几乎相同,且井网格的水头差很小;而其它情况两者的差别很明显,且采用流量分配法计算井网格的水头差大于耦合法计算井网格的水头差。根据Neville等的相关结论可知采用耦合法对于文中的两个例子都比较合理。     

含水层层状非均质对地下水流系统的影响

区域尺度上含水层非均质具有复杂的结构性和随机性,难以准确刻画,造成非均质对区域地下水流系统的影响机制研究不够深入。本文以鄂尔多斯盆地白垩系地下水流系统为研究实例,选择典型剖面,采用剖面二维随机数值模拟方法,通过对比不同非均质刻画方法下地下水流场的变化,探讨含水层层状非均质对地下水流系统的影响机制。结果显示,均质条件下模型各向异性（含水层水平和垂向渗透系数比值Kh/Kv）取值为1000时,地下水流场与实际条件较为接近;非均质条件下,渗透系数方差取值0.91,水平相关长度取值5000 m,Kh/Kv取值150时,接近实际条件。研究表明,在大尺度地下水流模拟研究中,采用水平相关长度、渗透系数方差和各向异性值三个变量生成的随机场能很好地刻画含水层的层状非均质特征及其对水流系统的影响控制作用。由于含水层不同尺度层状非均质的叠加效应,采用均质各向异性介质等效概化含水层层状非均质性会造成等效各向异性值偏大失真的效应。     

成层地基轴对称问题的基本解

基于各向同性弹性体基本方程的转换及Hankel变换，得到了轴对称荷载作用下，无限弹性层轴向不同深度经Hankel变换的位移应力向量间的传递矩阵，运用该传递矩阵可求解成层的、层间完全接触情形和各向同性空间轴对称问题。     

A simple procedure to simulate a smooth elastic-plastic transition in Cam-Clay models

A simple procedure is proposed to simulate a smooth transition from elastic to elastoplastic behaviour in Cam-Clay models. The procedure consists of the definition of an external constitutive surface where full yield is assumed, and an internal one that allows the definition of the position in which plastic strains start to appear before the external yield surface is reached. The comparison of the model results with different laboratory tests shows the validity of the procedure. The method considers one additional parameter with regard to a “standard” critical state model, and it can easily be implemented in existing integration modules.     

Folder: A numerical tool to simulate the development of structures in layered media

We present Folder, a numerical toolbox for modelling deformation in layered media subject to layer parallel shortening or extension in two dimensions. The toolbox includes a range of features that ensure maximum flexibility to configure model geometry, define material parameters, specify numerical parameters, and choose the plotting options. Folder builds on an efficient finite element method model and implements state of the art iterative and time integration schemes. We describe the basic Folder features and present several case studies of single and multilayer stacks subject to layer parallel shortening and extension. Folder additionally comprises an application that illustrates various analytical solutions of growth rates calculated for the cases of layer parallel shortening and extension of a single layer with interfaces perturbed with a single sinusoidal waveform. We further derive two novel analytical expressions for the growth rate in the cases of layer parallel shortening and extension of a linear viscous layer embedded in a linear viscous medium of a finite thickness. These solutions help understand mechanical instabilities in layered rocks and provide a unique opportunity for benchmarking of numerical codes. We demonstrate how Folder can be used for benchmarking of numerical codes. We test the accuracy of single-layer folding simulations using various 1) spatial and temporal resolutions, 2) iterative algorithms for non-linear materials, and 3) time integration schemes. The accuracy of the numerical results is quantified by: 1) comparing them to analytical solutions, if available, or 2) running convergence tests. As a result, we provide a map of the most optimal choice of grid size, time step, and number of iterations to keep the results of the numerical simulations below a given error for a given time integration scheme. Folder is an open source MATLAB application and comes with a user-friendly graphical interface. Folder is suitable for both educational and research purposes.     

Vertical dynamic response of pile in a radially heterogeneous soil layer

An analysis of a pile vertical response considering soil inhomogeneity in the radial direction under dynamic loads is presented. The solution technique is based on a three‐dimensional axisymmetric model, which includes the consideration of the vertical displacement of the soil. The soil domain is subdivided into a number of annular vertical zones, and the continuity of the displacements and stresses are imposed at both the interface of pile–soil and the interfaces of adjacent soil zones to establish the dynamic equilibrium equations of the pile–soil interaction. Then, the equations of each soil zone and of the pile are solved one by one to obtain the analytical and semi‐analytical dynamic responses at the top of the pile in the frequency domain and time domain. Parametric studies have been performed to examine the influence of soil parameters' variations in the radial direction caused by the construction effect on the dynamic responses of pile. The results of the studies have been summarized and presented in figures to illustrate the influences of the soil parameters as they change radially. The effect of the radius of the disturbed soil zone caused by construction is also studied in this paper. Copyright © 2008 John Wiley & Sons, Ltd.     

Interconnection of karst systems and flow piracy through karst collapse in layered carbonate rocks

A new mode of interconnecting karst systems separated by impermeable bed due to karst collapse was discovered in the study of dam site in Guizhou, South China. Karst flow may be diverted from conduits in one layer to another, thus forming a connected karst system. Comprehensive methodology and techniques used in the investigation included surface geological surveys, geophysical investigations, special drilling, and tracer tests. In the stage of preliminary study, the karst conduits were considered to be developed separately along individual karstified layers. However, further investigation shows that karst collapse may be associated with conduit and cavern development, damaging the impermeable bed and its watertight function. Accordingly, a new pattern of karst conduit system was reestablished. The results obtained enable the dam designer to plan a reliable alternative for seepage protection.     

Quantitative and qualitative simulation of groundwater by mathematical models in Rafsanjan aquifer using MODFLOW and MT3DMS

Agriculture sector by using 80% of freshwater is the greatest water consumer in Iran. Excessive use of agricultural fertilizers in last decade, caused accumulation of enormous amounts of salts and subsequence declined the physical properties of soil. In desert and dry regions such as Rafsanjan plain, use of the groundwater resources is more than the surface water resources. Therefore, information about the quality of these resources remains a necessary task for optimum management, protection of water resources, and stopping the future damages. In this study, the groundwater quantity and quality of Rafsanjan plain was investigated by MODFLOW and MT3DMS. The presented quantitative model for this aquifer was compared by observed data and calibrated. This model was used to predict a 10-year period. Results show that water elevation decreases approximately 15 m for 10 years to come in this plain. Qualitative model results show that most quality parameters will increase. Electrical conductivity will increase more than other parameters. As values of this parameter will reach 16,000 µs/l for next 5 years. Therefore, we suggest that exploitation of water from these resources should be reduced and discharge from some of agricultural wells stop; also we suggested that recharge to groundwater resources should be increased and agricultural activities should be limited or improved using of modern irrigation systems in this plain.     

An optimal procedure for identifying parameter structure and application to a confined aquifer

This study applies an optimal procedure to identify the spatial distribution of groundwater hydraulic conductivity for a confined aquifer in north Taiwan. The parameter structure is determined by the number of zones, zonation pattern, and an uniform hydraulic conductivity associated with each zone. The proposed optimal procedure uses the Voronoi diagram in describing zonation and applies simulated annealing algorithm to optimize its pattern and associated hydraulic conductivity. Three criteria are defined to stop the searching process, including the residual error, the parameter uncertainty, and the structure error. Observation hydraulic heads in years 2000 and 2001 and hydraulic conductivity value from pumping tests are used. The results show that the parameter structure with five zones conforms to the three criteria and, thus, is recommended for future groundwater simulation for the study site. Different heuristic algorithms may also play the role of simulated annealing to optimize the parameter structure. However, which optimization algorithm is more efficient is not discussed and requires further study.     

层状非均质结构包气带入渗过程单相流与两相流数值模拟对比研究

包气带水分入渗过程受多种因素的影响。定量研究层状非均质岩性结构和入渗速率对其影响,有助于解决根据不同条件选择单相流模型或水气二相流模型模拟包气带水分入渗过程的问题。结合填埋场等场地地层条件及污废水入渗特征,分别建立了“上细下粗”和“上粗下细”包气带层状非均质岩性结构水分入渗单相流和水气二相流模型,探讨不同层状非均质岩性结构条件下模型的适用性。在“上粗下细”岩性结构模型基础上,进一步探究入渗速率对水气两相运移结果的影响。基于论文模型研究表明：（1）在包气带岩性结构为“上细下粗”的条件下,气相的影响基本可以忽略,可直接采用单相流模型对包气带水分运移进行模拟;在“上粗下细”岩性结构和本次模型设定的底部压力保持不变及污废水泄漏前场地未接受降水入渗补给等条件下,当包气带上下层介质渗透率比值大于16倍时,气相会对水相运移产生明显影响,且下层介质渗透率越小、上下层介质渗透率比值越大,单相流与两相流的运移结果差别越大,需要采用水气二相流模型模拟包气带水分运移。（2）在包气带“上粗下细”岩性结构条件下,入渗速率越大,气相对水流入渗的阻滞作用越明显,此时包气带水分运移模拟应采用水气二相流模型。     

Application of MODFLOW and geographic information system to groundwater flow simulation in North China Plain, China

MODFLOW is a groundwater modeling program. It can be compiled and remedied according to the practical applications. Because of its structure and fixed data format, MODFLOW can be integrated with Geographic Information Systems (GIS) technology for water resource management. The North China Plain (NCP), which is the politic, economic and cultural center of China, is facing with water resources shortage and water pollution. Groundwater is the main water resource for industrial, agricultural and domestic usage. It is necessary to evaluate the groundwater resources of the NCP as an entire aquifer system. With the development of computer and internet information technology it is also necessary to integrate the groundwater model with the GIS technology. Because the geological and hydrogeological data in the NCP was mainly in MAPGIS format, the powerful function of GIS of disposing of and analyzing spatial data and computer languages such as Visual C and Visual Basic were used to define the relationship between the original data and model data. After analyzing the geological and hydrogeological conditions of the NCP, the groundwater flow numerical simulation modeling was constructed with MODFLOW. On the basis of GIS, a dynamic evaluation system for groundwater resources under the internet circumstance was completed. During the process of constructing the groundwater model, a water budget was analyzed, which showed a negative budget in the NCP. The simulation period was from 1 January 2002 to 31 December 2003. During this period, the total recharge of the groundwater system was 49,374 × 10⁶ m³ and the total discharge was 56,530 × 10⁶ m³ the budget deficit was −7,156 × 10⁶ m³. In this integrated system, the original data including graphs and attribution data could be stored in the database. When the process of evaluating and predicting groundwater flow was started, these data were transformed into files that the core program of MODFLOW could read. The calculated water level and drawdown could be displayed and reviewed online.     

Strain refraction in layered systems

Strain refraction across competence contrasts is presented as a simple model consisting of two components, a homogeneous strain and a heterogeneous simple shear. For Newtonian materials, the ratio of the layer-parallel simple shear component in adjacent layers is the inverse of their viscosity ratio. Strong changes in ellipsoid size, shape and orientation are predicted across viscosity contrasts.The geological implications of strain refraction theory are considered within the context of the ‘cleavage/strain debate’. The particular relationships of relative competence and strain revealed by the refraction model may contribute to the problem of why cleavages of different morphologies in rocks of different lithologies (and kinematic histories) should appear to be subparallel to the XY planes of measured strain ellipsoids. Competent rocks should develop dominantly layer-orthogonal strain, and incompetent layers shear-dominated deformation. A variety of structural features ranging from cleavage refraction, changing lineation orientations, folds transected by cleavage, changes from coaxial to non-coaxial deformation, and ramp-flat fault geometry may be the result of stress and strain refraction in rocks.     

Geochemical controls on sediment reactivity and buffering processes in a heterogeneous aquifer

The injection and recovery of oxic water into deep anoxic aquifers may help to alleviate short- and long-term imbalance between freshwater supply and demand. The extent and structure of physical and geochemical heterogeneity of the aquifer will impact the water quality evolution during injection, storage and recovery. Water–sediment interactions within the most permeable parts of the aquifer, where the bulk of the injectant will penetrate, may dominate, however, water quality may also be impacted by interactions within the finer-grained, less permeable but potentially highly reactive media. In this study, the heterogeneity of the reductive capacity of an aquifer selected for water reuse projects was characterised, the amount, type and reactivity of the sedimentary reductants present determined, and the relationship between reductive capacity and sedimentary lithologies quantified. The average potential reductive capacities (PRC_TOT), based on total organic C and pyrite concentrations of the sediment, were quantified for sands (382 μmol O₂ g⁻¹), clays (1522 μmol O₂ g⁻¹), and silts (1957 μmol O₂ g⁻¹). Twenty-seven samples, spanning the three different lithologies, were then incubated for 50 days and the measured reductive capacities (MRC) determined for the sands (29.2 μmol O₂ g⁻¹), silts (136 μmol O₂ g⁻¹), and clays (143 μmol O₂ g⁻¹). On average, the MRC were 10% of the PRC_TOT. The main consumers of O₂ were pyrite (20–100%), sedimentary organic matter (SOM; 3–56%), siderite (3–28%) and Fe(II)-aluminosilicates (8–55%). The incubation data plus hydrogeochemical modelling, indicated that pH-buffering was controlled firstly by dissolution of trace level carbonates, followed by dissolution of feldspars. Zinc, Co, Ni, Cd and Pb were readily mobilized during incubation.     

Inverse modelling of aquifer parameters in basaltic rock with the help of pumping test method using MODFLOW software

The origin and movement of groundwater are the fundamental questions that address both the temporal and spatial aspects of ground water run and water supply related issues in hydrological systems. As groundwater flows through an aquifer, its composition and temperature may variation dependent on the aquifer condition through which it flows. Thus, hydrologic investigations can also provide useful information about the subsurface geology of a region. But because such studies investigate processes that follow under the Earth's shallow, obtaining the information necessary to answer these questions is not continuously easy. Springs, which discharge groundwater table directly, afford to study subsurface hydrogeological processes.The present study of estimation of aquifer factors such as transmissivity (T) and storativity (S) are vital for the evaluation of groundwater resources. There are several methods to estimate the accurate aquifer parameters (i.e. hydrograph analysis, pumping test, etc.). In initial days, these parameters are projected either by means of in-situ test or execution test on aquifer well samples carried in the laboratory. The simultaneous information on the hydraulic behavior of the well (borehole) that provides on this method, the reservoir and the reservoir boundaries, are important for efficient aquifer and well data management and analysis. The most common in-situ test is pumping test performed on wells, which involves the measurement of the fall and increase of groundwater level with respect to time. The alteration in groundwater level (drawdown/recovery) is caused due to pumping of water from the well. Theis (1935) was first to propose method to evaluate aquifer parameters from the pumping test on a bore well in a confined aquifer. It is essential to know the transmissivity (T = Kb, where b is the aquifer thickness; pumping flow rate, Q = TW (dh/dl) flow through an aquifer) and storativity (confined aquifer: S = bS_s, unconfined: S = S_y), for the characterization of the aquifer parameters in an unknown area so as to predict the rate of drawdown of the groundwater table/potentiometric surface throughout the pumping test of an aquifer. The determination of aquifer's parameters is an important basis for groundwater resources evaluation, numerical simulation, development and protection as well as scientific management. For determining aquifer's parameters, pumping test is a main method. A case study shows that these techniques have been fast speed and high correctness. The results of parameter's determination are optimized so that it has important applied value for scientific research and geology engineering preparation.     

Complementary use of tracer and pumping tests to characterize a heterogeneous channelized aquifer system in New Zealand

The combined use of pumping and tracer test data enabled the derivation of equivalent average hydraulic conductivities (K_avg) for each test in a heterogeneous channelized alluvial aquifer, whereas K values of the preferential flow paths were two orders of magnitude higher. Greater and earlier drawdown was generally observed along preferential flow lines in a pumping test, within an array of 21 wells. The study aim was to characterize hydraulic properties of a channelized aquifer system in New Zealand by combining tracer and pumping test data. Estimates were able to be made of the percentage of highly permeable channels within the profile (～1.2%), effective porosity that reflected the maximum fraction of highly permeable channels within the aquifer (?_eff–pc ～0.0038), and flows through highly permeable channels (～98%) and the sandy gravel matrix material (～2%). Using ?_eff–pc, a tracer test K_avg value (～93 m/day) was estimated that was equivalent to pumping test values (～100 m/day), but two orders of magnitude smaller than K calculated solely from transport through permeable channels (K_pc ～8,400 m/day). Derived K values of permeable and matrix material were similar to values derived from grain size distribution using the Kozeny-Carman equation.     

Erratum to: A spatio-temporal three-dimensional conceptualization and simulation of Dera Ismail Khan alluvial aquifer in visual MODFLOW: a case study from Pakistan

The Gour Oumelalen area exposes Paleoproterozoic (1.9 Ga) marbles and calc-silicate granulites. Some marbles show a specific mineralogy characterized by the presence of a highly aluminous clinopyroxene with Al₂O₃ content exceeding16 wt%. This clinopyroxene shows a marked zoning with a hedenbergitic core rimmed by fassaite. Phase relations are expressed by spectacular reaction textures in calc-silicate granulites as Opx + Cpx + Pl + H₂O  == > Grt + Qtz ± Am and Cpx + Ilm + Pl ± Mt = > Grt + Qtz + Spn. In olivine-bearing marbles, clinopyroxene and dolomite occur around olivine and calcite. According to thermodynamic modeling in the Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–Fe₂O₃ (NCFMASHTO) system, the first stage of metamorphism is located at 800 °C and 6–7 kbar, which is followed by an increase in pressure at 9–10 kbar and 800 °C and an isobaric cooling at 680 °C. The deduced anticlockwise P–T path is consistent with a granulitic metamorphism occurring in an active continental margin context.

     

稳定井流直线图解法确定含水层参数

对于潜水井流,利用Dupuit公式计算的参数往往相差很大,难以直接选用。对Dupuit公式进行线性化,建立降深(s)与距离(r)的s-lnr直线关系,利用直线斜率、直线在x轴上的截距,可以直接求得唯一的渗透系数K和影响半径R。利用松花江河谷的承压水井抽水试验资料和洮儿河扇形地27个潜水抽水井及其观测孔的抽水试验资料,应用直线图解法分析计算,得到唯一的含水层参数T、K和R。将计算结果与直接利用Dupuit公式所计算的结果相比较,前者的求参效果较好。