Improving groundwater-flow modeling using optimal zoning methods

Hydraulic conductivity sometimes exhibits complicated spatial variation over a site. A thorough understanding of the spatial distributions of hydraulic conductivity helps to make deterministic models of groundwater more accurate. This study presents a novel procedure that combines simulated annealing algorithms (SA) and the shortest distance method (SD) with the modular three-dimensional groundwater flow model (MODFLOW). The procedure is applied to a hypothetical site with groundwater-monitoring wells to minimize the difference between simulated and observed hydraulic head for optimal zoning of the spatial distribution of hydraulic conductivity. The results of this optimal zoning method indicate that this new procedure not only improves the efficiency of optimization, but also increases the probability of finding the global optimum, minimizing the errors of the hydraulic head simulated by MODFLOW in two scenarios, one with known and the other with unknown hydraulic conductivity. The results also illustrated that the procedure can effectively determine and delineate hydrogeological zones.     

Application of differential evolutionary optimization methodology for parameter structure identification in groundwater modeling

Parameter structure identification is formulated in terms of solving an inverse problem, which allows for a determination of an appropriate level of parameter structure complexity, and the identification of its pattern and the associated parameter values. With the increasing complexity of parameter structure identification in groundwater modeling, demand for robust, fast, and accurate optimizers is on the rise among researchers from groundwater hydrology fields. A novel global optimizer, differential evolution (DE), has been proposed to solve the parameter-structure-identification problem. The Voronoi tessellation is adopted for the automatic parameterization. The stepwise regression method and the error covariance matrix are used to determine the optimal structure complexity. Numerical experiments with a continuous hydraulic conductivity distribution are conducted to demonstrate the proposed methodology. The results indicate that the DE can identify the global optimum effectively and efficiently. A sensitivity analysis of the control parameters and mutation schemes implemented in the DE is employed to examine their influence on the objective function. The comparison between DE and genetic algorithm shows the advantage of DE in terms of robustness and efficiency. The proposed methodology is also applied to a real groundwater system, Pingtung Plain in Taiwan, and the properties of aquifers are successfully identified.     

中国北方岩溶区优势面控水机理及优势参数的确定与应用

在地下水数值模拟过程中，由于介质的空间变异性大，水文地质参数的优分工至今仍是一个重要而又难以解决的问题，本文将非饱和带土壤中的优势流概念推广到岩溶裂隙介质中，系统地分析了形成优势流的优势结构面控水机理，结合中国北方岩溶特征提出了实际工作中优势参数分方法，并依据有限元方法进一步求解，实例计算表明：利用优势面分析方法可以确定参数最优分区，所计算结果与实际情况基本一致，该结论对地下水流数值模拟参数的识别提供一种新的途径，同时对中国北方岩溶区地下水优势流的研究地以及地下水资源的科学评价等具有重要的参考价值。     

Groundwater flow and capture zone analysis of the Central Passaic River Basin, New Jersey

Delineating capture zones of pumping wells is an important part of safe drinking water and well protection programs. Capture zones or contributing areas of a groundwater extraction well are the parts of the aquifer recharge areas from which the wells draw their water. Their extent and location depend on the hydrogeologic conditions such as groundwater recharge, pumping scenario and the aquifer properties such as hydraulic conductivity, porosity, heterogeneity of the medium and hydraulic gradient. Different methods of delineation can be used depending on the complexity of the hydrogeologic conditions. In this study, a 3-dimensional transient numerical MODFLOW model was developed for the Central Passaic River Basin (CPRB), and used with a MODPATH particle tracking code to determine 3-dimensional transient capture zones. Analytically calculated capture zones from previous studies at the site were compared with the new numerically simulated capture zones. The study results revealed that the analytical solution was more conservative, estimating larger capture zones than the numerical models. Of all the parameters that can impact the size, shape and location of a capture zone, the hydraulic conductivity is one of the most critical. Capture zones tend to be smaller in lower hydraulic conductivity areas.     

The hydraulic conductivity field and groundwater flow in the unconfined aquifer system of the Keta Strip,Ghana

This study investigates the hydraulic conductivity field and the groundwater flow pattern as predicted by a calibrated steady state groundwater flow model for the Keta Strip, southeastern Ghana. The hydraulic conductivity field is an important parameter in evaluating aquifer properties in space, and in general basin-wide groundwater resources evaluation and management. This study finds that the general hydraulic conductivity of the unconsolidated unconfined aquifer system of the Keta Strip ranges between 2 m/d and 20 m/d, with an average of 15 m/d. The spatial variation in horizontal hydraulic conductivity appears to take the trend in the variations in the nature of the material in space. Calibrated groundwater recharge suggests that 6.9–34% of annual precipitation recharges the shallow aquifer system. This amount of recharge is significant and suggests high fortunes in terms of groundwater resources development for agriculture and industrial activities in the area. A spatial distribution of groundwater recharge from precipitation is presented in this study. The spatial pattern appears to take the form of the distribution in horizontal hydraulic conductivity, and suggests that the vertical hydraulic conductivity takes the same pattern of spatial variation as the horizontal hydraulic conductivity. This is consistent with observations in other areas. The resulting groundwater flow is dominated by local flow systems as the unconfined system is quite shallow. A general northeast – southwest flow pattern has been observed in the study area.     

Toward reliable calibration of aquifer hydrodynamic parameters: characterizing and optimization of arid groundwater system using swarm intelligence optimization algorithm

Despite advanced development in computational techniques, the issue of how to adequately calibrate and minimize misfit between system properties and corresponding measurements remains a challenging task in groundwater modeling. Two important features of the groundwater regime, hydraulic conductivity (k) and specific yield (S _y), that control aquifer dynamic vary spatially within an aquifer system due to geologic heterogeneity. This paper provides the first attempt in using an advanced swarm-intelligence-based optimization algorithm (cuckoo optimization algorithm, COA) coupled with a distributed hydrogeology model (i.e., MODFLOW) to calibrate aquifer hydrodynamic parameters (S _y and k) over an arid groundwater system in east Iran. Our optimization approach was posed in a single-objective manner by the trade-off between sum of absolute error and the adherent swarm optimization approach. The COA optimization algorithm further yielded both hydraulic conductivity and specific yield parameters with high performance and the least error. Estimation of depth to water table revealed skillful prediction for a set of cells located at the middle of the aquifer system whereas showed unskillful prediction at the headwater due to frequent water storage changes at the inflow boundary. Groundwater depth reduced from east toward west and southwest parts of the aquifer because of extensive pumping activities that caused a smoothening influence on the shape of the simulated head curve. The results demonstrated a clear need to optimize arid aquifer parameters and to compute groundwater response across an arid region.     

利用趋势化随机参数场的地下水流数值模拟优化方法

水文地质参数场的刻画是建立地下水流数值模拟模型的关键问题和难点问题。通常来讲,参数场合理性程度越高,模型拟合精度越高。本次研究将随机方法和参数空间分布表达进行结合,提出了趋势化随机参数场的构建方法。以渗透系数为研究对象,首先利用MCMC采样和样本数据特征确定水文地质参数的基本数据结构,进而根据样本空间分布特征对其进行趋势化处理,最终形成趋势化的渗透系数场。通过算例分析,利用趋势化处理后的渗透系数场能够大幅提高模拟精度,相比传统赋均值方法其误差可降至原来的1/3。在北京大兴跌隆起地区进行的实例应用说明,趋势化渗透系数场对提升岩性粒径较大(中砂以上)地区模拟精度效果显著,案例中粗砂区域渗透系数经趋势化处理后平均拟合误差由2.76 m下降至0.64 m;而对岩性以细砂及以下粒径为主的区域模拟精度提升并不明显。总体来说,该方法可为地下水流数值模型的优化提供借鉴,提升模型拟合精度,从而更加合理地刻画地下水流系统。     

Determination of the parameter pattern and values for a one-dimensional multi-zone unconfined aquifer

In an aquifer, heterogeneity plays an important role in governing groundwater flow. Hence, aquifer characterization should involve both the pattern and values of the hydrogeological parameters. A new analytical solution describing the one-dimensional groundwater flow in a multi-zone unconfined aquifer is presented, and a methodology developed from the analytical solution and a heuristic approach for determining the pattern and values of the aquifer parameters are proposed. The analytical solution demonstrates that the hydraulic head varies spatially and is influenced by aquifer heterogeneity. Simulated annealing, a heuristic approach, is incorporated with the solution to simultaneously identify the pattern and values of the hydraulic conductivity for a horizontal multi-zone unconfined aquifer. This approach may be used to give an approximate result for a two-dimensional problem by dividing the model area into a number of transects along the transverse direction, identifying the parameter values along the longitudinal direction for each transect, and then smoothing the identified results.     

基于LHS方法的地下水随机模拟及开采量风险性 评价

地下水流数值模拟过程中,水文地质参数的不确定性对模拟结果影响很大。以内蒙古鄂尔多斯市某水源地为例,利用拉丁超立方抽样(LHS)方法获得了含水层渗透参数的随机组合,进行地下水流随机模拟。通过对观测资料与计算水位的绝对值平均(MAE)误差和误差均方根(RMSE)的统计分析,获得了模型较为稳定的随机模拟次数是243次。利用该随机模型对水源地设计开采量进行水位预测,并给出允许降深的风险性分布图。结果表明,预测水位和标准差分布符合实际情况,水位降深大于35 m的风险性最大达到75%。     

结构复杂滑坡活动对库水位变化的响应特征——以三峡库区柴湾滑坡为例

柴湾滑坡是三峡库区结构复杂的大型老滑坡之一,三峡水库蓄水后,该滑坡出现明显复活迹象。本文基于滑坡结构和2007-2015年监测数据,分析了该滑坡活动对库水位变化的响应特征;采用数值模拟手段分析了库水位变化时滑体内渗流场及孔隙水压力变化特征。研究发现,该滑坡在平、剖面上分别呈现牵引式分块与浅、中层分层的缓慢活动特征;当库水位降速>0 8 m/d时,滑坡活动呈现滞后的台阶式加剧趋势;越接近地表,滑坡活动对库水位变化愈敏感。柴湾滑坡活动特征受其复杂结构控制,滑坡中前部地下水与库水密切的水力联系以及中层、深层滑体良好的渗透性决定了滑坡的分块和分层活动特征。库水位上升时透水性较强滑体内的扬压力和库水位下降时透水性较弱滑体内的动水压力是造成滑坡分块分层活动的内在动力。     

Determining groundwater protection zones for the Quaternary aquifer of northeastern Nile Delta using GIS-based vulnerability mapping

The area of study lies at the northeastern part of Nile Delta. Global shoreline regression and sea-level rise have their own-bearing on the groundwater salinization due to seawater intrusion. A new adopted approach for vulnerability mapping using the hydrochemical investigations, geographic information system and a weighted multi-criteria decision support system (WMCDSS) was developed to determine the trend of groundwater contamination by seawater intrusion. Six thematic layers were digitally integrated and assigned different weights and rates. These have been created to comprise the most decisive criteria used for the delineation of groundwater degradation due to seawater intrusion. These criteria are represented by the total dissolved solids, well discharge, sodium adsorption ratio, hydrochemical parameter (Cl/HCO₃), hydraulic conductivity and water types. The WMCDSS modeling was tried, where a groundwater vulnerability map with four classes ranging from very low to high vulnerability was gained. The map pinpointed the promising localities for groundwater protection, which are almost represented by the very low or low vulnerability areas (53.69 % of the total study area). The regions having high and moderate groundwater vulnerability occupy 46.31 % of total study area, which designate to a deteriorated territory of groundwater quality, and needs special treatment and cropping pattern before use. However, the moderate groundwater vulnerability class occupies an area of about 28.77 % of the total mapped area, which highlighted the need for certain management practices to prevent the saltwater intrusion from expanding further to the south. There was a good correlation of the constructed vulnerability map with the recently gathered water quality data and hydrochemical facies evolution. The plotting of water quality data on Piper trilinear diagram revealed the evolution of freshwater into the mixing and the saline zones as an impact of seawater intrusion, which validates the model results.     

鄂尔多斯高原毛乌素沙地湖盆周缘植被与地下水关系研究

受气候变化和人类活动的两重影响,鄂尔多斯高原湖泊呈现不同程度的萎缩趋势,对本区的生态环境产生重大影响。在鄂尔多斯高原毛乌素沙漠腹地选择有代表性湖泊—布寨淖尔湖为研究区,在野外调查的基础上,选取典型剖面详细研究优势植被与地下水的关系,系统总结湖盆周缘地形地貌、包气带岩性结构、地下水水位埋深、水化学特征与植物类型和植被种群的关系,分析影响植被生态的主要因素,揭示湖盆周缘生态水文地质分带规律,划分4个生态水文地质区,提出湖盆周缘优势植被沙蒿(Artemisia)、沙柳(Salix psammophila)和苔草(Carex)的适生地下水位埋深。     

Uncertainty analysis of groundwater model based on data assimilation北大核心CSCD

黑河流域中下游地下水系统受上游冰冻圈融水和降雨的补给,由气候变暖导致的冰冻圈萎缩致使中下游地下水系统的稳定性面临更多的风险。地下水模型是地下水系统稳定性评估的有效手段,但是地下水模型参数往往存在较大的不确定性。为此,本文提出了基于数据同化算法的不确定性分析方法,通过包含观测资料信息减小模型不确定性。采用所提方法分析了(基于MODFLOW构建)黑河流域中游地下水模型中13个参数的不确定性,讨论了算法超参数的影响及其最优取值,分析了地下水模型参数的不确定性。实验结果证明数据同化算法可有效减小地下水模型参数的不确定性,观测资料的种类与数量对参数不确定性的减小起到重要作用;不同地下水模型参数的不确定性不同,地表水与地下水相互作用频繁的区域参数不确定性较大;含水层渗透系数、含水层给水度以及灌溉回流系数对模型输出的地下水位输出影响显著,河床水力传导系数对模型输出的河流流量影响较大。本研究将为地下水研究提供更加可靠的模型方法,为西北内流区地下水哺育的绿洲生态系统稳定可持续研究提供重要支撑。     

Deformation mechanisms and hydraulic properties of fault zones in unconsolidated sediments; the Roer Valley Rift System,The Netherlands

In general, faults cutting through the unconsolidated sediments of the Roer Valley Rift System (RVRS), The Netherlands, form strong barriers to horizontal groundwater flow. The relationships between deformation mechanisms along fault zones and their impact on the hydrogeological structure of the fault zone are analyzed in a shallow (0–5 m below land surface) trench over one of the faults in the study area. Recently developed digital-image-analysis techniques are used to estimate the spatial distribution of hydraulic conductivity at the millimeter-scale and to describe the micromorphologic characteristics of the fault zone. In addition, laboratory measurements of hydraulic conductivity on core-plug samples show the larger-scale distribution of hydraulic conductivity in the damage zone flanking the main fault plane. Particulate flow is the deformation mechanism at shallow depths, which causes the damage zone around the fault, in the sand-rich parts, to have a relatively enhanced hydraulic conductivity. The fault core is characterized by reduced hydraulic conductivity due to clay smearing, grain-scale mixing, and iron-oxide precipitation. Electronic Publication     

岩溶发育强度垂直分带方法

讨论了岩溶发育强度分带的现状,提出了岩溶发育强度垂直分带的原则,以钻孔岩溶率、溶洞规模和钻孔涌(漏)水量作为定量指标,以岩组特征、地质构造特征和地下水运动特征作为定性指标,划分为强烈、中等和微弱3个岩溶发育带,并用类比、主因素判别法及模糊综合评判方法确定岩溶发育的强度等级。     

Groundwater flow modelling of Yamuna-Krishni interstream,a part of central Ganga Plain Uttar Pradesh

Groundwater is a major source of water for agricultural and domestic requirements in western Uttar Pradesh. Due to increasing agricultural requirements the abstraction of groundwater has increased manifold in the last two-to-three decades. The quaternary alluvium hosts the aquifer in the region. The study area forms a part of Yamuna-Krishni interfluve. Although the area hosts potential aquifers these have been adversely affected by poor management. For effective groundwater management of a basin it is essential that a careful water balance study should be carried out. Keeping this in mind groundwater flow modelling was attempted to simulate the behaviour of the flow system and evaluate the water balance. The groundwater flow modelling was carried out. The horizontal flows, seepage losses from unlined canals, recharge from rainfall and irrigation return flows were applied using different boundary packages available in Visual MODFLOW, Pro 4.1. The river-aquifer interaction was simulated using the river boundary package. Hydraulic conductivity values were applied to specific zones and these ranged from 9.8 to 26.6m/day. Recharge due to rainfall and irrigation returns were assigned to respective zones. Pumping rates of 500m³/day, 1000m³/day, 1500m³/day, 2000m³/day and 2500m³/day were applied to appropriate areas of the model to simulate areas of stress. The zone budget shows a water balance deficit for the period June 2006 to June 2007. The total recharge to the study area is 160.21 million m³ (Mcum). The groundwater draft through pumping is of the order of 233.56 Mcum, thus leaving a deficit balance of −73.35 Mcum. The sensitivity of the model to input parameters was tested by varying the parameters of interest over a range of values, monitoring the response of the model and determining the root mean square error of the simulated groundwater heads to the measured heads. These analyses showed that the model is most sensitive to hydraulic conductivity and recharge parameters. Three scenarios were considered to predict aquifer responses under varied conditions of groundwater bstraction.     

Assessment of groundwater potential of Gandhinagar region,Gujarat

With burgeoning population, the groundwater demands of any area increased by many fold and therefore, it is essential to assess the groundwater potential to choose suitable sites for further groundwater development. Present study determines the groundwater potential of different parts of Gandhinagar region located at Gandhinagar district, Gujarat, India. Here, excluding city dwellers, all villagers are mostly dependent on groundwater for drinking and domestic purposes. With increasing population, there is a rise in daily human consumption and hence reduction in groundwater quantity.Various types of industries of Gandhinagar such as textile industries, food processing industries, ceramic industries etc. also require groundwater. Industrial discharges deteriorate the water quality of this region. Therefore, water level monitoring and quality assessment of groundwater in regular intervals is essential. The groundwater potential zoning is an indicator, which gives the overall idea about the groundwater condition. Overlay analysis in GIS using multiple criteria such as WQI, hydraulic conductivity, groundwater velocity, and depth to piezometric surface discloses that there are five groundwater potential zones in Gandhinagar region. This study reveals that majority of the study area is covered with medium potential zone. Different management plans such as treated surface water supply, reduction in tubewell operation time, development of rooftop rainwater harvesting system and artificial recharge system etc. are recommended for different potential zones for sustainable development of groundwater of Gandhinagar region.     

Aquifer hydraulic conductivity prediction via coupling model of MCMC-ANN

Grain-size distribution data,as a substitute for measuring hydraulic conductivity(K),has often been used to get K value indirectly.With grain-size distribution data of 150 sets of samples being input data,this study combined the Artificial Neural Network technology(ANN)and Markov Chain Monte Carlo method(MCMC),which replaced the Monte Carlo method(MC)of Generalized Likelihood Uncertainty Estimation(GLUE),to establish the GLUE-ANN model for hydraulic conductivity prediction and uncertainty analysis.By means of applying the GLUE-ANN model to a typical piedmont region and central region of North China Plain,and being compared with actually measured values of hydraulic conductivity,the relative error ranges are between 1.55%and 23.53%and between 14.08%and 27.22%respectively,the accuracy of which can meet the requirements of groundwater resources assessment.The global best parameter gained through posterior distribution test indicates that the GLUEANN model,which has satisfying sampling efficiency and optimization capability,is able to reasonably reflect the uncertainty of hydrogeological parameters.Furthermore,the influence of stochastic observation error(SOE)in grain-size analysis upon prediction of hydraulic conductivity was discussed,and it is believed that the influence can not be neglected.     

Hydrogeologic productivity in response to a conjugate compressive strike-slip relay: example of Sidi Bou Krime-Jalta area (northern Tunisia)

Bore holes were drilled in the Senonian limestone of the Hedils-Jalta area (northern Tunisia) in order to determine their potential as an aquifer. Structural, tectonic and hydrogeologic data compilation shows the discrimination of productive and not productive zones. Differential hydraulic productivity was recognised with four distinct productive geological zones separated by a sterile corridor trending NW–SE. The structure consists of two compressional dihedrons, limited by two conjugate strike-slip faults, trending NNE–SSW and nearly E–W. The reduction of the (1) potential reservoir, (2) the low hydraulic productivity of the central band, (3) the torsion of the fold axis in eccentric arcs on both sides of the compressive relay and (4) the differential hydrogeological zonation are all related to the distribution of stress in the interference zone between conjugate strike-slip faults and to the reorientation of the stress field in their vicinity. This study constitutes a main database in establishing strategies for groundwater exploration in the similar zones.     

Groundwater dewatering optimization in the Shengli no. 1 open-pit coalmine, Inner Mongolia, China

Impacted by groundwater, faults, lithology, and other factors, the slope of the Shengli no. 1 open-pit coalmine has been in a state of instability. Among these factors, groundwater in the quaternary aquifer is considered primary. Thus, an optimum design for dewatering well pumping rates is presented in this paper. A two-dimensional groundwater simulation model is built to characterize the groundwater flow of the study area. A steady-state model was applied to the observed data (head and discharge) to verify and calibrate the groundwater model. The pilot point method, with a regularization option provided by parameter estimation, was used to identify the hydraulic conductivity field. Afterward, a groundwater optimization model is integrated with the calibrated simulation model to realize groundwater dewatering optimization in the studied open-pit coalmine, and an optimization method called modified Pareto dominance-based real-coded genetic algorithm is adopted. Taking into account the safety of the mine, slope and dewatering wells, seepage discharge is added to objective function and the maximum aquifer saturated thickness is set as the constraint condition in the optimization model. The results indicate that the dewatering optimization procedure developed in this paper can serve as a useful template and framework for solving mining related water problems.