Assessment of groundwater vulnerability to pollution: a combination of GIS, fuzzy logic and decision making techniques

The assessment of groundwater vulnerability to pollution aims at highlighting areas at a high risk of being polluted. This study presents a methodology, to estimate the risk of an aquifer to be polluted from concentrated and/or dispersed sources, which applies an overlay and index method involving several parameters. The parameters are categorized into three factor groups: factor group 1 includes parameters relevant to the internal aquifer system’s properties, thus determining the intrinsic aquifer vulnerability to pollution; factor group 2 comprises parameters relevant to the external stresses to the system, such as human activities and rainfall effects; factor group 3 incorporates specific geological settings, such as the presence of geothermal fields or salt intrusion zones, into the computation process. Geographical information systems have been used for data acquisition and processing, coupled with a multicriteria evaluation technique enhanced with fuzzy factor standardization. Moreover, besides assigning weights to factors, a second set of weights, i.e., order weights, has been applied to factors on a pixel by pixel basis, thus allowing control of the level of risk in the vulnerability determination and the enhancement of local site characteristics. Individual analysis of each factor group resulted in three intermediate groundwater vulnerability to pollution maps, which were combined in order to produce the final composite groundwater vulnerability map for the study area. The method has been applied in the region of Eastern Macedonia and Thrace (Northern Greece), an area of approximately 14,000 km². The methodology has been tested and calibrated against the measured nitrate concentration in wells, in the northwest part of the study area, providing results related to the aggregation and weighting procedure.     

唐山城市土壤重金属污染及潜在生态危害评价

以唐山城市土壤为对象,采用单因子指数法和尼梅罗综合指数法对土壤重金属的环境质量及污染特征进行评价,并采用Hakanson的潜在生态危害指数法对土壤中重金属的潜在生态危害进行评价。结果表明,没有重金属元素出现污染状态,其中Hg、Ni、Cr、As都处于清洁状态,Pb、Zn、Cu绝大部分样点处于清洁状态,7.94%、6.35%、1.59%处于安全状态,Cd元素绝大部分样点处于清洁安全状态,只有1.59%处于警戒状态;综合污染评价土壤环境整体优良,清洁、安全土壤面积比例分别为98.41%、1.59%,没有出现警戒和污染土壤;各重金属元素中,产生潜在生态危害的重金属主要是Hg,已达到强潜在生态危害水平,其余重金属均为轻度潜在生态危害,综合考虑多种重金属的潜在生态危害性,其轻微生态危害、中等生态危害、强生态危害、很强生态危害的百分比分别是73.02%、26.98%、0%、0%,整体表现为轻微潜在生态危害。     

Spatial assessment of the potential of groundwater quality using fuzzy AHP in GIS

In this study, fuzzy AHP method is used for extracting the water quality indicators based on the Schuler standard and World Health Organization (WHO) guidelines during a 20-year period. For this purpose, the best fit of the zoning model was performed. Furthermore, by comparing the standard errors, the continuous Raster layer was extracted from the important parameters used in generating the qualitative potential assessment index. The classified layer was generated by integrating continuous layers in the GIS environment and with the use of Python programming. The similarity of the outputs of both methods indicates the presence of large sections of aquifers in the middle and southwestern regions of Iran in the “temporarily drinkable” and “bad” classes. The calculations showed that the majority of aquifers that were located in the “inappropriate” class during the first 10 years fell to less valuable class types. Based on the results of the model, there is a direct correlation between the drop in water resources and the decline in the quality indices. In addition, in the Urmia and Bushehr coastal aquifers, due to excessive water withdrawal and salty water penetration, the quality of the table water is in critical condition. Based on the results of the research, the aquifers in the range of Zagros and Alborz mountains show the least change in water quality. The reason for this is the depth of the aquifer and the ability to recharge it.     

Land subsidence risk assessment using GIS fuzzy logic spatial modeling in Varamin aquifer,Iran

GeoJournal - The extent of the subsidence and the consequents damage to most of the residential and populated areas of Iran have made this phenomenon one of the most important natural hazards after...     

Definition of kriging in terms of fuzzy logic

In this paper, we have basically attempted to solve two problems: (i) the restricted kriging problem as stated by Matheron, and (ii) the defining of Matheron's kriging problem within the framework of fuzzy logic in order to interpret the Lagrange multiplier, which is a function of kriging variance and is a dual variable with respect to which the generalized Lagrange function F(X, ) is minimized.on leave from Department of Geology, Indian Institute of Technology, Kharagphur 721302, West Bengal, India.     

An interval fuzzy model for magnetic monitoring: estimation of a pollution index

In this contribution, a methodology is reported in order to build an interval fuzzy model for the pollution index PLI (a composite index using relevant heavy metal concentration) with magnetic parameters as input variables. In general, modelling based on fuzzy set theory is designed to mimic how the human brain tends to classify imprecise information or data. The “interval fuzzy model” reported here, based on fuzzy logic and arithmetic of fuzzy numbers, calculates an “estimation interval” and seems to be an adequate mathematical tool for this nonlinear problem. For this model, fuzzy c-means clustering is used to partition data, hence the membership functions and rules are built. In addition, interval arithmetic is used to obtain the fuzzy intervals. The studied sets are different examples of pollution by different anthropogenic sources, in two different study areas: (a) soil samples collected in Antarctica and (b) road-deposited sediments collected in Argentina. The datasets comprise magnetic and chemical variables, and for both cases, relevant variables were selected: magnetic concentration-dependent variables, magnetic features-dependent variables and one chemical variable. The model output gives an estimation interval; its width depends on the data density, for the measured values. The results show not only satisfactory agreement between the estimation interval and data, but also provide valued information from the rules analysis that allows understanding the magnetic behaviour of the studied variables under different conditions.     

模糊逻辑在物理栖息模拟中的应用

为了克服已有物理栖息地模型仅能在具有较完善监测资料河流使用的局限性,介绍了一种应用模糊逻辑的物理栖息地模拟方法。该方法以河道平面二维流场模拟结果为基础,将鱼类学和生态学专家的知识经验融入物理栖息地模型中,运用模糊逻辑推理计算栖息地各单元适宜度,最后根据加权可用面积、高适宜度面积比例与流量的关系曲线确定生态需水量。运用该方法对葛洲坝坝下中华鲟产卵栖息地进行模拟。研究结果表明,中华鲟产卵期适宜生态需水量为10 000~17 000 m3/s。分析认为该方法对监测资料依赖程度低,使用专家知识经验能够弥补数据不足造成的不利影响,具有一定的可行性及实用性。该研究有助于监测资料不足的河流开展生态保护及河流管理工作,并且能够为模糊数学理论在水生态学中的应用提供参考。     

应用模糊集合论方法评价华南若干花岗岩体铀成矿远景

集合论是现代数学的基础。集合可以表达概念。设论域U、α是U上的一个概念,它的外延是U的一个子集A,对于U中的任一元素u,u应符合概念uεA,否则u(?)A,二者必居其一,绝不摸棱两可。因此,建立在普通集合论基础上的现代数学所讨论和解决的问题是严格、精确和绝对的。然而,在现实生活中的许多概念都是不确切的,对于每个对象很难用绝对的“符合”与“不符合”概念来回答。在“符合”与“不符合”之间还存在着既符合又不     

Modeling and risk assessment of landslides using fuzzy logic. Application on the slopes of the Algerian Tell (Algeria)

Natural risk regains the notion of exposure to natural disaster or dangers of any natural hazard. Its management consists in the assessment and the anticipation of risks, as well as to the setting up of an alert system. From natural risk, we mentioned one bound to landslides in natural slopes that are difficult to surround and approach. Nevertheless, the assessment of landslides risk is the object of several works of research and many models, based on the multicriteria analysis, have been established. It should be noted that based on multicriteria approach, we evaluated, in a previous work, the landslide risk using the weighted sum model. The results reveal that the use of qualitative parameters influenced the classification of slope. This led us to adopt fuzzy logic approaches for assessment. This work examines the contribution of fuzzy sets theory to modeling and assessment of landslides risk in natural slopes. It brought to use this approach that permits the survey of these imprecision in adopting a Mamdani model. The method has been applied on slopes, situated in four areas of the Algerian Tell, where each is characterized by the different natural conditions. The result, put in evidence, summarizes modeling and risk assessment of landslides in an optimal classification of slopes according to the degree of instability risk. It allows decision makers to put in strategies for possible work of these slopes.     

Use of GIS-based fuzzy logic relations and its cross application to produce landslide susceptibility maps in three test areas in Malaysia

Landslides are one of the most frequent and common natural hazards in Malaysia. Preparation of landslide susceptibility maps is one of the first and most important steps in the landslide hazard mitigation. However, due to complex nature of landslides, producing a reliable susceptibility map is not easy. For this reason, a number of different approaches have been used, including direct and indirect heuristic approaches, deterministic, probabilistic, statistical, and data mining approaches. Moreover, these landslides can be systematically assessed and mapped through a traditional mapping framework using geoinformation technologies. Since the early 1990s, several mathematical models have been developed and applied to landslide hazard mapping using geographic information system (GIS). Among various approaches, fuzzy logic relation for mapping landslide susceptibility is one of the techniques that allows to describe the role of each predisposing factor (landslide-conditioning parameters) and their optimal combination. This paper presents a new attempt at landslide susceptibility mapping using fuzzy logic relations and their cross application of membership values to three study areas in Malaysia using a GIS. The possibility of capturing the judgment and the modeling of conditioning factors are the main advantages of using fuzzy logic. These models are capable to capture the conditioning factors directly affecting the landslides and also the inter-relationship among them. In the first stage of the study, a landslide inventory was complied for each of the three study areas using both field surveys and airphoto studies. Using total 12 topographic and lithological variables, landslide susceptibility models were developed using the fuzzy logic approach. Then the landslide inventory and the parameter maps were analyzed together using the fuzzy relations and the landslide susceptibility maps produced. Finally, the prediction performance of the susceptibility maps was checked by considering field-verified landslide locations in the studied areas. Further, the susceptibility maps were validated using the receiver-operating characteristics (ROC) success rate curves. The ROC curve technique is based on plotting model sensitivity—true positive fraction values calculated for different threshold values versus model specificity—true negative fraction values on a graph. The ROC curves were calculated for the landslide susceptibility maps obtained from the application and cross application of fuzzy logic relations. Qualitatively, the produced landslide susceptibility maps showed greater than 82% landslide susceptibility in all nine cases. The results indicated that, when compared with the landslide susceptibility maps, the landslides identified in the study areas were found to be located in the very high and high susceptibility zones. This shows that as far as the performance of the fuzzy logic relation approach is concerned, the results appeared to be quite satisfactory, the zones determined on the map being zones of relative susceptibility.     

多层次模糊数学在煤层气开发潜力评价中的应用

对影响煤层气勘探开发潜力的各种因素进行了综合研究,确定了煤层气勘探开发潜力评价的4个二级指标(含气丰度、封盖性能、开采条件和产气性能)及相应的三级指标。采用模糊数学方法对各级因素指标赋予了权重,建立了用于煤层气勘探开发潜力评价的多层次模糊数学评判模型。利用该模型,对川南盆地群煤层气资源条件较好的古叙、松藻、筠连和芙蓉4个无烟煤矿区的煤层气开发潜力进行了评价,认为松藻矿区是川南盆地煤层气勘探开发的最佳试验区。建立的评价体系,可以作为高煤阶煤层气资源开发潜力评价的参考体系。     

An assessment of miniaturised electrical imaging equipment to monitor pollution plume evolution in scaled centrifuge modelling

This paper demonstrates the capabilities and limitations of a miniaturised electrical imaging technique (resistivity tomography) developed at Cardiff University to image contaminant plumes in scaled centrifuge models of the vadose zone. For this purpose a generic model of contaminant infiltration into unsaturated sand was designed. The imaging technique produces two-dimensional contoured plots of the resistivity distribution before and during contaminant infiltration experiments. During the experiments, dyed NaCl solution was released into the model and the change in resistivity associated with the contaminant plume evolution was imaged as a function of time and g-level. Capillary pressure was monitored constantly by matrix potential probes (tensiometers) in order to investigate the effect of capillary forces on plume evolution. Tests at 1g (static conditions) and 10g are described in this paper. Comparison of resulting two-dimensional tomography with observed plume geometry at the end of the 1g test showed this imaging technique to be highly effective.

Contaminant plume evolution in the unsaturated sand model was observed to be mainly gravity-driven, with plume migration and geometry being strongly affected by a tenfold increase in gravity in the centrifuge experiment. It is concluded that miniaturised electrical imaging can be a useful tool for monitoring pollution plume evolution during centrifuge tests, but when plume evolution is rapid, the time taken to interrogate each array restricts the effectiveness of the technique in monitoring changes in plume geometry. However, in such cases, resistivity tomography does provide valuable information on residual levels of contaminant fluid retained within the soil after passage of the plume.     

Ensemble of ground subsidence hazard maps using fuzzy logic

Hazard maps of ground subsidence around abandoned underground coal mines (AUCMs) in Samcheok, Korea, were constructed using fuzzy ensemble techniques and a geographical information system (GIS). To evaluate the factors related to ground subsidence, a spatial database was constructed from topographic, geologic, mine tunnel, land use, groundwater, and ground subsidence maps. Spatial data, topography, geology, and various ground-engineering data for the subsidence area were collected and compiled in a database for mapping ground-subsidence hazard (GSH). The subsidence area was randomly split 70/30 for training and validation of the models. The relationships between the detected ground-subsidence area and the factors were identified and quantified by frequency ratio (FR), logistic regression (LR) and artificial neural network (ANN) models. The relationships were used as factor ratings in the overlay analysis to create ground-subsidence hazard indexes and maps. The three GSH maps were then used as new input factors and integrated using fuzzy-ensemble methods to make better hazard maps. All of the hazard maps were validated by comparison with known subsidence areas that were not used directly in the analysis. As the result, the ensemble model was found to be more effective in terms of prediction accuracy than the individual model.     

An extension to the DRASTIC model to assess groundwater vulnerability to pollution: application to the Haouz aquifer of Marrakech (Morocco)

An extension to the DRASTIC model is proposed in order to assess aquifer vulnerability to pollution. In contrast to the DRASTIC model, which considers the unsaturated and saturated zones together and computes a global intrinsic vulnerability index, the suggested approach discriminates between the aquifer vertical vulnerability (a concept related to the pollutant percolation) and the groundwater susceptibility (a concept that depends on the behaviour and uses of the groundwater). This approach is applied to the Haouz aquifer (Morocco) that supplies water to the Marrakech area. This aquifer is widely overexploited and there is evidence that the groundwater quality is threatened by various sources of pollution. Evaluation of the vertical vulnerability indicates that the aquifer mainly presents a moderate-to-weak vertical vulnerability. The zones potentially most favourable to pollutant percolation are mainly located in Central Haouz, along or near the surface wadis. The aquifer susceptibility is high in places located near the N’Fis, Baaja and Issil wadis. Everywhere else, low-to-moderate susceptibility is observed. This new approach therefore enables areas of vertical vulnerability and areas of susceptibility to be delineated separately. As a result, it constitutes a valuable decision-making tool for optimising the management of aquifer water resources and land-use planning.     

An assessment of geologic sequestration potential in the panhandle of Florida USA

One alternative to reduce global greenhouse gas emissions is to store the emissions in underground geologic sequestration repositories. The efficacy of this approach has been favorably evaluated by numerous authors over the last 15 years. This paper discusses an assessment of the overall feasibility of storing emissions in three different repositories in the Florida panhandle located in the Southeastern United States. The feasibility assessment evaluates both saline aquifers and oil reservoirs located in the panhandle region. The overall feasibility is driven by the available geologic sequestration capacity, the transportation cost to deliver emissions to a respective repository, and other engineering and regulatory issues. The geologic sequestration capacity is generally controlled by the so-called storage efficiency, a variable dependent on the site-specific geology, reservoir conditions, and the injected fluid characteristics. For this paper, storage efficiency for saline repositories was assessed in more detail using numerical modeling. Based on the work completed, the 3 repositories studied have at least 4.55 gigatonnes of capacity to sequester CO₂.     

天津海域底质重金属污染及其潜在生态风险评价

根据2015年采集的天津海域48个底质样品的粒度分析、重金属分析结果,综合研究了天津海域表层沉积物类型分布特征和重金属元素的分布特征,使用Hakanson多元潜在生态风险指数法对天津海域的底质环境进行了评价.结果表明:1)位于永定新河河口的B46站位的潜在生态风险程度达到中度,其他各站位均为低度.Cd元素的污染程度最大,Zn元素的污染程度最小.几种重金属的危害系数顺序为:Cd> Hg> As> Pb> Cu> Cr> Zn.2)南部海区的重金属元素含量水平普遍高于北部海区.重金属元素富集区分别位于独流减河北部至临港产业区的围海造陆地区和永定新河口至东疆港外侧的地区,这两个地区水动力较缓,沉积物粒度较细.对各采样点进行对比得出,重金属污染程度顺序为:河口>内湾>外湾.     

Assessment of failure susceptibility of soil slopes using fuzzy logic

Generally, the process of land occupation in urban areas involves spaces that are not suitable for construction. In most cases these areas are subject to landslides. Therefore it is mister the development of models to evaluate the susceptibility of occurrence of landslides in these areas. For this, Fuzzy Logic is used herein for modeling such areas where landslides are susceptible to occur and, therefore, a direct evaluation is important. The possibility of capturing the judgment and the modeling of linguistic variables are the main advantages of using Fuzzy Logic. These models are capable to capture the factors directly affecting the slope stability and also the inter-relationship amongst them. These factors were chosen by experts to whom a questionnaire was sent. Fuzzy Logic was then used to transform the linguistic variables into fuzzy number, allowing thus, the calculation of failure potential index (FPI). Herein the MAX-MIN Mamdani strategy for the inference of the rule base was used. This methodology has been applied to identify the susceptibility of landslides in a chaotic occupied urban area of Itaperuna City in northeastern of Rio de Janeiro, Brazil, where some occurrences have been reported.     

Vectorial fuzzy logic: A novel technique for enhanced mineral prospectivity mapping,with reference to the orogenic gold mineralisation potential of the Kalgoorlie Terrane,Western Australia

Modern exploration is a multidisciplinary task requiring the simultaneous consideration of multiple disparate geological, geochemical and geophysical datasets. Over the past decade, several research groups have investigated the role of Geographic Information Systems as a tool to analyse these data. From this research, a number of techniques has been developed that allow the extraction of exploration‐relevant spatial factors from the datasets. The spatial factors are ultimately condensed into a single prospectivity map. Most techniques used to construct prospectivity maps tend to agree, in general, as to which areas have the lowest and highest prospectivities, but disagree for regions of intermediate prospectivity. In such areas, the prospectivity map requires detailed interpretation, and the end‐user must normally resort to analysis of the original datasets to determine which conjunction of factors results in each intermediate prospectivity value. To reduce this burden, a new technique, based on fuzzy logic principles, has been developed for the integration of spatial data. Called vectorial fuzzy logic, it differs from existing methods in that it displays prospectivity as a continuous surface and allows a measure of confidence to be incorporated. With this technique, two maps are produced: one displays the calculated prospectivity and the other shows the similarity of input values (or confidence). The two datasets can be viewed simultaneously as a three‐dimensional perspective image in which colour represents prospectivity and topography represents confidence. With the vectorial fuzzy logic method, factors such as null data and incomplete knowledge can also be incorporated into the prospectivity analysis.     

Supervised committee fuzzy logic model to assess groundwater intrinsic vulnerability in multiple aquifer systems

Groundwater vulnerability modeling is an alternative approach to evaluate groundwater contamination especially in areas affected by intensive anthropogenic activities. However, the DRASTIC model as a well-known method to assess groundwater vulnerability suffers from the inherent uncertainty associated with its seven essential parameters. In this study, three different fuzzy logic (FL) models (Sugeno fuzzy logic, Mamdani fuzzy logic, and Larsen fuzzy logic) are adopted to improve the DRASTIC system to be more realistic. The vulnerability map of groundwater from multiple aquifer systems (i.e., karstic, alluvium, and complex) in Basara basin, Iraq, was created using the FL models. Validation of the FL models results using NO₃-N concentration obtained from wells and springs of the study area indicating that all of the three FL models are applicable for improving the DRASTIC model. However, each of the FL models has its own advantages for groundwater vulnerability estimation in different types of aquifer systems in the Basara basin. Therefore, this study proposes the supervised committee fuzzy logic (SCFL) as a multimodel method to combine the advantages of individual FL models. The SCFL method confirms that no water well with high NO₃-N levels would be classified as low risk and vice versa. The study suggests that this approach has provided a convenient estimation of pollution risk in the study area and therefore, a more accurate prediction of the intrinsic vulnerability to pollution in the multiple aquifer system can be achieved through SCFL method.     

An empirical equation for tunnel inflow assessment: application to sedimentary rock masses

Groundwater inflow assessment is essential for the design of tunnel drainage systems, as well as for assessment of the environmental impact of the associated drainage. Analytical and empirical methods used in current engineering practice do not adequately account for the effect of the jointed-rock-mass anisotropy and heterogeneity. The impact of geo-structural anisotropy of fractured rocks on tunnel inflows is addressed and the limitations of analytical solutions assuming isotropic hydraulic conductivity are discussed. In particular, the study develops an empirical correction to the analytical formula frequently used to predict groundwater tunnel inflow. In order to obtain this, a discrete network flow modelling study was carried out. Numerical simulation results provided a dataset useful for the calibration of some empirical coefficient to correct the well-known Goodman’s equation. This correction accounts for geo-structural parameters of the rock masses such as joint orientation, aperture, spacing and persistence. The obtained empirical equation was then applied to a medium-depth open tunnel in Bergamo District, northern Italy. The results, compared with the monitoring data, showed that the traditional analytical equations give the highest overestimation where the hydraulic conductivity shows great anisotropy. On the other hand, the empirical relation allows a better estimation of the tunnel inflow.