Cluster-based fuzzy models for groundwater flow in the unsaturated zone

In this paper fuzzy models are used as an alternative to describe groundwater flow in the unsaturated zone. The core of these models consists of a fuzzy rule-based model of the Takagi–Sugeno type. Various fuzzy clustering algorithms are compared in the data-driven identification of these Takagi–Sugeno models. The performance of the resulting fuzzy models is evaluated on the training surface on which they were identified, and on time series measurements of water content values obtained through an experiment carried out by the non-vegetated terrain (NVT) workgroup of the European Microwave Signature Laboratory (EMSL) (see [Mancini M, Hoeben R, Troch PA. Multifrequency radar observations of bare surface soil moisture content: a laboratory experiment. Water Resour Res 1999;35(6):1827–38] and [Hoeben R, Troch PA. Assimilation of active microwave observation data for soil moisture profile estimation. Water Resour Res 2000;36(10):2805–19]). Despite higher errors at the borders of high water content values in the training surface, good results are obtained on the simulation of the time series.     

Origin of sulphate in the unsaturated zone and groundwater of a loess aquifer

The use of the sulphate mass balance (SMB) between precipitation and soil water as a supplementary method to estimate the diffuse recharge rate assumes that the sulphate in soil water originated entirely from atmospheric deposition; however, the origin of sulphate in soil and groundwater is often unclear, especially in loess aquifers. This study analysed the sulphur (δ³⁴S-SO₄) and oxygen (δ¹⁸O-SO₄) isotopes of sulphate in precipitation, water-extractable soil water, and shallow groundwater samples and used these data along with hydrochemical data to determine the sources of sulphate in the thick unsaturated zone and groundwater of a loess aquifer. The results suggest that sulphate in groundwater mainly originated from old precipitation. When precipitation percolates through the unsaturated zone to recharge groundwater, sulphates were rarely dissolved due to the formation of CaCO₃ film on the surface of sulphate minerals. The water-extractable sulphate in the deep unsaturated zone (>10 m) was mainly derived from the dissolution of evaporite minerals and there was no oxidation of sulphide minerals during the extraction of soil water by elutriating soil samples with deionized water. The water-extractable concentration of SO₄ was not representative of the actual SO₄ concentration in mobile soil water. Therefore, the recharge rate cannot be estimated by the SMB method using the water-extractable concentration of SO₄ in the loess areas. This study is important for identifying sulphate sources and clarifying the proper method for estimating the recharge rate in loess aquifers.     

An integrated technique to quantify sewage,oil and PAH pollution in estuarine and coastal environments

An analytical protocol is described which allows parallel quantification of sewage, oil and PAH pollution on the same sample, thus maximizing the information gained for the effort expended. Capillary gas chromatography-flame ionization detection (GC-FID), now a routine technique in many laboratories, has been selected as the method for quantification. The protocol described is evaluated, and analyses of sediments from estuaries of the Rivers Mersey, Dee and Tamar, UK, are given as examples of how to interpret results achieved using the technique.     

Hydrogeological aspects of groundwater drainage of the urban areas in Kuwait City

Residential areas in Kuwait City have witnessed a dramatic rise in subsurface water tables over the last three decades. This water rise phenomenon is attributed mainly to over irrigation practices of private gardens along with leakage from domestic and sewage networks. This paper presents a comprehensive study for urban drainage in two selected areas representing the two hydrogeological settings encountered in Kuwait City. In the first area, a vertical drainage scheme was applied successfully over an area of 1 km². The system has been under continuous operation and monitoring for more than 4 years without problems, providing a permanent solution for the water rise problem in this area. The hydrogeological system has approached steady state conditions and the water levels have dropped to about 3·5 m below the ground surface. In the second area a dual drainage scheme, composing of horizontal and vertical elements, is proposed. Horizontal elements are suggested in the areas where the deep groundwater contains hazardous gases that may pose environmental problems. The proposed drainage scheme in the second area has not yet been implemented. Field tests were conducted to assess the aquifer parameters in both areas and a numerical model has been developed to predict the long‐term response of the hydrogeological system in the two areas under consideration. Copyright © 2001 John Wiley & Sons, Ltd.     

Compensation for oil pollution damage caused by oil spills from ships and the international oil pollution compensation fund

Liability and compensation for pollution damage caused by oil spills from laden tankers is governed by two international conventions: the 1969 Civil Liability Convention and the 1971 Fund Convention. The Civil Liability Convention established a system of strict liability for tanker owners and introduced compulsory liability insurance. The Fund Convention created a system of supplementary compensation administered by an intergovernmental organization, the International Oil Pollution Compensation Fund (IOPC Fund), which at present has 56 member states (August 1993). The IOPC Fund pays compensation to victims of oil pollution in member states when the compensation from the shipowner and his insurer is insufficient. Over the years (up to August 1993), the IOPC Fund has been involved in 66 incidents and has paid US$92 million to victims. Only three of these incidents have been taken to court, whereas in all other cases claims have been settled out of court. The IOPC Fund has developed a policy on the admissibility of claims covering clean-up costs, measures to prevent pollution, damage to property and economic loss suffered by fishermen, hotel-owners and others who depend directly for their livelihood on sea-related activities.     

Anticipating the effects of groundwater withdrawal on seawater intrusion and soil settlement in urban coastal areas

Intensive pumping in urban coastal areas is a common threat to water resource quality due to seawater intrusion. In those areas where subsurface water resources are not usually used for human consumption or irrigation, intensive pumping is associated with other activities like the lowering of the water table necessary to support underground structures and building foundations. This activity also increases the likelihood of soil settlement that affects building stability and the corrosion of concrete structures due to groundwater salinity. Under these circumstances, the awareness of a certain municipality (Calonge, NE Spain) of the potential effects of groundwater withdrawal upon foundations has led to an integrated approach to anticipate seawater intrusion related to urban development. Geological mapping and correlation of borehole logs, electrical resistivity tomography, and hydrochemical data provide comprehensive knowledge of the geology and hydrogeology of the area and act as screening tools necessary to discern the influence of hydrological processes in coastal areas. Developing Strack's analytical solution, new comprehensive, dimensionless expressions are herein derived to determine the critical pumping rate necessary to prevent seawater intrusion, as well as to reproduce the evolution of the wedge toe and the water table stagnation point under different withdrawal rates. Furthermore, the Dupuit–Forchheimer well discharge formula allows the estimation of the effects of the water table lowering due to such critical pumping in the surrounding building foundations. Field data from the Calonge coastal plain illustrate this approach and provide assessment criteria for future urban development and planning. Copyright © 2012 John Wiley & Sons, Ltd.     

The effect of oil pollution in Bantry Bay

The biological damage caused by the large oil spill in Bantry Bay and the clean-up measures adopted to deal with it (already reported in the Marine Pollution Bulletin) has been followed up in the months following the oil spill. This report refers to damage to algae and lichens.     

大气污染对北京冬季城市和郊区辐射收支影响的观测分析

近年来城市化和大气污染对辐射收支的影响日益显著.本研究利用2013-2014年中国科学院大气物理研究所325m铁塔、南郊观象台、密云气象塔、上甸子区域大气本底站四个观测站点的辐射及自动站气象要素数据,采用南郊观象台的能见度资料将观测数据分为清洁天和污染天,并进行类比分析,以1月份为例,研究了北京地区大气污染和城郊差异对辐射收支的影响.结果表明：（1）从月平均值来看,各站污染天入射短波辐射均小于清洁天,衰减最大可达55.8 W·m-2,直接辐射亦然,衰减最大可达161.1 W·m-2,散射辐射相反,增加最大值为72.2 W·m-2;长波辐射污染天大于清洁天,向下向上长波辐射增加最大值分别为85.0 W·m2和70.0 W·m-2,且长波辐射的衰减与污染物浓度和大气温度相关;净辐射白天污染天小于清洁天,夜间相反.（2）从各站的对比可知,大气污染对入射短波辐射的衰减,南部郊区（13.2%）大于北部城区（7.4%）,与北京地区“南北两重天”的污染物分布特征一致;且污染物对长短波辐射的影响呈现了从城区到郊区衰减率依次减小的现象.本研究为大气污染与气象条件的相互作用研究提供了观测基础.     

The significance of flow in the matrix of the Chalk unsaturated zone

The significance of flow in the matrix of the Chalk unsaturated zone, in comparison with flow in fractures, has been the subject of much debate. In this article, important elements of the literature are discussed in detail and several simple modelling analyses based on steady-state flow are presented. A study of the sensitivity of solute spreading to fracture spacing in models that ignore matrix flow shows that this latter assumption is generally incompatible with observed solute profiles, unless unrealistically small fracture spacings are assumed. The effect of air phase continuities (e.g. bedding planes) on matrix flow has also been examined. These discontinuities are frequently interrupted by points of connectivity between matrix blocks. An issue therefore is the relationship between connectivity and its effect on inter-block conductance. A simple analysis of the Laplace equation shows that just 1% connectivity represents an effective pathway equivalent to 18% of the local rock hydraulic conductivity. Obviously, when there is no fracture flow, solute spreading is significantly reduced. However, dual permeability model simulations show that matrix flow reduces solute spreading in the presence of persistent fracture flow. All of the above studies suggest that flow in the matrix of the Chalk unsaturated zone is significant and that ignoring it may result in a serious misunderstanding of the system.     

Small-scale heterogeneity and soil-moisture variability in the unsaturated zone

The distribution of water within a soil profile can only be partly explained by the time distribution and rate of surface-water input. Observed differences in soil moisture within the unsaturated zone result from the interaction of surface-water inputs with spatially inhomogeneous soil characteristics. Water which initially percolates vertically is differentially impeded as a result of subtle textural changes in the soil, and is then preferentially retained in such zones of transition, causing large differences in soil-water content to occur. The scale of this vertical variability is of tenths of metres, whilst lateral variability of soil moisture reflects textural changes over a few metres. The observed influence of small-scale heterogeneity on soil-water content suggests that the conventional assumptions of isotropicity and homogeneity of the textural and hydraulic properties of porous media used in drainage basin and hillslope hydrological models need scrutiny, even for single stratigraphic units.     

Risk assessment of underflooding of areas by groundwater during floods

Approaches to risk assessment of underflooding of areas by groundwater during extreme floods, using probabilistic and deterministic methods are considered. The latter methods are based on indicators of groundwater sustainability to adverse impacts.     

Seismic attenuation and velocity dispersion in fractured rocks: The role played by fracture contact areas

The presence of fractures in fluid‐saturated porous rocks is usually associated with strong seismic P‐wave attenuation and velocity dispersion. This energy dissipation can be caused by oscillatory wave‐induced fluid pressure diffusion between the fractures and the host rock, an intrinsic attenuation mechanism generally referred to as wave‐induced fluid flow. Geological observations suggest that fracture surfaces are highly irregular at the millimetre and sub‐millimetre scale, which finds its expression in geometrical and mechanical complexities of the contact area between the fracture faces. It is well known that contact areas strongly affect the overall mechanical fracture properties. However, existing models for seismic attenuation and velocity dispersion in fractured rocks neglect this complexity. In this work, we explore the effects of fracture contact areas on seismic P‐wave attenuation and velocity dispersion using oscillatory relaxation simulations based on quasi‐static poroelastic equations. We verify that the geometrical and mechanical details of fracture contact areas have a strong impact on seismic signatures. In addition, our numerical approach allows us to quantify the vertical solid displacement jump across fractures, the key quantity in the linear slip theory. We find that the displacement jump is strongly affected by the geometrical details of the fracture contact area and, due to the oscillatory fluid pressure diffusion process, is complex‐valued and frequency‐dependent. By using laboratory measurements of stress‐induced changes in the fracture contact area, we relate seismic attenuation and dispersion to the effective stress. The corresponding results do indeed indicate that seismic attenuation and phase velocity may constitute useful attributes to constrain the effective stress. Alternatively, knowledge of the effective stress may help to identify the regions in which wave induced fluid flow is expected to be the dominant attenuation mechanism.     

Assessment of groundwater inflow in urban territories

Analytical and numerical methods are proposed for the calculation of water inflow into construction pits under various geological—engineering and hydrogeological conditions at the construction site. Water inflow into the pit is shown to depend not only on lateral seepage but also on the leakage from underlying aquifers at appropriate parameters of their interaction. Under certain natural conditions, the most efficient method for construction pit draining at low water yield of soils in the construction area are light wellpoint systems, the capacity and layout of which is determined by the potential inflow through the pit contour. The results of analytical and numerical calculations for the assessment of groundwater inflow into a pit are given, and light wellpoint systems are shown to be effective under different combinations of natural and engineering conditions.     

Principles of zoning a territory by the hazard and risks of groundwater pollution

Principles of zoning a territory by the pollution hazard to groundwater depending on the pollution sources and their position in the environment are considered. Pollution hazard classifications are proposed for groundwater, pollutants (by their chemical and hydrochemical properties), and groundwater pollution risks, depending on the degree of hazard and the type of pollutant. A procedure is proposed for mapping the hazard and risks of groundwater pollution by various pollutants on the basis of the performed zoning.     

中尺度模拟土壤油污染区探地雷达探测效果分析

为使物理模拟实验效果与实际探测情形更为接近,在室外自然条件下建立中尺度土壤石油污染实验模型,油污染区扩展深度超过1 m,采用实地探测中常用的500 MHz雷达天线进行长期定时探测.通过实测雷达图像特征、土壤含水量含油量分析,并对比前人开展的小尺度室内模拟试验结果,综合评价探地雷达对油污染区的探测效果.研究表明探地雷达探测图像异常特征与污染区扩散阶段密切相关:包气带内油污染区会引起振幅增强;毛细带的油污染区则表现为水位面反射轴附近清晰可辨的高幅异常区,且水位面反射轴呈下凹状;随扩散过程持续进行,异常区下移与水位面反射轴相交,并产生水平扩张.当污染土含油饱和度大于20%时,可通过雷达图像异常区圈定污染范围;当污染土含油饱和度大于15%时,可通过频谱图出现低频响应的位置圈定污染区水平范围.中尺度实验结果与室内小尺度模拟结果具有一致性,可作为油污染区雷达图像异常的解译依据.     

Relationships between groundwater in permafrost zone and climate changes

The paper presents the results of statistical analysis and estimation of long-term changes in surface air temperature, the gas composition of the atmosphere, the depth of seasonal thawing, and the temperature and area of permafrost occurrence in the circumpolar zone of the Northern Hemisphere. Preliminary estimates were obtained for the possible influence of the current changes in the thermophysical parameters of permafrost rocks on the albedo of the underlying surface, air moisture content, and the concentrations of carbon dioxide and methane in the atmosphere. The density of anthropogenic and natural methane fluxes from the underlying surface to the atmosphere is evaluated. The possible formation mechanisms of global maximums in carbon dioxide and methane concentration in the atmosphere of circumpolar areas in the context of interaction between methane cycle and the processes of permafrost thawing are described.     

Isotopic-hydrochemical study of changes in the dynamics and geoenvironmental conditions of groundwater in urban areas resulting from the development of aquifers

An integrated study with the use of uranium-isotope and microelement hydrogeochemical methods showed the possibility of studying changes in the dynamics and geoenvironmental condition of groundwater in an urban area by the indicator modeling of groundwater formation and circulation, as well as interaction of waters from different horizons, including water ingress from deeper aquifers.     

Non-passive transport of volatile organic compounds in the unsaturated zone

A detailed model was formulated to describe the non-passive transport of water-soluble chemicals in the unsaturated zone and used to illustrate one-dimensional infiltration and redistribution of alcohol–water mixtures. The model includes the dependence of density, viscosity, surface tension, molecular diffusion coefficient in the liquid-phase, and gas–liquid partition coefficient on the aqueous mixture composition. It also takes into account the decrease in the gas–liquid partition coefficient at high capillary pressures, in accordance with Kelvin’s equation for multi-component mixtures. Simulation of butanol–water mixtures infiltration in sand was in agreement with the experimental data and simulations reported in the literature. Simulation of methanol infiltration and redistribution in two different soils showed that methanol concentration significantly affects volumetric liquid content and concentration profiles, as well as the normalized volatilization and evaporation fluxes. Dispersion in the liquid-phase was the predominant mechanism in the transport of methanol when dispersivity at saturation was set to 7.8 cm. Liquid flow was mainly due to capillary pressure gradients induced by changes in volumetric liquid content. However, for dispersivity at saturation set to 0.2 cm, changes in surface tension due to variation in composition induced important liquid flow and convection in the liquid-phase was the most active transport mechanism. When the Kelvin effect was ignored within the soil, the gas-phase diffusion was significantly lower, leading to lower evaporation flux of water and higher volumetric liquid contents near the soil surface.