Prediction criteria for groundwater potential zones in Kemuning District,Indonesia using the integration of geoelectrical and physical parameters

The presence of groundwater is strongly related to its geological and geohydrological conditions.It is,however,important to study the groundwater potential in an area before it is utilized to provide clean water.Werner-Schlumberger’s method was used to analyze the groundwater potential while hydraulic properties such as soil porosity and hydraulic conductivity were used to determine the quality and ability of the soil to allow water’s movement in the aquifer.The results show that the aquifer in the Sekara and Kemuning Muda is at a depth of more than 6 meters below the ground level with moderate groundwater potential.It is also found that the aquifer at depths of over 60 m have high groundwater potential.Moreover,soil porosity in Kemuning is found to be average while the ability to conduct water was moderate.This makes it possible for some surface water to seep into the soil while the remaining flows to the rivers and ditches.     

Modelling groundwater flow of the Trifa aquifer, Morocco

Trifa is the most productive agricultural plain of north-eastern Morocco. The development of agricultural activities during the last few decades has been mainly based on imported water for irrigation. However, irrigation requirements have become so large that groundwater is used as a secondary source to supply the agricultural and domestic water needs, causing a depletion of the groundwater resources, especially during dry periods. A hydrological and a hydrogeological model for the Trifa plain have been developed, which yield information on relevant parameters such as groundwater recharge, and estimate the amount of pumped groundwater needed to meet the irrigation needs. The models (MODFLOW and WetSpass) provide insight into the status and evolution of the groundwater reserves. The results of the study are useful to predict the sustainability of the groundwater resources in the Trifa plain and to evaluate possible management actions. A reduction in groundwater abstraction by at least 25% may be necessary to achieve sustainable conditions.

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Resumen Trifa es la planicie agrícola más productiva del noreste de Marruecos. El desarrollo de las actividades agrícolas durante las últimas décadas se ha basado principalmente en agua importada para riego. Sin embargo, los requerimientos de riego han llegado a ser tan grandes ocasionando que se utilice el agua subterránea como una fuente secundaria para abastecer las necesidades de agua para uso doméstico y agrícola, lo que causa un agotamiento de los recursos de agua subterránea, especialmente durante periodos secos. Se ha desarrollado un modelo hidrogeológico e hidrológico para la planicie Trifa el cual aporta información de parámetros relevantes tal como recarga de agua subterránea y estima la cantidad de agua subterránea que necesita bombearse para satisfacer las necesidades de riego. Los modelos (MODFLOW y WetSpass) aportan una idea acerca del estado actual y la evolución de las reservas de agua subterránea. Los resultados de este estudio son útiles para predecir la sostenibilidad de los recursos de agua subterránea en la planicie Trifa y para evaluar posibles acciones de gestión. Puede ser necesario reducir la explotación de agua subterránea en por lo menos 25% para alcanzar condiciones sostenibles.

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Résumé Trifa est la plaine agricole la plus productive du Nord-Est marocain. Le développement de l’activité agricole durant ces dernières décennies a essentiellement reposé sur l’irrigation. Néanmoins les besoins de l’irrigation sont devenus tels que l’eau souterraine est utilisée comme ressource secondaire, pour combler la demande en eau domestique et agricole, induisant un rabattement d’autant plus important durant les périodes sèches. Un modèle hydrologique et hydrogéologique de la plaine de Trifa a été développé sur base des paramètres les plus importants, tels la recharge, et permet d’estimer le pompage nécessaire des eaux souterraines pour combler les besoins de l’irrigation. Les modèles (MODFLOW et WetSpass) apportent une bonne connaissance de l’état et de l’évolution des réserves souterraines. Les résultats de l’étude sont utiles pour prédire la longévité des ressources et pour évaluer différents scénarios de gestion. Une réduction de l’extraction de 25% serait nécessaire pour atteindre un état durable.

     

Adaptive state estimation of groundwater contaminant boundary input flux in a 2-dimensional aquifer

In many circumstances involving heat and mass transfer issues,it is considered impractical to measure the input flux and the resulting state distribution in the domain.Therefore,the need to develop techniques to provide solutions for such problems and estimate the inverse mass flux becomes imperative.Adaptive state estimator(ASE)is increasingly becoming a popular inverse estimation technique which resolves inverse problems by incorporating the semi-Markovian concept into a Bayesian estimation technique,thereby developing an inverse input and state estimator consisting of a bank of parallel adaptively weighted Kalman filters.The ASE is particularly designed for a system that encompasses independent unknowns and/or random switching of input and measurement biases.The present study describes the scheme to estimate the groundwater input contaminant flux and its transient distribution in a conjectural two-dimensional aquifer by means of ASE,which in particular is because of its unique ability to efficiently handle the process noise giving an estimation of keeping the relative error range within 10%in 2-dimensional problems.Numerical simulation results show that the proposed estimator presents decent estimation performance for both smoothly and abruptly varying input flux scenarios.Results also show that ASE enjoys a better estimation performance than its competitor,Recursive Least Square Estimator(RLSE)due to its larger error tolerance in greater process noise regimes.ASE's inherent deficiency of being slower than the RLSE,resulting from the complexity of algorithm,was also noticed.The chosen input scenarios are tested to calculate the effect of input area and both estimators show improved results with an increase in input flux area especially as sensors are moved closer to the assumed input location.     

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.     

Hydrochemical characterization of groundwater in Balad district,Salah Al-Din Governorate,Iraq

The assessment of hydrochemical quality of groundwater is very important to explore its nature and usefulness. In this paper, groundwater quality evaluation is carried out in the Balad district, Salah Al-Din Governorate, Iraq. A total of 28 groundwater samples are collected from shallow tube wells and analyzed for various physicochemical parameters. Groundwater suitability for drinking is evaluated based on the World Health Organization (WHO) and Iraqi standards, and suitability of groundwater for irrigation is assessed based on various hydrochemical parameters. The results reveal that the dominant types of groundwater based on piper diagram are mixed CaMgCl and CaCl. Gibbs ratio indicates that the groundwater in the studied area is affected by the evaporation process. The cation-anion exchange reaction in the studied area demonstrates that 54% of the groundwater samples indicate a direct base (cation-anion) exchange reaction, while 46% of the groundwater samples indicating the chloro-alkaline disequilibrium. Furthermore, generally all of the groundwater samples are unsuitable for drinking and irrigation. Cluster analysis reveals two different groups of similarities between the groundwater samples, reflecting different pollution levels in the studied area.     

Development of groundwater modeling for the Azraq Basin, Jordan

 The three-dimensional groundwater flow model MODFLOW was applied to simulate water level change in the complex multi-aquifer systems (the Upper and Middle Aquifers) of the Azraq basin. The model was calibrated by matching observed and simulated drawdown for steady and transient states over the period 1970–1992. Drawdown data for the period 1993–1997 were used to test the model's ability to predict the response of the aquifers. The model performed well in representing the water level contours of the Upper and Middle Aquifers for steady state calibration. Agreement between the observed and simulated drawdowns was obtained for transient state calibration. To predict the aquifer system responses for the period of 1997–2025, four different pumping schemes (scenarios) have been investigated. The first scenario (present pumping rate) reveals that there will be approximately a 25 m drop in the water level at the well-field area in 2025. However, the worst scenario (pumping rate at 1.5 times the present rate) reveals an approximate 39 m drop in the water level at the well-field area in 2025. The safe yield for the Upper Aquifer System was found to be about 25 million cubic meters (MCM) yearly. Received: 24 June 1999 · Accepted: 30 November 1999     

Adaptive state estimation of groundwater contaminant boundary input flux in a 2-dimensional aquifer

In many circumstances involving heat and mass transfer issues, it is considered impractical to measure the input flux and the resulting state distribution in the domain. Therefore, the need to develop techniques to provide solutions for such problems and estimate the inverse mass flux becomes imperative. Adaptive state estimator (ASE) is increasingly becoming a popular inverse estimation technique which resolves inverse problems by incorporating the semi-Markovian concept into a Bayesian estimation technique, thereby developing an inverse input and state estimator consisting of a bank of parallel adaptively weighted Kalman filters. The ASE is particularly designed for a system that encompasses independent unknowns and /or random switching of input and measurement biases. The present study describes the scheme to estimate the groundwater input contaminant flux and its transient distribution in a conjectural two-dimensional aquifer by means of ASE, which in particular is because of its unique ability to efficiently handle the process noise giving an estimation of keeping the relative error range within 10% in 2-dimensional problems. Numerical simulation results show that the proposed estimator presents decent estimation performance for both smoothly and abruptly varying input flux scenarios. Results also show that ASE enjoys a better estimation performance than its competitor, Recursive Least Square Estimator (RLSE) due to its larger error tolerance in greater process noise regimes. ASE’s inherent deficiency of being slower than the RLSE, resulting from the complexity of algorithm, was also noticed. The chosen input scenarios are tested to calculate the effect of input area and both estimators show improved results with an increase in input flux area especially as sensors are moved closer to the assumed input location.     

Managing for sustainability in an arid climate: lessons learned from 20 years of groundwater management in Arizona,USA

Substantial progress has been made within central Arizona in moving towards a more sustainable water future, particularly in transitioning the urban demand from a primarily nonrenewable groundwater-based supply to increasing dependence on the Colorado River, Salt River and effluent. Management efforts include a wide range of regulatory and voluntary programs which have had mixed success. The Department of Water Resources has learned a number of key lessons throughout the years, and this paper attempts to establish the water management context and identify those lessons for the benefit of others who may want to evaluate alternative approaches to groundwater management. Themes to be discussed include evaluating water management approaches in a public policy context, the effectiveness of alternative management approaches and the relative merits of regulatory vs. nonregulatory efforts, and the importance of high-quality data in making management decisions.

Interactions between groundwater and surface water: the state of the science

The interactions between groundwater and surface water are complex. To understand these interactions in relation to climate, landform, geology, and biotic factors, a sound hydrogeoecological framework is needed. All these aspects are synthesized and exemplified in this overview. In addition, the mechanisms of interactions between groundwater and surface water (GW–SW) as they affect recharge–discharge processes are comprehensively outlined, and the ecological significance and the human impacts of such interactions are emphasized. Surface-water and groundwater ecosystems are viewed as linked components of a hydrologic continuum leading to related sustainability issues. This overview concludes with a discussion of research needs and challenges facing this evolving field. The biogeochemical processes within the upper few centimeters of sediments beneath nearly all surface-water bodies (hyporheic zone) have a profound effect on the chemistry of the water interchange, and here is where most of the recent research has been focusing. However, to advance conceptual and other modeling of GW–SW systems, a broader perspective of such interactions across and between surface-water bodies is needed, including multidimensional analyses, interface hydraulic characterization and spatial variability, site-to-region regionalization approaches, as well as cross-disciplinary collaborations. Electronic Publication     

Assessment of well design and sustainability in hard-rock formations in northern Ghana

Some of the main problems in well construction are associated with installation of casing, especially in the overburden. A total of 1,485 lined and open wells, drilled in the hard rocks of the Precambrian basement complex and Palaeozoic sedimentary (Voltaian) formations in northern Ghana were studied. Of these, 500 were directly monitored. It was observed that the surfaces within the production zones of open wells had weathered, leading to silting and reductions in depth and yield, posing physical water-quality challenges. Also, the average life span of the open wells is about 15 years. The fully lined wells, on the other hand, perform very well with time, lasting for over 40 years on average, with a more sustainable physical water quality over their life span. The comparative cost of constructing an open well was found to be about 26% less than that of a lined well due to less construction material requirements. Although open wells may be relatively cheaper than lined wells to construct in hard rocks, the life span is shorter and should not be encouraged for groundwater exploitation especially in community or rural water supply schemes.     

A catchment water balance model for estimating groundwater recharge in arid and semiarid regions of south-east Iran

This paper presents a new model of the rainfall-runoff-groundwater flow processes applicable to semiarid and arid catchments in south-east Iran. The main purpose of the model is to assess the groundwater recharge to aquifers in these catchments. The model takes into account main recharge mechanisms in the region, including subsurface flow in the valley alluvium in mountainous areas and recharge from the bed of ephemeral rivers. It deals with the effects of spatial variation in the hydrological processes by dividing the catchment into regions of broad hydrologic similarity named as highland, intermediate and aquifer areas. The model is based on the concept of routing precipitation within and through the catchment. The model has been applied to the Zahedan catchment and the results indicate that the groundwater level estimated by the recharge model generally is in agreement with the behaviour of groundwater levels in observation wells. The sensitivity analysis indicates that when the rainfall in the aquifer area is used to replace the values recorded in the intermediate area and the highland area, the recharge estimates are reduced by 42-87%. This result supports the division of the catchment into different zones of hydrological similarity to account for spatial variability of hydrological processes. Electronic Publication     

Geochemical evolution of groundwater in the Maneadero coastal aquifer during a dry year in Baja California, Mexico

Water pumped from 25 shallow wells (<31 m) in the Maneadero unconfined coastal aquifer was studied geochemically in order to determine the short-term compositional variability of the aquifer due to seawater intrusion during a drier than normal year (Fall 2001 to Fall 2002). The groundwater was commonly found to be mixed with seawater, with TDS concentrations in November 2002 ranging from 0.99 to 9.46 g l^–1, having an intermediate Na⁺Cl^– to Ca²⁺Cl^– water-type. Rapid recharge events of short duration, after low and short rainfall events during the study period, are suggested from short-term fluctuations in water quality. Seawater intrusion is progressing faster in the central and southern coastal sections of the aquifer and has recently affected the quality of the sites pumping water to the nearby city of Ensenada. Only one of the wells used for the Ensenada water supply had a TDS concentration lower than the 1.0 g l^–1 official limit. Low flow rates and high residence times of water are inferred to be the cause for high alkalinity in the east-central section of the aquifer. High NO₃ in the east-central aquifer indicates that any NO₃ infiltration due to fertilizer use was only slightly dispersed. After a short rainfall season during winter 2001, a significant decrease was seen for the previously most enriched site. However, concentrations above the 10 mg l^–1 official limit persisted in 2002, affecting one well for urban supply (15.9 mg l^–1). The water from this well is nevertheless mixed with better-quality water from other wells before being distributed through the citys piping system.

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Resumen Se estudió la geoquímica de aguas bombeadas por medio de 25 pozos no muy profundos (<31 m) en el acuifero costero no confinado de Maneadero con el objetivo de determinar la variación de la composición en el corto plazo en el acuifero por la intrusión de agua de mar durante un año más seco de lo normal (otoño 2001 a otoño 2002). Se observó que comúnmente las aguas subterráneas estaban mezcladas con agua de mar, con concentraciones de sólidos totales disveltos (STD) de entre 0.99--9.46 g l^–1 y un tipo de agua intermedia Na⁺Cl^– to Ca²⁺Cl^–. A partir de las fluctuaciones en la calidad del agua en el corto plazo se puede inferir que se dan eventos de recarga rápida de poca duración después de eventos de poca lluvia de poca duración y poco volumen durante el periodo de estudio. La intrusión de agua de mar está progresando más rápido en el centro y sur del acuifero costero y ha afectado recientemente la calidad de los sitios de bombeo de agua para la ciudad de Ensenada. Solamente uno de los pozos usados para el abastamiento de Ensenada tiene un STD por debajo del límite oficial de 1.0 g l^–1. Se presume que las razones lentas de flujo y los tiempos de residencia largos del agua son la causa de la alta alcalinidad en el centro-este del acuifero. Una concentración alta de NO₃ en el este-centro del acuifero indica que cualquier infiltración de NO₃ por aplicación de fertilizantes ha sido poco dispersad. Después de poca lluvia en el invierno de 2001, se observó una disminución importante en la zona previamente más enriquecida. Sin embargo, concentraciones sobre el límite oficial de 10 mg l^–1 continuaron en 2002, afectando a un pozo para suministro de agua urbana (15.9 mg l^–1). El agua extraída de este pozo es mezclada con agua de mejor calidad y se distribuye por el sistema urbano de suministro de agua.

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Résumé Leau de pompage de 25 puits peu profonds (<31 m) situés dans laquifère côtier non-confiné de Maneadero a été étudiée dans le but de déterminer la variation géochimique à court terme qui résulte de lintrusion deau de mer lors dune année plus sèche quà lhabitude (automne 2001 à automne 2002). Leau souterraine est souvent retrouvée mélangée avec de leau de mer, avec des concentrations en résidus solides dissous (RSD) qui sétalent entre 0.99 et 9.46 g l^–1 pour novembre 2002, avec un type intermédiaire en Na⁺Cl^– jusquà Ca²⁺Cl^–. Les processus suggérés pour les fluctuations rapides de la qualité de leau sont des événements de recharge de courte duré suite à de faibles et brèves périodes de précipitations. Lintrusion deau de mer progresse plus rapidement dans les parties centrales et sud de laquifère côtier où la qualité de leau pompée vers la ville de Ensenada a récemment été affectée. Un seul des puits utilisés par la ville de Ensenada pour lapprovisionnement en eau potable a une concentration en RSD sous la limite officielle permise de 1.0 g l^–1. Le temps de résidence élevé et le faible taux découlement de leau souterraine sont présumés être la cause de lalcalinité élevée dans la partie centrale-est de laquifère. La concentration élevée en NO₃ dans cette partie de laquifère indique que la totalité de linfiltration de NO₃ dû à lutilisation de fertilisants ne sest que très peu dispersée. Suite à une courte saison des pluies à lhiver 2001, une diminution substantielle a été notée au site qui était le plus enrichi avant la saison des pluies. Malgré tout, des concentrations dépassant la limite officielle permise de 10 mg l^–1 ont persisté, affectant un puits utilisé pour lapprovisionnement urbain (15.9 mg l^–1). Leau provenant de ce puits est toutefois mélangée avec de leau de meilleure qualité provenant dautres puits avant dêtre distribuée par laqueduc municipal.

     

Water quality analysis of groundwater in crystalline basement rocks,Northern Ghana

Hydrochemical data are presented for groundwater samples, collected from fractured aquifers in parts of northern Ghana. The data was collected to assess the groundwater suitability for domestic and agricultural use. Results of the study reveal that the pH of the groundwater in the area is slightly acidic to slightly alkaline. The electrical conductivity values, total dissolved solids (TDS) values and calcium, magnesium and sodium concentrations in the groundwater are generally below the limit set by the WHO for potable water supply. On the basis of activity diagrams, groundwater from the fractured aquifers appears to be stable within the montmorillonite field, suggesting weathering of silicate minerals. An inverse distance weighting interpolator with a power of 2 was applied to the data points to produce prediction maps for nitrate and fluoride. The distribution maps show the presence of high nitrate concentrations (50–194 mg/l) in some of the boreholes in the western part of the study area indicating anthropogenic impact on the groundwater. Elevated fluoride level (1.5–4 mg/l), higher than the WHO allowable fluoride concentration of 1.5, is recorded in the groundwater underlying the northeastern part of the study area, more specifically Bongo and its surrounding communities of the Upper East region. Results of this study suggest that groundwater from the fractured aquifers in the area exhibit low sodicity–low salinity (S1–C1), low sodicity–medium salinity (S1–C2) characteristics [United States Salinity Laboratory (USSL) classification scheme]. All data points from this study plot within the ‘Excellent to good’ category on a Wilcox diagram. Groundwater in this area thus appears to provide irrigation water of excellent quality. The hydrochemical results indicate that, although nitrate and fluoride concentrations in some boreholes are high, the groundwater in the study area, based on the parameters analyzed, is chemically potable and suitable for domestic and agricultural purposes.     

Integration of geoelectric and hydrochemical approaches for delineation of groundwater potential zones in alluvial aquifer

Geoelectric and hydrochemical approaches are employed to delineate the ground-water potential zones in District Okara, a part of Bari Doab, Punjab, Pakistan. Sixty-seven VES surveys are conducted with the Electrical Resistivity Meter. The resultant resistivity verses depth model for each site is estimated using computer-based software IX1D. Aquifer thickness maps and interpreted resistivity maps were generated from interpreted VES results. Dar-Zarrouk parameters, transverse resistance (TR), longitudinal conductance (SL) and anisotropy (λ) were also calculated from resistivity data to delineate the potential zones of aquifer. 70% of SL value is ≤3S, 30% of SL value is > 3S. According to SL and TR values, the whole area is divided into three potential zones, high, medium and low potential zones. The spatial distribution maps show that north, south and central parts of study area are marked as good potential aquifer zones. Longitudinal conductance values are further utilized to determine aquifer protective capacity of area. The whole area is characterized by moderate to good and up to some extent very good aquifer protective area on the basis of SL values. The groundwater samples from sixty-seven installed tube wells are collected for hydro-chemical analysis. The electrical conductivity values are determined. Correlation is then developed between the EC (μS/cm) of groundwater samples vs. interpreted aquifer resistivity showing R2 value 0.90.     

Development of a conjunctive use model to evaluate alternative management options for surface and groundwater resources

A conjunctive use model has been developed to evaluate alternative management options for surface and groundwater resources. A simple water balance approach was used to estimate net recharge to the aquifer. The groundwater model FEFLOW takes net recharge as an input for the water balance calculation and simulates flow in the groundwater under all boundary stresses. The developed model was applied to an irrigated area in the Indus Basin, Pakistan, to predict groundwater levels up to 2010 in response to the possible need for intervention in irrigation and/or agricultural practices. A geographical information system (GIS) was used to assemble various types of spatial data. The study revealed that an increase in pumpage from the present rate would further strain the scarce water resources. Lining of watercourses and adjustment in cropping pattern could be adopted as alternatives for better management of surface and groundwater resources.

Evaluation of groundwater availability and sustainable extraction rate for the Upper Santiago Valley Aquifer,Chile

The use of groundwater as water supply has increased dramatically in Santiago, Chile, during the last decades, and there is a need for accurately estimating the actual groundwater supply capacity in the upper Santiago Valley aquifer. The behavior of this aquifer was studied in order to determine the availability of water and the long-range sustainable extraction rate.Water-table depths were simulated using a numerical model with information on recharge from the last 48 years under different extraction policies. With this series of groundwater level data, groundwater level probability distribution functions were determined and extraction statistics were estimated by fitting time series models and by using the crossing theory. With this information, it has been possible to calculate the risk of being unable to supply groundwater demand because the results verify that only 67% of the water rights granted are able to be extracted on a sustained basis with a 90% exceedance probability. Furthermore, the results obtained demonstrate that the method is adequate for determining exceedance probabilities of groundwater flow.

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Resumen El uso de las aguas subterráneas como fuente de abastecimiento se ha incrementado enormemente en Santiago de Chile durante las últimas décadas, por lo que se necesita estimar de forma adecuada la capacidad actual de suministro del acuífero superior del Valle de Santiago. Se ha estudiado el comportamiento de este acuífero para determinar la disponibilidad de recursos y la tasa de extracción sustentable a largo plazo.Se ha simulado los niveles freáticos del acuífero utilizando un modelo numérico con información de la recarga en los últimos 48 años bajo diferentes regímenes de extracción. Con esta serie de datos de los niveles en el acuífero, se ha determinado la distribución de probabilidad de los niveles de las aguas subterráneas y se ha estimado las estadísticas de las extracciones mediante el ajuste de modelos de series temporales y la teoría de cruce. Con esta información, se ha podido calcular el riego de no satisfacer la demanda de abastecimiento, puesto que los resultados verifican que sólo se podría extraer el 67% de las concesiones de agua existentes de manera sustentable con un 90% de probabilidad de excedencia. Aún más, los resultados obtenidos demuestran que el método es adecuado para determinar las probabilidades de excedencia del flujo de las aguas subterráneas.

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Resumé Lutilisation de leau souterraine pour leau potable sest considérablement accrue à Santiago (Chili) au cours des derniers lustres; cest pourquoi il est maintenant nécessaire destimer avec précision la capacité réelle dalimentation de la nappe de laquifère supérieur de la vallée de Santiago. Le fonctionnement de cet aquifère a été étudié afin de déterminer la disponibilité en eau et le taux dextraction durable à long terme.Les niveaux de la nappe ont été simulés avec un modèle numérique à partir dinformation sur la recharge au cours des 48 dernières années pour différentes politiques dextraction. A partir de cette série de données piézométriques, des fonctions de distribution de probabilité des niveaux de la nappe ont été déterminées et des statistiques dextraction ont été estimées par ajustement de modèles de séries chronologiques en utilisant la théorie du croisement. Avec ces informations, il a été possible de calculer le risque de ne pas pouvoir satisfaire la demande deau souterraine, puisque les résultats vérifient que seulement 67% des droits deau attribués peuvent être extraits sur une base durable avec une probabilité de dépassement de 90%. En outre, les résultats obtenus démontrent que la méthode est adaptée à la détermination des probabilités de dépassement de lécoulement souterrain.

     

Simulation of groundwater level recovery in abandoned mines,Fengfeng coalfield,China

Abandoned mines are of high potential risk as they could be a large underground storage of pollutants(heavy metals and organic wastes, etc.). Various physical, chemical and biological reactions would take place when groundwater flows into underground spaces, which makes abandoned mine a huge potential hazard to groundwater environment. The recovery of groundwater level is one of the key elements controlling the reactions and causing such hazards. This paper simulated groundwater level recovery processes in the abandoned mines, Fengfeng coalfield by using the computer program FEFLOW. The paper integrated the pipe flow model, "three zones" model and groundwater inrush(discharge) model in the simulation of groundwater in the complex laneway-aquifer system. Groundwater flow in the laneway systems was considered pipe flow and described in Bernoulli equation. The water-bearing medium(coal seam roof) overlying the laneway systems was divided into "three zones" composed of the caving zone, fissure zone and bending zone based on the disruption degrees of previous mining. Groundwater in the Ordovician limestone aquifer(bottom of coal seam) flowing into laneway systems was considered a major inrush/recharge source, and its flow rate was calculated by an inrush(discharge) model which was newly developed in this study and incorporated into FEFLOW. The results showed that it would take approximately 95 days for groundwater in abandoned mines to recover to regional groundwater level elevation, and the total amount of water filling up would be about 1.41195×10~7 m~3, which is consistent with the actual data. The study could be of theoretical and practical significance to mitigate abandoned mines' hazards and improve mine groundwater utilization.     

Responses of groundwater system to water development in northern China

The increased demands on water resources in northern China have had a significant impact on groundwater systems in the last three to four decades, including reductions in groundwater recharge capacity and overall water quality. These changes limit the potential for groundwater uses in this area. This paper discusses the issues surrounding groundwater system use in the eight basins of northern China as water resources have been developed. The results demonstrate that the recharge zone has shifted from the piedmont to the agricultural area, and that the total recharge rate in the basins tended to decrease. This decrease in arid inland basins was mainly caused by both the excessive use of water in the watershed area and irrigated channel anti-seepage. In semi-arid basins, the decrease observed in the groundwater recharge rate is related to an overall reduction in precipitation and increasing river impoundment. In addition, intensive exploitation of groundwater resources has resulted in disturbances to the groundwater flow regime in arid and semi-arid inland basins. Arid inland basins demonstrated fast falling groundwater levels in the piedmont plains resulting in declines of spring flow rates and movement of spring sites to lower locations. In the semi-arid basins, i.e. the North China Plain and the Song-nen Plain, groundwater depression cones developed and intersected regional groundwater flow. The semi-arid basins of the North China Plain and the Song-nen Plain have experienced significant hydrochemical evolution of groundwater characterized by changing water type including increase of TDS and pollutants.     

Climate change and groundwater resources in Thailand

The average temperature of Thailand is projected to increase by 2-3 °C, and the annual rainfall is projected to increase by 25% and up to 50% in certain areas. The climate change in future is expected to provide changes in hydrological cycle and therefore impacts the groundwater resources too. In this study, we analyzed the general climate change trends and reviewed the groundwater conditions of Thailand. The climate changes, hydrologic variability and the impact of climate change on groundwater sustainability are also discussed based on a national groundwater monitoring program. Currently, there are 864 groundwater monitoring stations and 1 524 monitoring wells installed in Thailand. Moreover, the impact of climate change on groundwater-dependent systems and sectors is also discussed according to certain case studies, such as saline water intrusion in coastal and inland areas. Managing aquifer recharge and other projects are examples of groundwater adaptation project for the future.