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Groundwater sustainability is still an open question. Theoretical and practical approaches to the definition of groundwater sustainability were mainly developed on large scales, while few studies are available for its definition at a single well scale, especially in fractured aquifers. This study examines how much the sustainable yield of a well in fractured aquifers depends on the trend of drawdown over time. For this aim, pumping tests conducted in fractured rocks were considered and analytical models were applied to examine the long-term response of groundwater levels in some wells. To define the operational pumping flow of a well in these aquifers, results show that long constant flow rate pumping tests are preferred to step-drawdown tests. The late drawdown–time curve and residual drawdown segment-curves during the recovery, approximated by power, exponential or polynomial equations, represent the first step to extrapolating the long-term drawdown in the well. This prediction combined with the assessment of a drawdown limit in the well (as a function of the saturated thickness of the aquifer) are essential to plan the first operation of the well (flow rate and time of pumping). Subsequently, through the monitoring of this first operation step, the following operation phases can be updated and improved. [ABSTRACT FROM AUTHOR]

Groundwater is one of the most valuable natural resources, and the most dependable source of fresh water. For sustainable groundwater management, the present study aimed to model groundwater potential zones in the north–central region of Bangladesh using GIS, remote sensing, and the analytical hierarchy process. The present study included eight thematic layers: lineament density, geomorphology, soil types, slope, land use/land cover, drainage density, elevation, and rainfall features to delineate a groundwater potential zone of the area. Integration of the eight thematic layers was performed through weighted overlay analysis, which assisted in delineating groundwater potential zones. This simple and systematic method successfully provides a satisfactory result concerning the delineation of groundwater potential zones. The study resulted in a groundwater potential zone map, which identifies about 11.51% of the study area as being under a very high groundwater potential zone, covering an area of 504.09 km2. The AHP analysis shows that the physiographical parameters, such as lineament density, slope, and drainage density, and meteorological factors such as annual rainfall, have greater influence over groundwater potentiality. The result obtained from the weighted overlay analysis was verified with actual well yield and groundwater depth data, which show a significant positive correlation. The outcome of the study will help in taking effective measures to ensure sustainable use and extraction of groundwater in this region. [ABSTRACT FROM AUTHOR]

Due to rapid urbanization, the development of megacities and metropolises worldwide is creating water scarcity, social-environmental risk, and challenges to the regions where water supply from rivers and alluvial aquifers is insufficient and unstable. Groundwater exploration in fractured bedrock of mountainous regions is thus a crucial issue in the search for substitute water resources. To achieve cost effectiveness on groundwater exploration, the use of comprehensive remote sensing (RS)- and geographic information system (GIS)-based models appears feasible. The required parameters selected and analyzed from the literature depend on the hydrogeological characteristics. This study intends to investigate and improve the proposed parameters and data sources upon those presented in the literature. A total of 17 hydrogeological units of concern was delineated from 105 complex geological formations of the geological sections and main rock types. The other parameters related to groundwater potential were derived from the digital elevation model and Landsat imagery. In addition, 118 drilling cores were inspected and in-situ well yield data from 72 wells were employed to assess the normalized groundwater potential index in the raster-based empirical GIS model with a higher spatial resolution. The results show that the accuracy of the interpretation of groundwater potential sites improved from 48.6% to 84.7%. The three-dimensional (3D) visualization of a thematic map integrated with satellite imagery is useful as a cost-effective approach for assessing groundwater potential. [ABSTRACT FROM AUTHOR]

Due to rapid urbanization, the development of megacities and metropolises worldwide is creating water scarcity, social-environmental risk, and challenges to the regions where water supply from rivers and alluvial aquifers is insufficient and unstable. Groundwater exploration in fractured bedrock of mountainous regions is thus a crucial issue in the search for substitute water resources. To achieve cost effectiveness on groundwater exploration, the use of comprehensive remote sensing (RS)- and geographic information system (GIS)-based models appears feasible. The required parameters selected and analyzed from the literature depend on the hydrogeological characteristics. This study intends to investigate and improve the proposed parameters and data sources upon those presented in the literature. A total of 17 hydrogeological units of concern was delineated from 105 complex geological formations of the geological sections and main rock types. The other parameters related to groundwater potential were derived from the digital elevation model and Landsat imagery. In addition, 118 drilling cores were inspected and in-situ well yield data from 72 wells were employed to assess the normalized groundwater potential index in the raster-based empirical GIS model with a higher spatial resolution. The results show that the accuracy of the interpretation of groundwater potential sites improved from 48.6% to 84.7%. The three-dimensional (3D) visualization of a thematic map integrated with satellite imagery is useful as a cost-effective approach for assessing groundwater potential.

Most studies of fractured-rock aquifers are about analytical models used for evaluating aquifer tests or numerical methods for describing groundwater flow, but there have been few investigations on how to estimate the reliable long-term drought yields of individual hard-rock wells. During the drought period of 1998 to 2002, many municipal water suppliers in the Piedmont/Blue Ridge areas of central Maryland (USA) had to institute water restrictions due to declining well yields. Previous estimates of the yields of those wells were commonly based on extrapolating drawdowns, measured during short-term single-well hydraulic pumping tests, to the first primary water-bearing fracture in a well. The extrapolations were often made from pseudo-equilibrium phases, frequently resulting in substantially over-estimated well yields. The methods developed in the present study to predict yields consist of extrapolating drawdown data from infinite acting radial flow periods or by fitting type curves of other conceptual models to the data, using diagnostic plots, inverse analysis and derivative analysis. Available drawdowns were determined by the positions of transition zones in crystalline rocks or thin-bedded consolidated sandstone/limestone layers (reservoir rocks). Aquifer dewatering effects were detected by type-curve matching of step-test data or by breaks in the drawdown curves constructed from hydraulic tests. Operational data were then used to confirm the predicted yields and compared to regional groundwater levels to determine seasonal variations in well yields. Such well yield estimates are needed by hydrogeologists and water engineers for the engineering design of water systems, but should be verified by the collection of long-term monitoring data. [ABSTRACT FROM AUTHOR]

A large proportion of the total value of groundwater in conjunctive use systems is associated with the ability to smooth out shortfalls in surface water supply during droughts. Previous research has argued that aquifer depletion in these regions will impact farmers negatively by reducing the available stock of groundwater to buffer production in future periods, and also by increasing the costs of groundwater extraction. However, existing studies have not considered how depletion may impact the productivity of groundwater stocks in conjunctive use systems through reductions in well yields. In this work, we develop a hydro-economic modeling framework to quantify the effects of changes in well yields on the buffer value of groundwater, and apply this model to an illustrative case study of tomato production in California’s Central Valley. Our findings demonstrate that farmers with low well yields are forced to forgo significant production and profits because instantaneous groundwater supply is insufficient to buffer surface water shortfalls in drought years. Negative economic impacts of low well yields are an increasing function of surface water variability, and are also greatest for farmers operating less efficient irrigation systems. These results indicate that impacts of well yield reductions on the productivity of groundwater are an important economic impact of aquifer depletion, and that failure to consider this feedback may lead to significant errors in estimates of the value of groundwater management in conjunctive use systems. [ABSTRACT FROM AUTHOR]

Worldwide, there is growing recognition of the need to reduce agricultural groundwater use in response to rapid rates of aquifer depletion. To date, however, few studies have evaluated how benefits of conservation vary along an aquifer's depletion pathway. To address this question, we develop an integrated modeling framework that couples an agro-economic model of farmers' field-level irrigation decision-making with a borehole-scale groundwater flow model. Unique to this framework is the explicit consideration of the dynamic reductions in well yields that occur as an aquifer is depleted, and how these changes in intraseasonal groundwater supply affect farmers' ability to manage production risks caused by climate variability and, in particular, drought. For an illustrative case study in the High Plains region of the U.S., we apply our model to analyze the value of groundwater conservation activities for different initial aquifer conditions. Our results demonstrate that there is a range of initial conditions for which reducing pumping will have long-term economic benefits for farmers by slowing reductions in well yields and prolonging the usable lifetime of an aquifer for high-value irrigated agriculture. In contrast, restrictions on pumping that are applied too early or too late will provide limited welfare benefits. We suggest, therefore, that there are 'windows of opportunity' to implement groundwater conservation, which will depend on complex feedbacks between local hydrology, climate, crop growth, and economics. [ABSTRACT FROM AUTHOR]

While groundwater constitutes a crucial resource in many crystalline-rock regions worldwide, well-yield conditions are highly variable and barely understood. Nevertheless, it is well known that fault zones may have the capacity to ensure sustainable yield in crystalline media, but there are only a few and disparate examples in the literature that describe high-yield conditions related to fault zones in crystalline rock basements. By investigating structural and hydraulic properties of remarkable yielding sites identified in the Armorican Massif, western France, this study discusses the main factors that may explain such exceptional hydrogeological properties. Twenty-three sites, identified through analysis of databases available for the region, are investigated. Results show that: (1) the highly transmissive fractures are related to fault zones which ensure the main water inflow in the pumped wells; (2) the probability of intersecting such transmissive fault zones does not vary significantly with depth, at least within the range investigated in this study (0-200 m); and (3) high yield is mainly controlled by the structural features of the fault zones, in particular the fault dip and the presence of a connected storage reservoir. Conceptual models that summarize the hydrological properties of high-yield groundwater resources related to fault zones in crystalline basement are shown and discussed. [ABSTRACT FROM AUTHOR]

Present paper tries to understand the influence of hydrogeological characteristics on groundwater yield of shallow wells in regolith aquifer, Ilorin, Nigeria. The data on hydrogeological characteristics such as drawdown, water level, depth of borehole, depth of overburden and well yield for 78 borewells were collected from Kwara State Ministry of Water Resources and Lower Niger River Basin Development Authority in Ilorin. While the aquifer transmissivity and well specific capacity was calculated from this data. The data obtained were subjected to Pearson moment correlation, multiple and stepwise multiple regression analysis. The results of the stepwise multiple regression (R² of .929) indicates that aquifer transmissivity and drawdown contributed 92.9% to the variability in well yield in the study area. It is concluded that while constructing wells, aquifer transmissivity and the rate of drawdown be taking into account for the purpose of having productive well in the study area. [ABSTRACT FROM AUTHOR]

Determining the yield of a production well remains one of the main problems in hydrogeological studies. Starting from the results of a 3-year-long monitoring of a continuously exploited well functioning at constant head (i.e., at a variable discharge rate), a new pumping style has been examined using numerical models. The objective is to control the impact of pumping on the aquifer in accordance with the principle of sustainability. Different models were developed in a transient state and were calibrated using discharge data of the well during the recession periods. Successively, the trends of the residual outflow from the aquifer system with the well operating at variable discharge and at constant discharge were simulated. The results indicate that the ratio of the volume of water pumped from the well to the volume of residual outflow is a significant indicator of the sustainability of groundwater withdrawals. Modeling confirms that a constant discharge rate can be derived from the information gained through a preliminary production phase of a well at constant head. This approach appears to be particularly useful when the problem is determining the sustainable yield of a single well from aquifers with low hydraulic diffusivity. [ABSTRACT FROM AUTHOR]

Summary: Groundwater resources in crystalline rock are typically associated with the weathered zone and regional sub-vertical faults that are well connected to the surface. However, some sub-horizontal and shallowly dipping fractured zones can also be highly-productive aquifers. In this paper, numerical simulations of a conceptual hydrogeological model show that the flow to such strongly transmissive fractured zones is controlled by their transmissivity or by their deepening structure. While leakage through the overlying rock units is generally the limiting factor, recharge always occurs at least close to the outcrop of the fractured zone where the overlying rock is thinner and guarantees the availability of some groundwater. At small dip angles, recharge extends spatially and the flow within the fractured zone may even become the limiting factor when the hydraulic conductivity of the overlying rock is not less than two orders of magnitude smaller than the fractured zone transmissivity. This is precisely the case of the Plœmeur aquifer (Brittany, France) located in a crystalline rock geologic setting, where groundwater in a shallowly dipping fractured zone is used as the source of water supply for a nearby city of 20,000 people. Simulation results show that the fractured zones may represent potential aquifers under a large variety of hydrogeological conditions. Aquifers in shallowly dipping structures differ strongly from those located in regional sub-vertical fault zones in terms of flow patterns, and thus supposedly in terms of management of the groundwater resource. They are more local than regional in scale, and consequently do not require regional fracture connectivity. The leakage through the overlying rock unit enhances water quality. Finally, we argue that the potential widespread occurrence of these alternative and possibly less accessible resources should promote the development of appropriate identification methods. [Copyright &y& Elsevier]

It is not possible, using numerical methods, to model groundwater flow and transport in the fractured crystalline rock of northeastern Brazil. As an alternative, the usefulness of self-organizing map (SOM), k-means clustering, and Davies-Bouldin techniques to conceptualize the hydrogeology was evaluated. Also estimated was the well yield and groundwater quality across the Juá region. This process relies on relations in the underlying multivariate density function associated with a sparse local set of hydrogeologic (electrical conductivity, geology, temperature, and well yield) and a complete regional set of airborne geophysical (electromagnetic, magnetic, and radiometric) and satellite spectrometric measurements. Resampling of the regional well yield and electrical conductivity estimates provides sufficient resolution to construct variograms for stochastic modeling of the hydrogeologic variables. The combination of these stochastic maps provides a way to identify potential drilling targets for future groundwater development. The data-driven estimation approach, when applied to available airborne electromagnetic and water-well hydrogeologic measurements, provides a low-cost alternative to numerical groundwater flow modeling. In addition to fractured rock environments, the alternative modeling framework can provide spatial parameter estimates and associated variograms for constraints to improve the traditional calibration of equivalent groundwater-porous-media models. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the response of groundwater level and well yields in the Halacli aquifer to climate variations in Central Anatolia, Turkey. The Halacli aquifer is a typical aquifer due to its vulnerability to the climate variations. The aquifer is shallow and its recharge area is small. The waters from rains and snow melts can rapidly infiltrate down to the groundwater body because the vadose zone is thin and formed from coarse material. Therefore, the groundwater system responds to the short-term recharges by raising its level. Although any exploitation did not occur, the groundwater levels have declined from 1989 to 1997. However, the groundwater levels began rising when the exploitation started in the summer of 1998. After the year 2000, although the amount and duration of yearly exploitation was constant, fluctuations of water level continued. Fluctuation of groundwater levels and well yields bewilders the water users and imperils the sustainable water management in the study area and also in arid and semi-arid regions of Turkey. In order to overcome this problem, behavior of groundwater level and discharges of the wells must be recorded and the water users must be informed about the current conditions and the possible trend in the future of the system. [ABSTRACT FROM AUTHOR]

Public water supply to the Federal Capital Territory (FCT) of Nigeria is inadequate and an alternative source of water includes streams, hand-dug wells and boreholes. A survey showed that 41% of the territory uses hand-dug wells, while 23% depends on boreholes and 16% depends on streams. Measurements were taken from 84 wells in 2002 and 2003 to assess the contribution of hand-dug wells. The parameters considered include ground surface elevation, water level, permeability and well yield. The well diameter ranged between 0.7 and 1.2 m, while the depth ranged between 4.5 and 16 m. The permeability ranged between 0.000518 and 0.002541 cm/s. The source of recharge to the aquifer is rain, and well productivity ranged between 211 and 1806 L/day. Wells located in seven out of nine groups considered cannot meet the water demand of an average household (20 people) in the territory. [ABSTRACT FROM AUTHOR]

It is generally understood that groundwater flow is greatly affected by linear features associated with geologic structures such as fractures, faults, lithologic boundaries, and fold axes. In crystalline rock aquifers, such geologic structures seem to be closely related to large-scale groundwater flow field and well productivity. However, quantification of how the structures are related with the flow and well productivity is not so simple, because it involves many factors of hydraulic properties and flow phenomena. This study proposes a semianalytical method to analyze the effects of highly permeable geologic discontinuities on the groundwater flow system. Effects of geological discontinuities on groundwater productivity are interpreted from the geometry of linear geologic features by the conformal mapping of the spatial distribution function. The proposed method is compared with the numerical methods, and the applicability and usefulness of the method to delineate high well yield areas from a limited number of well productivity measurements is discussed. [ABSTRACT FROM AUTHOR]

Principal components analysis of fracture trace and sinkhole characteristics near 33 wells drawing water from the Ocala aquifer identified three hydro geologically significant components. Multiple regression analysis using these components as independent variables showed that the flow of water to a well bore is influenced in order of importance by (1) proximity to a zone of high secondary permeability: (2) average aquifer transmissivity near the well; and (3) degree of cavity development in the closest zone of high secondary permeability. [ABSTRACT FROM AUTHOR]

• A water resources research approach is provided for water scarce areas in Africa. • Well yield potential can be estimated to use two geophysical parameters. • Distribution of the estimated well yield is consistent to the access time to water. • Application map for estimated well yield would solve the water supply issues. • Areas suitable for residence in the Tabora Region, Tanzania are identified. In inland Tanzania, because of the low annual rainfall and poor surface water runoff, increasing the supply of safe drinking water is a major issue. To solve the issue and to design for the drinking water supply at region of fractured zones in crystalline rocks, the simple method is applied to find the relationships between the pumping discharge of drilling wells and the field survey data in the Tabora Region, Tanzania. The field data used included results of electrical resistivity tomography (ERT) survey, electric resistivity borehole logging, the geological column (as geological information) and size of lineaments (as spatial information). A multiple correlation equation developed in this study demonstrates that the pumping discharge of a drilling well can be determined from two surface data sets: ERT survey results and lengths of topographic lineaments. This study also demonstrates that surface hydro-geophysical surveys are highly effective for exploration of groundwater resources in Tabora Region, and thus assist in locating potential drilling sites where water resources are scarce. Application of this equation enables prediction of the well yield potential in developing areas and is expected to increase the water supply in the Tabora Region, where water resource surveys are being conducted. Areas suitable for residential use, which are identified as regions on the application map where the well yield potential exceeds 5 m3hr-1, are found at the northern part of the Tabora Urban and Tabora Rural east and north from Tabora Urban. From the case study in the Tabora Region, this proposed simple method has possibilities to be able to apply for other regions in Tanzania and surrounding countries of Tanzania where are under similar conditions and environments to the Tabora Region. [ABSTRACT FROM AUTHOR]

A pipe plant for measurements of the quantity of crude oil and gas that assures a high precision in measurements of the volume flow rate of liquid is developed. The error of the computed degree of flooding is determined. [ABSTRACT FROM AUTHOR]