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  • groundwater  (16)
  • Key words. GPS  (11)
  • Architecture, Civil Engineering, Surveying  (27)
  • 1
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    Stochastic environmental research and risk assessment 1 (1987), S. 263-279 
    ISSN: 1436-3259
    Keywords: Porous media ; heterogeneity ; groundwater ; dispersion ; stochastic theory ; plume evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The migration of contaminants in heterogeneous aquifers involves dispersive processes that act at different scales. The interaction of these processes as a plume evolves can be studied by micro-scale modelling whereby two scales, a local- or micro-scale and an aquifer- or macro-scale, are covered simultaneously. Local-scale dispersive processes are represented through the local dispersion coefficient in the transport equation, while large-scale dispersion due to heterogeneities is represented through the resolution of the flow field and the diffusive exchange between streamtubes. The micro-scale model provides both the high degree of resolution compatible with local-scale processes, and the extent required for the approach to asymptotic conditions, using grids of up to a million nodal points. The model is based on the dual potential-streamfunction formulation for flow, and the transport problem is formulated in a natural coordinate system provided by the flownet. Simulations can be used to verify stochastic theories of dispersion, without the restrictive assumptions inherent in the theory. For the two-dimensional case, results indicate convergence of the effective dispersivity to the theoretical macrodispersivity value. Convergence takes place within a travel distance of about 50 correlation lengths of the hydraulic conductivity field. However, the approach taken to asymptotic conditions, as well as the macrodispersivity value, may differ for different realizations of the same medium. The influence of early-time events such as plume splitting on the asymptotic convergence remains to be investigated.
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  • 2
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    Stochastic environmental research and risk assessment 13 (1999), S. 85-99 
    ISSN: 1436-3259
    Keywords: Key words: Hydraulic diffusivity ; groundwater ; spectral analysis ; stochastic boundaries.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract: This study uses the cyclical frequency to develop the mathematical relationship between hydraulic diffusivity and spectral density functions calculated from groundwater level variation. Such relationship can be applied to (1) unsteady state, one-dimensional confined aquifer with time-dependent water level on both end boundaries, and (2) linearized unconfined aquifer with or without vertical recharge. The spectral density functions of groundwater fluctuations are largely affected by the spectral density functions obtained from time-dependent end boundaries and their cross-spectral density functions. Hydraulic diffusivity of an aquifer can be solved by type-curve matching technique at a specified frequency band under the conditions of (1) confined aquifer having equal time-dependent boundaries on both ends, (2) unconfined aquifer having equal time-dependent boundaries on both ends with surface recharge, and (3) unconfined aquifer subjected to surface recharge but neglecting the water table fluctuations on both end boundaries.
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  • 3
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    Journal of geodesy 72 (1998), S. 107-111 
    ISSN: 1432-1394
    Keywords: Key words. GPS ; Baseline precision ; Gain-numbers ; Ionosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. In this contribution we consider the precision of the floated and the fixed GPS baseline for the case of weighted ionosphere. Canonical forms of the baseline variance matrices are developed for different measurement scenarios. These forms make the relation between the various variance matrices transparent and thus present a simple way of studying their relative merits. It is also shown how these canonical forms give an intrinsic description of the gain in baseline precision which is experienced when the carrier-phase double-differenced ambiguities are treated as integers instead of as reals. The dependence of this gain on the various contributing factors, such as the decorrelation of the ionosphere, is also included.
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  • 4
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    Journal of geodesy 73 (1999), S. 246-258 
    ISSN: 1432-1394
    Keywords: Key words. GPS ; Temporal correlations ; Sensitivity analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. Due to the steady progress in global positioning system (GPS) technology and methods of data evaluation, it is possible to obtain highly precise relative point positions also for extensive geodetic networks. However, some limiting influences such as temporal correlations of observational data are neglected in most of the GPS processing programs. Therefore, it is necessary to consider the impact of these neglected correlations on the coordinates and their accuracy measures. In this paper the sensitivity and reliability of GPS positioning over long baselines when temporal correlations are modelled with the aid of a correlation function are discussed. The implementation in the variance–covariance matrix and the subsequent evaluation process require a considerable amount of computing time and memory. Therefore it is necessary to use appropriate numerical methods such as approximated matrix inversion in order to reduce the numerical requirements. After the description of the methodical and numerical handling of the temporal correlations, exemplary results are given to illustrate the effects on position and accuracy of GPS stations.
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  • 5
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    Journal of geodesy 71 (1997), S. 290-301 
    ISSN: 1432-1394
    Keywords: Key words. GPS ; ambiguity ; volume
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. In this contribution we consider the time-averaged GPS single-baseline model and study in a qualitative sense its relation with the geometry-free model and the geometry-based model. The least-squares estimators of the model are derived and their properties discussed. Special attention is given to the ambiguity search space, since it plays such a crucial role in the problem of integer ambiguity estimation and validation. Easy-to-evaluate, closed-form expressions are presented for the volumes of the ambiguity search spaces that belong to the geometry-free model, the single-epoch geometry-based model and the time-averaged model. By means of an eigenvalue analysis, the geometry of the ambiguity search spaces is revealed and its impact on the search for the integer least-squares ambiguities discussed.
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  • 6
    ISSN: 1432-1394
    Keywords: Key words. GPS ; Ambiguity search space ; Stochastic model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. In this contribution we analyse in a qualitative sense for the geometry-free model the dependency of the location, the size and the shape of the ambiguity search space on different factors of the stochastic model. For this purpose a rather general stochastic model is used. It includes time-correlation, cross-correlation, satellite elevation dependency and the use of an a priori weighted ionospheric model, having the ionosphere-fixed model and the ionosphere-float model as special cases. It is shown that the location is invariant for changes in the cofactor matrix of the phase observables. This also holds true for the cofactor matrix of the code observables in the ionosphere-float case. As for time-correlation and satellite elevation dependency, it is shown that they only affect the size of the search space, but not its shape and orientation. It is also shown that the least-squares ambiguities, their variance matrix and its determinant, for, respectively, the ionosphere-fixed model, the ionosphere-float model and the ionosphere-weighted model, are all related through the same scalar weighted mean, the weight of which is governed by the variance ratio of the ionospheric delays and the code observables. A closed-form expression is given for the area of the search space in which all contributing factors are easily recognized. From it one can infer by how much the area gets blown up when the ionospheric spatial decorrelation increases. This multiplication factor is largest when one switches from the ionosphere-fixed model to the ionosphere-float model, in which case it is approximately equal to the ratio of the standard deviation of phase with that of code. The area gives an indication of the number of grid points inside the search space.
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  • 7
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    Journal of geodesy 72 (1997), S. 1-10 
    ISSN: 1432-1394
    Keywords: Key words. GPS ; Kalman filtering ; Internal stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. Internal stability is referred to as the uniform asymptotic stability of Kalman filtering solutions, addressing the effects of initial-state errors, observation sample rates, lengths of observation sessions and so on. This paper presents the theory of the internal stability of GPS solutions, including mathematical definitions, properties and theorems addressing the dependence of internal stability of the filtering solutions on the controllability and observability of a GPS dynamic positioning system. The theory has been applied in analysing the stability performance of different GPS positioning modes, and the actual GPS positioning results have demonstrated graphically the asymptotic convergence of those stable solutions versus observation tracking time/filtering time-steps. The internal stability is therefore considered as an important performance criterion to evaluate different GPS positioning solutions.
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  • 8
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    Journal of geodesy 72 (1998), S. 236-244 
    ISSN: 1432-1394
    Keywords: Key words. GPS ; MDB ; Outliers ; Cycle slips
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. In this contribution closed-form expressions are given for the minimal detectable biases of single- and dual-frequency pseudo-range and carrier-phase data. They are given for three different single-baseline models. These are the geometry-free model and two variants of the geometry-based model, namely the roving and stationary variants. The baselines are considered to be sufficiently short such that orbital uncertainties in the fixed orbits and residual ionospheric and tropospheric delays can be assumed absent. The stochastic model used is one that permits cross-correlation and the use of different variances for individual GPS observables, including the possibility to weigh the observables in dependence on which satellite is tracked.
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  • 9
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    Journal of geodesy 73 (1999), S. 147-157 
    ISSN: 1432-1394
    Keywords: Key words. GPS ; Solar radiation pressure ; Orbit estimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. The Extended Center for Orbit Determination in Europe (CODE) Orbit Model, an empirical orbit model proposed by Beutler and colleagues in 1994, has been tested extensively since January 1996. Apart from six osculating Keplerian elements, this orbit model consists of nine (instead of the conventional two) parameters to take into account the deterministic part of the force field acting on the satellites. Based on the test results an improved orbit parameterization is proposed. The new orbit parameterization consists of the conventional two parameters plus three additional parameters, a constant and two periodic terms (a cosine and a sine term), in the X-direction to model the effects of the solar radiation pressure. Results based on one full year of routine orbit estimation, using the original and the new orbit parameterization, are presented to demonstrate the superiority of the new approach. An improvement of the orbit estimates with at least a factor of two is observed!
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  • 10
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    Journal of geodesy 73 (1999), S. 158-167 
    ISSN: 1432-1394
    Keywords: Key words. GPS ; Sensitivity ; Accuracy ; Deformation experiment ; Non-permanent array
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. This paper illustrates the surveys and the results obtained in an experiment whose goal is to evaluate the Global Positioning System (GPS) sensitivity and accuracy for deformation control on non-permanent network of different extensions. To this aim a high-precision device was properly built to set up known displacements along three orthogonal axes of a GPS antenna. One of the antennas in the considered GPS networks was moved according to centimeter and sub-centimeter displacements; after careful GPS data processing, it was evaluated whether these simulated deformations were correctly a posteriori detected and at which probability level. This experiment was carried out both on a local (baselines ranging between 3 and 30 km) and on a regional (baselines ranging between 300 and 600 km) GPS network. The results show that in the local network it is possible to identify the displacements at a level of 10 mm in height and at a level of 5 mm in horizontal position. The analysis of the regional network showed that it is fundamental to investigate new strategies to model the troposphere; in fact, it is necessary to improve the precision of the height in order to correctly identify displacements lower than 60–80 mm; on the contrary, horizontal displacements can be evidenced at the level of 20 mm.
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  • 11
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    Journal of geodesy 71 (1997), S. 370-383 
    ISSN: 1432-1394
    Keywords: Key words. GPS ; ambiguity ; ionosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. In this contribution the impact of a presumed presence or absence of the ionospheric delays on the quality of the least-squares ambiguities is analysed. The spatial correlation and the time correlation of the ionospheric delays are captured in an a priori ionospheric variance matrix. It is shown how the size and shape of the ambiguity search space is affected by the use of these a priori ionospheric weights. As a result an exact description can be given of the interpolatory character of the ambiguity variance matrix as function of the ionospheric weights. In order to give a qualitative analysis of the various effects, analytical rather than numerical results are emphasized.
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  • 12
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    Journal of geodesy 71 (1997), S. 577-587 
    ISSN: 1432-1394
    Keywords: Key words. GPS ; Ambiguity decorrelation ; Widelane ; Ionosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. In this contribution we consider the popular widelaning technique from the viewpoint of ambiguity decorrelation. It enables us to cast the technique into the framework of the least-squares ambiguity decorrelation adjustment (LAMBDA) and to analyse its relative merits. In doing so, we will provide answers to the following three questions. Does the widelane decorrelate? Does it explicitly appear in the automated transformation step of the LAMBDA method? Can one do better than the widelane? It is shown that all three questions can be answered in the affirmative. This holds true for the ionosphere-fixed case, the ionosphere-float case, as well as for the ionosphere-weighted case.
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  • 13
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    Journal of geodesy 72 (1998), S. 644-653 
    ISSN: 1432-1394
    Keywords: Key words. GPS ; Ambiguity resolution ; Acceptance test ; Discrimination test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. Ambiguity validation tests include the acceptance test and discrimination test, which are both important steps in the Global Positioning System ambiguity resolution process. An ambiguity discrimination test procedure based on a test statistic which is constructed by the difference (not the ratio as used in current procedures) between the minimum and second minimum quadratic form of the residuals in ambiguity identification, and its standard deviation, is proposed. The distribution function of the proposed test statistic is theoretically identified as a standard normal distribution when the known a priori variance factor is used, or as a Student's t distribution when the estimated variance factor is used. With this procedure, the ambiguity discrimination test is based on a more rigorous test statistic whose critical value can be calculated with any chosen level of significance. Test results indicate that the proposed ambiguity discrimination test procedure is reliable for use in ambiguity resolution on-the-fly.
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  • 14
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    Water resources management 10 (1996), S. 241-250 
    ISSN: 1573-1650
    Keywords: groundwater ; aquifer ; water table ; drainage ; random recharge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract Variation in the level of the water table is closely linked with recharge. Therefore, any uncertainty associated with the recharge rate is bound to affect the nature of the water-table fluctuation. In this note, a ditch-drainage problem of a sloping aquifer is considered to investigate the effect of uncertainty in the recharge rate on water-table fluctuation. The rate of recharge is taken as an exponentially decaying function with its decay constant as a Gaussian random variable. Expressions for the first two moments of the water-table height, i.e. mean and standard deviation, are presented. By using these expressions, the effect of uncertainty in the recharge rate on the water-table fluctuation has been analyzed with the help of a numerical example.
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  • 15
    ISSN: 1573-1650
    Keywords: Argentina ; groundwater ; irrigation ; simulation model ; surface water ; water use
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract In this paper, the theoretical approach presented in Part I is demonstrated by means of case studies on the irrigation schemes of Rio Mendoza and Rio Tunuyán in the Province of Mendoza, Argentina. The object of the case studies was the determination of optimal allocation of surface water to reduce the use of groundwater. Current and optimal conjunctive allocation of ground and surface water is studied by means of the developed simulation and optimization models. The second case study was designed on the basis of the experience gathered during the first one: each step of the case studies is compared. The comparison between the two case studies illustrates how to apply the proposed approach when the amount and quality of available data are different. For the more detailed Rio Tunuyán study, we determined the following physical characteristics of all terminal nodes: on-farm rotational intervals, mean water application depth, actual soil water storage capacity, crop water requirements, depth of groundwater table, aquifer transmissivity, and efficiency of groundwater use. The performance of the entire system is sensitive to changes in the water application depth, as it was shown by a simulation study. The application of our optimization approach to the conjunctive use of ground- and surface water showed that the total water requirements over a year can be met by a reassignment of water that reduces the total costs of a great amount.
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  • 16
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    Water resources management 7 (1993), S. 3-37 
    ISSN: 1573-1650
    Keywords: Coastal aquifers ; saltwater intrusion ; groundwater ; mathematical models ; analytical and numerical models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract Flow of freshwater and saltwater intrusion in coastal aquifers has drawn the attention of many investigators. Several laboratory, as well as mathematical models have been developed to study the pattern of flow of groundwater in coastal aquifers. Mathematical models have wider range of application and are the concern of this paper. Due to the complex nature of the problem, each of these mathematical models are based on certain simplifying assumptions and approximations. This paper presents a critical review of various methods of solution which have been proposed. The validity of the results abtained and the limitations of these models are also discussed.
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  • 17
    ISSN: 1573-1650
    Keywords: Danube ; environmental impacts ; floodplain ; Gabcikovo ; groundwater ; hydropower ; integrated modelling ; river branch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract A unique integrated modelling system has been developed and applied for environmental assessment studies in connection with the Gabcikovo hydropower scheme along the Danube. The modelling system integrates model codes for describing the reservoir (2D flow, eutrophication, sediment transport), the river and river branches (1D flow including effects of hydraulic control structures, water quality, sediment transport), the ground water (3D flow, solute transport, geochemistry), agricultural aspects (crop yield, irrigation, nitrogen leaching) and flood plain conditions (dynamics of inundation pattern, ground water and soil moisture conditions, and water quality). The uniqueness of the established modelling system is the integration between the individual model codes, each of which provides complex descriptions of the various processes. The validation tests have generally been carried out for the individual models, whereas only a few tests on the integrated model were possible. Based on discussion and examples, it is concluded that the results from the integrated model can be assumed less uncertain than outputs from the individual model components. In an example, the impacts of the Gabcikovo scheme on the ecologically unique wetlands created by the river branch system downstream of the new reservoir have been simulated. In this case, the impacts of alternative water management scenarios on ecologically important factors such as flood frequency and duration, depth of flooding, depth to ground water table, capillary rise, flow velocities, sedimentation and water quality in the river system have been explicitly calculated.
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  • 18
    ISSN: 1573-1642
    Keywords: bacterial indicators ; health indicators ; groundwater ; water quality ; Mexico City
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Groundwater quality was evaluated in the southern and western zones of Mexico City, using bacterial indicators and pathogens. Water quality from 40 wells was related to rates of diarrheal disease with 995 individuals interviewed. The focus of this first study on environmental health indicators (EHI) was based on population data (e.g., drinking water supplies and basic sanitation) and displayed using a Geographic Information System (GIS). Sixty percent of the wells monitored comply with the Mexican drinking water standards; however, based on other microbial evidence, 95% of the wells did not provide good quality water for human consumption. No significant differences were detected among hydrogeological zones. When analyzing by microbial indicators, the southern area was shown to be statistically different (p 〈 0.01) from the western area of the city. The highest rates of diarrheal diseases were detected in the south; the lowest rates were observed in the west. Although wells in the western side of the city appeared to be more contaminated (54%) than in the south (40%), no significant association with health indicators was detected. These preliminary findings suggest ways to improve the potential of EHI, by framing epidemiological data and the use of GIS.
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  • 19
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    Water resources management 9 (1995), S. 161-173 
    ISSN: 1573-1650
    Keywords: Toposheet ; lineaments ; georesistivity ; geomorphology ; drainage ; groundwater
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract With the help of the information drawn from a survey of India toposheet and by visual interpretation of satellite imagery of bands 2, 3 and 4, different thematic maps such as geomorphology and lineaments, drainage and land use, and land cover were prepared. These thematic maps have been superimposed and finally a groundwater potential zone map delineated on a survey of India toposheet. The whole block has been demarcated into 5 zones. Zones 1 and 2 are considered ideal groundwater potential areas, zone 3 is moderately ideal, and zones 4 and 5 are unfavourable for groundwater exploration. The validity of demarcation of the study area into different zones, as decided by remote sensing technology, has been justified by analysing the georesistivity sounding data of a number of places in this area. The net potential of the study area is estimated by GEC norm. It is observed that only 11.8% of annual utilisable groundwater is now used and there is vast scope of further exploitation of this resource.
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  • 20
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    Water resources management 13 (1999), S. 443-470 
    ISSN: 1573-1650
    Keywords: freshwater crisis ; groundwater ; hydrogeology ; Japan ; konan basin ; pumping-tests ; safe pumpage ; sustainable water supply
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract The Konan groundwater basin of Kochi Prefecture, Japan, is experiencing freshwater shortages for the past few years, particularly during the winter season. The present study aimed at analyzing the problem and exploring increased groundwater withdrawals to meet burgeoning freshwater demands in various sectors. The trend analysis of waterconsumption indicates that the groundwater demandwould increase by 43 and 52% by the years 2010 and2025, respectively, compared to 32 100 m3 d-1 at present.The streamflow of the Monobe River reduces to a minimumin winter and it shows a decreasing trend in recentyears. The geologic investigation results indicatethat unconfined (phreatic) aquifers comprisingalluvial sand and gravel and/or diluvial silty sandand gravel are dominant, and that the northwestern andwestern portions of the basin have greater potentialfor groundwater. Groundwater flows essentially fromnorth to south into the ocean. Groundwater levelfluctuations over the basin vary appreciably in spaceand time, indicating a wide variation of naturalrecharge. Field observations confirm the hypothesisthat stream-aquifer interaction also significantlycontributes to groundwater recharge, besides therainfall infiltration. Further, the pumping testsresults demonstrate that though the aquifers arelow-yielding, enhanced groundwater withdrawals couldbe possible. The aquifer hydraulic conductivity ischaracterized as high and ranges from 65 to 804 m d-1(mean = 229 m d-1), thereby suggesting great aquiferheterogeneity. Finally, it is concluded that thelong-term sustainability of the scarce groundwaterresource of the Konan basin is doubtful, and that acomprehensive analysis of the groundwater system isessential prior to formulating plans for the futuregroundwater development and management.
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  • 21
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    Water resources management 3 (1989), S. 231-239 
    ISSN: 1573-1650
    Keywords: Artificial recharge ; well ; successive variation of steady state ; groundwater ; action radius ; finite elements ; dimensionless graphs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract The artificial recharge of groundwater aims at the modification of water quality, an increase of groundwater resources, and the optimization of the exploitation and recovery of contaminated aquifers. The purpose of this work is to develop a new mathematical model for the problem of an artificial recharge well, using the method of successive variations of steady states. Applying this method, one arrives at an expression of time as a double integral. This integral contains the time-dependent radius of the recharge boundary and the piezometric head of the well, calculated with the finite-element method. The new model is simple and useful, and can be applied to many practical problems, using the designed dimensionless graphs.
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  • 22
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    Water resources management 8 (1994), S. 245-264 
    ISSN: 1573-1650
    Keywords: groundwater ; hydrogeochemical investigation ; simulation ; urban area ; arid climate groundwater management ; conservation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract The urban area of Greater Dhahran has an extremely arid climate where the average annual rainfail is less than 71 mm. The Umm Er Radhuma (UER) aquifer in that area is the main source of domestic and landscape irrigation demands. Groudwater use has increased drastically during the last 15 years due to extensive developments in the area. Numerical simulation techiques and hydrogeochemical investigations were carried out to assess the effects of increasing pumping rates on the piezometric surface in the UER aquifer and to predict the future levels and quality of water under different pumping scenarios. A groundwater flow model was developed and calibrated for the area. The increase in the water extraction rate between 1967 and 1990 has resulted in a decline in the piezometric surface by about 4 m in the Dhahran area. The results of simulation investigations indicated that if the present trend of the groundwater withdrawal rate continues, the water level is expected to drop by an additional 2 and by the end of the year 2000, by an additional 6 m by the end of 2010. If the present increasing rate in groundwater withdrawal is reduced by 50%, the additional drawdown will also be reduced to about 1 and 2.5 m by the end of years 2000 and 2010, respectively. The average total dissolved solids (TDS) has increased from 2750 to 3545 mg/l between 1967 and 1990 and will continue to rise to 3922 and 4361 by the end of years 2000 and 2010, respectively. These original findings are important because they postulates the negative impacts of increasing groundwater pumping from an aquifer in an arid urban area on future groundwater levels and quality. Therefore, effective groundwater management and conservation schemes should be adopted to maintain the long-term productivity and quality of aquifers in the area.
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  • 23
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    Water resources management 10 (1996), S. 251-277 
    ISSN: 1573-1650
    Keywords: Geographic information systems (GIS) ; modeling ; hydrology ; surface water ; groundwater ; water supply ; sewer design ; agricultural pollution ; nonpoint source pollution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract Increasing public awareness, stricter measures and promulgation of new laws in the area of water resources have made the use of advanced technologies indispensable. Geographic Information Systems (GIS) are an effective tool for storing, managing, and displaying spatial data often encountered in water resources management. The application of GIS in water resources is constantly on the rise. In order to stress the importance of GIS in water resources management, applications related to this area are addressed and evaluated for efficient future research and development. Fundamentals of GIS are summarized and the history of the GIS evolution in water resources is discussed. Current GIS applications are presented including surface hydrologic and groundwater modeling, water supply and sewer system modeling, stormwater and nonpoint source pollution modeling for urban and agricultural areas, and other related applications. Future research and development needs are presented, based on these reviews.
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  • 24
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    Water resources management 11 (1997), S. 69-81 
    ISSN: 1573-1650
    Keywords: groundwater ; sloping bed ; finite element method ; free surface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract A numerical solution of the nonlinear two-dimensional unsteady groundwater flow over sloping beds, using the Galerkin finite element method, is presented. The applied differential equation is based on the assumption that the streamlines are parallel to the sloping bed while the conventional differential equation is based on the Dupuit–Forchheimer assumption of horizontal flow. Furthermore, the gradient of the piezometric head is evaluated as a function of the unknown slope of the groundwater free surface and not simply as the absolute slope of the water table. Water table profiles and seepage rates obtained from the model are compared with those obtained by analytical solutions and experimental results for steady one-dimensional flow and for different values of bed slope. Results of the present model compares reasonably well with experimental results and with the results of Childs' analytical solution. The unsteady-state solution for different values of bed slope are compared to the results of a model based on the assumption that the water table slope is equal to the bed slope. The differences in the predicted water table by these two models are insignificant for small slopes but increase with increasing slope.
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  • 25
    Electronic Resource
    Electronic Resource
    Springer
    Water resources management 13 (1999), S. 205-218 
    ISSN: 1573-1650
    Keywords: groundwater ; management ; monitoring ; pollution prevention ; saline intrusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract The Chalk aquifer of the English South Downs is very heavily utilised. The groundwater resources have enjoyed a formal programme of management which started in the 1950s, although a number of actions had been taken earlier in order to deal with saline intrusion and potential risk to groundwater quality from urbanisation. In the late 1950s the policy of ‘leakage/storage’ boreholes was first adopted, whereby the ‘leakage’ boreholes along the coast were pumped in winter to intercept fresh water discharge to the sea and to maximise the recharge potential inland, and inland ‘storage’ boreholes were used, as much as possible, in the summer months only. A comprehensive monitoring programme supported by aquifer modelling has enabled a gradual increase in overall abstraction to take place without increasing groundwater degradation due to saline intrusion. There have been various pollution prevention strategies over the years, and these have been effective in protecting the groundwater despite the high population density and widespread agricultural activity within the South Downs. The management of the aquifer has clearly been successful; there are many lessons from this experience that can be applied to other regions and other aquifers.
    Type of Medium: Electronic Resource
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  • 26
    Electronic Resource
    Electronic Resource
    Springer
    Studia geophysica et geodaetica 44 (2000), S. 442-459 
    ISSN: 1573-1626
    Keywords: temperature ; groundwater ; sedimentary basin ; exploitation ; transient effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract The subsurface temperature field was studied on a set of 46 borehole logs measured in the vicinity of uranium deposits in the Bohemian Cretaceous Basin. Vertical variations of the steady state temperature and the temperature gradient are governed by thermal conductivity which strongly varies in dependence on lithology. Large departures from undisturbed temperature detected in many holes are associated with uranium mining. A positive anomaly is observed in leaching fields where large amounts of acid are injected into the uranium-bearing Cenomanian. A negative anomaly is linked to the operation of hydraulic barriers which enclose the mining area and helps to contain pollution by pumping clean water into the Cenomanian aquifer. The spatial distribution of the observed temperature anomalies helps to map the migration of the fluids used in both processes. The temperature disturbance is propagated from the Cenomanian aquifer up through overlying impermeable sediments. The good fit of transient conductive models to the measured temperatures rules out heat advection and hence upward water flow towards and contamination of the upper Middle Turonian aquifer in the vicinity of the holes studied.
    Type of Medium: Electronic Resource
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  • 27
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 815-830 
    ISSN: 0363-9061
    Keywords: groundwater ; velocity ; heat transquent ; heated cylinder ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: An isothermally heated, impervious cylinder, which is placed normal to the path of flowing groundwater, is theoretically evaluated for its potential to serve as a kind of ‘groundwater velocimeter’. The essential task is to determine whether the variation in heat output along the cylinder perimeter is sufficiently large to permit measurement for typical groundwater velocities. Using finite elements, the governing equations of advective thermal transport in saturated porous media are solved to obtain the variation in heat output along the circumference of the heated cylinder. An annular region of different hydraulic conductivity is assumed to separate the cylinder from the surrounding formation. The creation of such a region during placement of a cylinder is inevitable. A parametric study led to the following conclusions: (1) A smaller cylinder radius is preferable since the time to achieve a particular degree of asymmetry in heat output is then greatly reduced. (2) An annular region of lower hydraulic conductivity, relative to formation, reduces output asymmetry by no more than 25%, but if hydraulic conductivity is increased, output asymmetry can increase several times. (3) For annular regions having a higher hydraulic conductivity than the surrounding formation, annular thickness is not important. (4) The least groundwater speed which may be accurately measured by such a device will depend heavily upon instrumentation but is tentatively placed at about 5⋅0×10-5 cm/s. Theoretical results are approximately confirmed by preliminary experiments with a prototype device which has been constructed so as to directly measure the expected variation in thermal output. Partial construction details are provided.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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