Aquifer Parameters Research Articles

Hybrid homotopy-PSO global searching approach with multi-kernel extreme learning machine for efficient source identification of DNAPL-polluted aquifer

Groundwater pollution source identification (GPSI), which is critical for taking effective measures to protect groundwater resources, assess risks, and design remediation strategies, typically involves the solution of a nonlinear and ill-posed inverse problem. Regarding the inversion of dense non-aqueous phase liquid (DNAPL) sources, the special characteristics of pollutants render related research more complex. In the present study, homotopy-based optimization inverse theory and multi-kernel extreme learning machine (MK-ELM) were combined for efficiently solving GPSI problem while estimating aquifer parameters at a DNAPL-polluted site. The extreme learning machine incorporating multi kernels and whose parameters are obtained by means of a genetic algorithm (GA) was embedded in an optimization model for GPSI to replace the multiphase flow simulation model and to mitigate the considerable computational burdens of inversion iteration. The hybrid homotopy-particle swarm optimization (PSO) algorithm was constructed as a more efficient method for segmentally searching the global optimum in wide areas with low dependence on initial values. Results showed that the application of GA-based MK-ELM and hybrid homotopy-PSO effectively accomplish the simultaneous identification of source characteristics and aquifer parameters. The MK-ELM approximate the outputs of multiphase flow simulation model sufficiently with the certainty coefficient (R2) increased to 0.9982, whereas the mean relative error was limited to 1.5168%. Compared to the widely used PSO algorithm, the hybrid homotopy-PSO algorithm significantly reduced the mean relative error of identification results from 6.77% to 2.89%.

Determination of Mining-Induced Changes in Hydrogeological Parameters of Overburden Aquifer in a Coalfield, Northwest China: Approaches Using the Water Level Response to Earth Tides

The determination of changes in hydrogeological properties (e.g., permeability and specific storage) of aquifers disturbed by mining activity is significant to groundwater resource and ecological environment protection in coal mine areas. However, such parameters are difficult to continuously measure in situ using conventional hydrogeological methods, and their temporal changes associated with coal mining are not well understood. The response of well water level to Earth tides provides a unique probe to determine the in situ hydrogeological parameters and their variations. In this study, the tidal responses of well water level were employed to characterize the changes in hydrogeological parameters of the overburden aquifer induced by longwall mining in a coalfield, northwest China. Based on the long-term hourly recorded water level data, two analytical models were used to determine the temporal changes of permeability and specific storage of the overburden aquifer. The results showed that the hydrogeological parameters changed with the longwall coal face advance. When the longwall coal face approached the wells, the aquifer permeability increased several to dozens of times, and the response distance ranged from 80 m to 300 m. The specific storage decreased before the coal face reached wells and recovered after the coal face passed. The results of this study indicate that the hydrogeological parameter changes induced by coal mining are related to the location of the well relative to the coal face and the stress distribution in the overburden aquifer. This study revealed the changes in permeability and specific storage associated with the mining disturbance which could have great significance for quantitative assessment of the impact of mining on overburden aquifer.

Determination of Aquifer Parameters Using Theis Method in Malamawi Island, Isabela City, Basilan, Philippines

The study aims to determine the hydrologic properties of an aquifer of Malamawi Island in terms of transmissivity, storage coefficient, and specific discharge using the Theis method. The study was conducted in March of 2015. The 4 inches 2- boreholes are drilled in two different locations (Diki and Santa Barbara villages) to identify the lithologic properties. A pumping test was performed for forty-five (45) minutes and, drawdowns are observed from the observation well. The shallow aquifer is confined with a transmissivity of 1.70 m2/d, storage coefficient of 0.001012, and specific discharge of 6.53 m2/d.

Aquifer hydraulic parameters estimation based on hydrogeophysical methods in West Nile Delta, Egypt

Water scarcity is becoming a major constraint not only to the reclamation and cultivation of new areas, but also to the irrigation of already reclaimed areas, which could lead to global desertification. Groundwater exploration is one of the solutions to overcome the water resource shortage crisis in Egypt, especially after the building of the Ethiopian Renaissance Dam and its effects with unfavorable consequences for the water supply. The West Nile Delta region (WND) has been chosen by the Egyptian government in the past 30 years to develop several agricultural programs that rely mainly on groundwater for different aquifers. Vertical Electrical Sounding (VES) is the main method for determining the depths to groundwater, aquifer thicknesses, salinity and possibly hydrophysical parameters (transverse resistance and average transverse resistivity). The hydraulic parameters of aquifer and their important role in estimating the safe yields from production wells are essential for agriculture water management. To estimate of main aquifer parameters using geoelectric measurements, which are of great importance in selecting the suitable wells locations and in maintaining the sustainable management of groundwater, hydrogeological data are collected for 32 drilled wells and the Schlumberger array was used to implement 22 VES at specific sites in the study area. Some VES are performed alongside the already drilled wells that have lithology and pumping test data and others are carried out in well-free places especially in the northern and southern parts. Using the partial-curve matching technique, 22 VES data are interpreted to obtain the different geoelectric parameters (e.g., transverse resistance and average transverse resistivity). The constructed relationships between transmissivity—transverse resistance, hydraulic conductivity—average transverse resistivity, and salinity—average transverse resistivity showed well correlation between these parameters, where R2 equal 0.86, 0.7 and 0.8, respectively. Based on these relationships and the data of 22 VES, the predicted values of transmissivity range between 396.4 and 8830.7 m2/day, hydraulic conductivity range from 107.6 to 7.6 m/day and the TDS vary from 413.2 to 1991.6 mg/l. These results showed that VES is a useful method for exploring the groundwater aquifer and predicting its hydraulic parameters (for example, transmissivity and hydraulic conductivity) and salinity, which can be used as a primary data for drilling groundwater wells and further agricultural irrigation in the West Nile Delta, Egypt.

Modelling the effect of geo-matrix conduction on the bulk and pore water resistivity in hydrogeological sedimentary beddings

Generally, the electrical method of geophysics is potentially valuable in typifying the subsurface conductivity and its surrounding medium. Sixteen datasets of 1-D electrical resistivity survey was integrated with 8 core samples, which were taken in the neighbourhood of eight of the sixteen VES datasets. The two sets of data were intertwined with geological and hydrogeological datasets to enhance the realization of unique results used in assessing the aquifer geo-matrix and pore water geo-resistivity in four counties in the coastal province of Akwa Ibom State, southern Nigeria. The current electrode separations of 1-D resistivity data were extended up to 300 m to ensure that the prolifically exploited water-bearing units were assessed. The VES data were manually and electronically modeled and each of them showed characteristic four geo-electric layers with KH, HK, KQ, HA and A group of curves. The core samples, which cut across the local Government Areas under survey, included sandy clay (12.5%), fine-grained sand (50.0%), medium-grained sand (12.5%) and coarse sand (25.0%). Bulk resistivities of water-bearing units and other primary geo-electrical indices were measured in all sixteen locations. However, in the eight aquifer core sample locations, water resistivities were measured in situ. The core samples were taken to the laboratory for measurements of fractional porosity and volumetric water content. The measured fractional porosity ranged from 0.189 to 0.267 with an average of 0.232, whilst volumetric water content varied from 0.23 to 0.31 with an average value of 0.268. The transmission coefficients were computed from volumetric water content and other parameters in the work. The values ranged from 0.4135 to 0.5612 with an average value of 0.4945. Fractional porosity was also modeled from field parameters and the results showed a good match with laboratory measurement as the root—mean square error was just 1.3%. Intrinsic specific resistance and conductivity of soil aquifer matrix were found to be $$3.333 \times 10^{3} \;\Omega {\text{m}}$$ and $$3.000 \times 10^{ - 4} \;{\text{Sm}}^{ - 1}$$ respectively. The study has provided useful information about the geo-electrical and geo-pore properties of the prolifically exploited aquifers in the study area. The aquifer parameter contour maps have been delineated and these, together with other parameter relations generated in this study could help in predicting the volumetric conductivity between pore water and the matrix texture of hydrogeological units in the study area and other areas with similar geology.

Use of microgravity for identification of delayed gravity drainage and conceptual model selection in unconfined aquifers

The estimation of hydraulic parameters at the aquifer scale typically relies in the analysis of pumping tests. Drawdown data, from a frequently limited number of boreholes and piezometers, is used in conjunction with analytical formulas derived for conceptually simplified models in a history matching procedure. In unconfined aquifers it is well known that the drainage process is controlled by the unsaturated zone. Several models have been proposed in the literature for the calculation of drawdown caused by pumping. Approaches range from the assumption of instantaneous and complete drainage to the inclusion of a delay term or the full implementation of the unsaturated zone to represent the delayed drainage in the unsaturated zone. Because borehole drawdown data is not informative about the unsaturated zone processes, it is common for practitioners to rely in the simplest models available, usually in some pumping test interpretation software. For example, Neuman’s instantaneous drainage model is still widely used in the industry even when it has been demonstrated that under some circumstances provides incorrect estimations of key aquifer parameters. Additionally, as boreholes are scarce, spatial information is ignored and conceptual assumptions of axial-symmetry are a normal practice. In this work we show how the use of microgravity instruments, sensitive to storage variations in the near subsurface, could be a simple, cheap and convenient tool for the identification of delayed drainage processes in unconfined aquifers. The joint use of drawdown and gravity data can be utilized to select the most preferable conceptual model for the parameter estimation problem.

Characterization of Groundwater in the Shallow and Deep Aquifers of an Agriculture-Dominated Tropical Subhumid to Semiarid Region, India: a Multivariate and GIS Approach

Hydrochemistry, sources of ions, identification of pollution hotspot, and potability of groundwater in shallow and deep aquifers of Palakkad and Chittur taluks (area = 1875 km2) of Bharathapuzha river basin, the largest river basin in Kerala, India, are discussed in this paper. The study area belongs to one of the rice bowls of the State. Geologically, the study area consists of Archaean crystallines, overlaid by laterite. Due to the unique geography, subhumid to semiarid climate, and intense agricultural activities, the quality of groundwater is a serious concern and warrants attention. For delineating the major ions and nutrients, water samples were analyzed for shallow (dug wells) and deep (bore wells) aquifers during monsoon (MON) and postmonsoon (POM) seasons. Physicochemical parameters showed distinct spatiotemporal variation and quality degradation, which was more prominent in deep groundwater. The relative abundance of cations and anions is in the order Na > Ca > Mg > K and HCO3 > Cl > CO3 for both the aquifers. The spatial distribution trend of parameters in deep and shallow aquifers showed a similar pattern indicating a common influence on water quality. Multivariate factor analysis (R-mode) employed in the study derived three main factors controlling the groundwater chemistry, viz. geogenic, anthropogenic, and pH. Among these, water chemistry is chiefly controlled by the geogenic factor and partly by the other two. It is also reflected well in the correlation analysis of various parameters. Since the eastern part of Chittur taluk in the study area is more impacted by anthropogenic and climatic influences, a pollution hotspot has been identified in this region through the application of Geographic Information System (GIS) overlay analysis. Thus, the study reveals agrochemical, climatic, and geologic influences on the chemistry and quality of groundwater.

მუხრანის არტეზიული აუზის ჰიდროდინამიკური თავისებურებები

The article contains a description of the hydrodynamic features of the Mukhran artesian basin and a generalization of the hydrogeological conditions. Based on the results of experimental filtration studies carried out in the wells of existing water intakes, the hydrodynamic parameters of pressure aquifers were determined, according to which a map of the permeability of aquifers of the Quaternary period was compiled. The peculiarities of changes in water conductivity indicators formed the basis of isolated hydrodynamic zones, which is a clear expression of the filtration structure of the Mukhran artesian basin, in terms of the distribution of pressurized groundwater resources.

მუხრანის არტეზიული აუზის მიწისქვეშა წყლების რესურსები

The Mukhrani artesian basin is a reservoir containing high quality groundwater. Well-known aquifers and galleries are located within the artesian basin, which are one of the main sources of drinking and household water supply for the city of Tbilisi. The article summarizes the hydrogeological conditions of the Mukhrani artesian basin. The hydrogeological parameters of the productive aquifer were determined based on the results of studies carried out at the existing water intakes. A hydrodynamic map of the artesian basin was compiled. The spatial and quantitative distribution of groundwater resources in the basin has been estimated. Established dynamic (natural) resources and static (natural) reserves of groundwater.

Mathematical Modelling of Surface-Groundwater Interactions under Varying Hydrological Conditions: Review of Past Works

Surface-groundwater interaction is a research area of significant importance for its central role in wastewater treatment, irrigation, drainage, flood control, erosion and sediment control. Mathematical models are often used for the estimation of surface-groundwater interactions under the variety of hydrological conditions. Due to cost effectiveness and ability to accommodate variations in aquifer parameters, mathematical models have gained immense importance in the past few decades. The objective of this review paper is to portray the contribution of the hydrologist towards the growing area of surface-ground water interaction from all over the world who proposed, analyzed, executed and validated the developed Mathematical models. To begin with, we briefly introduce the main mathematical equations that govern the flow of groundwater in unconfined and confined aquifer systems. The development of stream-aquifer models is presented in a chronological order to provide a clear understanding of the contributions of past works. The methodology used in the past work is adequately discussed without going into mathematical details. Furthermore, we also summarize recent developments concerning groundwater flow in presence of vertical streambed, partial penetration, stream-stage variations and multiple recharge/discharge basins.

Simultaneous identification of groundwater contamination source and aquifer parameters with a new weighted-average wavelet variable-threshold denoising method.

This paper first proposed a parallel heuristic search strategy for simultaneous identification of groundwater contamination source and aquifer parameters. As identification results are influenced by many factors, such as noisy contamination concentration data, data denoising is necessary. The existing wavelet threshold denoising method has unavoidable shortcomings; therefore, this paper first proposed a new weighted-average wavelet variable-threshold denoising (WWVD) method to improve the denoising effect for concentration data, which further enhanced the subsequent identification accuracy. However, frequent calls to the simulation model could produce high computational cost during likelihood calculation. Hence, single surrogate model of the simulation model was developed to reduce cost; however, it presented limitation. Thus, this paper first developed a differential evolution-tabu search (DE-TS) hybrid algorithm to construct an optimal ensemble surrogate model, which assembled Gaussian process, kernel extreme learning machine, and support vector regression. The first proposed DE-TS algorithm also improved the approximation accuracy of surrogate model to simulation model. This paper first proposed and implemented a parallel heuristic search iterative process for simultaneous identification, and the identification results were obtained when the iteration process terminated. The accuracy and efficiency of these newly proposed approaches were tested through a hypothetical case. Results showed that the WWVD method not only improved the denoising effect for concentration data but also enhanced the subsequent identification accuracy. The OES model using DE-TS hybrid algorithm improved the approximation accuracy of surrogate model to simulation model, and the parallel heuristic search strategy is helpful for simultaneous identification of groundwater contamination source and aquifer parameters.

Application of stochastic programming in groundwater pollution source identification

Groundwater pollution is a serious threat to the ecological environment and human life. It is necessary to determine the characteristics of pollution sources accurately and efficiently after the occurrence of pollution. The main basis for determining the characteristics of pollution sources is the pollutant concentration data of each observation well. However, due to the layout of the monitoring wells, the noise intensity of observation well concentration and unknown aquifer parameters, inversion results of groundwater pollution sources will be influenced significantly. Therefore, this article focuses on how to reduce its influence on the inversion results. In this article, a stochastic programming optimization model is introduced to explore its ability to control errors in complex situations. Results show that: in homogeneous aquifer, the normalized error (NE%) produced by simulation-optimization method is stable at about 2%, and the NE generated by stochastic programming method in confidence interval of 60%∼95% is between 0.20% and 5.42%. Moreover, stochastic programming model can effectively control the influence of noise. In the simulation-optimization model, when the noise intensity is 0.1 ∼ 0.5, the NE value is 2.01%∼12.68%, and the corresponding NE of stochastic programming model is 0.12%∼11.87%. Finally, this article considers the case that aquifer parameters are unknown (simultaneous identification of aquifer parameters and groundwater pollution sources). The results show that with the increase of the number of unknown aquifer parameters, the NE of the simulation-optimization model gradually increases from 1.16% to 8.75%. The NE value of the stochastic programming model decreases by 30% compared with the simulation-optimization model when the confidence level is 80%.

Estimating hydraulic properties from tidal propagation in circular islands

Observations of tidal propagation in coastal aquifers allow for rapid, low-cost quantification of aquifer parameters that are integrated over significant distances. Previous methods for aquifer property estimation from tidal propagation have focussed on continental aquifers and assumed straight, infinite shorelines. A recent investigation has proposed a correction to the Ferris analytical solution for straight shorelines (‘Ferris solution’) to be applied under radial flow conditions. In this paper, an existing analytical solution as a function of radial flow conditions (‘circular solution’) and the corrected Ferris solution are applied for the first time to obtain aquifer diffusivity in orbiculate-shaped islands. Inversion of the circular solution (to obtain diffusivity) requires iterative methods, which are applied to synthetic island aquifers with known diffusivity values ranging between 150,000 m2/d and 500,000 m2/d. The circular solution was tested for both confined and unconfined conditions and for tidal periods ranging from around 8 to 24 h. Known aquifer diffusivity values were reproduced within 2.5% of known values, even where randomised noise was added to synthetic groundwater tidal signals, and for both confined and unconfined aquifer conditions. Application of the corrected Ferris solution was found to be reliable for both confined and unconfined conditions, with discrepancies in aquifer diffusivity < 1% and < 2.5%, respectively, including with noise added to the groundwater tidal signals. The methodology presented in this work to estimate aquifer diffusivity in orbiculate-shaped islands is an improvement over classic approaches (e.g., the Ferris solution). In particular, the radial-flow correction to the Ferris solution provides for simple calculations of aquifer diffusivity of similar accuracy to the more complex radial analytical solution.

Hydrogeophysical Evaluation of Parts of River Mamu Sub-Basin, Southeastern Nigeria

Hydrogeophysical evaluation of parts of River Mamu Sub-Basin, Southeastern Nigeria was carried out using the Vertical Electrical Sounding technique (VES). Schlumberger array was used to acquire thirty (30) VES stations and were interpreted using software 1D-Interpex. The predominate VES curve types within the area are typically K-curves which is about 47%, whereas, the remaining 53% belongs to the other five curve types namely; KH, HK, H, Q, and KHK-curves. The calculated Da-Zarrouk parameters outcomes ranged from low to high within the study area: longitudinal conductance (0.0028-0.0571 mhom); transverse resistance (6630-10290 ohm-m2); aquifer resistivity (455-4900 ohm-m), aquifer thickness (4.70-38.00 m); depth to the aquifer (33-172 m); conductivity (0.0002-0.0022 mho. Two aquifer parameters were computed within the area namely; hydraulic conductivity (6.137-0.792 m/day) and transmissivity (1.007-20.597 m2/day). Two major aquifer systems were obtained specifically; a shallow aquifer belonging to Nanka Sands with depth (33-62m) and a far aquifer belonging to Ebenebe Sandstone with depth (69-172m). The groundwater flow paths within the study area trend predominantly in the NW-SE direction. The findings revealed that the study area possesses high groundwater potentials in some areas, hence, it is more economical to drill a borehole at the southwestern part of the study area than the southeastern part.

On Inflow to a Tunnel in a Fractured Double-Porosity Aquifer.

Inflow to a tunnel is a great public concern and is closely related to groundwater hydrology, geotechnical engineering, and mining engineering, among other disciplines. Rapid computation of inflow to a tunnel provides a timely means for quickly assessing the inflow discharge, thus is critical for safe operation of tunnels. Dewatering of tunnels is another engineering practice that should be planned. In this study, an analytical solution of the inflow to a tunnel in a fractured unconfined aquifer is obtained. The solution takes into account either the spherical or slab-shaped matrix block and the unsteady state interporosity flow. The instantaneous drainage water table and anisotropic hydraulic conductivities of the fractures network are also considered. Both uniform flux and uniform head boundary condition are considered to simulate the constant head boundary condition in the tunnel. The effects of the hydraulic parameters of the fractured aquifer on the inflow variation of the tunnel are explored. The application of the presented solution to obtain the optimum location and discharge of the well to minimize the inflow to a tunnel is illustrated.

Evaluation of Groundwater Potential and Safe Yield of Heterogeneous Unconsolidated Aquifers in Chiang Mai Basin, Northern Thailand

Chiang Mai basin has an escalating population growth resulting in high demand for water consumption. Lack of surface water supply in most parts of the basin gives rise to the increasing use of groundwater which leads to a continuous decline in groundwater level in the past decades. This study is the first long-term groundwater monitoring and modeling study that aims at developing a transient, regional groundwater flow model of heterogeneous unconsolidated aquifers based on the MODFLOW program. Long-term groundwater monitoring data from 49 piezometers were used in model calibration and validation. The pilot points technique was used to account for the spatial variability of hydrogeologic parameters of heterogeneous aquifers. The simulation results and statistics showed that most sensitive and significant model parameters were spatially variable hydraulic conductivities and recharge rates. The Chiang Mai basin’s unconsolidated aquifers do not have high potential. The water table and/or potentiometric surface in the southeast and southwest areas of Chiang Mai city were continuously decreasing with no sign of recovery indicating critical groundwater condition and careful management must be considered. Safe yield calculation, based on a 2-m average drawdown threshold, suggested that unconsolidated aquifers of the Chiang Mai basin can sustain overall abstraction rates up to 51.2 Mm3/y or approximately 214% of the current extraction rates.

Homotopy-based hyper-heuristic searching approach for reciprocal feedback inversion of groundwater contamination source and aquifer parameters

Groundwater contamination source identification is critical for taking effective measures to design remediation strategies, assess contamination risks, and confirm contamination responsibilities. To resolve the “equifinality” problem resulting from simultaneous inversion of contamination source characteristics and aquifer parameters at dense non-aqueous phase liquid-contaminated sites, two reciprocal optimization frames for separately identifying the contamination sources and aquifer parameters were designed and connected. The two sets of identification results were corrected stepwise by means of a feedback correction iteration process, thereby sufficiently improving the identification accuracy. The ensemble learning machine (ESLM) incorporating Kriging, radical basis function neural network, support vector regression, and wavelet kernel extreme learning machine with swarm intelligence (SI) algorithm was embedded into the reciprocal inversion iterations to replace the multiphase flow simulation model for significantly improving the computational efficiency. To improve the optimization efficiency, a hyper-heuristic homotopy algorithm was constructed for segmentally searching the global optimum in wider areas with low dependence on initial values. Results showed that the combined application of SI-based ensemble learning machine (SI-ESLM) and hyper-heuristic homotopy algorithm effectively accomplished the simultaneous identification of contamination sources and aquifer parameters with high efficiency, while maintaining high accuracy. The SI-ESLM sufficiently approximated the outputs of the multiphase flow simulation model with increased certainty (R2=0.9977), while the mean relative error was limited to 1.5388%. Compared to traditional heuristic algorithms, this application of reciprocal inversion iterations and the hyper-heuristic homotopy algorithm significantly reduced the mean relative error of identification results from 6.51% to 1.03%.

Optimization of particle swarm algorithm and its usage in calculation of hydrogeological parameter

In order to improve the accuracy, sensitivity, and convergence, the particle swarm optimization (PSO) algorithm is optimized and applied in the calculation of hydrogeological parameters to improve the accuracy of the hydrogeological model. The sensitivity and accuracy of the algorithm are improved through derivation of the appropriate value of the particles. Based on convergency analysis of this algorithm with the three intelligent optimization algorithms (Sphere function, Rosenbrock function, and Griewank function), the convergence of the algorithm is analyzed through different intelligently optimized algorithms. At the same time, the accuracy is validated through comparison between the optimized and unoptimized particle swarm algorithm as well as the actually observed hydrogeological data, and the sensitivity of the water conductivity coefficient and water storage coefficient under the algorithm is analyzed. The results show that the calculated value of the optimized PSO algorithm is very close to the theoretical value 0 of the intelligent optimization algorithm Sphere function and the theoretical value 1 of the Rosenbrock function as well as the theoretical value 1 of the Griewank function. The results reveal that the calculation results are very close to the theoretical value in the intelligent optimization algorithm test of optimized particle swarm algorithm; the maximum absolute error between the calculated value and the observed value of the optimized particle swarm algorithm is 0.011, and the maximum relative error of which is 8.1%; the maximum absolute error between the calculated value of particle swarm algorithm and the observed value is 0.021, and the maximum relative error reaches 29.1%; the number of iterations of the optimized particle swarm algorithm is 87 on average, while it of the unoptimized particle swarm algorithm is 450, reaching the optimal value. In addition, the optimized PSO algorithm has a standard function of 0.00659, which is significantly smaller than that of the PSO algorithm of 0.00684. When the interference coefficient is −20%~20%, the water conductivity coefficient and water storage coefficient are in negative phase with the drop depth of the aquifer. It suggests that the optimized particle swarm optimization algorithm has high accuracy and convergence, and its sensitivity of water conductivity coefficient and sensitivity of water storage coefficient are both good, which can provide a reliable algorithm basis for the construction of hydrogeological model and the establishment of aquifer parameters.

A New Randomized Binary Prior Model for Hydraulic Tomography in Fractured Aquifers.

We present a novel pilot-point-based hydraulic tomography (HT) inversion procedure to delineate preferential flow paths and estimate hydraulic properties in a fractured aquifer. Our procedure considers a binary prior model developed using a randomized algorithm. The randomized algorithm involves discretizing the domain into grid cells, assigning a binary label to each cell, traversing the grid randomly, and choosing the optimal grid configuration cell-by-cell. This binary prior model is used to guide the placement of pilot points and to constrain aquifer parameters during pilot-point-based HT inversion. A two-dimensional fractured granite rock block was considered to test our methodology under controlled laboratory conditions. Multiple pumping tests were conducted at selected ports and the pressure responses were monitored. The pumping datasets thus obtained were preprocessed using median filters to remove random noise, and then analyzed using the proposed procedure. The proposed binary prior algorithm was implemented in C++ by supplying the forward groundwater model, HydroGeoSphere (HGS). Pilot-point-assisted HT inversion was performed using the parameter-estimation tool, coupled to HGS. The resulting parameter distributions were assessed by: (1) a visual comparison of the K- and Ss -tomograms with the known topology of the fractures and (2) comparing model predictions with measurements made at two validation ports that were not used in calibration. The performance assessment revealed that HT with the proposed randomized binary prior could be used to recover fracture-connectivity and to predict drawdowns in fractured aquifers with reasonable accuracy, when compared to a conventional pilot-point inversion scheme.

Vertical Electrical Sounding (VES) for Estimation of Hydraulic Parameters in the Porous Aquifer

Similarities in both water and electric current flows allow the relation of hydraulic and geoelectric parameters of porous aquifers. Based on this assumption and the importance of the hydraulic parameters for groundwater analyses, this study aimed to estimate hydraulic conductivity (K) and transmissivity (T) with vertical electrical sounding (VES) in the porous aquifer at the experimental farm of the University of Brasilia, Brazil. VES is a geophysical technique that provides electrical resistivity (ρ, Ω m) and thickness (h) of the subsurface layers. The ρ and h aquifer data, associated with lithology, water table level (WTL), and groundwater electrical resistivity (ρw, Ω m), allowed the calculation of complementary geoelectric parameters (formation factor, F, and Dar Zarrouk parameters) and the relation with K and T, determined via slug test. VES data allowed the elaboration of geoelectric models, with mean absolute percentage error (MAPE) below 6% compared to field data, and the identification of the aquifer in each VES station. Significant exponential regression models (R2 &gt; 0.5 and p-value &lt; 0.05) showed the possibility of using geoelectric parameters to estimate hydraulic parameters. This study allowed the verification of the applicability of consolidated models and the identification of appropriate empirical relationships for hydrogeological characterization in the Brazilian tropical porous aquifers. The results of this work, besides the rapid sampling and low cost of performing vertical electrical sounding (VES), may justify the use of this geophysical technique for preliminary porous aquifer characterization, especially in regions absent of or with insufficient monitoring wells.