Groundwater Hydraulics Research Articles

Assessment of factors and mechanism contributing to groundwater depressurisation due to longwall mining

Assessment of mining impact on groundwater is one of critical considerations for longwall extension and sustainability, however usually constrained by limited data availability, hydrogeological variation, and the complex coupled hydro-mechanical behaviour. This paper aims to determine the factors and mechanism of groundwater depressurisation and identify knowledge gaps and methodological limitations for improving groundwater impact assessment. Analysis of dewatering cases in Australian, Chinese, and US coalfields demonstrates that piezometric drawdown can further lead to surface hydrology degradation, while the hydraulic responses vary with longwall parameters and geological conditions. Statistical interpretation of 422 height of fracturing datasets indicates that the groundwater impact positively correlates to panel geometry and depth of cover, and more pronounced in panel interaction and top coal caving cases. In situ stress, rock competency, clay mineral infillings, fault, valley topography, and surface–subsurface water interaction are geological and hydrogeological factors influencing groundwater hydraulics and long-term recovery. The dewatering mechanism involves permeability enhancement and extensive flow through fracture networks, where interconnected fractures provide steep hydraulic gradients and smooth flow pathways draining the overlying water to goaf of lower heads. Future research should improve fracture network identification and interconnectivity quantification, accompanied by description of fluid flow dynamics in the high fracture frequency and large fracture aperture context. The paper recommends a research framework to address the knowledge gaps with continuous data collection and field-scale numerical modelling as key technical support. The paper consolidates the understanding of longwall mining impacting mine hydrology and provides viewpoints that facilitate an improved assessment of groundwater depressurisation.

The origin and water quality of spring systems in Monchique, Portugal: A focus on Long-Term sustainability and elevated sodium levels

Spring water systems in Monchique, SW Portugal, not only serve diverse local utilities–from thermal baths to bottled water–but also represent a microcosm of a global concern: elevated sodium levels in spring-sourced bottled waters. This research employs hydrogeochemical and isotopic analyses to investigate the origin, hierarchy and quality of the springs offering a new focus on elevated sodium concentrations, a known global cardiometabolic risk factor. The springs arise from a complex hydrogeological system formed by extensive faulting between argillaceous country-rocks and intruded Cretaceous syenites. Here we show that thermal springs with temperatures of 23–31 °C, have a groundwater age of 5000 years, indicative of extended water–rock interactions and recharge at elevations of 450 to 650 m revealing a hitherto unreported resilience in regional groundwater hydraulics. Conversely, cold springs recharging from 200 m to the area’s peak at 900 m follow shorter paths within the regolith influenced by shallow geological features. The study detects nitrate contamination from surface sources in the cold springs and relatively high sodium levels in the geothermal springs that approach or surpass guideline values. Elevated sodium is attributed, for the first time, to long-term interactions and cation exchange with Na-rich syenites, possibly intensified by heat-induced dissolution at depth. This study informs current perspectives on the long-term sustainability and public health implications of spring water systems. The ion chemistry and isotopic evidence suggest that thermal springs, due to their longer circulation times, are less vulnerable to climatic shifts compared to the more susceptible cold springs. While offering specific insights into the Monchique springs, the research has broad implications to similar high-sodium thermal springs across the Iberian Peninsula and potentially worldwide.

Pumping‐induced Well Hydraulics and Groundwater Budget in a Leaky Aquifer System with Vertical Heterogeneity in Aquitard Hydraulic Properties

AbstractIn groundwater hydrology, aquitard heterogeneity is often less considered compared to aquifers, despite its significant impact on groundwater hydraulics and groundwater resources evaluation. A semi‐analytical solution is derived for pumping‐induced well hydraulics and groundwater budget with consideration of vertical heterogeneity in aquitard hydraulic conductivity (K) and specific storage (Ss). The proposed new solution is innovative in its partitioning of the aquitard into multiple homogeneous sub‐layers to enable consideration of various forms of vertically heterogeneous K or Ss. Two scenarios of analytical investigations are explored: one is the presence of aquitard interlayers with distinct K or Ss values, a common field‐scale occurrence; another is an exponentially depth‐decaying aquitard Ss, a regional‐scale phenomenon supported by statistical analysis. Analytical investigations reveal that a low‐K interlayer can significantly increase aquifer drawdown and enhance aquifer/aquitard depletion; a high‐Ss interlayer can noticeably reduce aquifer drawdown and increase aquitard depletion. Locations of low‐K or high‐Ss interlayers also significantly impact well hydraulics and groundwater budget. In the context of an exponentially depth‐decaying aquitard Ss, a larger decay exponent can enhance aquifer drawdown. When using current models with a vertically homogeneous aquitard, half the sum of the geometric and harmonic means of exponentially depth‐decaying aquitard Ss should be used to calculate aquitard depletion and unconfined aquifer leakage.

Groundwater Hydraulics in Increased Spring Discharge following Earthquakes: Some Applications and Considerations

Earthquakes often entail alterations in the groundwater flow regime, in the phreatic level, surges and losses of springs, and the discharge in brooks. A variety of theoretical approaches attempt to elucidate the post-earthquake effects on spring discharge. This study adopts a conceptual approach, primarily presenting diverse methods to estimate water released by earthquakes involving calculations of discharge surpluses in springs. This study delves into refined techniques rooted in groundwater hydraulics, displaying applications of analytical and simulation methodologies to quantify earthquake-induced groundwater discharge in springs. This research investigates springs as natural indicators and applies mathematical precipitation–runoff models, particularly the CREC model, to simulate hydrographs in post-earthquake scenarios. We apply analytical procedures or mathematical simulation techniques employed in groundwater hydraulics for natural aquifer recharge calculations. Firstly, we briefly describe the methods based on the analysis of depletion curves of hydrographs in spring discharge. Additionally, specific mathematical rainfall–runoff models used to simulate hydrographs of karstic springs, along with derived analytical approximations, are adapted for this scenario. These hydraulic calculations involve the depletion coefficient and hydrodynamic volumes of aquifers, parameters that reveal certain aspects of the relation between groundwater and earthquakes. Three main features are: (a) Acknowledging faults as the primary geological structures in transmitting pore pressures due to earthquakes. Thus, for large and deep faults, which connect the ground surface with the Earth’s crust bottom—where earthquakes trigger—the depletion coefficient, α, usually reaches high values (α = 0.1 days−1). Therefore, these faults become more sensitive to pore pressure than other lithologies. (b) Elucidating the mechanisms of permeability enhancement caused by earthquakes. (c) Highlighting the substantial volumes in motion within the Earth’s interior, which, for instance, could constitute a significant source for the origin of mineral deposits. Mathematical calculations enable the determination of the volume of mobilized water that can be discharged by gravity in each earthquake. This, along with its recurrence, justifies the substantial mineralization volumes.

Analytical Solutions of Water Inflow for Foundation Pit in Confined Water Stratum

This paper is aimed at the problem of inaccurate calculation of the water inflow of a foundation pit with a suspended water-proof curtain in a confined water stratum. According to the groundwater hydraulics principle, the theoretical model of the seepage field of the foundation pit is established, and the analytical formula of the water inflow for the circular, strip, and rectangular foundation pits is deduced. The seepage path influence coefficient α related to the water-proof curtain insertion ratio, the thickness of the confined aquifer, and the radius of the foundation pit is proposed and obtained by the positive and negative analysis of numerical simulation. The coefficient is used to correct the equivalent seepage length in the pit and directly affect the calculation result of water inflow. Finally, based on the calculation results of the analytical solution of water inflow, the relationship between the scale of the foundation pit and the water control effect is discussed. The research results show that the theoretical analysis results in this paper are in good agreement with the numerical results and the measured data in the field: when the size of the foundation pit is too large, it is not suitable to use the suspended water-proof curtain as the water control measure.

Fluid injection through artificially reconstituted bio-cemented sands

The hydraulic fracturing technology is widely applied in the fields of groundwater hydraulics, hydrogeology, geo-environmental engineering and the oil and gas industry. Bio-cemented granular media were used as a proxy for weakly-cemented and poorly-consolidated sands in fluid injection experiments. The experiments were conducted in a testing apparatus which is capable of applying true triaxial stresses and allowed for visualisation of fracture propagation. Tests were conducted with bio-treated sands across various cementation levels at three stress states. In all tests, an opening was observed whose major principal direction was parallel to the maximum horizontal stress. A cavity was also developed with associated plastic deformation which in lower cementation levels reached even the boundaries of the specimen causing extensive ‘damage’ — disaggregation at the grain scale. At higher cementation levels, the cavity was developed near the injection point and then fractures made their presence in the expected direction. The peak pressures were approximately 10–15 times higher compared to the mean stress, while for lower cementations the pressure profiles were very noisy due to continuous breakdown of cementation. The fracture response is clearly dependant on the material properties (strength, hydraulic conductivity) and on the applied stresses. The combined effects of the applied stresses of the system, the strength and stiffness of the material were seen through the calculation of brittleness index derived from the Mohr–Coulomb and the Lade–Duncan failure criteria. The peak pressures agree better with the limit pressure calculated from the cavity expansion theory rather than the hydraulic fracturing theory.

Experimental Investigation of the Effects of Porosity, Hydraulic Conductivity, Strength, and Flow Rate on Fluid Flow in Weakly Cemented Bio-Treated Sands

Fluid injection in a porous medium is the underlying mechanism for many applications in the fields of groundwater hydraulics, hydrology and hydrogeology, and geo-environmental engineering and in the oil and gas industry. Fluid flow experiments in porous media with a viscous fluid at varying injection rates were conducted in a modified Hele-Shaw setup. The granular media were three-dimensional bio-cemented sands of various grain sizes across various cementation levels, generating a matrix of various hydraulic conductivities, porosities, and strengths. The fluid injection experiments showed that a cavity-like fracture developed, which transitioned to crack-like fractures at higher cementation levels (hence, higher strength). As the flow rate increased, less infiltration was evident and higher breakdown pressure was observed, with propagation pressure reducing to zero. It was harder to induce an opening in cemented specimens with higher hydraulic conductivity and a larger pore network despite their lower strength due to excessive infiltration dominance, which inhibited the build-up of pressure required to generate a fracture. The results of this study suggest that, when designing fluid injection programs, the combined effects of hydraulic conductivity and strength need to be carefully considered.

Surface water and groundwater hydraulics of lowland karst aquifers of Estonia

In Estonia, karst aquifers supply roughly a third of annually abstracted domestic groundwater. Karst systems recharged by allogenic humic-rich streams originating from mire-dominated watersheds are common in Lower Estonia (lowlands). This study aimed to characterize the hydrology and hydraulics of two binary lowland karst systems: Salajõe (SKS) and Tuhala karst system (TKS), and their interaction with the hosting karst aquifer. High-resolution water level, discharge, specific conductance time series data combined with tracer test results were analyzed to assess the two systems. The temporal effect of evapotranspiration, snow deposition and snowmelt floods contributed to the variability in recharge event sensitivity of studied watersheds and aquifers, resulting in time-varying CCF strength between precipitation and discharge. The greatest event sensitivity was observed during the autumn and snowless winter seasons. The celerity and solute transport were the greatest in the preferential flow paths of both karst systems, however, solute transport characteristics varied significantly because of differences in structure and maturity of karst porosity. While the dilute allogenic recharge flushed the karst systems occasionally, the contribution of high-SEC groundwater baseflow was significant. During flood events, the matrix-conduit hydraulic gradient could be inverted, resulting in dilute floodwater being pushed into the hosting aquifer from the karst system.

Groundwater age persistence in topography-driven groundwater flow over paleohydrogeologic time scales

AbstractThe Pleistocene-Holocene climate transition resulted in a dramatic reduction in groundwater recharge in many aquifers in arid and semiarid regions throughout the world. This study conducted numerical experiments to compare the evolution of groundwater hydraulics and age patterns in arid and semiarid aquifers in response to transient conditions associated with recharge decline from the Pleistocene to the Holocene. Our results show that after a rapid reduction in recharge, the amplitude of water-table undulations and regional groundwater slope both reduced. This resulted in a general, and relatively rapid, contraction of local flow systems and an increase in the extent of intermediate and regional systems. The previous hierarchy of local, intermediate, and regional flow systems was completely replaced by largely horizontal and regional flow patterns after ~10,000 yr. However, in stark contrast, we observed that the original Pleistocene age patterns have remained almost unchanged throughout the 10,000 yr Holocene period. Thus, groundwater age is more likely to be indicative of past rather than current flow systems. Consequently, due to this age persistence, the use of modern groundwater age data to calibrate models or compute recharge with methods that do not account for this potentially significant spatial and temporal mismatch between age and hydraulics will be misleading and erroneous. This has significant implications for hydrogeologic analyses. The findings of this study may also apply to areas that have undergone dramatic changes in land cover or land use that strongly influence transient groundwater recharge processes.

Revisiting hydraulics of flowing artesian wells: A perspective from basinal groundwater hydraulics

Causes and water sources of flowing artesian wells attracted the interest of many hydrogeologists throughout history, however, a quantitative model that satisfactorily considers the roles of topography, groundwater recharge/discharge and aquitards on hydraulics of flowing wells is still lacking. In this study, a three-layer river-valley basin with a recharge boundary is used to obtain the basinal flow field, spatial distribution and transient discharge rates of flowing wells. Even if there is an aquitard separating the unconfined and the confined aquifers, groundwater discharge to the river still plays a critical role in occurrence of flowing wells. An aquitard with lower permeability would enlarge the zone with flowing wells, implying that flowing wells are more likely to occur in basins with continuous aquitards. By comparing flowpaths and inter-aquifer leakages before and after numerically installing a flowing well in a three-layer basin, we find decreased upward leakage in the discharge limb plays a much larger role than increased downward leakage in the recharge limb in the stable discharge rate of a flowing well. This recognition is different from previous studies where the stable discharge rate is supported only by downward leakage from the overlying aquifer. By considering well hydraulics in a basinal background flow field, this study improves understanding of the mechanisms of flowing artesian wells and the interaction of surface water and deep groundwater, indicating that flowing wells are valuable for sampling deep groundwater representative of deep and old groundwater in the discharge area of a basin.

Evaluating the impacts of groundwater extraction on land subsidence in Cai Rang district, Can Tho city

Groundwater is among the Nation’s most important natural resources. It provides drinking water to urban and rural communities, supports irrigation and industry, sustains the flow of streams and rivers, and maintains riparian and wetland ecosystems. In many areas of the Nation, the future sustainability of groundwater resources is at risk from overuse and contamination. Groundwater extraction not only regulates the shape of the ground surface and but also has a significant influence on human life. However, the occurrence of estimating the settlement of ground surface is still not well-studied. The objective of this study is to assess relation between groundwater pumping and land subsidence in Cai Rang district, Can Tho city. It is carried out by following steps: (1) Collecting geological prospecting data;(2) Conducting the method of ground water pumping test; (3) Processing the collected data; (4) Using Riley, Lohman and Poland methods in estimating the settlement of ground surface; (5) Using Finite element method to stimulate land subsidence. The result shows that the hydro-geological parameters, K is of 18.05 m/h; S is of 0.0083; T is of 299.608 m2/d. The cumulative land subsidence varies in the range of from 0 to 0.66 cm. Consequence of the land subsidence does not considerably affect construction work in the area. The analytical and interpretive methods described in this study will be useful to scientists involved in studies of ground-water hydraulics and aquifersystem deformation.

Analytical and Numerical Solutions to Selected Research Problems in Geomechanics and Geohydraulics

Geomechanical and geohydraulic engineering is a promising study area with several emerging research concerns. Most of such problems requires advanced level of mathematics to arrive at specific solutions. A wide range of approaches includes several analytical and numerical techniques for better understanding of such problems. In this paper, a few selected research problems are identified, and their solution techniques are demonstrated. The specific areas relevant to such problems are soil-structure interaction, ground improvement and groundwater hydraulics. This paper presents the problem identification, their mathematical solutions and results as well as pertinent analyses and useful interpretations to practice.

Physical and analytical modeling of rhythmic karst springs

Rhythmic Karst Springs (RKSs) are rare geologic features that rhythmically outflow water. A mechanical model for the rhythmic flow with rhythmic spill-over configuration was constructed in this work. The evolution of the RKS was revealed by using geological process analysis. The analytical model can directly explain the existence of RKSs in soluble rock regions and their formation mechanism in nature. Visual observations and flow measurements were performed using a laboratory physical model of RKS. The physical model components included a soluble rock simulation area, karst pipes, cave-reservoir, karst depression terrain, water tank, rhythmic spring, and the outflow measurement system. Groups of tests were carried out to recreate the process of RKS functioning and to confirm the rhythmic cycle duration and the threshold of replenishment intensity. This research helped to interpret the behavior of rhythmic springs using the recharge and evacuation of the subsurface cave-reservoir by means of fluid mechanics and groundwater hydraulics theories.

A physically constrained wavelet‐aided statistical model for multi‐decadal groundwater dynamics predictions

AbstractA physically constrained wavelet‐aided statistical model (PCWASM) is presented to analyse and predict monthly groundwater dynamics on multi‐decadal or longer time scales. The approach retains the simplicity of regression modelling but is constrained by temporal scales of processes responsible for groundwater level variation, including aquifer recharge and pumping. The methodology integrates statistical correlations enhanced with wavelet analysis into established principles of groundwater hydraulics including convolution, superposition and the Cooper–Jacob solution. The systematic approach includes (1) identification of hydrologic trends and correlations using cross‐correlation and multi‐time scale wavelet analyses; (2) integrating temperature‐based evapotranspiration and groundwater pumping stresses and (3) assessing model prediction performances using fixed‐block k‐fold cross‐validation and split calibration‐validation methods. The approach is applied at three hydrogeologicaly distinct sites in North Florida in the United States using over 40 years of monthly groundwater levels. The systematic approach identifies two patterns of cross‐correlations between groundwater levels and historical rainfall, indicating low‐frequency variabilities are critical for long‐term predictions. The models performed well for predicting monthly groundwater levels from 7 to 22 years with less than 2.1 ft (0.7 m) errors. Further evaluation by the moving‐block bootstrap regression indicates the PCWASM can be a reliable tool for long‐term groundwater level predictions. This study provides a parsimonious approach to predict multi‐decadal groundwater dynamics with the ability to discern impacts of pumping and climate change on aquifer levels. The PCWASM is computationally efficient and can be implemented using publicly available datasets. Thus, it should provide a versatile tool for managers and researchers for predicting multi‐decadal monthly groundwater levels under changing climatic and pumping impacts over a long time period.

Runoff and focused groundwater-recharge response to flooding rains in the arid zone of Australia

A groundwater recharge investigation in the arid zone of Australia is presented. The investigation used a wide range of hydrogeological techniques including geological mapping, surface and borehole geophysics, groundwater hydraulics, streambed temperature and pressure monitoring, and hydrogeochemical and environmental tracer sampling, and it was complemented by analysis of rainfall intensity from 18 tipping-bucked rain gauges, climate data and stream runoff measurements. Run-off and recharge from a 200-mm rainfall event in January 2015, the largest daily rainfall in the local 50-year record, were investigated in detail. While this major storm provided substantial run-off as a potential source for focused, indirect recharge, it only produced enough actual recharge to the shallow aquifer to temporarily halt a long-term groundwater recession. A series of smaller rainfall-runoff events in 2016 produced a similar recharge response. The results suggest that the total magnitude of a flood event is not the main control on indirect groundwater recharge at this location. A deeper aquifer shows no hydraulic response to surface-water flow events and is isolated from the shallow system, consistent with its Pleistocene groundwater age. This supports a growing body of evidence indicating that attributing or predicting generalised changes in recharge to changes in climate in dryland environments should not be attempted without first unravelling the dynamic processes governing groundwater recharge in the locality of interest. The results should prompt more detailed and long-term field investigation in other arid zone locations to further understand the episodic and nonlinear nature of recharge in such environments.

Modelling Groundwater Hydraulics to Design a Groundwater Level Monitoring Network for Sustainable Management of Fresh Groundwater Lens in Lower Indus Basin, Pakistan

The over-extraction of groundwater from thin fresh groundwater lenses is a threat to the livelihood of farmers in the Lower Indus Basin (LIB). It is essential to monitor and regulate this pumping to sustain fresh groundwater lenses. In this study, we applied a modelling approach in combination with geostatistical analysis to identify the critical locations to monitor the groundwater levels for sustaining fresh groundwater in the LIB. Our approach included four steps: (i) simulating temporal heads using a calibrated hydrogeological model; (ii) sampling monitoring locations using a hexagonal pattern of sampling; (iii) applying principal component analysis (PCA) of the temporal head observations, and selecting high scoring locations from the PCA; and (iv) minimizing the observation points to represent the water level contours. The calibrated model was able to replicate the hydro-dynamic behavior of the study area, with a root mean square of 0.95 and an absolute residual mean of 0.74 m. The hexagonal pattern of spatial sampling resulted in a 195 point network, but PCA reduced this network to 135 points and contour classification reduced it even further to 59 points. The 195, 135, and 59 point networks represented the water levels with average standard errors of 0.098, 0.318, and 0.610 m, respectively. Long-term simulations with increased pumping showed that the water levels would best be assessed by 195 monitoring points, although 135 and 59 points would represent the depleting area but would not capture the water logging area.

Assessment of subsidence risk associated with aquifer storage and recovery in the Coastal Lowlands Aquifer System, Houston, Texas, USA

Abstract. In the Houston, Texas region, groundwater use is regulated by the Harris-Galveston Subsidence District (District) because of historical regional subsidence from groundwater development. The District regulates groundwater production in the Coastal Lowlands Aquifer System (CLAS) to mitigate subsidence through the implementation of District Groundwater Regulatory Plan. The District has successfully reduced groundwater pumping as a percent of demand regionally while controlling subsidence through the implementation of alternative water supplies. Aquifer Storage and Recovery (ASR) is an alternative water supply strategy that provides a means to store water underground and increase water supply more cost effectively than traditional storage expansion strategies. Groundwater users in the District are interested in the many potential benefits of ASR as a water supply strategy. Little is known about the potential effects on compaction and land surface subsidence resulting from ASR operations. Recognizing this, the District funded research on the potential subsidence risk associated with ASR. Two hypothetical, though representative, ASR projects were developed and analysed: (1) an industrial ASR project meant to provide water supply during a drought of record (DOR), and (2) a municipal ASR project designed to provide an annual municipal summer peaking water supply. Simulations of groundwater hydraulics and subsidence were performed at three potential locations within the CLAS to provide insight into variability associated with location and aquifer depth. Theoretical simulations confirmed the potential for subsidence associated with the application of ASR in the CLAS, although operating an ASR for summer peaking needs has less potential risk of subsidence than the DOR scenario in the scenarios simulated. The study simulations provide insight into how an ASR project may be designed and operated to minimize compaction and potential subsidence. Based on this study, ASR operated to address summer peaking showed the greatest potential to reduce additional compaction verses sourcing all water from groundwater. This theoretical study provides a basis for future research on subsidence associated with ASR and provides a framework for consideration for the regulation of ASR within the District.

New analytical model for constant-head pumping: Considering rate-dependent factor at well screen

Non-Darcy flow due to pumping may occur at the well screen and yields some head loss. Unlike the wellbore skin yielding a constant head loss at the well, the studies in petroleum engineering indicate that the head loss due to the non-Darcy flow is proportional to the pumping rate. The head loss due to non-Darcy flow is quantified by a rate-dependent factor at the well screen. To our knowledge, such a head loss is never considered in the area of groundwater hydraulics. In light of this, this study develops a groundwater flow model for the constant-head pumping with a head loss expressed in terms of a rate-dependent factor at a fully penetrating well in a confined aquifer. A skin factor representing the head loss due to the presence of wellbore skin is also incorporated into the model. The consideration of the rate-dependent factor, however, would make the model nonlinear. The model has a steady-state flow equation with a time-dependent finite outer boundary to approximate the transient groundwater flow in the aquifer system. The solutions to the model for the drawdown and wellbore flowrate are developed and compared with the finite difference solutions. With the help of the present solutions, the sensitivity analyses of the aquifer drawdown and wellbore flowrate are made. The effects of the wellbore skin and non-Darcy flow on the drawdown are also investigated. The wellbore flowrate solution is then applied to estimate the aquifer parameters based on the field data from a constant-head injection test in a confined aquifer. The prediction of the present solution gives the best fit to the field measured data as compared with three existing solutions, indicating that the consideration of the rate-dependent factor improves the aquifer parameter estimation. The results of the parameter estimation also reflect the quality of the well installation.

A new benchmark optimization problem of adaptable difficulty: theoretical considerations and practical testing

In this paper, we present a new benchmark problem for testing both local and global optimization techniques. This problem is based on ideas from groundwater hydraulics and simple Euclidian geometry and has the following attractive features: (a) known values of the infinite global optima, which can be classified in a restricted number of sets, with known location in the search space (b) simple form and (c) quick computation of objective function values. Moreover, the number of local optima sets, their location in the search space and thus the respective values of the objective function can be easily determined by the user, without affecting the global optimum value. In this way, the difficulty of finding the global optimum can be changed from quite small to almost insurmountable, as demonstrated by applying five widely used optimization methods, namely genetic algorithms, sequential quadratic programming, simulated annealing, Knitro and branch and bound. Moreover, some observations on the different behavior of optimization methods are discussed.

Stable isotope systematics and geochemical signatures constraining groundwater hydraulics in the mining environment of the Korba Coalfield, Central India

The present study explores the use of stable isotopes and major ion chemistry of various water sources such as mine water, groundwater, river water, and rainwater to identify the dominant hydrogeochemical process that controls the water quality in the active opencast coal mining area of the Korba Coalfield, India. Different hydrochemical models have revealed that the study area is mostly characterized by two facies alongside a dominance by ion exchange: i.e., a slightly mineralized Ca2+–Mg2+–Cl− and a meteorically derived Ca2+–HCO3− fresh water facies. In the isotope bivariate plot, the samples plot to the right of the LMWL and slopes observed in pre (4.94) and post-monsoon (5.85) seasons are not as steep as the LMWL (7.95) and this warrants the suggestion that meteoric water is the major source that replenishes the dynamic groundwater resource in the study area after being subjected to evaporation. The negative d-excess values (< 0) and enrichment of the δ18O ratio observed at some locations suggests a non-equilibrium process and a “mechanism of mixing”. A noteworthy fact is that isotopically river water is in tandem with the mine water samples for both seasons and testifies to a hydraulic connectivity between Hasdeo River water and mine water through a major fault. It is substantiated by mine inflows assessed by the sump test for Kusmunda and Gevra, which is two times higher than the predicted values by Darcy’s law. The wide variation in the isotopic composition is attributed to different vapor sources viz., southwest monsoon (SW) that originates in the Arabian Sea and locally driven air moisture from surface water bodies.