Groundwater Flow In Aquifers Research Articles

Comparison between downdip and updip groundwater flow on early CO2 migration in dipping storage aquifers

The impact of the aquifer dip angle and groundwater flow have been investigated in the field of carbon dioxide (CO2) storage efficiency and security. However, no consideration has been given to the significance of the direction of groundwater flow in aquifers on the CO2 plume migration and the storage performance. In this study, we analyse the effect of the direction of groundwater flow on CO2 plume migration in the subsurface, implementing a numerical modelling approach. We compare the early plume migration in storage aquifers of various dip angles when the groundwater flows downdip with when it flows updip. We estimate the injected plume size, and the instantaneous velocity of the leading tip of the plume. When the groundwater flows downdip, against the direction of CO2 plume migration, the plume becomes more stretched, its greater extent and thus height causing it to accelerate during its updip migration due to the increase in buoyancy. By contrast, the plume decelerates over time when groundwater flows updip. This is because of a decrease in the size of the mobile CO2 plume due to enhanced residual and dissolution trapping at its trailing edge, reducing buoyancy, and hence decreasing the risk of CO2 leakage during its early migration.

Exact simulation of the groundwater flow in anisotropic confined aquifer near time-varying streams by comprehensive new analytical solutions

This paper presents some new analytical solutions to an accurate prediction of the behavior of the groundwater flow in aquifers in response to changes in surface water. The new analytical solutions are obtained using integral transforms. An anisotropic rectangular confined aquifer bounded with four time-varying streams is undertaken. The effects of anisotropy on groundwater head and flow rate near time-varying streams are investigated. Depending on the change rates of the streams level, an anisotropic aquifer may render either lower or higher hydraulic head than an isotropic aquifer. In addition, an anisotropic aquifer has provided less water exchange at the interfaces than an isotropic one. The sensitivity of the hydraulic head to change rate of the streams level in both isotropic and anisotropic aquifers is evaluated. It is shown that the aquifer response is more sensitive to change rate of the streams parallel to y-direction and less sensitive to change rate of the streams parallel to x-direction in an anisotropic aquifer and vice versa in an isotropic aquifer. The results of the present new analytical solutions are compared with numerical model of MODFLOW. The results obtained from the presented solutions showed good agreement with the results of MODFLOW. The results show that the presented new analytical solutions are accurate, robust and efficient. Therefore, the results indicate that the presented new analytical solutions are very effective in the simulation of the groundwater flow in river–aquifer systems. Furthermore, one of the advantages of the new analytical solutions is to investigate the sensitivity analysis of aquifer parameters, which has been carried out in this paper. Also, some other new analytical solutions for steady-state conditions and sudden fall in streams level are provided as well. Feasibility of the proposed new analytical solutions is presented via calculating and simulating the hydraulics of groundwater flow in river–aquifer systems by means of integral transforms.

Calibration of Hydrodynamic Models of Groundwater Flow in Aquifers Polluted by Liquid Radioactive Waste

Pollution of aquifers by liquid radioactive waste is especially hazardous due to high permeability of aquifer rocks. Pollution can take place as a result of deep injection disposal of liquid waste or due to its leakage from a surface reservoir. The ecological hazard depends on distribution of aquifer permeability, which can be highly heterogeneous. The only source of data for determination of such distribution is measurements in exploratory boreholes at the polluted site. A technique is proposed for determination of spatial distribution of aquifer transmissibility on the basis of hydrological measurements in a limited number of boreholes. The problem is reduced to a minimization problem which was solved numerically.

Time‐Fractional Flow Equations (t‐FFEs) to Upscale Transient Groundwater Flow Characterized by Temporally Non‐Darcian Flow Due to Medium Heterogeneity

AbstractUpscaling groundwater flow is a fundamental challenge in hydrogeology. This study proposed time‐fractional flow equations (t‐FFEs) for upscaling long‐term, transient groundwater flow and propagation of pressure heads in heterogeneous media. Monte Carlo simulations showed that, with increasing variance and correlation of the hydraulic conductivity (K), flow dynamics gradually deviated from Darcian flow and exhibit sub‐diffusive, time‐dependent evolution which can be separated into three major stages. At the early stage, the interconnected high‐K zones dominated flow, while at intermediate times, the transverse flow due to mixed high‐ and low‐K zones caused delayed rise of the piezometric head. At late times when flow in the relatively high‐K domains reached stability, cells with very low‐K continued to block the entry of water and generate “islands” with low piezometric head, significantly extending the temporal evolution of the piezometric head. The elongated water breakthrough curve cannot be quantified by the flow equation with an effective K, the space‐fractional flow equation, or the multi‐rate mass transfer (MRMT) flow model with a few rates, motivating the development of t‐FFEs assuming temporally non‐Darcian flow. Model applications showed that both the early and intermediate stages of flow dynamics can be captured by a single‐index t‐FFE (whose index is the exponent of the power‐law probability density function of the random operational time for water parcels), but the overall evolution of flow dynamics, especially the enhanced retention of flow at later times, required a distributed‐order t‐FFE with variable indexes for different flow phases that can dominate flow dynamics at different stages. Therefore, transient groundwater flow in aquifers with spatially stationary heterogeneity can be temporally non‐Darcian and non‐stationary, due to the time‐sensitive, combined effects of interconnected high‐K channels and isolated low‐K deposits on flow dynamics (which is the hydrogeological mechanism for the temporally non‐Darcian flow and sub‐diffusive pressure propagation), whose long‐term behavior can be quantified by multi‐index stochastic models.

Stochastic nitrate simulation under hydraulic conductivity uncertainty of an agricultural basin aquifer at Eastern Thessaly, Greece.

Lake Karla Watershed is an agricultural basin characterized by intense agricultural activities, which lead to quantitative and qualitative aquifer degradation. The exploitation of non-renewable groundwater resources and nitrate contamination are the major threats to aquifer sustainability. Groundwater resources cover mainly irrigation and domestic water needs. Hence, the simulation of groundwater resources is necessary to (a) determine the quantity available for water supply and (b) estimate probable nitrate contamination to propose subsequent remediation techniques to protect public health. Furthermore, the aquifer's heterogeneity as well as the lack of hydraulic conductivity data, in a large-scale study area, creates uncertainty regarding groundwater flow and nitrate transport simulation. Deterministic modelling approaches for spatially distributed nitrate concentration simulation could not estimate the contamination risk, since it can address only one realization of the aquifer. This study estimates the effect of hydraulic conductivity uncertainty on the simulation of groundwater nitrate concentration. The proposed framework uses Geostatistical Sequential Gaussian Simulation (SGSIM) for the generation of equally probable realizations of the spatial distribution of hydraulic conductivity. It includes the application of a modelling system based on the following inter-linked models: a rainfall-runoff model, a reservoir operation model, a lake-aquifer interaction model, a groundwater flow model, and a nitrate transport and dispersion model. The last two models simulate the multiple realizations of aquifer's groundwater flow and nitrate concentration. Furthermore, two analyses (a statistical and a threshold analysis) are employed to estimate the exceedance probability of the nitrate concentrations and their spatial extent. The results indicate that hydraulic conductivity uncertainty does affect the simulation of nitrate concentration and that nitrate concentrations will most probably exceed the thresholds in areas where groundwater is extracted for domestic use.

General analytical solutions of groundwater flow toward multi-dimensional sources/sinks in a confined aquifer with leakage and distributed recharge

A variety of hydrogeologic conditions and parameters play roles in obtaining analytical solutions for groundwater flow in aquifers. Changes of these influencing conditions typically require finding a new solution. Therefore, it is very useful if a general approach and solution can be provided to conveniently construct the solutions corresponding to the condition changes. In this study, two general analytical solutions for multi-dimensional groundwater flow in homogeneous, confined aquifers are derived using Green’s function method for instantaneous and continuous sources/sinks. A library of analytical solutions can be readily obtained by combining the general solutions with directional solutions for a variety of hydrogeologic and geometric conditions. The aquifer can be one-, two-, or three-dimensional and vertically and horizontally finite, semi-infinite, or infinite. The geometry of sources/sinks can be point, line, areal, and volumetric. Leakage from adjacent aquifers and distributed precipitation recharge are also included. The general solutions are validated by reported analytical solutions. A series of typical solutions for one-, two-, and three-dimensional groundwater flow are presented. A computational example is provided to compare the drawdown distributions caused by point, vertical line, vertical areal, and volumetric sinks. A field investigation and design at a groundwater-contaminated site using the derived analytical solution suggests that drainage slots (vertical areal sinks) can be an effective alternative to pumping wells (vertical line sinks) in lowering the groundwater level for a shallow aquifer.

Fractional governing equations of transient groundwater flow in unconfined aquifers with multi-fractional dimensions in fractional time

Abstract. In this study, a dimensionally consistent governing equation of transient unconfined groundwater flow in fractional time and multi-fractional space is developed. First, a fractional continuity equation for transient unconfined groundwater flow is developed in fractional time and space. For the equation of groundwater motion within a multi-fractional multidimensional unconfined aquifer, a previously developed dimensionally consistent equation for water flux in unsaturated/saturated porous media is combined with the Dupuit approximation to obtain an equation for groundwater motion in multi-fractional space in unconfined aquifers. Combining the fractional continuity and groundwater motion equations, the fractional governing equation of transient unconfined aquifer flow is then obtained. Finally, two numerical applications to unconfined aquifer groundwater flow are presented to show the skills of the proposed fractional governing equation. As shown in one of the numerical applications, the newly developed governing equation can produce heavy-tailed recession behavior in unconfined aquifer discharges.

Fractional governing equations of transient groundwater flow in confined aquifers with multi-fractional dimensions in fractional time

Abstract. Using fractional calculus, a dimensionally consistent governing equation of transient, saturated groundwater flow in fractional time in a multi-fractional confined aquifer is developed. First, a dimensionally consistent continuity equation for transient saturated groundwater flow in fractional time and in a multi-fractional, multidimensional confined aquifer is developed. For the equation of water flux within a multi-fractional multidimensional confined aquifer, a dimensionally consistent equation is also developed. The governing equation of transient saturated groundwater flow in a multi-fractional, multidimensional confined aquifer in fractional time is then obtained by combining the fractional continuity and water flux equations. To illustrate the capability of the proposed governing equation of groundwater flow in a confined aquifer, a numerical application of the fractional governing equation to a confined aquifer groundwater flow problem was also performed.

Hydrodynamic Modeling of the Albian Aquifer of the Plain of Ain Oussera (Semi-Arid Area, Algeria)

The Ain Oussera plain, a semi-arid zone in the central part of northern Algeria, has developed significantly since the early 2000 years when a number of agricultural development programs were launched. The increase in irrigated areas has led to a significant increase in water needs and consequently an overexploitation of the aquifer that has been observed over more than 30 years (1985). A significant decrease in its piezometric level caused its deterioration in the chemical quality of its water.This paper is a contribution about the effective management of groundwater in the area of study, using a mathematical model of the water potential and its quality preservation. In this regard, we have established a conceptual model using the MODFLOW computer program to provide us with a deterministic and twodimensional numerical simulation, in steady and transient state, of the studied aquifer groundwater flow. The main results allowed us to develop a better view of the different scenarios underlying the piezometric fluctuations. The predictions show that the water table is in an alarming state which requires integrated management of its underground resources in order to guarantee sustainable development.

Systemic Approach for the Capacity Expansion of Multisource Water-Supply Systems under Uncertainty

AbstractIncreased demand, reduced supply, or the imposition of new regulations might evince the physical limitations of the current infrastructure of a water-supply system and force structural intervention. The problem consists of determining capacity expansion solutions for multisource water-supply systems from a long-term perspective, with some representation of the uncertainty that can be involved and the risk-averse behavior of the decision makers. The systemic approach proposed includes a detailed simulation of physical processes, such as the water storage in surface reservoirs, the groundwater flow in aquifers, and the water transport, with explicit representation of water quality. Water quality is a crucial element in multisource systems because the quality of the source water often varies. Different capacity expansion solutions can be obtained that explicitly balance the trade­offs between the gains in system performance and the cost of the solution. The application of the systemic approach develo...

Modeling of a Contaminant Plume in a Tidally Influenced River Using Domenico’s Equation

Currently, the mathematical code Modflow is widely used to simulate groundwater flow in aquifers. Due to the ease which exists today to create mathematical models through Modflow visual Interfaces, it is possible to obtain contamiant transport results which may not have much support, especially when simulating the transport of contaminants with little groundwater flow information. Domenico’s equation is an analytical solution for transport of contaminants in groundwater that can be used when not much groundwater flow information exists. The objective of this study is to model, using Domenico’s equation, a groundwater contaminant plume that discharges into a tidally influenced river. The study area was a wood treatment facility located on the bank of a river which is influenced by tides. Previous studies have found the presence of creosote in the subsurface and the formation of a groundwater plume that apparently discharges into the river. Domenico’s equation was selected to model this site because of the limited piezometric data available at the site to properly simulate the daily hydraulic gradient inversion due to the river tides. Domenico’s equation was successfully used to model this plume and reproduce the field distribution of naphthalene, benzene and 1-methyl-naphthalene. Two sources 40 minland had to be defined to properly simulate the plume behavior. It was determined through modeling that biodegradation plays an important role on the plume’s behavior. These were key issues in the conceptual model understanding of the plume at this site.

Barrier effect of underground structures on aquifers

Impervious structures below the water table modify the natural groundwater flow in aquifers. They act as barriers, causing heads to rise upgradient and to fall downgradient. We define the barrier effect as the increase in head loss across the barrier with respect to the natural conditions prior to construction. We distinguish between regional (the minimum head loss observed at long distances) and local (the maximum head loss observed close to the structure) barrier effects. We use numerical and analytical methods to derive semi-empirical equations to quantify the two barrier effects for semi-permeable, partially penetrating (or fully penetrating but finite in length), and barriers with a by-pass in confined aquifers. The resulting equations depend on the barrier geometry and on the natural head gradient in the aquifer and they are easy to apply. We test their validity at two construction sites, obtaining excellent agreement between the computed and observed barrier effects.

Thermal performance of borehole heat exchangers in different aquifers: a case study from Shouguang

Groundwater flow plays an important role in affecting the thermal performance of borehole heat exchangers (BHEs). In the present work, a few field tests are conducted in Shouguang, China, to compare the thermal performance of three BHEs in different aquifers. The results show that there is a good linear correlation between the heat transfer rate of BHEs at steady state and the average fluid temperature. A larger slope usually means a higher heat transfer rate of a BHE, under the same borehole conditions. The thermal performance of BHEs is extremely enhanced, especially in those regions with multiple aquifers, and even the thermal response test results can be enlarged to a great extent by groundwater flow. The enhanced effect of groundwater flow depends mainly on the amount, thickness and depth of aquifers. It is found that when the depth of aquifers covers the middle or lower part of BHEs, at least exceeding the depth of the constant temperature ground layer, the enhancement on the thermal performance of BHEs becomes more intense due to the increase of the heat transfer temperature difference and the decrease of the total thermal resistance from the inner fluid to the surrounding ground. Groundwater flow in aquifers is helpful to reduce the required length of BHEs and the construction cost of ground source heat pump systems. Copyright , Oxford University Press.

Permeability mapping in porous media by magnetization prepared centric-scan SPRITE

The ability of porous media to transmit fluids is commonly referred to as permeability. The concept of permeability is central for hydrocarbon recovery from petroleum reservoirs and for studies of groundwater flow in aquifers. Spatially resolved measurements of permeability are of great significance for fluid dynamics studies. A convenient concept of local Darcy’s law is suggested for parallel flow systems. The product of porosity and mean velocity images in the plane across the average flow direction is directly proportional to permeability. Single Point Ramped Imaging with T 1 Enhancement (SPRITE) permits reliable quantification of local fluid content and flow in porous media. It is particularly advantageous for reservoir rocks characterized by fast magnetic relaxation of a saturating fluid. Velocity encoding using the Cotts pulsed field gradient scheme improves the accuracy of measured flow parameters. The method is illustrated through measurements of 2D permeability maps in a capillary bundle, glass bead packs and composite sandstone samples.

The generation of 2-D random velocity fields of groundwater flows via stream functions

This paper is a further development of former papers of the authors on the direct simulation of random velocity fields describing groundwater flow in aquifers of spatially variable, but stochastically homogeneous hydraulic conductivity. We use the so-called dual description of groundwater flow by means of stream functions. Further assumptions are therefore steady state flow, far boundaries and no sources and sinks. By a perturbation approach we get a first-order approximation of the spectra of the random stream function and the random velocity field. The generation of random velocity fields via stream functions is attractive because of its parsimony in the use of parameters. Only a scalar random field must be generated. Again we adopt Mikhailov's method of “partitioning and randomizing the spectrum” for the simulation of a homogeneous Gaussian field. We also tackle the problem of conditional simulation of random velocity fields honoring measured velocity values at several locations. The generation method is illustrated by a comparison of empirical and theoretical spectra.

Postaudit evaluation of conceptual model uncertainty for a glacial aquifer groundwater flow and contaminant transport model

Numerical groundwater flow and contaminant transport modeling incorporating three alternative conceptual models was conducted in 2005 to assess remedial actions and predict contaminant concentrations in an unconfined glacial aquifer located in Milford, Michigan, USA. Three alternative conceptual models were constructed and independently calibrated to evaluate uncertainty in the geometry of an aquitard underlying the aquifer and the extent to which infiltration from two manmade surface water bodies influenced the groundwater flow field. Contaminant transport for benzene, cis-DCE, and MTBE was modeled for a 5-year period that included a 2-year history match from July 2003 to May 2005 and predictions for a 3-year period ending in July 2008. A postaudit of model performance indicates that predictions for pumping wells, which integrated the transport signal across multiple model layers, were reliable but unable to differentiate between alternative conceptual model responses. In contrast, predictions for individual monitoring wells with limited screened intervals were less consistent, but held promise for evaluating alternative hydrogeologic models. Results of this study suggest that model conceptualization can have important practical implications for the delineation of contaminant transport pathways using monitoring wells, but may exert less influence on integrated predictions for pumping wells screened over multiple numerical model layers.

同位体・希ガストレーサによる地下水研究の現状と新展開

Environmental tracers become a common tool for the groundwater study and a number of methods have been presented in order to understand groundwater flow processes, water budget, origins, chemical reaction processes and retention time. Tracers often used are selected and reviewed for their various methods and advantages as follows; 1) stable 18O, D in water, 2) stable 13C and radioactive 14C in DIC, 3) noble gases such as He, Ne, Ar, Kr, Xe and their isotopes, 4) radioactive 36Cl in dissolved chloride and some heavier isotopes, and 5) inert gaseous species such as CFCs.If they are less reactive species, they likely preserve information at the time of recharge or their origin. Use of D, 18O and the d-value of water is the powerful tool to determine the recharge area because recharged meteoric water have their inherent isotopic ratios correlated with the recharge elevation, distance from the coast, or the local topography. Carbon-bearing species are more reactive though, use of stable isotopes of DIC leads to identify its origin and helps to analyze the chemical reaction between minerals and water or gas addition processes during the groundwater flow in aquifers. Radioactive 14C has been used to estimate groundwater age however special attention should be paid for, i.e., the origin of DIC, before applying the method. Noble gas tracers are the useful species to presume recharge temperature from their concentrations in water using their temperature dependence of solubilities. Radiogenic 4He concentration can be used for the very long-term groundwater dating since the 4He is produced in the crust and is accumulated in the deep aquifers, if the local accumulation rate of 4He is known. Radioactive 36Cl has been used to determine the age of very old saline waters up to million years. This isotope will also be convenient for the dating of very younger waters, by the use of bomb-produced 36Cl resulted from surface nuclear experiments near the seawater in the 1950s. Chlorofluorocarbons (CFCs) are the gas species produced by the recent human activity and dissolve in water during the recharge, therefore, the affected younger groundwater will have equivalent CFCs concentrations with the atmospheric CFCs concentrations at the time of the recharge. As these species are easy to detect with very high sensitivity, this tracer has now been applied not only for the age determination but for the mixing or contamination of shallow young water to a deep old groundwater. As an individual method listed above is valid only for the very simple flow system, appropriate assumptions or coupling of using different tracers is necessary to understand natural complex groundwater flow system where mixing of groundwaters of different origin or age occurs. Combination of tracers helps us simulating the complex system in detail and is being a growing trend in groundwater study.

Combination of Tank Model and 3-D Unconfined Groundwater Flow (GWF) Simulation in Tropical Floodplain, THAILAND

Thailand is located in a tropical, monsoonal area and is one of the world's top five rice producing countries. However, Thailand's paddy fields in floodplains often have flood problems, and those that require extraction of groundwater for cultivation face problems of the fall of groundwater levels due to over-pumping. The modeling of the 3-D unconfined aquifer groundwater flow (GWF) in tropical floodplains with quaternary sediments such as Phichit floodplain in Thailand is rather complex for several factors concerning the input data. Complicated recharges are caused by floods, river water, rainwater, water held in rice fields, agriculture ponds, and commercial sandpits. This paper presents an estimated recharge rate by the Thiessen polygon tank model with the use of field observation data and the application of the Visual MODFLOW program for the 3-D unconfined aquifer groundwater flow simulation. The simulated groundwater level appears to be in accordance with the observed values with the exception of a few certain locations. In addition, the simulation results indicate that in tropical floodplains, floodwater recharge is the main income of unconfined groundwater.

Steepness expansion for free surface flows in coastal aquifers

Free surface flow of groundwater in aquifers has been studied since the early 1960s. Previous investigations have been based on the Boussinesq equation, derived from the non-linear kinematic boundary condition. In fact, the Boussinesq equation is the zeroth-order equation in the shallow-water expansion. A key assumption in this expansion is that the mean thickness of the aquifer is small compared with a reference length, normally taken to be the linear decay length. In this study, we re-examine the expansion scheme for free surface groundwater flows, and propose a new expansion wherein the shallow-water assumption is replaced by a steepness assumption. A comparison with experimental data shows that the new model provides a better prediction of water table levels than the conventional shallow-water expansion. The applicable ranges of the two expansions are exhibited.

Application of spectral analysis to determine hydraulic diffusivity of a sandy aquifer (Pingtung County, Taiwan)

AbstractThe study demonstrates spectral relationships in the time–frequency domain for one‐dimensional groundwater flow in aquifers bounded by fluctuating boundaries. By nature, the solutions of spectral equations are non‐linear complex functions. To determine hydraulic diffusivity in the governing equations, it is required that the data are collected from the spectra of water levels at the fluctuating boundaries and observation wells. Hydraulic diffusivity thus can be obtained by an iterative inverse approach. This paper presents an application in Pingtung County of Taiwan to determine the hydraulic diffusivity of a sandy aquifer under confined conditions. Spectral density function of water level obtained from tidal boundaries and observation wells are used to approximate hydraulic diffusivity, which yields an averaged value of 1·26 × 106 m2/h. Copyright © 2004 John Wiley & Sons, Ltd.