Groundwater Hydraulics Research Articles

Remember Groundwater Flow

Groundwater flow is governed by groundwater hydraulics and is key to understanding the subsurface migration of groundwater, dissolved contaminants, and emplaced injection fluids. Yet groundwater flow appears to be largely forgotten or ignored in many subsurface injection-based remedial studies. Over the past decade, numerous studies of subsurface injection technologies (in situ oxidation, enhanced biodegradation, etc.) have been presented at conferences and published as peer-reviewed papers. These studies discuss the effectiveness of these remediation technologies and present chemical and biological data to support their results. However, rarely do these studies consider the impact of groundwater flow on data interpretation and their results. Often the studies do not even provide basic information on groundwater seepage velocities. I recently read a professional paper, an in situ oxidation (ISCO) study, that prompted me to write this editorial. I will use this unnamed study as an example, but I could equally use one of numerous other studies as an example. This ISCO study showed reductions in contaminant concentrations with some rebound and, in many respects, was well designed and well documented. The groundwater seepage velocity was reported to be about 46 ft/year. Three ISCO injection events were completed, during a period of about 9 months, at the source and at other injection locations extending about 30 ft downgradient from the source. The monitoring network consisted of three transects of discrete monitoring wells located 15, 45, and 75 ft downgradient from the source injection location. Evaluations of the effectiveness of the injections were completed based on a groundwater sampling event 3 months after the last injection. A final groundwater sampling event, which occurred 11 months after the last injection event, was used to evaluate rebound. Do you see what troubles me here? Consider this ISCO study and assume idealized horizontal groundwater flow while disregarding aquifer heterogeneity that complicates groundwater flow. Based on the distances of the monitoring transects (15, 45, and 75 ft downgradient) and the groundwater seepage velocity (46 ft/year), it would take approximately 119 (almost 4 months), 357, and 595 days for the injected ISCO fluid from the source injection to flow past the three monitoring transects, respectively. Yet this ISCO study evaluated the results and effectiveness of the ISCO injections based on groundwater samples collected 3 months after the last injection, before the injected fluid had migrated past the closest monitoring well transect. During the final sampling event, 11 months postinjection, the injected fluid would be expected to be found around two of the three well transects under these idealized groundwater flow conditions. The real world is not homogeneous and isotropic. Heterogeneity can result in varying migration rates for injected fluid and can affect the composition of well samples. Injected fluids in higher permeable zones will flow past downgradient monitoring wells faster than injected fluids in lower permeable zones. Groundwater samples reflect a combination of groundwater from the different permeability zones intersected by the well. If a groundwater sample is collected from a well that intersects both a higher permeable zone, where the original contaminated groundwater has displaced the injected fluid, and a lower permeable zone, which still has the noncontaminated injected fluid, the resulting groundwater sample would reflect a mixture of groundwater from these two zones. If, for example, 70% of the sample water comes from the higher permeable zone and 30% of the sample water comes from the lower permeable zone, the resulting groundwater sample would indicate a contaminant concentration 30% lower than the original groundwater contaminant concentration. This could be interpreted to suggest that the postinjection groundwater concentrations had declined by 30%. Groundwater flow needs to be understood and specifically addressed during studies of injection-based in situ remediation because groundwater flow is key to understanding the subsurface migration of groundwater and emplaced injection fluids. The characterization and heterogeneity of groundwater flow need to be integral to the design, data collection, and data interpretation of injection-based remedial studies if we wish to truly understand the effectiveness of our in situ injection remedial technologies. Therefore, for the design, implementation, interpretation, and presentation of studies involving injection based in situ remedial technologies, remember groundwater flow. Guy Swenson, BA, MS, Marcellus, NY; [email protected]

Submarine Groundwater Discharge in the Coastal Zone

Indonesia is one of the archipelagic countries that has the longest coastline in the world. Because it is located in the tropics, in general it has a very high rainfall. Each island has a different morphology which is composed of a variety of rocks with different hydrogeological properties. This natural condition allows for the presence of groundwater in different amount in each island. The difference in groundwater hydraulics gradients in aquifer continuous to the sea has triggered the discharge of groundwater to offshore known as submarine groundwater discharge (SGD). Its presence can be as seepage or submarine springs with components derived from land and sea and a mixture between them. The understanding of SGD phenomenon is very important because it can be useful as a source of clean water in coastal areas, affecting marine health, and improving marine environment.

Analytical Solution of Seepage Field in Karst Tunnel

An analytical solution for the seepage field in water‐filled karst tunnel is derived based on the inversion of complex function and groundwater hydraulics theory. The solution considers the distance between the tunnel and the cavern, the size of the cavern, and the properties of the lining structure, such as the permeability coefficient as well as the radius of the grouting ring. This paper also performed numerical simulations for two cases: the application of gravity and the absence of gravity. The numerical solution was obtained to verify the analytical solution, and a good agreement was found. Then, the effect of parameters is discussed in detail, including the distance between the tunnel and the cavern, the radius of the cavern, the grouting ring, and the initial support. The results show that when the radius of the cavern is constant, the pressure head and seepage flow decrease as the distance between the tunnel and the cavern increases. When the distance is constant, the pressure head and seepage flow increase with the increase of the radius of the cavern. In addition, the pressure head and the seepage flow decrease with the increase of the thickness of the grouting ring and decrease with the decrease of the permeability coefficient. As the thickness of the initial support increases, the pressure head gradually increases and the percolation decreases. Furthermore, due to the great influence of the grouting ring and initial support on the pressure head and seepage flow, the thickness and permeability coefficient of the grouting ring and initial support should be taken into account carefully during construction.

3D numerical modelling of the thermal state of deep geological nuclear waste repositories

One of the important aspects of the high-level radioactive waste (HLW) disposal in deep geological repositories is ensuring the integrity of the engineered barriers which is, among other phenomena, considerably influenced by the thermal loads. As the HLW produce significant amount of heat, the design of the repository should maintain the balance between the cost-effectiveness of the construction and the sufficiency of the safety margins, including those imposed on the thermal conditions of the barriers. The 3D finite-element computer code FENIA was developed as a tool for simulation of thermal processes in deep geological repositories. Further the models for mechanical phenomena and groundwater hydraulics will be added resulting in a fully coupled thermo-hydro-mechanical (THM) solution. The long-term simulations of the thermal state were performed for two possible layouts of the repository. One was based on the proposed project of Russian repository, and another features larger HLW amount within the same space. The obtained results describe the spatial and temporal evolution of the temperature filed inside the repository and in the surrounding rock for 3500 years. These results show that practically all generated heat was ultimately absorbed by the host rock without any significant temperature increase. Still in the short time span even in case of smaller amount of the HLW the temperature maximum exceeds 100 °C, and for larger amount of the HLW the local temperature remains above 100 °C for considerable time. Thus, the substantiation of the long-term stability of the repository would require an extensive study of the materials properties and behaviour in order to remove the excessive conservatism from the simulations and to reduce the uncertainty of the input data.

Detecting inter-aquifer leakage in areas with limited data using hydraulics and multiple environmental tracers, including 4He, 36Cl/Cl, 14C and 87Sr/86Sr

The investigation of regionally extensive groundwater systems in remote areas is hindered by a shortage of data due to a sparse observation network, which limits our understanding of the hydrogeological processes in arid regions. The study used a multidisciplinary approach to determine hydraulic connectivity between the Great Artesian Basin (GAB) and the underlying Arckaringa Basin in the desert region of Central Australia. In order to manage the impacts of groundwater abstraction from the Arckaringa Basin, it is vital to understand its connectivity with the GAB (upper aquifer), as the latter supports local pastoral stations and groundwater-dependent springs with unique endemic flora and fauna. The study is based on the collation of available geological information, a detailed analysis of hydraulic data, and data on environmental tracers. Enhanced inter-aquifer leakage in the centre of the study area was identified, as well as recharge to the GAB from ephemeral rivers and waterholes. Throughout the rest of the study area, inter-aquifer leakage is likely controlled by diffuse inter-aquifer leakage, but the coarse spatial resolution means that the presence of additional enhanced inter-aquifer leakage sites cannot be excluded. This study makes the case that a multi-tracer approach along with groundwater hydraulics and geology provides a tool-set to investigate enhanced inter-aquifer leakage even in a groundwater basin with a paucity of data. A particular problem encountered in this study was the ambiguous interpretation of different age tracers, which is attributed to diffusive transport across flow paths caused by low recharge rates.

A Foundation for Modeling Time-Periodic Groundwater Flow

The authors of a new book on groundwater hydraulics and hydrology describe a theoretical foundation for modeling time-periodic groundwater flow.

Debates—Stochastic subsurface hydrology from theory to practice: A geologic perspective

AbstractA geologic perspective on stochastic subsurface hydrology offers insights on representativeness of prominent field experiments and their general relevance to other hydrogeologic settings. Although the gains in understanding afforded by some 30 years of research in stochastic hydrogeology have been important and even essential, adoption of the technologies and insights by practitioners has been limited, due in part to a lack of geologic context in both the field and theoretical studies. In general, unintentional, biased sampling of hydraulic conductivity (K) using mainly hydrologic, well‐based methods has resulted in the tacit assumption by many in the community that the subsurface is much less heterogeneous than in reality. Origins of the bias range from perspectives that are limited by scale and the separation of disciplines (geology, soils, aquifer hydrology, groundwater hydraulics, etc.). Consequences include a misfit between stochastic hydrogeology research results and the needs of, for example, practitioners who are dealing with local plume site cleanup that is often severely hampered by very low velocities in the very aquitard facies that are commonly overlooked or missing from low‐variance stochastic models or theories. We suggest that answers to many of the problems exposed by stochastic hydrogeology research can be found through greater geologic integration into the analyses, including the recognition of not only the nearly ubiquitously high variances of K but also the strong tendency for the good connectivity of the high‐K facies when spatially persistent geologic unconformities are absent. We further suggest that although such integration may appear to make the contaminant transport problem more complex, expensive and intractable, it may in fact lead to greater simplification and more reliable, less expensive site characterizations and models.

Using environmental isotopes and dissolved methane concentrations to constrain hydrochemical processes and inter-aquifer mixing in the Galilee and Eromanga Basins, Great Artesian Basin, Australia

Summary Groundwater recharge processes, water–rock interaction and the hydraulic connectivity between aquifers of the Galilee and Eromanga Basins in central Queensland, Australia, were investigated using stable (δ 2 H, δ 18 O, δ 13 C and 87 Sr/ 86 Sr) and radiogenic ( 36 Cl) isotopes and dissolved methane concentrations, complemented by major ion chemistry. The central Eromanga and the upper sequence of the Galilee basins are both sub-basins of the Great Artesian Basin (GAB), and the coal seams of the Galilee Basin are currently explored for their potential as commercial coal seam gas deposits. In order to understand the potential influence of depressurisation of coal seams required to release the gas on adjacent aquifers, a detailed understanding of recharge processes and groundwater hydraulics of these basins prior to any development is required. Each of the different isotope systems were used in this study to provide different information on specific processes. For example, the assessment of δ 13 C and 87 Sr/ 86 Sr ratios suggested that carbonate dissolution is one of the major processes controlling the water chemistry within some aquifers. In addition, the combined assessment of δ 2 H, δ 18 O and major ion chemistry indicates that transpiration is the primary process controlling the solute concentration in the GAB recharge area, whereas evaporation appears to be less significant. Groundwaters in the Galilee Basin recharge area (outside the limits of the GAB) are different to any groundwater within the GAB units. This difference is attributed to the dissolution of potassium-bearing micas, which are absent in the GAB. Groundwater age estimates based on 36 Cl/Cl ratios suggest that there is a steady increase along the flow paths, and this lack of anomalous age estimates from the recharge areas to the deeper parts of the basin indicates that there is no evidence for regional inter-aquifer mixing based in isotopes only. However, dissolved methane concentrations and groundwater chemistry near faults indicates the potential mix of gas and/or water from the coal seams into the GAB groundwaters, suggesting that there may be local influence of faults as gas/water conduits.

Sea-level rise impacts on seawater intrusion in coastal aquifers: Review and integration

Summary Sea-level rise (SLR) influences groundwater hydraulics and in particular seawater intrusion (SWI) in many coastal aquifers. The quantification of the combined and relative impacts of influential factors on SWI has not previously been considered in coastal aquifers. In the present study, a systematic review of the available literature on this topic is first provided. Then, the potential remaining challenges are scrutinized. Open questions on the effects of more realistic complexities such as gradual SLR, parameter uncertainties, and the associated influences in decision-making models are issues requiring further investigation. We assess and quantify the seawater toe location under the impacts of SLR in combination with recharge rate variations, land-surface inundation (LSI) due to SLR, aquifer bed slope variation, and changing landward boundary conditions (LWBCs). This is the first study to include all of these factors in a single analysis framework. Both analytical and numerical models are used for these sensitivity assessments. It is demonstrated that (1) LSI caused by SLR has a significant incremental impact on the seawater toe location, especially in the flatter coasts and the flux-controlled (FC) LWBCs, however this impact is less than the reported orders of magnitude differences which were estimated using only analytical solutions; (2) LWBCs significantly influence the SLR impacts under almost all conditions considered in this study; (3) The main controlling factors of seawater toe location are the magnitudes of fresh groundwater discharge to sea and recharge rate. Regional freshwater flux entering from the landward boundary and the groundwater hydraulic gradient are the major contributors of fresh groundwater discharge to sea for both FC and head-controlled (HC) systems, respectively; (4) A larger response of the aquifer and larger seawater toe location changes are demonstrable for a larger ratio of the aquifer thickness to the aquifer length particularly in the HC systems; (5) The lowest sensitivity of seawater toe location is found for the density difference ratio of the seawater and freshwater, and also for the aquifer bed slope; (6) The early-time observations show seawater fingers below the inundated lands due to SLR which are diminished and ultimately extinguished; and (7) A less than 2% reversal effect on the seawater toe location after overshoot mechanism is observed in the transient simulations which suggests that this mechanism is an insignificant and impractical factor compared to other more significant factors.

On the transition of base flow recession from early stage to late stage

This paper is focused on the transition of base flow recession from early stage to late stage. The volume flow rate that takes place when such a transition occurs is identified for each of the twenty-three recession events observed at the Panola Mountain Research Watershed (PMRW) in Georgia, USA, using a newly developed cumulative regression analysis method. Meanwhile, the flow at the watershed outlet, which was recorded when the discharge at the perennial stream head diminishes to zero, is identified for each recession event. As evidenced by a correlation coefficient of 0.90, these two characteristic flows are found to be highly correlated, suggesting a fundamental linkage between the transition of base flow recession from early stage to late stage and the drying up of ephemeral streams. During the early stage, the contraction of ephemeral streams largely controls the recession behavior, whereas in the late stage when perennial streams dominate the flowing streams, the contraction of flowing streams is minimal and groundwater hydraulics governs the recession behavior.

Equivalent Porous Media (EPM) Simulation of Groundwater Hydraulics and Contaminant Transport in Karst Aquifers.

Karst aquifers have a high degree of heterogeneity and anisotropy in their geologic and hydrogeologic properties which makes predicting their behavior difficult. This paper evaluates the application of the Equivalent Porous Media (EPM) approach to simulate groundwater hydraulics and contaminant transport in karst aquifers using an example from the North Coast limestone aquifer system in Puerto Rico. The goal is to evaluate if the EPM approach, which approximates the karst features with a conceptualized, equivalent continuous medium, is feasible for an actual project, based on available data and the study scale and purpose. Existing National Oceanic Atmospheric Administration (NOAA) data and previous hydrogeological U. S. Geological Survey (USGS) studies were used to define the model input parameters. Hydraulic conductivity and specific yield were estimated using measured groundwater heads over the study area and further calibrated against continuous water level data of three USGS observation wells. The water-table fluctuation results indicate that the model can practically reflect the steady-state groundwater hydraulics (normalized RMSE of 12.4%) and long-term variability (normalized RMSE of 3.0%) at regional and intermediate scales and can be applied to predict future water table behavior under different hydrogeological conditions. The application of the EPM approach to simulate transport is limited because it does not directly consider possible irregular conduit flow pathways. However, the results from the present study suggest that the EPM approach is capable to reproduce the spreading of a TCE plume at intermediate scales with sufficient accuracy (normalized RMSE of 8.45%) for groundwater resources management and the planning of contamination mitigation strategies.

Book Review: “Hydraulic Conductivity—Issues, Determination and Applications”, L. Elango (ed.), InTech, Croatia

Hydraulic conductivity is probably the most important hydrogeological parameter, as it governs, along with other parameters, the flow of fluids and migration of contaminants beneath the ground surface, especially in soils and aquifers. There are already many books on broad aspects of hydrogeology and groundwater hydraulics that briefly review the determination of hydraulic conductivity. However, over the past several decades, due to the rapid development of science and technology and the ever-increasing groundwater extraction and contamination, many new theories, methodologies and applications regarding hydraulic conductivity have emerged. As a result, a book is needed to provide a useful collection of the current state of knowledge on the topic. Hydraulic Conductivity—Issues, Determination and Applications, edited by L. Elango (ISBN 978-953-307-288-3, 446p.) was recently published by InTech, an open access publisher based in Croatia (Elango 2011). Just 7 months before the publication of this book, another book entitled “Developments in Hydraulic Conductivity Research”, edited by Oagile Dikinya (2011), was published by the same publisher. Both these books report the latest advances of research within the hydraulic conductivity field of study and are worth reading, but the book by Elango (2011) is more extensive in content and has a more applied focus than the former one. It was published as open access, which enables everyone interested in this topic to read it free of charge, benefitting readers, authors, as well as science in general. Contributing authors come from around the world including Turkey, India, Brazil, Nigeria, Poland, Spain, USA, Iran, Germany, Canada, Mexico, Taiwan, Italy, France, Bolivia, Thailand and Australia. This book is organized into five clustered themes, and comprises a total of 21 chapters. A reference list is appended at the end of each chapter, which includes several recent references that allow readers to gain further information on specific topics. However, a shortcoming is the lack of an abstract for each chapter, thus readers are unable to get a quick glance at the main findings of each chapter. Environ. Process. (2014) 1:613–616 DOI 10.1007/s40710-014-0033-7

Hydrology and its role in water engineering

Hydrology is the basic science for water engineering, including a wide list of research topics ranging from atmospheric water and surface hydrology to groundwater hydraulics. To initiate the new publication period of the journal Ingenieria del Agua, we present here a brief review paper where the current state of research in many hydrologic fields is discussed. The aim of the paper is not to present a complete picture of current state-of-the-art research topics, but rather to provide a broad overview and stimulate new and innovative publication of Hydrology papers in the journal Ingenieria del Agua.

Hydraulic and thermal effects of in‐stream structure‐induced hyporheic exchange across a range of hydraulic conductivities

AbstractIn‐stream structure‐induced hyporheic exchange and associated thermal dynamics affect stream ecosystems. Their importance is controlled by spatial variability of sediment hydraulic conductivity (K). We calibrated a computational fluid dynamics (CFD) model of surface and groundwater hydraulics near a channel‐spanning weir (represents log dams, boulder weirs) to field data and varied K from 10−7 to 10−2 m/s (silt to gravel). Surface water stopped cresting the weir for K > 10−3 m/s. Non‐Darcy hyporheic flow was also prevalent for K > 10−3 m/s, and velocity errors using non‐CFD models ranged up to 32.2%. We also modeled weir‐induced heat transport during summer. As K increased from 10−7 to 10−3 m/s, weir‐induced hyporheic heat advection steadily increased. Cooling and buffering along hyporheic flow paths decreased with increasing K, particularly above K = 10−5 and 10−4 m/s, respectively. Vertical heat conduction between surface water and groundwater near the weir decreased with increasing K, particularly for K > 10−5 m/s. Conduction between hyporheic flow paths and adjacent groundwater helped cool hyporheic flow. Downstream surface water cooling by hyporheic advection increased steadily with K as increases in hyporheic flow overwhelmed decreases in cooling along hyporheic flow paths. Yet such effects were small (0.016°C) even at K = 10−3 m/s. The largest thermal effect of weir‐induced exchange was therefore spatial expansion of subsurface diel variability (particularly for K > 10−5 m/s) which affects benthic habitat and chemical reactions. The specific values of K where such trend shifts occur is likely variable among streams based on flow conditions, but we expect the presence of such trend shifts to be widespread.

Cauchy data requirement of the inverse problem of the mean age equation

AbstractA classical theoretical inverse problem in groundwater hydraulics is the calibration of a heterogeneous isotropic hydraulic conductivity field using known hydraulic head data at each point in the domain. It has been long known that a necessary condition for the uniqueness of the solution to this theoretical inverse problem is the Cauchy data, i.e., the hydraulic conductivity values (or, equivalently, flux) along a line crossing all streamtubes in the entire domain. This result has been cited in identifying the value of boundary flux data in practical inverse problems, although in general such data are generally not available. In this work, we show that groundwater mean age data replace this Cauchy data requirement.

Numerical simulation of a new two-dimensional variable-order fractional percolation equation in non-homogeneous porous media

Percolation flow problems are discussed in many research fields, such as seepage hydraulics, groundwater hydraulics, groundwater dynamics and fluid dynamics in porous media. Many physical processes appear to exhibit fractional-order behavior that may vary with time, or space, or space and time. The theory of pseudodifferential operators and equations has been used to deal with this situation. In this paper we use a fractional Darcy’s law with variable order Riemann–Liouville fractional derivatives; this leads to a new variable-order fractional percolation equation.In this paper, a new two-dimensional variable-order fractional percolation equation is considered. A new implicit numerical method and an alternating direct method for the two-dimensional variable-order fractional model is proposed. Consistency, stability and convergence of the implicit finite difference method are established. Finally, some numerical examples are given. The numerical results demonstrate the effectiveness of the methods. This technique can be used to simulate a three-dimensional variable-order fractional percolation equation.

A meshless solution for two dimensional density-driven groundwater flow

Abstract Density-driven groundwater flow is a complicated nonlinear problem in groundwater hydraulics. The local boundary integral method is a promising meshless scheme that is used for solving several difficult problems in different areas. This method applies the boundary integral equations to the local domain around every node. The nodes can be randomly distributed in the domain and on the global boundary. Therefore, this method is characterised as meshless. The unknown potentials and concentrations in all of the nodes are approximated by interpolation to obtain a system of linear equations. Solving this system of equations leads to the numerical solution for the main problem. In this paper, a combination of the radial basis function interpolation and the local boundary element method is used to solve groundwater flow problem combined with the transport of pollution, which also influences the density of groundwater.

Consolidation Settlement in Aquifers Caused by Pumping

AbstractEquations are derived to calculate one-dimensional (vertical) consolidation settlement in aquifers caused by groundwater extraction. The settlement equations capture the effect that the decline in pore-water pressure caused by groundwater extraction has on increased vertical effective stress. The settlement equations for single-layered confined or unconfined aquifers and multiple-layered aquifers are derived by linking the increase in vertical effective stress to the reduction of the void ratio using the reconstructed field consolidation curve of aquifer sediments. This paper’s approach blends groundwater hydraulics with the classical theory of one-dimensional consolidation widely used in geotechnical engineering. Closed-form consolidation settlement equations are presented for single-layer, homogeneous, isotropic confined aquifers with steady-state or transient groundwater flow and for single-layer, homogeneous, isotropic, unconfined aquifers under steady-state flow. The consolidation equations f...

Simulating MODFLOW‐Based Reactive Transport Under Radially Symmetric Flow Conditions

Radially symmetric flow and solute transport around point sources and sinks is an important specialized topic of groundwater hydraulics. Analysis of radial flow fields is routinely used to determine heads and flows in the vicinity of point sources or sinks. Increasingly, studies also consider solute transport, biogeochemical processes, and thermal changes that occur in the vicinity of point sources/sinks. Commonly, the analysis of hydraulic processes involves numerical or (semi-) analytical modeling methods. For the description of solute transport, analytical solutions are only available for the most basic transport phenomena. Solving advanced transport problems numerically is often associated with a significant computational burden. However, where axis-symmetry applies, computational cost can be decreased substantially in comparison with full three-dimensional (3D) solutions. In this study, we explore several techniques of simulating conservative and reactive transport within radial flow fields using MODFLOW as the flow simulator, based on its widespread use and ability to be coupled with multiple solute and reactive transport codes of different complexity. The selected transport simulators are MT3DMS and PHT3D. Computational efficiency and accuracy of the approaches are evaluated through comparisons with full 2D/3D model simulations, analytical solutions, and benchmark problems. We demonstrate that radial transport models are capable of accurately reproducing a wide variety of conservative and reactive transport problems provided that an adequate spatial discretization and advection scheme is selected. For the investigated test problems, the computational load was substantially reduced, with the improvement varying, depending on the complexity of the considered reaction network.

A meshless solution of two-dimensional unsteady flow

The boundary element method (BEM) is a very useful numerical method for groundwater flow models. Particularly, this method was used to solve problems in homogeneous domains. However, it presents even greater difficulties than the other numerical methods when coping with non-homogeneities which are so characteristic in the groundwater hydraulics. Recently, meshless method which is based on a local boundary integral approach is introduced. It uses distributed nodal points, covering the domain. These points can be randomly spread over the domain. Every node is surrounded by a simple surface centered at the collocation point and the boundary integral equation is written on this local boundary. The unknown variables, in the local sub-domains, are approximated by some of the interpolation method. In this paper the combination of radial basis functions and the dual reciprocity method is used to solve the time-dependent groundwater flow.