Transport In Aquifers Research Articles

A New Numerical Model Coupling Modified Method of Characteristics and Galerkin Finite Element Method for Simulation of Solute Transport in Groundwater Flow System

A new numerical model coupling the modified method of characteristics (MMOC) with the Galerkin finite element method (GFE) is proposed for the assessment of groundwater pollution in regional groundwater flow system. The MMOC-GFE solves governing solute transport equation which involves the simulation of advection and dispersion parts by MMOC and GFE, respectively. This model allows the use of large time steps (large Courant numbers) and large spatial steps (large Peclet numbers) with stable and convergent solutions. The proposed model is successfully implemented for a test case which includes comparison of the model results with reported solutions of other numerical models. It is found that MMOC-GFE model is quite adequate in simulating solute transport in heterogeneous aquifer with combined pumping and injection schemes.

Dispersion in non-Newtonian fluid flows in a conduit with porous walls

Solute transport in a conduit (channel or tube) adjacent to a porous medium is drastically influenced by the porous walls. However, an appropriate relationship between the porous walls and the transport coefficients due to non-Newtonian fluid flows still needs further investigation. In this study, a reduced-order model for advective–dispersive transport due to flow of a non-Newtonian power-law (or Ostwald-de Waele) fluid in a conduit with porous walls is derived through which the dispersion coefficient can be obtained. It is revealed that the dispersion coefficient is controlled by the Peclet number and the flow behavior index. The dispersion coefficients for shear-thinning fluids are smaller than the case of Newtonian fluid while the dispersion coefficients for shear-thickening fluids are larger than that for Newtonian fluid. The ratio of dispersion coefficient in a conduit with porous walls to that in a conduit with non-porous walls recognizes three distinct transport regimes of diffusion-dominated, transition, and advection-dominated. The results exhibit that the exchange of solute between the conduit and the neighboring porous medium should be taken into consideration in determination of the dispersion coefficient for the last two transport regimes. It is also found that the larger the flow behavior index the earlier the breakthrough of a solute in a conduit with porous walls. In addition, the breakthrough time in a conduit with porous walls is larger than that in a conduit with non-porous walls. The presented results in this study are of great importance in many science and engineering applications, including drug delivery to blood vessels, separation of emulsions using membranes, nutrient uptake from soils, contaminant transport in fractured aquifers, and oil recovery from carbonate reservoirs.

Hydrodynamic dispersion in heterogeneous anisotropic porous media: A simple model for anomalous diffusion emergence

Anomalous transport processes in porous media have become a central physical issue due to the increasing amount of processes and applications where it appears, ranging from contaminant transport in aquifers and oil recovery to anomalous diffusion in biological membranes. In all these cases, the existence of strong heterogeneities and anisotropies make proper physical and mathematical modelling a complicated problem, leading to simplified models where these spatial features and their implications for transport and diffusion are treated separately. In this work we propose a simple model for transport in porous media that includes anisotropy and strong heterogeneities. We show that depending on how strong the medium heterogeneities are, different regimes of superdiffusive transport emerge, going from superdiffusion due to long-range correlations to Lévy walks and ballistic diffusion.

Time–space fractional governing equations of transient groundwater flow in confined aquifers: Numerical investigation

AbstractIn order to model non‐Fickian transport behaviour in groundwater aquifers, various forms of the time–space fractional advection–dispersion equation have been developed and used by several researchers in the last decade. The solute transport in groundwater aquifers in fractional time–space takes place by means of an underlying groundwater flow field. However, the governing equations for such groundwater flow in fractional time–space are yet to be developed in a comprehensive framework. In this study, a finite difference numerical scheme based on Caputo fractional derivative is proposed to investigate the properties of a newly developed time–space fractional governing equations of transient groundwater flow in confined aquifers in terms of the time–space fractional mass conservation equation and the time–space fractional water flux equation. Here, we apply these time–space fractional governing equations numerically to transient groundwater flow in a confined aquifer for different boundary conditions to explore their behaviour in modelling groundwater flow in fractional time–space. The numerical results demonstrate that the proposed time–space fractional governing equation for groundwater flow in confined aquifers may provide a new perspective on modelling groundwater flow and on interpreting the dynamics of groundwater level fluctuations. Additionally, the numerical results may imply that the newly derived fractional groundwater governing equation may help explain the observed heavy‐tailed solute transport behaviour in groundwater flow by incorporating nonlocal or long‐range dependence of the underlying groundwater flow field.

The effects of floods on the temperature of riparian groundwater

AbstractThe transition area between rivers and their adjacent riparian aquifers, which may comprise the hyporheic zone, hosts important biochemical reactions, which control water quality. The rates of these reactions and metabolic processes are temperature dependent. Yet the thermal dynamics of riparian aquifers, especially during flooding and dynamic groundwater flow conditions, has seldom been studied. Thus, we investigated heat transport in riparian aquifers during 3 flood events of different magnitudes at 2 sites along the same river. River and riparian aquifer temperature and water‐level data along the Lower Colorado River in Central Texas, USA, were monitored across 2‐dimensional vertical sections perpendicular to the bank. At the downstream site, preflood temperature penetration distance into the bank suggested that advective heat transport from lateral hyporheic exchange of river water into the riparian aquifer was occurring during relatively steady low‐flow river conditions. Although a small (20‐cm stage increase) dam‐controlled flood pulse had no observable influence on groundwater temperature, larger floods (40‐cm and >3‐m stage increases) caused lateral movement of distinct heat plumes away from the river during flood stage, which then retreated back towards the river after flood recession. These plumes result from advective heat transport caused by flood waters being forced into the riparian aquifer. These flood‐induced temperature responses were controlled by the size of the flood, river water temperature during the flood, and local factors at the study sites, such as topography and local ambient water table configuration. For the intermediate and large floods, the thermal disturbance in the riparian aquifer lasted days after flood waters receded. Large floods therefore have impacts on the temperature regime of riparian aquifers lasting long beyond the flood's timescale. These persistent thermal disturbances may have a significant impact on biochemical reaction rates, nutrient cycling, and ecological niches in the river corridor.

Transport of bacteriophage MS2 and PRD1 in saturated dune sand under suboxic conditions

Soil passage of (pretreated) surface water to remove pathogenic microorganisms is a highly efficient process under oxic conditions, reducing microorganism concentrations about 8 log10 within tens of meters. However, under anoxic conditions, it has been shown that removal of microorganisms can be limited very much. Setback distances for adequate protection of natural groundwater may, therefore, be too short if anoxic conditions apply. Because removal of microorganisms under suboxic conditions is unknown, this research investigated removal of bacteriophage MS2 and PRD1 by soil passage under suboxic conditions at field scale. At the field location (dune area), one injection well and six monitoring wells were installed at different depths along three suboxic flow lines, where oxygen concentrations ranged from 0.4 to 1.7 mg/l and nitrate concentrations ranged from 13 to 16 mg/L. PRD1 and MS2 were injected directly at the corresponding depths and their removal in each flow line was determined. The highest bacteriophage removal was observed in the top layer, with about 9 log removal of MS2, and 7 log removal of PRD1 after 16 meters of aquifer transport. Less removal was observed at 12 m below surface, probably due to a higher groundwater velocity in this coarser grained layer. MS2 was removed more effectively than PRD1 under all conditions. Due to short travel times, inactivation of the phages was limited and the reported log removal was mainly associated with attachment of phages to the aquifer matrix. This study shows that attachment of MS2 and PRD1 is similar for oxic and suboxic sandy aquifers, and, therefore, setback distances used for sandy aquifers under oxic and suboxic conditions provide a similar level of safety. Sticking efficiency and the attachment rate coefficient, as measures for virus attachment, were evaluated as a function of the physico-chemical conditions.

Semianalytical solutions for contaminant transport under variable velocity field in a coastal aquifer

Existing closed-form solutions of contaminant transport problems are limited by the mathematically convenient assumption of uniform flow. These solutions cannot be used to investigate contaminant transport in coastal aquifers where seawater intrusion induces a variable velocity field. An adaptation of the Fourier-Galerkin method is introduced to obtain semi-analytical solutions for contaminant transport in a confined coastal aquifer in which the saltwater wedge is in equilibrium with a freshwater discharge flow. Two scenarios dealing with contaminant leakage from the aquifer top surface and contaminant migration from a source at the landward boundary are considered. Robust implementation of the Fourier-Galerkin method is developed to efficiently solve the coupled flow, salt and contaminant transport equations. Various illustrative examples are generated and the semi-analytical solutions are compared against an in-house numerical code. The Fourier series are used to evaluate relevant metrics characterizing contaminant transport such as the discharge flux to the sea, amount of contaminant persisting in the groundwater and solute flux from the source. These metrics represent quantitative data for numerical code validation and are relevant to understand the effect of seawater intrusion on contaminant transport. It is observed that, for the surface contamination scenario, seawater intrusion limits the spread of the contaminant but intensifies the contaminant discharge to the sea. For the landward contamination scenario, moderate seawater intrusion affects only the spatial distribution of the contaminant plume while extreme seawater intrusion can increase the contaminant discharge to the sea. The developed semi-analytical solution presents an efficient tool for the verification of numerical models. It provides a clear interpretation of the contaminant transport processes in coastal aquifers subject to seawater intrusion. For practical usage in further studies, the full open source semi-analytical codes are made available at the website https://lhyges.unistra.fr/FAHS-Marwan.

Models of pollutant transport in natural aquifers

We present an approach for modelling the transport of pollution within a groundwater aquifer. The model is based on vertical discretisation of the aquifer into a number of horizontal layers. The approach can be used in a variety of situations. In particular, aquifers with lenses and phreatic surfaces are discussed. The use of the model is illustrated with examples including a comparison with experimental field data and the use of a second transported substance for remediation of the pollution. References A. Ali (2015) Simplified modelling of pollutant transport in naturally-layered aquifers , PhD Thesis, Massey University, NZ. https://mro.massey.ac.nz/handle/10179/6782 A. Ali, R. McKibbin, W.L. Sweatman (2012) Fluid flow and solute transport in unevenly-stratified groundwater aquifers , AIP Conference Proceedings, 1453, 11–16. doi:10.1063/1.4711146 A. Ali, R. McKibbin, W.L. Sweatman (2012) Simplified modelling of pollutant transport in stratified groundwater aquifers , Proceedings of IEMSs 2012, 2739–2746. http://www.iemss.org/sites/iemss2012/proceedings/I1_0675_Ali_et_al.pdf A. Ali, R. McKibbin, W.L. Sweatman (2012) Tracer transport: Appearing or disappearing sub-layer in a groundwater aquifer , In: G. Mallinson, ed., Proceedings of the 23rd International Symposium on Transport Phenomena (ISTP), The University of Auckland, NZ. A. Ali, R. McKibbin, W.L. Sweatman (2014) A simplified model for transport in aquifers , Proceedings of ICPM5, ECI Symposium Series. http://dc.engconfintl.org/porous_media_V/56 A. Ali, W.L. Sweatman, R. McKibbin (2014) Pollutant transport and its alleviation in groundwater aquifers , Mathematics in Industry, 19, 53–58. doi:10.1007/978-3-319-05365-3_8 M.P. Anderson, J.A. Cherry (1979) Using models to simulate the movement of contaminants through groundwater flow systems , CRC Critical Reviews in Environmental Control, 9(2):97–156. doi:10.1080/10643387909381669 , J. Bear (1972) Dynamics of fluid in porous media Dover, New York. ISBN 10 0486656756 J. Bear, Y. Bachmat (1991) Introduction to modeling of transport phenomena in porous media , Kluwer. ISBN 978-94-009-1926-6 J. Bear, A. Verruijt (1978) Modeling groundwater flow and pollution D. Reidel, Dordrecht, Holland. H.P.G. Darcy (1856) Les fontaines publiques de la ville de dijon , Technical report, Victor Dalmont, Paris. J. Dupuit (1863) Etudes theoriques et pratiques sur le mouvement des eaux dans les canaux decouverts et a travers les terrains permeables , Dunod, Paris, 2nd edition. D.L. Freyberg (1986) A natural gradient experiment on solute transport in a sand aquifer: 2. Spatial moments and the advection and dispersion of nonreactive tracers , Water Resources Research, 22, 2031–2046. doi:10.1029/WR022i013p02031 D.M. Mackay, D.L. Freyberg, P.V. Roberts, J.A. Cherry (1986) A natural gradient experiment on solute transport in a sand aquifer: 1. Approach and overview of plume movement , Water Resources Research, 22, 2017–2029. doi:10.1029/WR022i013p02017 R. McKibbin (2009) Groundwater pollutant transport: transforming layered models to dynamical systems , An. St. Univ. Ovidius Constanta, Ser. Mat., 17(3), 183–196. http://www.emis.ams.org/journals/ASUO/mathematics/pdf19/McKibbin.pdf R. McKibbin (2010) Some aspects of modelling pollution transport in groundwater aquifers , In: L.H. Weiranto, S. Pudjaprasetya, editors, Proceedings of CIAM 2010, 9–16, ITB, Indonesia.

Fractal advection-dispersion equation for groundwater transport in fractured aquifers with self-similarities

.Groundwater transport within a fractured aquifer with a fractal nature exhibiting self-similarity cannot be accurately simulated by the classical Fickian advection-dispersion transport equation without a detailed characterisation of the fracture network and heterogeneity of the system. Because the information to characterise such a system to an appropriate level of detail is often not available, most applications fail to accurately simulate the observed contaminant transport. In response to the current limitations of transport modelling using the advection-dispersion equation, especially in fractured media, a fractal advection-dispersion groundwater transport equation is developed. Fractal differentiation is discussed in terms of the fractal derivative and the fractal integral. The fractal derivative is commonly applied and known, yet the fractal integral is developed in this paper along with the appropriate theorem and proof. The numerical approximation of the fractal derivative and integral are given, where Simpson’s 3/8Rule and Boole’s Rule for numerical integration are applied for the fractal integral, and the forward and Crank-Nicolson finite difference schemes are applied for the fractal derivative. Upon the given foundation, the fractal advection-dispersion transport equation is formulated to develop a new groundwater transport model. The qualitative properties of the fractal advection-dispersion equation are investigated to determine boundedness, existence and uniqueness of the solution. To validate the developed fractal advection-dispersion equation, a numerical simulation is performed with different fractal dimensions to demonstrate the applicability of the model to fractal groundwater systems. The numerical simulations found that anomalous diffusion could be better modelled by incorporating a fractal dimension, especially where limited information is available on preferential pathways.

Laboratory Scale Investigation of Dispersion Effects on Saltwater Movement due to Cutoff Wall Installation

In the numerical investigation of saltwater transport in coastal aquifers, we need to correctly evaluate the hydrodynamic dispersion in the flow field. In this study, we focused on the role of dispersivity in the removal process of residual saltwater in a laboratory scale cutoff wall experiment. From a pulse-type fluorescent tracer injection experiment in a saturated porous media of glass beads with a mean diameter of 0.088 cm, the estimated longitudinal and transverse dispersivities were found to be 0.07 cm and 0.0025 cm, respectively. Numerical analysis of the saltwater intrusion and subsequent removal after cutoff wall installation using SEAWAT and the generated dispersivity ratio (αL/αT) of 28 reproduces well the measured salt concentration changes with time. Whereas, if a dispersivity ratio of 10 is used in the numerical simulation, transverse dispersion in the saltwater and freshwater mixing zone becomes large and the residual saltwater is removed faster than the laboratory experiment. Inversely, if 100 was used, the residual saltwater removal time took longer. The transverse dispersion is a key parameter in the mechanical dispersion of saltwater in the mixing zone after cutoff wall installation.

NUMERICAL ANALYSIS OF EFFECTS OF HYDRAULIC GRADIENT ON MASS FLUX OF SALTWATER INTRUSION IN COASTAL AQUIFERS

<p>Coastal aquifers are distinguished from other aquifers because of saltwater intrusion effects, which cause contamination of groundwater in coastal regions. This study addressed the significance of hydraulic gradient and porosity of the coastal aquifers on contaminant transport of saltwater. Results showed hydraulic gradient of the aquifer has significant impact on the contaminant transport in coastal aquifer. When the hydraulic gradient between freshwater and saltwater is high and directed toward the sea, diffused rate of saltwater into the groundwater would be low. Therefore, hydraulic head of freshwater in coastal aquifer must be maintained at high level to control saltwater intrusion.</p>

Oscillatory Pumping Test to Estimate Aquifer Hydraulic Parameters in a Bayesian Geostatistical Framework

Comprehensive information about the spatial distribution of the subsurface hydraulic properties is crucial to model groundwater flow, to predict solute transport in aquifers and to design remediation actions. In this work, a Bayesian Geostatistical approach, as implemented in bgaPEST, was adopted to estimate the hydraulic properties of a well field located at the Campus of Science and Technology of the University of Parma (Northern Italy), in a contest of a highly parameterized inversion. Head data, collected by means of multi frequency oscillatory pumping tests, were used to both estimate the hydraulic parameters and validate the results. The groundwater flow processes were modelled by means of MODFLOW 2005 and an adjoint-state formulation of the same software was used to efficiently calculate the sensitivity matrix, required by the inverse procedure. The Bayesian Geostatistical approach estimated the hydraulic conductivity and specific storage fields, handling a large number of parameters. The results of the inversion are consistent with the alluvial nature of the investigated aquifer and the preliminary traditional pumping tests carried out at the site.

An Integrated Approach Based on Numerical Modelling and Geophysical Survey to Map Groundwater Salinity in Fractured Coastal Aquifers

Aquifer over-exploitation may increase coastal seawater intrusion by reducing freshwater availability. Fractured subsurface formations commonly host important freshwater reservoirs along sea coasts. These water resources are particularly vulnerable to the contamination due to seawater infiltration occurring through rapid pathways via fractures. Modeling of density driven fluid flow in fractured aquifers is complex, as their hydrodynamics are controlled by interactions between preferential flow pathways, 3D interconnected fractures and rock-matrix porosity distribution. Moreover, physical heterogeneities produce highly localized water infiltrations that make the modeling of saltwater transport in such aquifers very challenging. The new approach described in this work provides a reliable hydrogeological model suitable to reproduce local advancements of the freshwater/saltwater wedge in coastal aquifers. The proposed model use flow simulation results to estimate water salinities in groundwater at a specific depth (1 m) below water table by means of positions of the Ghyben-Herzberg saltwater/freshwater sharp interface along the coast. Measurements of salinity in 25 boreholes (i.e., salinity profiles) have been used for the model calibration. The results provide the groundwater salinity map in freshwater/saltwater transition coastal zones of the Bari (Southern Italy) fractured aquifer. Non-invasive geophysical measurements in groundwater, particularly into vertical 2D vertical cross-sections, were carried out by using the electrical resistivity tomography (ERT) in order to validate the model results. The presented integrated approach is very easy to apply and gives very realistic salinity maps in heterogeneous aquifers, without simulating density driven water flow in fractures.

Modeling sewage leakage and transport in carbonate aquifer using carbamazepine as an indicator

The Western Mountain Aquifer (Yarkon-Taninim) of Israel is one of the country's major water resources and partially flows through a karst system. During late winter 2013, maintenance actions were performed on a central sewage pipe that caused sewage to leak into the creek located in the study area. Carbamazepine (CBZ) was used as an indicator for the presence of sewage in the groundwater. The research goal was to develop a mathematical model for quantifying flow and contaminant transport processes in the karst/fractured-porous unsaturated zone and groundwater system. The model was used to simulate CBZ transport during and after an observed sewage leakage event. A quasi-3D dual permeability numerical model represents the 'vadose zone – aquifer' system, by a series of 1D vertical flow and transport equations solved in a variably-saturated zone and by 3D-saturated flow and transport equation in groundwater. The results of simulation showed that after the leakage stopped, significant amounts of CBZ were retained in the porous matrix of the unsaturated zone below the creek. Water redistribution and slow recharge during the dry summer season contributed to a continuous supply of CBZ to the groundwater in the vicinity of the creek and hundreds of meters downstream.

Solute transport in aquifers: The comeback of the advection dispersion equation and the First Order Approximation

Abstract Natural gradient steady flow of mean velocity U takes place in heterogeneous aquifers of random logconductivity Y = ln K , characterized by the normal univariate PDF f(Y) and autocorrelation ρY, of variance σ Y 2 and horizontal integral scale I. Solute transport is quantified by the Breakthrough Curve (BTC) M at planes at distance x from the injection plane. The study builds on the extensive 3D numerical simulations of flow and transport of Jankovic et al. (2017) for different conductivity structures. The present study further explores the predictive capabilities of the Advection Dispersion Equation (ADE), with macrodispersivity αL given by the First Order Approximation (FOA), by checking in a quantitative manner its applicability. After a discussion on the suitable boundary conditions for ADE, we find that the ADE-FOA solution is a sufficiently accurate predictor for applications, the many other sources of uncertainty prevailing in practice notwithstanding. We checked by least squares and by comparison of travel time of quantiles of M that indeed the analytical Inverse Gaussian M with α L = σ Y 2 I , is able to fit well the bulk of the simulated BTCs. It tends to underestimate the late arrival time of the thin and persistent tail. The tail is better reproduced by the semi-analytical MIMSCA model, which also allows for a physical explanation of the success of the Inverse Gaussian solution. Examination of the pertinent longitudinal mass distribution shows that it is different from the commonly used Gaussian one in the analysis of field experiments, and it captures the main features of the plume measurements of the MADE experiment. The results strengthen the confidence in the applicability of the ADE and the FOA to predicting longitudinal spreading in solute transport through heterogeneous aquifers of stationary random structure.

Dynamics of a Highly Viscous Circular Blob in Homogeneous Porous Media

Viscous fingering is ubiquitous in miscible displacements in porous media, in particular, oil recovery, contaminant transport in aquifers, chromatography separation, and geological CO2 sequestration. The viscosity contrasts between heavy oil and water is several orders of magnitude larger than typical viscosity contrasts considered in the majority of the literature. We use the finite element method (FEM)-based COMSOL Multiphysics simulator to simulate miscible displacements in homogeneous porous media with very large viscosity contrasts. Our numerical model is suitable for a wide range of viscosity contrasts covering chromatographic separation as well as heavy oil recovery. We have successfully captured some interesting and previously unexplored dynamics of miscible blobs with very large viscosity contrasts in homogeneous porous media. We study the effect of viscosity contrast on the spreading and the degree of mixing of the blob. Spreading (variance of transversely averaged concentration) follows the power law t 3 . 34 for the blobs with viscosity ∼ O ( 10 2 ) and higher, while degree of mixing is found to vary non-monotonically with log-mobility ratio. Moreover, in the limit of very large viscosity contrast, the circular blob behaves like an erodible solid body and the degree of mixing approaches the viscosity-matched case.

Experimental study of conservative solute transport in heterogeneous aquifers

Aquifer heterogeneity affects the characteristics of solute breakthrough curves (BTCs). A better understanding of the relationship between aquifer heterogeneity and BTCs will help improve prediction of the fate of contaminants in an aquifer. Previous studies have shown that systematic research of aquifer heterogeneity on solute transport is limited. Therefore, this study investigates the impacts of aquifer heterogeneity on conservative solute BTCs and transport mechanism via experimental and modeling approaches. Tracer experiments are conducted in four flow-through columns exhibiting different patterns of heterogeneities. Furthermore, this study also examines the influence of hydraulic conductivity on transport mechanism. In addition, this paper analyses the correlation between hydraulic conductivity and dispersivity, which are the key parameters of conservative solute transport in an aquifer. Experimental data indicates the impacts of aquifer heterogeneity on transport of tracer. Tracer BTCs in a homogeneous aquifer have the typical sigmoid shape without tailing. In a heterogeneous aquifer, tracer BTCs display a strong and persistent tailing. In a preferential flow aquifer, tracer BTCs have pronounced tailing and early arrival time. The hydraulic conductivity of an aquifer significantly affects the transport mechanism of tracer. When the hydraulic conductivity is higher than 1.53 cm/min, transport of tracer is applicable to the ADE. When the hydraulic conductivity is lower than 1.53 cm/min, transport of tracer is applicable to the TRM. This work offers insight into the correlation between the hydraulic conductivity of an aquifer and the dispersivity of a conservative solute. A critical finding is that hydraulic conductivity K and dispersivity $$\lambda$$ correspond to an exponential regression form $$\lambda = e^{{ - 0.24555 - 4.54413K + 2.27308K^{2} }}$$ (R 2 = 0.957).

Effects of beach slope breaks on nearshore groundwater dynamics

AbstractInteractions between fresh groundwater and seawater affect significantly the nearshore pore water flow, which in turn influences the fate of nutrients and contaminants in coastal aquifers prior to discharge to the marine environment. Field investigations and numerical simulations were carried out to examine the groundwater dynamics in the intertidal zone of a carbonate sandy aquifer on the tropical island of Rarotonga, Cook Islands. The study site was featured by distinct cross‐shore slope breaks on the beach surface. Measured pore water salinities revealed different distributions under the influences of different beach profiles, inland heads, and tidal oscillations. Fresh groundwater was found to discharge around a beach slope break located in the middle area of the intertidal zone. The results indicate a strong interplay between the slope break beach morphology and tidal force in controlling the nearshore groundwater flow and solute transport. The fresh groundwater discharge location was largely determined by the beach morphology in combination with the tidal force. The nearshore groundwater flow can be very sensitive to beach slope breaks, which induce local circulation and flow instabilities. As slope breaks are a common feature of beaches around the world, these results have important, general implications for future studies of nutrients transport and transformations in nearshore aquifers and associated fluxes via submarine groundwater discharge.

A methodology for regionalizing 3‐D effective porosity at watershed scale in crystalline aquifers

AbstractAn innovative approach for regionalizing the 3‐D effective porosity field is presented and applied to two large, overexploited, and deeply weathered crystalline aquifers located in southern India. The method derives from earlier work on regionalizing a 2‐D effective porosity field in that part of an aquifer where the water table fluctuates, which is now extended over the entire aquifer using a 3‐D approach. A method based on geological and geophysical surveys has also been developed for mapping the weathering profile layers (saprolite and fractured layers). The method for regionalizing 3‐D effective porosity combines water table fluctuation and groundwater budget techniques at various cell sizes with the use of satellite‐based data (for groundwater abstraction), the structure of the weathering profile, and geostatistical techniques. The approach is presented in detail for the Kudaliar watershed (983 km2) and tested on the 730 km2 Anantapur watershed. At watershed scale, the effective porosity of the aquifer ranges from 0.5% to 2% in Kudaliar and between 0.3% and 1% in Anantapur, which agrees with earlier works. Results show that (a) depending on the geology and on the structure of the weathering profile, the vertical distribution of effective porosity can be very different and that the fractured layers in crystalline aquifers are not necessarily characterized by a rapid decrease in effective porosity and (b) that the lateral variations in effective porosity can be larger than the vertical ones. These variations suggest that within a same weathering profile, the density of open fractures and/or degree of weathering in the fractured zone may significantly vary from a place to another. The proposed method provides information on the spatial distribution of effective porosity that is of prime interest in terms of flux and contaminant transport in crystalline aquifers. Implications for mapping groundwater storage and scarcity are also discussed, which should help in improving groundwater resource management strategies.

Dynamic reduced-order models of integrated physics-specific systems for carbon sequestration

$$\text {CO}_2$$ leakage from a deep storage reservoir into a shallow groundwater aquifer through a wellbore is simulated using physics-specific models conceptualized as nonisothermal two-phase flow in a deep storage reservoir and through the wellbore, and reactive transport in the aquifer. Supercritical $$\text {CO}_2$$ is injected into the reservoir subsystem with uncertain permeabilities of reservoir and injection strategies (rate and duration as decision variables). The simulated pressure and $$\text {CO}_2$$ saturation at an uncertain location are connected to the wellbore model as a boundary condition to output $$\text {CO}_2$$ flux to the reactive transport model in the shallow aquifer. Uncertainties are propagated from the deep reservoir model, to the wellbore leakage model, and eventually to the reactive transport model, thus contributing to system performance. To minimize the risk associated with the $$\text {CO}_2$$ leakage, we develop dynamic reduced order models for quantifying and managing the uncertainty propagation.