NATIONAL CONFERENCE ON RECENT ADVANCES IN MECHANICAL & CIVIL ENGINEERING AJAY KUMAR GARG ENGINEERING COLLEGE, GHAZIABAD
Recent Trends in Flow through Porous Media Dr. Ashok K. Keshari Professor, Department of Civil Engineering, Indian Institute of Technology Delhi, New Delhi 110016, India, E-mail:
[email protected],
[email protected]
ABSTRACT The objective of this paper is to present a state of art on the advancements in porous media theories and a critical review of research carried out worldwide to identify current and future research directions in this subject. The understanding of the flow through porous media was started a long back after the pioneering work of Darcy in 1856. Later, basic foundations for flow through porous media were laid down by a number of researchers (Thiem, Theis, Ghyben-Herzberg, Glover, Cooper-Jacob, Hantush, Scheidegger, BearBachmat, Cooper-Bredehoeft-Papadopulos, Neuman). Research carried out in the 1940s and 1950s produced a number of quantitative analytical tools to predict response of aquifers to pumping and to determine aquifer parameters and impact on the hydraulic head in the aquifers. Then after, significant developments took place that focused on the development of numerical models, constitutive relationships, processes descriptions, subsurface characterization and integrating analytical and numerical models with emerging and decision making techniques such as optimization, geostatistics, fuzzy algorithms, ANNs, GIS and remote sensing that has helped to improve the understanding of subsurface and groundwater flows through various geological formations and deposits. These developments have enabled to address increasingly complex water and environmental problems encountered in today’s life. It is gaining significance as the availability of freshwater resources is decreasing due to increased demand, declining groundwater level, reduced river flows, growing water pollution, hydrological uncertainty and adverse implications of climate change. Further, the dependence on groundwater is increasing because of water scarcity and growing water pollution problems resulting from various natural and anthropogenic activities and geogenic processes.
also. The recent trends are also witnessing its applications in solving a number of emerging problems in infrastructural engineering and built environment. The study reveals that researches in the areas of flow through fractured rocks or hard rock areas, multiphase flows, reactive contaminant transport, multicomponent and multispecies transport through unsaturated and saturated porous media, subsurface heat and energy transport, subsurface characterization, vulnerability assessment, bioremediation, streamaquifer interactions, conjunctive water use planning, integrated water resources management and sustainable development are drawing attention and gaining momentum. It is observed that the techniques that are becoming popular and indispensable in addressing various groundwater problems include numerical modeling, optimization, geostatistics, GIS, remote sensing and uncertainty analysis. The industrial and engineering applications discussed in this paper include construction dewatering, retrofitting structures, ceramics, groundwater quantity and quality problems associated with coal, petroleum, distillery, sugar and leather industries, leachate drainage system, infiltration galleries, riverbank filtration, rainwater harvesting and development of sustainable materials and reactive permeable systems. 1.
Flow through porous media involves a variety of real life situations varying in nature, complexity and scale. The flowing fluid as well as the porous media also varies in various examples encountered in real world. The porous media could be soil, sand, aquifer, fissured rocks, sandstone, Karstic limestone, ceramics, foam rubber or concrete, and the flowing fluid could be water, air, non-aqueous phase liquids (NAPLs) such as oil or gaseous substances. The flow through an aquifer or subsurface involves a complex network of pores and channels comprising the void space and is bounded by the complex configuration
Advancements in porous media theories have resulted into numerous industrial applications
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INTRODUCTION
NATIONAL CONFERENCE ON RECENT ADVANCES IN MECHANICAL & CIVIL ENGINEERING AJAY KUMAR GARG ENGINEERING COLLEGE, GHAZIABAD of solid-water interface. The understanding of the flow through porous media was started a long back after the pioneering work of Darcy in 1856 who investigated water flow through vertical homogeneous sand filters in connection with the fountains of the city of Dijon. This experiment established the basic foundation of porous media theory and is popularly known as Darcy’s law. It paved the way to describe the groundwater motion mathematically, and in turn quantitatively understand the hydrological cycle and various natural and artificial processes involving groundwater motion or porous media flow.
media emerged due to the scientific investigations carried out by Saffman (1960), Bear (1961), Scheidegger (1961), and Bear and Bachmat (1967). Although, these scientific developments were breakthrough in understanding the flow through porous media and mechanisms of contaminant transport in porous media, the increasing complexity of groundwater problems compelled the scientific community to look at groundwater problems with a different approach. This culminated into the emergence of a spectrum of mathematical models to address various kinds of groundwater problems. These mathematical models primarily utilized the basic theories and solutions as constitutive relations and building blocks of mathematical models. The following sections present various kinds of mathematical models that are commonly used in solving groundwater problems. In this paper, the current and future research directions in mathematical modeling of flow through porous media are also identified and discussed with the perspectives of practical applications in real world systems. The emerging industrial applications of porous media flows are also presented in this paper.
Research works carried out in the 1940s and 1950s produced a number of quantitative analytical tools to predict response of aquifers to pumping and to determine aquifer parameters and impact on the hydraulic head in the aquifers. In fact, the quantitative tools that focus on predicting the response of aquifer or impact on the hydraulic head in the aquifer to any excitation or hydraulic stress expressed in terms of groundwater pumping or recharge can be classified as forecasting or predictive model and such problems are said to be forecasting problems. The problems of other kind that focus on the determination/estimation of aquifer parameters or processes are termed as identification problems and the mathematical models or tools used for analyzing such problems are classified as inverse models. Some problems involve managing groundwater resources in terms of quantity and/or quality in a particular region or study area within the available constraints or restrictions on operating conditions and resources available are classified as management problems and the mathematical models utilized for addressing such problems are known as management models.
2.
The mathematical modelling is introduced when it is not possible to address the problem by carrying out experiments and tests standalone or the response of the aquifer system cannot be ascertained or determined as the event has not taken place. A mathematical model is also warranted when the complexity of physical reality and the processes is encountered. It is obvious that the experiments and tests in the aquifer cannot be carried out to determine its response in terms of water levels and/or concentration of various groundwater quality parameters to activities proposed in the future. It is also not possible to make comparisons among responses to different possible activities in order to determine the most desirable one with reference to some specified criteria, or to incorporate the responses in some decision making procedure. Further, it may not be possible to generate scenarios and investigate the aquifer responses under these scenarios for decision making. In such cases and also whenever the treatment of real systems or phenomena is impossible, mathematical models of the considered systems or phenomena become powerful tools to address such issues/problems. Instead of treating the real system, mathematical models can be subjected to manipulations (generated scenarios or excitations) to investigate and quantitatively assess the aquifer response parameters and the obtained results of these manipulations can be used in making decisions for the real world system.
Later, a number of researchers utilized Darcy’s law to analyze the response of aquifer under hydraulic loading in order to estimate the drawdown resulting from groundwater pumping through a well. Among them, Thiem’s equation for steady flow to a well in a confined aquifer, Dupuit-Forchheimer well discharge formula for steady flow to a well in a phreatic aquifer, Theis equation for unsteady flow to a well in a confined aquifer and solutions of Boulton and Hantush for unsteady flow to a well in a phreatic aquifer laid down basic foundation for well hydraulics (Bear 1979, Freeze and Cherry 1979). These solutions along with the Cooper-Jacob method, Cooper-Bredehoeft-Papadopulos test and Neuman method enabled to analyze pumping or aquifer tests data to determine aquifer hydraulic parameters (Freeze and Cherry 1979, Schwartz and Zhang 2003). Similarly to address the groundwater quality problems, mathematical understandings of mechanical dispersion, molecular dispersion and hydrodynamic dispersion of contaminants in porous
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MATHEMATICAL MODELLING
NATIONAL CONFERENCE ON RECENT ADVANCES IN MECHANICAL & CIVIL ENGINEERING AJAY KUMAR GARG ENGINEERING COLLEGE, GHAZIABAD Analogs models are usually constructed to solve a particular flow problem as long as the geometry and parameters of aquifer are simpler and remain unchanged. An analog can be used for solving a number of cases which differ from each other only in input and output values. Analog is regarded as an apparatus used for simulating a regime in an aquifer. Every relevant aspect of aquifer behavior is reproduced in an analog. This includes the interaction among various parts of the aquifer system. Analog models are subjected to the planned future activities the analog’s responses are observed. The results obtained are analogous to that of the real aquifer system except the difference in values because of scales.
The most aquifer systems in real life are complicated and it is simplified or approximated while model is build up. For example, the microscopic level of flow through porous media is approximated at the macroscopic level as a continuum and the porous medium continuum is inhomogeneous and anisotropic. The flow is essentially assumed horizontal. Other assumptions, that are commonly made, include water in a prelatic aquifer is released from storage immediately upon a decline of the water table, or that the water table is a surface which separates between a fully saturated region and a region with no moisture at all. Based on the simplifying assumptions, a model of an investigated groundwater system is constructed and is presented in the form of a set of mathematical equations. The solution of model yields the behavior of the considered system.
The prototype and analog systems are said to be analogous if the characteristic equations governing their dynamic and kinematic behavior are similar in form. This is possible only if there is a one-to one correspondence between elements belonging to the two systems. For example, a sand box model can be an analog for simulating flow in an aquifer as both systems involve flow through a porous material. In an analogy, similarity is recognized when (a) for each dependent variable and all its derivatives in the equations describing a prototype system, there corresponds a variable with corresponding derivatives in the equations of the analog system, and (b) the dependent variables and their derivatives are related to each other in the same manner in the two sets of equations. Other analog models that are commonly used in studying flow through porous media are vertical and horizontal Hele-Shaw analogs, electric analogs of the electrolytic tank type, conducting paper type, or RC-network type, ion motion analog and membrane analog.
A forecasting problem is solved for a set of numerical values of the parameters appearing in the model. The parameters appearing in the model equation have physical interpretations. They represent physical properties of the aquifer, averaged over some volume, or area. When the problem refers to the determination of parameters appearing in an aquifer model, such problem is referred to as the inverse problem or the problem of identifying model parameters. The identification problem involves considering a period in the past for which information is available on both aquifer excitations such as pumping and responses such as water levels or concentration values. The model calibration is also a type of inverse problem. In some situations, boundary conditions and inputs to the model could be also determined in addition to the transport and storage parameters appearing in the groundwater or aquifer models. Although the problem of regional parameter identification is well recognized in terms of practical applications, it has not yet become a matter of routine in which well-established procedures are used especially for dispersion coefficients. The transmissivity and storage coefficients are generally obtained using pumping test data for local scales.
However, analytical models are not possible for most regional studies of practical interest. The irregularity of the shape of aquifer boundaries, types of boundary conditions, considered aquifer flow domain being inhomogeneous with respect to storativity and transmissivity and the inability to express the spatial distributions of these parameters in form of analytical expressions are the major reasons because of which analytical models are not available. Such situations may be true for initial conditions as well as various inputs and outputs such as natural replenishment, artificial recharge and pumping also. Further, the partial differential equation for a phreatic aquifer is nonlinear. As a consequence, analytical models are seldom applied in the practice to solve regional forecasting problems.
2.1 Analytical and Analog Models Analytical models are used whenever possible. The solutions of analytical models can be applied to different values of the parameters and inputs involved. Solution results clearly show the influence of each parameter. The analytical solutions derived for well hydraulics are examples of analytical models. Analytical models are also used for certain two-dimensional flows.
3.
NUMERICAL MODELS
With the advancement in computational methods and computer technology, numerical models emerged as
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NATIONAL CONFERENCE ON RECENT ADVANCES IN MECHANICAL & CIVIL ENGINEERING AJAY KUMAR GARG ENGINEERING COLLEGE, GHAZIABAD powerful mathematical tools to solve complex real world groundwater problems. A large variety of numerical models have been developed in the three decades to address various kinds of groundwater flow and groundwater quality problems. These models are capable of solving governing groundwater flow and solute transport involving even multispecies, multiphase and chemical reactions in terms of processes and complicated aquifer geometry characterized by heterogeneity, anisotropy, lithological structures, geological controls and subsurface configuration. Numerical models use finite differences or finite elements to solve the partial differential equations describing groundwater flow or solute transport. The approximations require that the model domain and time be discretized appropriately. In this discretization process, the model domain is represented by a network of grid cells or elements, and the time of the simulation is represented by time steps. The accuracy of numerical models depends upon the accuracy of the model input data, the size of the space and time discretization and the numerical method used to solve the model equations. In addition to complex three-dimensional groundwater flow and solute transport problems, numerical models may be used to simulate very simple flow and transport conditions also for understanding the system or process behavior and parameter identification. However, numerical models are generally used to simulate problems that cannot be accurately described using analytical models.
where Tij = transmissivity tensor h = hydraulic head S = storage coefficient xi and xj = cartesian coordinates t = time Kllzz = vertical hydraulic conductivity of the leaky aquifer hs = hydraulic head in the source bed m = thickness of the leaky layer qpw = specific point pumping from the wth pumping well located at (xw, yw) qrw = specific point recharge from the wth recharge well located at (xw, yw) (x-xw, y-yw) = Dirac delta function p = index set of the location of pumping cells within the system r = index set of the location of recharge cells within the system The groundwater quality is governed by the flow of contaminants either in dissolved or immiscible form through the porous media. A number of physical, chemical and biological processes affect the fate of the contaminants. The purpose of discussing transport mechanisms is to understand the processes that most strongly influence the migration of dissolved contaminants in saturated flow in granular aquifers. The transport mechanisms are: advection, diffusion and dispersion. The groundwater exploitation, recharge activities and various natural and anthropogenic activities do effect groundwater contaminant transport mechanisms, and thus influence the spatial and temporal distributions of contaminants. For the development of the numerical groundwater quality model, it is essential to precisely understand the processes that most strongly influence the migration of dissolved contaminants in groundwater systems. The various transport mechanisms that can be considered in the development of the model can be summarized as:
In the numerical model, the groundwater flow is described by the extended version of Darcy’s law. The rate of flow of water through a porous media depends upon the properties of water, the properties of the porous media and the gradient of the hydraulic head. Mathematically, the extended version of Darcy’s law can be written as (Bear 1979): qi = -Kij h/xj
(1)
where qi is the specific discharge, LT-1; Kij is the hydraulic conductivity of the porous medium ( a second order tensor), LT-1; and h is the hydraulic head, L. The basic governing partial differential equation of groundwater flow in most cases can be expressed as (McDonald and Harbaugh 1988, Keshari and Datta 1996a,b): xi
h h Tij S q pw ( x xw , y yw ) qrw ( x xw , y y w ) t w p w r x j
K zzll ( h s h ); i , j 1 , 2 m
The generalized governing partial differential equations for contaminant transport modelling for
(2)
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Advection Diffusion Dispersion Sorption Decay Physical natural or anthropogenic activities Hydrolysis, volatilization, and biotransformation Transport in aquifers with a pronounced bimodal permeability distribution Chemical reactions
NATIONAL CONFERENCE ON RECENT ADVANCES IN MECHANICAL & CIVIL ENGINEERING AJAY KUMAR GARG ENGINEERING COLLEGE, GHAZIABAD most numerical models include PDEs describing groundwater flow, and solute transport within groundwater systems. The solute transport equation is expressed as (Keshari and Datta 1996a,b, Keshari 1998, Keshari and Datta 2001):
Rd
(bC) C (bCvi ) (bDhij ) Rd bC t xi x j xi
qpwC q C Kll (h h)Cl (x xw, y yw) rw r (x xw, y yw) zz s n mn wp n wr
(3) where n = porosity b = saturated thickness of aquifer in m C = concentration of contaminant Cr = concentration of contaminant in recharging water Cl = concentration of contaminant in leaking water Dh= hydrodynamic dispersion tensor Rd = retardation factor = first-order kinetic decay rate vs = average groundwater velocity in i direction
The finite difference discretization may be block centered or mesh centered finite difference grid. A number of schemes are utilized in Finite Difference Method (FDM). The commonly utilized finite difference schemes are explicit, implicit, CrankNicholson, Alternate Direction Implicit (ADI), IADI, ADE, and predictor-corrector. After converting the PDEs into algebraic equations using the appropriate numerical scheme, numerical solutions are obtained depending up on the nature of system of equations; linear, nonlinear, banded, sparse, etc. The commonly used numerical solution techniques are Gauss elimination with no, partial, or full pivoting; GaussJordan, Gauss-Siedel, Cholesky decomposition, matrix inversion, SLOR, SLORC, Newton’s method, Thoma’s algorithm, etc. Define Purpose Field Data
Conceptual Model Mathematical Model Numerical Formulation Computer Program
Code
3.1 Initial and Boundary Conditions The initial conditions describe the distribution of heads and concentrations throughout the model domain at the start of the simulation. The precise measurements or estimation of initial conditions are required as errors in initial conditions propagate through a transient solution that may cause unrealistic predictions. A model boundary is an interface between the model calculation domain and the surrounding environment. There are three types of boundary conditions: Dirichlet boundary Neumann boundary Cauchy boundary
Selectio n
Compariso n With Field
Code Verified
Yes Model Design
N o Field Data
Calibration Verification
Presentation of Results
Fig. 1 Flow diagram for groundwater modeling (after Keshari 2007)
3.2 Numerical Solution
Numerical models require calibration and validation before application to a specific problem. Model calibration consists of changing values of model input parameters to match field conditions within some acceptable criteria. This requires that field conditions at a site be properly characterized. Lack of proper site characterization may result in a model that is calibrated to a set of conditions, which are not representative of actual field conditions. The calibration process typically involves calibrating to steady state and transient conditions. With steadystate simulations, there are no observed changes in
The numerical model is solved using numerical techniques for a set of input parameters and the specified initial and boundary conditions. Fig. 1 shows the flow diagram of modelling framework, and describes the steps that are considered in modelling exercise. Numerical models generally utilize following methods for solving governing partial differential equations: MOC FDM FEM
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BIEM Hybrid Method
NATIONAL CONFERENCE ON RECENT ADVANCES IN MECHANICAL & CIVIL ENGINEERING AJAY KUMAR GARG ENGINEERING COLLEGE, GHAZIABAD hydraulic head or contaminant concentration with time for the field conditions being modeled. Transient simulations involve the change in hydraulic head or contaminant concentration with time. These simulations are needed to narrow the range of variability in model input data since there are numerous choices of model input data values which may result in similar steady-state simulations. The model is also validated for a particular area to see its applicability. The data for model calibration and validation are generally not overlapped. Most often, numerical model is evaluated for validation separately, and sometimes combining calibration and validation data. 4.
programming (LP) and involved mostly forecasting problems that dealt with the management of water resources or limited application in water quality management (Lynn et al. 1962, Deininger 1965, Dracup 1966, Futagami et al. 1976, Bear and Verruijt 1987, Keshari and Datta 1996a,b). The recent studies are utilizing nonlinear programming, stochastic programming, fuzzy based linear and nonlinear programming techniques for solving various kinds of groundwater problems classified as forecasting, identification or management problems (Keshari and Datta 1996a,b, Keshari and Datta 2001). 5. RECENT AND EMERGING APPLICATIONS OF POROUS MEDIA FLOWS
OPTIMIZATION MODELS
In a number of real life scenarios, the main objective of water resource systems is to make the decisions for effectively meeting the goals and managing the water resources appropriately and optimally. Such decisions often require solutions under some restrictions or constraints placed upon variables that influence the decision. For example, in such decisions, we may list those related to the quantity, location and time of pumping from an aquifer and /or artificially recharging it with imported water when making these decisions, we have to consider the need for additional pumping and recharge installations, the quality of pumped water, the dangers of quality deterioration such as sea water intrusion or encroachment of water of inferior quality from adjacent aquifers, and the level and quality of water to be maintained in water bodies connected to an aquifer. It leads to arrive at the best decisions according to some specified criteria and subject to specified constraints. Such problems constitute a groundwater management problem.
The uses of theories describing flows through porous media are increasing to address increasingly complex groundwater problems to get the desired tangible results at the field level and to ensure water and environmental sustainability. Its uses in industrial applications are also increasing for sustainable development and newer applications. Such recent and emerging applications are presented briefly in following sections. 5.1 Water Supply Projects With the growing water demand for various purposes and the increase in water scarcity and water pollution problems, the dependence on groundwater resources is going up at a rapid rate. This has necessitated the focus on the integrated water resources management involving surface water and groundwater. Recent studies reveal that a variety of integrated water resources management plans are being either planned or feasibility is being explored. Such applications include optimal management of groundwater and surface water, rainwater harvesting, rooftop rainwater harvesting, exploiting flood storages and induced recharge in flood plains, and utilization of poor quality groundwater (Keshari 2014).
Management policy or decision can be tested for physical feasibility by using a model. For each policy which is found to be physically and technologically feasible, we can compute the values of some criteria selected for evaluating the different policies. In this way, the best policy can be found. This is the simulation approach, but is repetitive to arrive at the best solution and moreover it does not ensure an optimal solution. The better is to seek an optimal policy or decision by using a management or optimization model which ensures to arrive at the optimal solution and ensures about the feasibility when simulation model is linked internally or externally to the optimization model.
5.2 Vulnerability and Impact Assessment There has been increasing concerns regarding degradation of river water quality as well as groundwater from various natural and anthropogenic sources. The growing water pollution problems vary significantly in nature, complexity, dimension and severity. Many rivers as well as groundwater are getting polluted because of direct and indirect anthropogenic activities, industrial activities, encroachments, urbanization, lack of appropriate water quality management plans and ineffective regulation policies for water pollution prevention and control. The increased number of infrastructural projects and industrial growth and its poor green
A number of management models involving simulation and optimization techniques have been developed in the last two decades for arriving at the best solution and managing groundwater resources optimally. The early studies were based on the linear
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NATIONAL CONFERENCE ON RECENT ADVANCES IN MECHANICAL & CIVIL ENGINEERING AJAY KUMAR GARG ENGINEERING COLLEGE, GHAZIABAD status are making groundwater vulnerable. The emerging water quality problems are posing major challenges and serious environmental threat to drinking water supply because of alarming level of toxic contaminants in many regions, which in turn causing drinking water supply at the stake of health risk in both rural and urban areas.
5.3 Conjunctive Use of Poor Quality Groundwater and Canal Water Researches are being directed to investigate and obtain the appropriate management policies for the conjunctive use of poor quality groundwater and canal water. A number of such studies are being reported to ensure water sustainability as well as managing soil and groundwater contamination and ensuring food security (Kaledhonkar and Keshari 2006a,b).
To arrive at the best pollution prevention, control and management plans, a Comprehensive Impact Assessment (CIA) approach is being advocated to investigate possible consequences of any developmental or infrastructural activity to the hydrologic regime as well as environmental systems in totality. Fig. 1 shows various components of the CIA that can facilitate systematic and comprehensive evaluations utilizing modeling and tools involving hydraulic and environmental conditions of surface and subsurface systems and diverse objectives dealing with social, environmental and demand goals in order to arrive at the operating optimal management plans for effectively control the water pollution.
5.3 Use of wastewater in artificial recharge projects A large amount of wastewater is being generated from municipality and industries. The attention is gaining momentum to make use of wastewater after certain level of treatment in groundwater recharging in a controlled manner by specialized organizations (Keshari 2014). Such studies require coupled applications of water flows, contaminant transport and fate of organic and microbiological contaminants through porous media.
A number of modeling tools that utilize different approaches and vary in terms of structure, complexity, skills required for adaptation, data requirement, solution techniques and accuracy exist to address various kinds of water quality problems cropping at different scales (Keshari 2003a,b). These models are used depending upon their suitability and applicability to deal with specific water quality problem and the desired accuracy. Among these modelling approaches, numerical models are the most commonly used models (Konikow and Bredehoeft 1978, Voss 1984, Zheng 1990, Walter et al. 1994, Keshari and Datta 1996a,b, 2001, Keshari 2003a,b, Keshari and Parmar 2006). However, analytical models are of much relevance for testing the numerical models and getting a quick rough understanding about the water quality either for surface water or groundwater system. Integrated models involving numerical and remote sensing and GIS techniques are also now coming up (Keshari 2001, Keshari 2004, Dhiman and Keshari 2003a,b,c). Such impact assessment studies may be classified as Groundwater Impact Assessment (GIA), Groundwater Vulnerability Assessment (GVA) and Hydrological Impact Assessment (HIA) to clearly reflect the aims and objectives of such studies, instead of labeling with the broad terminology of Environmental Impact Assessment (EIA) which is more focused on the broad environmental impacts involving consequences to land, air and water at larger scale and often miss in quantifying or assessing the adverse implications to groundwater and hydrology that have far large implications because of strong connectivity to ecosystems.
5.4 Applications involving heat transport through porous media A number of problems such as climate change implications on subsurface and groundwater, groundwater recharge calculations, effect of deforestation or removal of green cover, geothermal springs and some industrial applications including nuclear waste disposal, air-conditioning using groundwater require knowledge of heat transport through porous media. Such studies are being witnessed now-a-days (Keshari and Koo 2007a,b).
Fig. 2 Components of CIA hypothesis (after Keshari 2008)
5.6 Flows through Hard Rock Areas and Multiphase Flows The current researches are being directed to develop improved models for understanding flows through hard rock areas as it is characterized by faults,
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NATIONAL CONFERENCE ON RECENT ADVANCES IN MECHANICAL & CIVIL ENGINEERING AJAY KUMAR GARG ENGINEERING COLLEGE, GHAZIABAD fractures, fissures, joints and lineaments, and these are strongly influenced by geological and tectonic activities. The analysis of NAPLs, hydrocarbon pollution and contamination resulting from landfills are being reported which involve applications of multiphase flows. The different approaches such as equivalent porous media, Monte-Carlo simulation, stochastic model, dual porosity model and parallel plate flows are coming up for improving the understanding of flows through hard rock areas. One such application in the Bhatti mines area is shown in Figs. 3-6.
Figs. 3-4 Photographs showing Bhatti mines area characterized by fractured quartzite rock (after Keshari 2004)
Figs. 5-6 Velocity vectors and hydraulic head and TDS concentration obtained from numerical model for Bhatti mines area (after Keshari 2004)
locality of construction area. The applications of porous media flows are now-a-days increasing to address such engineering problems.
5.7 Infrastructural Projects The urban and semi-urban areas are witnessing large infrastructural growth because of urbanization and economic growth. These infrastructural projects may be real estate or housing sector, shopping malls, civic services, transport sector, educational and official infrastructure, hospitality sector, health sector, or industrial sector. All these infrastructural projects require large amount of construction water that are often met from the groundwater. Many times, groundwater is dewatered during the construction to lay down the foundation of the construction as the groundwater table has to be brought down below the lower level of foundation, particularly with the raft foundation. The construction dewatering and construction water adversely affect the hydrogeological and groundwater regime in the
5.8 Industrial Applications The applications of porous media flows are also increasing in industrial applications. These applications vary hugely depending upon the industry type. The mining industries are more concerned with the porous media flows in terms of operations of mining activities as it affects their mining operations significantly, especially open cast mining are more vulnerable. These industries along with other industries such as refinery, paper and pulp, leather, textile, automobile, sugar, distillery, beverages and stone industries are concerned with wastewater disposal. These industries require large amount of water for processing and operations of
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plants, and thus the disposal of generated wastewater becomes a big challenge as it has huge potential of groundwater contamination. The ceramic industries also require the knowledge of porous media flows for the manufacturing processes.
emerging problems in infrastructural engineering and built environment. The industrial and engineering applications include construction dewatering, retrofitting structures, ceramics, groundwater quantity and quality problems associated with coal, petroleum, distillery, sugar and leather industries, leachate drainage system, infiltration galleries, riverbank filtration, rainwater harvesting and development of sustainable materials and reactive permeable systems. The study reveals that researches in the areas of flow through fractured rocks or hard rock areas, multiphase flows, reactive contaminant transport, multicomponent and multispecies transport through unsaturated and saturated porous media, subsurface heat and energy transport, subsurface characterization, vulnerability assessment, bioremediation, stream-aquifer interactions, conjunctive water use planning, integrated water resources management and sustainable development are drawing attention and gaining momentum.
5.9 Structure Retrofitting The current research is also focusing on the life cycle of infrastructural projects. The structures are susceptible to deterioration with time because of weathering and interactions with the surrounding environment. The corrosion and ingress of chemical species into the pores of concrete are being witnessed and such studies are gaining attention with reference to retrofitting of structures. These studies require applications of porous media flows including unsaturated flows and solute transport. 6.
CONCLUSIONS
The study reveals that a long path in the advancement of porous media flows has taken place to address the increasing complex problems of natural systems and municipal, agricultural and industrial sectors. It has taken a long leap from the early pioneering work of Darcy in 1856 to the current knowledge of advanced numerical models coupled with advancements in its various facets characterized by geological, physical, chemical and biological systems. Research carried out in the 1940s and 1950s produced a number of quantitative analytical tools to predict response of aquifers to pumping and to determine aquifer parameters and impact on the hydraulic head in the aquifers, and subsequently significant developments took place that focused on the development of numerical models, constitutive relationships, processes descriptions, subsurface characterization and integrating analytical and numerical models with emerging and decision making techniques such as optimization, geostatistics, fuzzy algorithms, ANNs, GIS and remote sensing that has helped to improve the understanding of subsurface and groundwater flows through various geological formations and deposits. These developments have enabled to address increasingly complex pressing water and environmental problems encountered in today’s life as the availability of freshwater resources is decreasing due to increased demand, declining groundwater level, reduced river flows, growing water pollution, hydrological uncertainty and adverse implications of climate change. Advancements in porous media theories have resulted into numerous industrial applications also including addressing
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