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1987 | Buch

Introduction Kapitel lesen Erstes Kapitel lesen

Modeling Groundwater Flow and Pollution

verfasst von: Jacob Bear, Arnold Verruijt

Verlag: Springer Netherlands

Buchreihe : Theory and Applications of Transport in Porous Media

Enthalten in: Professional Book Archive

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Über dieses Buch

Groundwater constitutes an important component of many water resource systems, supplying water for domestic use, for industry, and for agriculture. Management of a groundwater system, an aquifer, or a system of aquifers, means making such decisions as to the total quantity of water to be withdrawn annually, the location of wells for pumping and for artificial recharge and their rates, and control conditions at aquifer boundaries. Not less important are decisions related to groundwater qUality. In fact, the quantity and quality problems cannot be separated. In many parts of the world, with the increased withdrawal of ground­ water, often beyond permissible limits, the quality of groundwater has been continuously deteriorating, causing much concern to both suppliers and users. In recent years, in addition to general groundwater quality aspects, public attention has been focused on groundwater contamination by hazardous industrial wastes, by leachate from landfills, by oil spills, and by agricultural activities such as the use of fertilizers, pesticides, and herbicides, and by radioactive waste in repositories located in deep geological formations, to mention some of the most acute contamination sources. In all these cases, management means making decisions to achieve goals without violating specified constraints. In order to enable the planner, or the decision maker, to compare alternative modes of action and to ensure that the constraints are not violated, a tool is needed that will provide information about the response of the system (the aquifer) to various alternatives.

Inhaltsverzeichnis

Frontmatter
Chapter One. Introduction
Abstract
The objective of this chapter is to set the stage for the modeling procedure and methodology presented in subsequent chapters: what is it that we wish to model and why and, especially, how do we model?
Jacob Bear, Arnold Verruijt
Chapter Two. Groundwater Motion
Abstract
As part of the hydrologic cycle, groundwater is always in motion from regions of natural and artificial replenishment to those of natural and artificial discharge. Bodies of stagnant, usually saline, water trapped in various porous geological formations do exist, but are of little interest to the groundwater hydrologist. When the salinity level of such water is acceptable, water can be mined from such nonreplenishable formations, until the resource is depleted.
Jacob Bear, Arnold Verruijt
Chapter Three. Modeling Three-Dimensional Flow
Abstract
The basic laws governing the flow of water were presented in the previous chapter. However, one cannot solve flow problems by using only these laws. Equation (2.1.19) is a single equation in two dependent variables: q(x, y, z, t) and ø(x, y, z, t). It can also be regarded as three equations in four unknowns ø, q x , q y ,q z . This means that one additional equation is required in order to obtain a complete description of the flow within any given domain. Similarly, we have Q’(x,y, t) and \(\tilde \phi \left( {x, y, t} \right)\) in the single equation (2.2.7) and Q’(x,y, t) and h(x,y, t) in the single equation (2.3.9). The additional basic law that we have to invoke is that of mass conservation,or mass balance.
Jacob Bear, Arnold Verruijt
Chapter Four. Modeling Two-Dimensional Flow in Aquifers
Abstract
In this chapter we shall develop models that describe groundwater flow in confined, phreatic, and leaky aquifers on the basis of the essentially horizontal flow approximation (≡ the hydraulic approach) discussed in Section 1.5. Obviously, such models may be used only when this approximation is indeed justified.
Jacob Bear, Arnold Verruijt
Chapter Five. Modeling Flow in the Unsaturated Zone
Abstract
In order to reach a phreatic aquifer, water from precipitation, from irrigation, or from an influent river, infiltrates through the ground surface and percolates downward through the unsaturated zone. The same is true for pollutants carried with the water. These pollutants may be already present in the water reaching the ground surface, or they may be added to the water by processes of leaching, dissolution, and desorption along its path, from the ground surface to an underlying aquifer. Solid waste in landfills, septic tanks, fertilizers, pesticides and herbicides, applied over extended areas and dissolved in the water applied to the ground surface, may serve as examples of sources of pollutants that travel through the unsaturated zone.
Jacob Bear, Arnold Verruijt
Chapter Six. Modeling Groundwater Pollution
Abstract
So far, we have discussed only the movement and storage of water in various types of aquifers, overlooking a major problem which is of interest in any development and management of a water resources system, namely that of water quality. In fact, with the increased demand for water in most parts of the world, and with the intensification of water utilization, the quality problem becomes the limiting factor in the development and use of water resources. Although in some regions, the quality of both surface and groundwater resources deteriorates, special attention should be devoted to the pollution of groundwater in aquifers due to the very slow velocity of the water and to the possibility of an interaction of the pollutants with the solid matrix. Although it may seem that groundwater is more protected than surface water, it is still subject to pollution, and when the latter occurs, the restoration to the original, nonpolluted state, is usually more difficult and lengthy.
Jacob Bear, Arnold Verruijt
Chapter Seven. Modeling Seawater Intrusion
Abstract
Coastal aquifers constitute important sources for water. Many coastal areas are also heavily urbanized, a fact which makes the need for fresh water even more acute. However, the proximity of the sea, with the contact between freshwater and seawater in a coastal aquifer, requires special attention and special management techniques.
Jacob Bear, Arnold Verruijt
Chapter Eight. Introduction to Numerical Methods
Abstract
In the previous chapters, the phenomena of transport in porous media have been described by mathematical models. The complete description was made up of a partial differential equation, or a system of several partial differential equations, together with initial conditions and boundary conditions. In order to solve a given groundwater problem, this system of equations must be solved, for the specific data of that problem. This can be done by using analytical methods, or numerical techniques. For most problems of practical interest, because of the irregular shape of the boundaries, the spatial variability of the coefficients appearing in the equations and in the boundary conditions, the nonuniformity of the initial conditions, and the nonanalytic form of the various source and sink terms, analytical solutions are virtually impossible, except for relatively simple problems. Solutions of most problems can be obtained only by numerical methods. Hence, in this book numerical methods of solution are used almost exclusively. They provide a most powerful and general tool for solving problems encountered in practice. In this chapter, some general aspects will be discussed. In Chapters 9–13 specific problems will be solved, and actual numerical models will be presented.
Jacob Bear, Arnold Verruijt
Chapter Nine. The Finite Difference Method
Abstract
In this chapter the finite difference method is presented, for problems of steady and nonsteady groundwater flow. The presentation will be oriented towards the introduction of simple computer programs, written in BASIC, that can be run on personal computers.
Jacob Bear, Arnold Verruijt
Chapter Ten. The Finite Element Method
Abstract
In this chapter the principles of the finite element method will be presented through the application to problems of steady and nonsteady groundwater flow. The method was developed in the 1950’s, first for problems of aeronautical engineering (the construction of airplanes), mechanical engineering (nuclear reactor vessels), and civil engineering (bridges). In later years, the method was generalized to practically all areas of engineering, including groundwater flow, where the solution to field equations is required.
Jacob Bear, Arnold Verruijt
Chapter Eleven. Transport by Advection
Abstract
The basic theory of pollution transport by advection, dispersion, and diffusion, in groundwater, has been presented in Chapter 6. Numerical models for that general case are considered in Chapter 12. In this chapter, numerical models are presented for an approximate model (Section 6.6), in which the transport of a polluting component is taking place by advection only, neglecting transport by mechanical dispersion and molecular diffusion. In such a model the pollutant is transported at the average velocity of the water, which acts as its carrier.
Jacob Bear, Arnold Verruijt
Chapter Twelve. Transport by Advection and Dispersion
Abstract
In the previous chapter, numerical models for the main mechanism of transport in porous media — advection — were presented. In reality, the transport of particles of a component of a pollutant is also influenced by diffusion and dispersion, which cause a spreading of the pollutant over an ever-growing region. Thus, the groundwater may be polluted over a much larger region than in the case of pure advection, with a corresponding reduction in the maximum and average concentrations of the pollutant. The conceptual and mathematical modeling of these phenomena are discussed in Chapter 6. In this chapter, some numerical models for the quantitative analysis of transport by advection and dispersion are presented. These include a fully numerical two-dimensional method, and a semi-analytical method, using a random walk model. For didactic reasons, the simple one-dimensional case will be considered first. This case is discussed in order to show that the numerical analysis of dispersion may involve a rather disturbing influence of discretization, i.e., numerical dispersion which should be recognized and, if possible, reduced, or at least controlled.
Jacob Bear, Arnold Verruijt
Chapter Thirteen. Numerical Modeling of Seawater Intrusion
Abstract
The conceptual and mathematical models for seawater intrusion are presented in Chapter 7. In this chapter, two numerical models are presented for the analysis of groundwater flow in an aquifer saturated with two fluids (e.g., fresh and salt water), separated by a sharp interface. The first model applies to the flow in a vertical plane, in which the location of the interface is time-dependent, because of boundary conditions, pumping wells, etc. In this model, the flow domain (in the vertical plane) is subdivided into small elements, such that the interface is represented by a series of elements, connecting certain nodes in the mesh. As the interface moves, the location of the nodes upon it changes, so that the entire mesh is changing as a function of time.
Jacob Bear, Arnold Verruijt
Backmatter
Metadaten
Titel
Modeling Groundwater Flow and Pollution
verfasst von
Jacob Bear
Arnold Verruijt
Copyright-Jahr
1987
Verlag
Springer Netherlands
Electronic ISBN
978-94-009-3379-8
Print ISBN
978-1-55608-015-9
DOI
https://doi.org/10.1007/978-94-009-3379-8