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Über dieses Buch

In many parts of the world, groundwater resources are under increasing threat from growing demands, wasteful use, and contamination. To face the challenge, good planning and management practices are needed. A key to the management of groundwater is the ability to model the movement of fluids and contaminants in the subsurface. The purpose of this book is to construct conceptual and mathematical models that can provide the information required for making decisions associated with the management of groundwater resources, and the remediation of contaminated aquifers.

The basic approach of this book is to accurately describe the underlying physics of groundwater flow and solute transport in heterogeneous porous media, starting at the microscopic level, and to rigorously derive their mathematical representation at the macroscopic levels. The well-posed, macroscopic mathematical models are formulated for saturated, single phase flow, as well as for unsaturated and multiphase flow, and for the transport of single and multiple chemical species. Numerical models are presented and computer codes are reviewed, as tools for solving the models. The problem of seawater intrusion into coastal aquifers is examined and modeled. The issues of uncertainty in model input data and output are addressed. The book concludes with a chapter on the management of groundwater resources. Although one of the main objectives of this book is to construct mathematical models, the amount of mathematics required is kept minimal.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
The objective of this book is to present the methodology and procedure for constructing complete conceptual and mathematical models of two types of problems: (1) groundwater flow, and (2) groundwater contaminant transport, both in the saturated and unsaturated zones. The construction of such models, however, is not the ultimate goal. In fact, these models are used as essential tools for the planning and management for sustainable use of groundwater resources. This use of models is based on our belief that the physical reality can be represented by mathematical models, albeit with acceptable approximations. In this chapter, we examine the concept, process, and limitations of modeling.
J. Jacob Bear, H.-D. Alexander Cheng

Chapter 2. Groundwater and Aquifers

Abstract
Subsurface water, or groundwater, is a term used to denote all the waters found beneath ground surface. However, groundwater hydrologists, who are primarily (but not exclusively) concerned with the water contained in the zone of saturation (Subs. 1.1.1), often use the term ‘groundwater’ to denote water in only this zone. In this book, we adhere to this definition, using the term subsurface water to denote all the water below ground surface. Practically, all groundwater can be regarded as part of the hydrological cycle (Fig. 1.1.1; or see any textbook on Hydrology). Very small amounts, however, may enter the cycle from other sources (e.g., magmatic water).
J. Jacob Bear, H.-D. Alexander Cheng

Chapter 3. Regional Groundwater Balance

Abstract
The groundwater part of the hydrological cycle is presented in Fig. 1.1.1. In the management of groundwater resources, man intervenes in the this cycle in order to achieve beneficial goals. This intervention takes the form of modifications imposed on the various components of the water balance, for example by pumping, by artificial recharge or by affecting natural replenishment. Another, unfortunately detrimental effect is the contamination of groundwater by human activities at ground surface.
J. Jacob Bear, H.-D. Alexander Cheng

Chapter 4. Groundwater Motion

Abstract
As part of the hydrological cycle (Subs. 1.1.1), water from precipitation infiltrates through ground surface and percolates, primarily downward, through the unsaturated zone, or vadose zone, until it reaches a water table. The source of the infiltrating water may also be irrigation, or infiltration ponds for the purpose of artificially recharging an underlying aquifer.
J. Jacob Bear, H.-D. Alexander Cheng

Chapter 5. Water Balance and Complete Flow Model

Abstract
Each of the motion equations discussed in Chap. 4 involves two dependent variables: the flux and the pressure (or piezometric head, or suction). For example, (4.1.24) involves q and h, while (4.2.43) involves q and p. Therefore, to obtain a solution, we need one additional equation. This is the mass balance equation of the fluid phase. This equation is considered in this chapter.
J. Jacob Bear, H.-D. Alexander Cheng

Chapter 6. Unsaturated Flow Models

Abstract
The previous two chapters dealt with the modeling of groundwater flow in aquifers, i.e., in the saturated zone. However, as emphasized on several occasions already in Chaps. 1 and 2, certain flow processes, which take place in the unsaturated zone, or zone of aeration (Fig. 2.2.1), are highly important also from the regional point of view and should be incorporated in our modeling considerations. The first example is the infiltration process. A phreatic aquifer is replenished from above by water from various sources: precipitation, irrigation, artificial recharge by surface spreading techniques, etc. In all these cases, water moves downward, from ground surface to the water table, through the unsaturated zone. The understanding of, and, consequently, the ability to calculate and predict the movement of water in the unsaturated zone is, therefore, essential when we wish to determine the replenishment of a phreatic aquifer. A second example is related to the contamination of groundwater from sources at ground surface. Contaminants from such sources dissolve in water applied to ground surface. The infiltrating water will then carry the dissolved contaminants as it moves downward towards the water table. As contaminants travel downward with the infiltrating water, various phenomena, e.g., dispersion and adsorption, take place. These affect the concentration of pollutants in the water, which, eventually, reaches the water table. The ability to forecast the movement and accumulation of contaminants in the unsaturated zone is required if we wish to clean the subsurface from these contaminants, or to determine the rate at which they will reach the water table. However, one cannot study the movement of contaminants carried by the water without information on the movement of the water itself. In this chapter we shall discuss the modeling of flow in unsaturated flow.
J. Jacob Bear, H.-D. Alexander Cheng

Chapter 7. Modeling Contaminant Transport

Abstract
The issue of contamination of water in the subsurface was introduced in Subs. 1.1.5. In that subsection, we have also listed a number of the more common sources of subsurface contamination.
J. Jacob Bear, H.-D. Alexander Cheng

Chapter 8. Numerical Models and Computer Codes

Abstract
As stated in the Preface, and emphasized repeatedly, the objective of this book is to present and discuss the underlying fundamentals, as well as the actual construction, of groundwater flow and solute transport models. Such models can predict the future behavior, e.g., in the form of water levels and solute concentrations, in specified subsurface domains. The relevant domains of interest here are aquifers and the unsaturated zone. So far, we have been focussing only on conceptual and mathematical models. We have repeatedly emphasized, and we shall do so again in Chap. 11, that optimal management decisions should not be made unless we use models to predict the consequences of implementing the proposed decision alternatives. By analyzing these consequences, or forecasts, we can make sure that constraints are not violated, and that the optimal decision alternative is, indeed, selected. Such forecasts can be made by solving the mathematical models that simulate the behavior in the domain of interest, in response to the implementation of various proposed alternative decisions. Unfortunately, although analytical solutions are preferable, they are seldom possible for problems of practical interest, because of the irregular boundaries of the problem domain, the heterogeneity of the domain, with respect to its physical parameters, and, sometimes, the nonlinearity of the equations. Instead, computer-based numerical methods are used in practice for solving (or ‘running’) these models.
J. Jacob Bear, H.-D. Alexander Cheng

Chapter 9. Seawater Intrusion

Abstract
In many parts of the world, coastal aquifers constitute an important source of water. Often, coastal areas are also heavily populated, a fact that makes the demand for freshwater even more acute. Due to the proximity and contact with the sea, the planning and management of such aquifers requires special attention associated with the danger of seawater (or saltwater) intrusion. In fact, this phenomenon constitutes one of the major constraints in the management of groundwater in costal aquifers. As seawater intrusion progresses, the part of the aquifer close to the sea becomes saline, and pumping wells that operate close to the coast have to be abandoned. Also, the area above the intruding seawater wedge, which remains fresh by natural replenishment, is lost as a source of freshwater.
J. Jacob Bear, H.-D. Alexander Cheng

Chapter 10. Modeling Under Uncertainty

Abstract
Up to this point, all the modeling efforts presented in this book have been based on the deterministic approach. This approach assumes (1) a full knowledge and understanding of the physical/chemical processes that occur within an investigated domain, (2) a mathematical model that correctly represents these processes and can be used to predict future responses to imposed excitations, (3) the availability of information (measured or derived) on all parameters and coefficients that appear in the mathematical model, and, on the domain’s geometry, as well as on the initial and boundary conditions.
J. Jacob Bear, H.-D. Alexander Cheng

Chapter 11. Optimization, Inverse, And Management Tools

Abstract
The management of a groundwater system—an aquifer, or a system of aquifers—alone, or conjunctively with surface water sources, aims at achieving certain goals through a set of decisions concerning the development and/or operation of the system. Typically, the same goal or goals can be achieved by different management alternatives, each involving a specific set of decisions. Management means the selection and implementation of the best, or optimal set of decisions.
J. Jacob Bear, H.-D. Alexander Cheng

Backmatter

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