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Über dieses Buch

Coastal aquifers serve as major sources for freshwater supply in many countries around the world, especially in arid and semi-arid zones. Many coastal areas are also heavily urbanized, a fact that makes the need for freshwater even more acute. Coastal aquifers are highly sensitive to disturbances. Inappropriate management of a coastal aquifer may lead to its destruction as a source for freshwater much earlier than other aquifers which are not connected to the sea. The reason is the threat of seawater intrusion. In many coastal aquifers, intrusion of seawater has become one of the major constraints imposed on groundwater utilization. As sea­ water intrusion progresses, existing pumping wells, especially those close to the coast, become saline and have to be abandoned. Also, the area above the intruding seawater wedge is lost as a source of natural replenishment to the aquifer. Despite the importance of this subject, so far there does not exist a book that integrates our present knowledge of seawater intrusion, its occurrences, physical mechanism, chemistry, exploration by geo­ physical and geochemical techniques, conceptual and mathematical modeling, analytical and numerical solution methods, engineering measures of combating seawater intrusion, management strategies, and experience learned from case studies. By presenting this fairly comprehensive volume on the state-of-the-art of knowledge and ex­ perience on saltwater intrusion, we hoped to transfer this body of knowledge to the geologists, hydrologists, hydraulic engineers, water resources planners, managers, and governmental policy makers, who are engaged in the sustainable development of coastal fresh ground­ water resources.



Chapter 1. Introduction

Of all the water on earth, it is estimated that 99.4% (1.4 x 109 km3) is surface water. Groundwater occurs only as 0.6% (9 x 106 km3) of the total. However, of the vast amount of surface water, most of it is in the form of saltwater in oceans and inland seas (97%). Fresh surface water accounts for only 2% of the total volume of water.
J. Bear, A. H.-D. Cheng

Chapter 2. Geophysical Investigations

Saltwater intrusion is the mass transport of saline waters into zones previously occupied by fresher waters. In hydrogeologic systems mass transport rates and pathways are determined by hydraulic gradients and the distribution of hydraulic conductivity. The configuration of the saltwater interface and its movement are determined by the configuration of the water table and the spatial variation in hydraulic conductivity. One objective of geophysical surveys in island and coastal environments is to help define the physical framework within which saltwater intrusion occurs. Geophysical methods which can distinguish geologic units on the basis of their physical properties, such as seismic methods, can be very useful even though they cannot detect saline waters directly.
M. T. Stewart

Chapter 3. Geochemical Investigations

Saltwater intrusion is one of the most wide-spread and important processes that degrades water-quality by raising salinity to levels exceeding acceptable drinking and irrigation water standards, and endangers future exploitation of coastal aquifers. This problem is intensified due to population growth, and the fact that about 70% of the world population occupies coastal plains. Human activities (e.g., water exploitation, including industry and agriculture, reuse of waste water) result in accelerating water development and salinization. The elucidation of the dynamic nature of the fresh-saline water transition zone is of both scientific and practical interest because it reflects or controls the extent of development or exploitation.
B. F. Jones, A. Vengosh, E. Rosenthal, Y. Yechieli

Chapter 4. Exploitation, Restoration and Management

When dealing with exploitation, restoration and management of fresh groundwater in coastal aquifers the key issue is saltwater intrusion. Saltwater intrusion in groundwater is defined as the inflow of saline water in an aquifer system. This inflow can be in a steady state but mostly it is a transient process. In the latter case the inflowing saline water replaces fresh groundwater which was originally present in the system. The freshwater disappears by outflow at a rate roughly equal to the rate of inflow of saline water. This simultaneous outflow of fresh groundwater can take place either in a natural way, by seepage, or by abstraction. The result is an increase of the volume of saline groundwater and a decrease of the volume of fresh groundwater.
J. C. van Dam

Chapter 5. Conceptual and Mathematical Modeling

In many coastal aquifers, intrusion of seawater has become one of the major constraints affecting groundwater management. As seawater intrusion progresses, existing pumping wells, especially close to the coast, become saline and have to be abandoned, thus, reducing the value of the aquifer as a source of freshwater. Also, the area above the intruding seawater wedge is lost as a source of water (by natural replenishment). A detailed review of exploitation, restoration, and management of fresh groundwater in coastal aquifers is presented in Chapter 4, as well as in other chapters throughout this volume.
J. Bear

Chapter 6. Analytical Solutions

Due to their simplified physical assumptions and geometry, analytical solutions normally do not directly solve “real-world” problems. Nevertheless, they serve a number of important purposes. First, they are useful as instructional tools. For a hydrogeologist investigating saltwater intrusion it is imperative that he attains a clear understanding of the mechanical trend of the flow. Elegant analytical solutions are most useful in presenting such fundamental insights, while numerical solutions are often not. In fact, a person without such physical insights should not be entrusted with a powerful numerical tool to solve complicated problems, as such a person can have blind spots that harbor catastrophic consequences.
A. H.-D. Cheng, D. Ouazar

Chapter 7. Steady Interface in Stratified Aquifers of Random Permeability Distribution

Models of salt and fresh waters flow in coastal aquifers serve as important tools for assessing the extent of saltwater intrusion and for planning the rational exploitation of water resources. In a few circumstances the seawater is separated from the overlaying freshwater body by a relatively narrow zone which can be approximated by a sharp interface. Then, the aim of modeling is to determine the shape of the interface and the flow field in the two water bodies.
G. Dagan, D. G. Zeitoun

Chapter 8. USGS SHARP Model

In many coastal settings, aquifer systems consist of sequences of layers with varying hydraulic properties. An idealized cross section through a layered coastal aquifer system extending offshore to a submarine canyon outcrop is shown in Figure 8.1. Under natural, undisturbed conditions an equilibrium seaward hydraulic gradient exists within each aquifer, with excess freshwater discharging to the sea (Figure 8.1a). In the uppermost, unconfined aquifer the freshwater flows out to sea across the ocean floor. In the lower, confined aquifers the freshwater discharges to the sea by leaking upward through the overlying layers and/or by flowing out the canyon outcrop. Within each layer a wedge-shaped body of denser seawater will develop beneath the lighter freshwater.
H. I. Essaid

Chapter 9. USGS SUTRA Code — History, Practical Use, and Application in Hawaii

The U.S. Geological Survey’s SUTRA code is the most widely used simulator in the world for seawater intrusion and other variabledensity groundwater flow problems based on solute transport or heat transport. Since its initial release in 1984, the SUTRA code has also been widely used for many other types of problems. It is routinely employed for hydrogeologic analyses published in both white and gray scientific literature, and for many practical engineering studies that are not widely distributed. It is used in university courses to teach hydrologic concepts and modeling.
C. I. Voss

Chapter 10. Three-Dimensional Model of Coupled Density-Dependent Flow and Miscible Salt Transport

Saltwater intrusion in coastal aquifers is a very serious threat to subsurface water quality worldwide. This contamination of freshwater resources occurs, in a typical scenario, when the wide cone of depression formed by extensive groundwater pumping comes into contact with underlying or surrounding seawater. Twenty years ago Newport [1977] reported that at least twenty coastal areas in the United States were contaminated by saline water. Documented cases have since been reported for many other countries. Contamination by salt deteriorates water quality dramatically. A two to three percent mixing with seawater makes freshwater unsuitable for human consumption, and five percent mixing makes it unusable for irrigation as well [Custodio et al., 1987; Sherif and Singh, 1996].
G. Gambolati, M. Putti, C. Paniconi

Chapter 11. Modified Eulerian Lagrangian Method for Density Dependent Miscible Transport

The lithologic sequence of the Israeli coastal aquifer is composed of calcareous sandstone of the Pleistocene age, silt and intercalation of clay and loam which can appear as lenses. The basis of this aquifer is built on sea clays and shales from the Neogene age. Within a zone of approximately five km. from the sea, these clay layers separate the aquifer into three major sub-aquifers. Mostly in the south, the central one is further subdivided into additional three sub-aquifers. Each of these sub-aquifers constitutes its own hydrologic characteristics. This type of aquifers is highly heterogeneous due to the influences of the following factors [Correns, 1950; McBrride, 1977; Curtis, 1961]:
Lithologic (i.e. high spatial variability of thickness of the silt, clay and sandstone layers)
Diagenesis (i.e. cement re-sedimentation, high spatial variability of the secondary porosity), and
Post sedimentation tectogenesis, that may be reflected as fractures of the cemented sandstones.
S. Sorek, V. Borisov, A. Yakirevich

Chapter 12. Survey of Computer Codes and Case Histories

To assemble the pertinent research in this field we have provided sections explaining the essence of each contribution. The contributors were asked to provide a series of short summaries introducing the attributes of their models and, where appropriate, case histories. Each contributor was asked to make a series of brief statements that would fit into a table (some are in a condensed form).
S. Sorek, G. F. Pinder

Chapter 13. Seawater Intrusion in the United States

The growth of industry and population in the United States during most of its history has been concentrated in coastal areas having good access to ports. Thus, those coastal areas that also had abundant groundwater resources were the areas where seawater intrusion became a serious concern or problem. These areas included much of the Atlantic and Gulf Coastal Plains, the carbonate aquifers of coastal Florida, alluvial basins along the California coast, and the volcanic islands of Hawaii. These coastal zones combined represent a total distance of approximately 5,000 km along which seawater is potentially intruding into productive aquifers (see Figure 13.1). The potential problem of seawater intrusion was recognized in the United States as soon as the first U.S. water well was drilled in 1824 in New Jersey [Back and Freeze, 1983, p. 90]. In reviewing the occurrence and geochemical significance of saltwater, Back and Freeze [1983] further note that the problem was recognized as early as 1854 on Long Island, New York.
L. F. Konikow, T. E. Reilly

Chapter 14. Impact of Sea Level Rise in the Netherlands

At this moment, a large number of coastal aquifers, especially shallow ones, already experience a severe saltwater intrusion caused by both natural as well as man-induced processes. Coastal aquifers, which are situated within the zone of influence of mean sea level (M.S.L.), will be threatened even more by the rise in global mean sea level. Present estimates of global mean sea level rise, as presented in the Intergovernmental Panel of Climate Change (IPCC) Second Assessment Report, range from 20 to 86 cm from the year 1990 to 2100, with a best estimate of 49 cm, including the cooling effect of aerosols [Warrick et al., 1995]. The extent of the impact of sea level rise on coastal aquifers depends on: (1) the time lag before a new state of dynamic equilibrium of the salinity distribution is reached and (2) the zone of influence of sea level rise in the aquifers.
G. H. P. Oude Essink

Chapter 15. Movement of Brackish Groundwater Near a Deep-Well Infiltration System in the Netherlands

The dune area along the Northsea coast in the western part of the Netherlands is one of the most valuable areas in the country. To keep the groundwater, for ecological reasons, at an adequately high level and to avoid regional rising of brackish groundwater, groundwater abstraction has been reduced in the last 30 years. However, in the Netherlands soil passage is preferred as disinfection method to produce drinking water. Therefore, the reduced groundwater abstraction is compensated by artificial recharge and abstraction of pre-treated surface water, which has become the predominant production method in the western part of the Netherlands. Particularly the method of deep-well infiltration is winning ground because of small space demands and relatively low hydrological or ecological impacts.
A. Stakelbeek

Chapter 16. A Semi-Empirical Approach to Intrusion Monitoring in Israeli Coastal Aquifer

The basic elements of groundwater quality monitoring programs in general, and saltwater intrusion control in particular, involve the definition of monitoring policy and objectives. The implementation of these objectives include design of facilities and instruments, field surveys, sample collection, data analysis, evaluation of the information, characterization of possible scenarios of saltwater intrusion and operational decisions. The strategy of designing a monitoring program depends mainly upon the natural and political-administrative boundaries of the area of concern, the quantity and quality of existing records regarding aquifer geology, the groundwater regime, other sources and types of contaminants, and available financial resources [WMO, 1988; Melloul and Goldenberg, 1994].
A. J. Melloul, D. G. Zeitoun

Chapter 17. Nile Delta Aquifer in Egypt

Egypt lies between latitudes 22° and 32° North, and longitudes 25° and 35° East. The North boundary of Egypt is the Mediterranean Sea, and the East is the Red Sea. The South and West are political boundaries with Sudan and Libya, respectively. Land area of Egypt is about one million km2, 94% of which is desert. The population of the country is currently estimated as 62 million.
M. Sherif


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