Государственный комитет Республики Узбекистан

Figure 8.38 (a) Saltwater-freshwater interface in a confined coastal aquifer under conditions of steady-state seaward flow; (b) seawater intrusion due to pumping.
One of the most intensively studied coastal aquifers in North America is the Biscayne aquifer of southeastern Florida (Kohout, 1960a, 1960b). It is an unconfined aquifer of limestone and calcareous sandstone extending to an average depth of 30m below sea level. Field data indicate that the saltwater front undergoes transient changes in position under the influence of seasonal recharge patterns and the resulting water-table fluctuations. Lee and Cheng (1974) and Segol and Pinder (1976) have simulated transient conditions in the Biscayne aquifer with finite-element numerical models. Both the field evidence and the numerical modeling confirm the necessity of considering dispersion in the steady-state and transient analyses. The nature of dispersion in groundwater flow will be considered more fully in Chapter 9 in the context of groundwater contamination.
Todd (1959) summarizes five methods that have been considered for controlling seawater intrusion: (1) reduction or rearrangement of the pattern of groundwater pumping, (2) artificial recharge of the intruded aquifer from spreading basins or recharge wells, (3) development of a pumping trough adjacent to the coast by means of a line of pumping wells parallel to the coastline, (4) development of a freshwater ridge adjacent to the coast by means of a line of recharge wells parallel to the coastline, and (5) construction of an artificial subsurface barrier. Of these five alternatives, only the first has been proven effective and economic. Both Todd (1959) and Kazmann (1972) describe the application of the freshwater-ridge concept in the Silverado aquifer, an unconsolidated, confined, sand-and-gravel aquifer in the Los Angeles coastal basin of California. Kazmann concludes that the project was technically successful, but he notes that the economics of the project remain a subject of debate.
^*Following Poland and Davis (1969), we are using the term “compaction” in its geological sense. In engineering jargon the term is often reserved for the increase in soil density achieved through the use of rollers, vibrators or other heavy machinery.
Suggested Readings
BOUWER, H., and R. D. JACKSON. 1974. Determining soil properties. Drainage for Agriculture, ed. J. van Schilfgaarde. American Society of Agronomy, Madison, Wis., pp. 611–672.
COOPER, H. H. JR., F. A. KOHOUT, H. R. HENRY, and R. E. GLOVER. 1964. Sea water in coastal aquifers. U.S. Geol. Surv. Water-Supply Paper 1613C, 84 pp.
FERRIS, J. G., D. B. KNOWLES, R. H. BROWNE, and R. W. STALLMAN. 1962. Theory of aquifer tests. U.S. Geol. Surv. Water-Supply Paper I536E.
HANTUSH, M. S. 1964. Hydraulics of wells. Adv. Hydrosci., 1, pp. 281–432.
KRUSEMAN, G. P., and N. A. DE RIDDER. 1970. Analysis and evaluation of pumping test data. Intern. Inst. for Land Reclamation and Improvement Bull. 11, Wageningen, The Netherlands.
NEUMAN, S. P., and P. A. WITHERSPOON. 1969. Applicability of current theories of flow in leaky aquifers. Water Resources Res., 5, pp. 817–829.
POLAND, J. F., and G. H. DAVIS. 1969. Land subsidence due to withdrawal of fluids. Geol. Soc. Amer. Rev. Eng. Geol., 2, pp. 187–269.
PRICKETT, T. A. 1975. Modeling techniques for groundwater evaluation. Adv. Hydrosci., 11, pp. 46–66, 91–116.
REMSON, I., G. M. HORNBERGER, and F. J. MOLZ. 1971. Numerical Methods in Subsurface Hydrology. Wiley Interscience, New York, pp. 56–122.
STALLMAN, R. W. 1971. Aquifer-test design, observation and data analysis. Techniques of Water Resources Investigations of the U.S. Geological Survey, Chapter B1. Government Printing Office, Washington, D.C.
YOUNG, R. A., and J. D. BREDEHOEFT. 1972. Digital computer simulation for solving management problems of conjunctive groundwater and surface-water systems. Water Resources Res., 8, pp. 533–556.