FIGURE 2.3 The effect of pumping on service flows provided by a hypothetical aquifer. With regard to this inventory, the following points are worth noting: (1) Prior to pumping the aquifer, natural recharge equaled natural discharge, and the ground water basin was in a steady state. (2) With the addition of pumping and in the course of withdrawals from storage, net recharge to the aquifer from stream flow increased and reached some maximum value (i.e., part of the stream flow was captured by pumping the aquifer), whereas discharge by evapotranspiration decreased and approached some minimum value (i.e., the amount of plant-viable water was reduced). (3) During the course of the withdrawals, the basin was in a transient state where water was continually being withdrawn from storage. Although not shown, this results in a continual decline in water levels. A new steady state could be achieved by reducing pumping to about 3.8' 107 m3 yr-1, but the steady state would include the reduced stream flow and evapotranspiration. Data for this figure were taken from Domenico and Schwartz, 1990. (Reprinted with permission from John Wiley & Sons, Inc., 1990. Copyright 1990 by John Wiley & Sons, Inc.)

supplies generally are far superior to surface water sources (American Water Works Association, 1990). Indeed, where available, ground water basins afford benefits of storage, conveyance, and treatment that often render the ground water resource preferable to surface water alternatives from the standpoint of health protection, technical simplicity, economy, and public acceptance.

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