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<br />Humans change the natural or predevelop- <br />ment flow system by withdrawing (pumping) <br />water for use, changing recharge patterns by irri- <br />gation and urban development, changing the type <br />of vegetation, and other activities. Focusing our <br />attention on the effects of withdrawing ground <br />water, we can conclude that the source of water <br />for pumpage must be supplied by (1) more water <br />entering the ground-water system (increased <br />recharge), (2) less water leaving the system <br />(decreased discharge), (3) removal of water that <br />was stored in the system, or some combination <br />of these three. <br /> <br />This statement, illustrated in Figure 88, can <br />be written in terms of rates (or volumes over a <br />specified period of time) as: <br /> <br />Pumpage = Increased recharge + Water removed <br />from storage + Decreased discharge. <br /> <br />It is the changes in the system that allow <br />water to be withdrawn. That is, the water pumped <br />must come from some change of flows and from <br />removal of water stored in the predevelopment <br />system (Theis, 1940; Lohman, 1972). The predevel- <br />opment water budget does not provide informa- <br />tion on where the water will come from to supply <br />the amount withdrawn. Furthermore, the prede- <br />velopment water budget only indirectly provides <br />information on the amount of water perennially <br />available, in that it can only indicate the magni- <br />tude of the original discharge that can be <br />decreased (captured) under possible, usually <br />extreme, development alternatives at possible <br />significant expense to the envirorunent. <br /> <br />The source of water for pumpage is supplied by <br />(1) more water entering the ground-water system <br />(increased recharge), (2) less water leaving the <br />system (decreased discharge), (3) removal of <br />water that was stored in the system, or some <br />combination of these three. <br /> <br />18 <br />