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<br />A <br /> <br />. <br /> <br />..../1'.........1'....... <br />....... _....'/<,.. <br /> <br />--' <br /> <br />ReCharge area <br />---land Surface -'.::: ~ <br />-- - .... .::: <br /> <br />\ <br />'" <br /> <br />\ <br /> <br />\ <br /> <br />" <br />:;- <br /> <br />E <br />. <br />~ <br />Iii <br /> <br />Water table <br /> <br />"'" <br /> <br />"-..... <br /> <br />" " <br />---- <br /> <br />~- <br /> <br />~- <br /> <br />---- <br /> <br />---- <br /> <br />- <br /> <br />Unconfined aquifer <br /> <br />---- <br /> <br />-- <br /> <br />--- <br /> <br />Confining unit <br /> <br />/11"...../' ,....... <br /> <br />,-' <br /> <br />---land surface -.::::- <br />-- - .... <br /> <br />01 <br /> <br />.. <br />. <br />~ . <br />, '" <br />-g :~ <br />0'" <br />o <br />" <br /> <br />E <br />. <br />~ <br />'" <br /> <br />B <br /> <br />" <br /> <br />-....' '/..... <br /> <br />" <br /> <br />~ <br /> <br />\ <br />"-... <br />------ '-...... <br />---- <br />- <br /> <br />\ <br />\ <br />---- <br />-- <br /> <br /> <br />Water table <br /> <br />\ <br />'" <br /> <br />\ <br /> <br />---- <br /> <br />Unconfined aquifer <br /> <br />---- <br /> <br />---- <br /> <br />-- <br /> <br />Confining unit <br /> <br />c <br /> <br />" <br /> <br />...."\,....",,........ <br />_....'1,.,....... <br /> <br />,- <br /> <br />--Land surface - ~ <br />-- .....-;; <br /> <br />O2 <br /> <br />E <br />. <br />~ <br />'" <br /> <br />" <br /> <br />~ <br /> <br />\ <br />"-... <br />------ '-...... <br />---- <br /> <br /> <br />-- <br /> <br />~ <br /> <br />Water table <br /> <br />\ <br />'" <br /> <br />\ <br /> <br />---- <br /> <br />Unconfined aquifer <br /> <br />---- <br /> <br />---- <br /> <br />-- <br /> <br />Confining unit <br /> <br />Figure 13. Effects of pumping from a hypothetical ground-water system that discharges to a stream. (Modified <br />from Heath, 1983.) <br /> <br />Under natural conditions (A), recharge at the water table is equal to ground-water discharge to the stream. <br />Assume a well is installed and is pumped continuously at a rate, Ql' as in (B). After a new state of dynamic equilib- <br />rium is achieved, inflow to the ground-water system from recharge will equal outflow to the stream plus the with- <br />drawal from the well. In this new equilibrium, some of the ground water that would have discharged to the stream is <br />intercepted by the well, and a ground-water divide, which is a line separating directions of flow, is established locally <br />betwem the well and the stream. If the well is pumped at a higher rate, Q2' a different equilibrium is reached, as <br />shown in (e). Under this condition, the ground-water divide between the well and the stream is no longer present, <br />and withdrawals from the well induce movement of water from the stream into the aquifer. Thus, pumping reverses <br />the hydrologic condition of the stream in this reach from ground-water discharge to ground-water recharge. Note <br />that in the hydrologic system depicted in (A) and (B), the quality of the stream water generally will have little effect <br />on the quality of ground water. In the case of the well pumping at the higher rate in (C), however, the quality of the <br />stream water can affect the quality of ground water between the well and the stream, as well as the quality of the <br />water withdrawn from the well. Although a stream is used in this example, the general concepts apply to all surface- <br />water bodies, including lakes. reservoirs, wetlands, and estuaries. <br /> <br />32 <br />