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<br /> <br />water from a reservoir upstream, As long as the <br />rise in stage does not overtop the streambanks, <br />most of the volume of stream water that enters the <br />stream banks returns to the stream within a few <br />days or weeks, The loss of stream water to bank <br />storage and return of this water to the stream in <br />a period of days or weeks tends to reduce flood <br />peaks and later supplement stream flows, If the <br />rise in stream stage is sufficient to overtop the <br />banks and flood large areas of the land surface, <br />widespread recharge to the water table can take <br />place throughout the flooded area (Figure 12C), <br />In this case, the time it takes for the recharged <br />floodwater to return to the stream by ground- <br />water flow may be weeks, months, or years <br />because the lengths of the ground-water flow <br />paths are much longer than those resulting from <br />local bank storage, Depending on the frequency, <br />magnitude, and intensity of storms and on the <br />related magnitude of increases in stream stage, <br />some streams and adjacent shallow aquifers may <br />be in a continuous readjustment from interactions <br />related to bank storage and overbank flooding, <br />In addition to bank storage, other processes <br />may affect the local exchange of water between <br />streams and adjacent shallow aquifers, Changes <br />in streamflow between gaining and losing condi- <br />tions can also be caused by pumping ground <br />water near streams (see Box C), Pumping can <br /> <br />~p~ <br />-..,' , <br />, - <br /> <br />~ <br /> <br />- <br /> <br /> <br />.::--.. <br /> <br /> <br />Flooding at the confluence of the Missouri <br />and Mississippi Rivers. (Photograph by <br />Robert Meade.) <br /> <br />A <br /> <br />Land surface <br />(flood plainl <br /> <br />--- <br />-- <br /> <br />__"Y.- <br />-- <br />_----;'"7ab1e <br />_ _ - - Qri91",alwa <br />.--- <br /> <br />--- <br /> <br />- Streambank <br /> <br />--- <br /> <br />~ <br /> <br />\ '- "- <br />Streambed <br /> <br />B <br /> <br /> <br />2 <br /> <br />_3- <br />-- <br />---___ _ _ - - - ;;table <br />--.: ---"";._--- Qrigioa\VJ8 <br />---- ~ <br /> <br />c <br /> <br /> <br />EXPLANATION <br /> <br />V V' 'V Sequential stream stages <br />1 2 3 <br />- Approximate direction of ground- <br />water flow or recharge through <br />the unsaturated zone <br /> <br />Figure 12, If stream levels rise higher than their <br />streambmrks (e), the floodwaters recharge grolllld <br />water throughout the flooded areas, <br /> <br />intercept ground water that would otherwise <br />have discharged to a gaining stream, or at higher <br />pumping rates it can induce flow from the stream <br />to the aquifer, <br /> <br />11 <br />