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<br /> <br />A <br /> <br /> <br />'C <br />~ <br />~ <br />" <br />. <br /> <br />~__1 Water table <br />-------------- <br /> <br /> <br />--------------- <br /> <br />------- <br /> <br />~ <br /> <br />Ground-water zone <br /> <br />.-/ <br /> <br />-- <br /> <br />-- <br /> <br />B <br /> <br />. <br />c <br />o <br />N <br /> <br /> <br />'C <br />~ <br />~ <br />o <br />~ I <br />c <br />:> ---= <br />_____ Water table _________ ~ <br />--------------------- ---- ----- <br /> <br /> <br />~ <br /> <br />Ground-water zone <br /> <br />.-/ <br /> <br />-- <br /> <br />-- <br /> <br />c <br /> <br /> <br />'C <br />~ <br />~ <br />" <br />. <br /> <br />~ _J Water table <br />----------------- <br /> <br />---- <br /> <br />~ <br /> <br />------------- <br /> <br /> <br />~ <br /> <br />Ground-water zone <br /> <br />-- <br /> <br />-- <br /> <br />Figure 20. Water from precipitation moves to moun- <br />tain streams along several pathways, Between <br />storms and snowmelt periods, most inflow to streams <br />commonly is from ground water (A), During storms <br />and snowmelt periods, much of the water inflow to <br />streams is from shallow flow in saturated macropores <br />in the soil zone, If illfiltratiolI to the water table is <br />large enough, the water table will rise to the land <br />surface and flow to the stream is from groulId water, <br />soil water, alId overlalId nl110ff (B), In arid areas <br />where soils are very dry alld plalIts are sparse, illfiltra- <br />tion is impeded and nmoff from precipitation call <br />occur as overlalId flow (e), (Modified from DUlIne, T" <br />and Leopold, L.B" 1978, Water ill environmental <br />plalIning: Sail Francisco, W,H. FreemalI,) (Used with <br />permission.! <br /> <br />the presence of wetlands, A more common <br />hydrologic process that results in the presence of <br />wetlands in some mountain valleys is the upward <br />discharge of ground water caused by the change in <br />slope of the water table from being steep on the <br />valley side to being relatively flat in the alluvial <br />valley (Figure 21, right side of valley), Where both <br />of these water-table conditions exist, wetlands fed <br />by ground water, which commonly are referred to <br />as fens, can be present. <br />Another dynamic aspect of the interaction <br />of ground water and surface water in mountain <br />settings is caused by the marked longitudinal <br />component of flow in mountain valleys, The high <br />gradient of mountain streams, coupled with the <br />coarse texture of streambed sediments, results in <br />a strong down-valley component of flow accom- <br />panied by frequent exchange of stream water <br />with water in the hyporheic zone (Figure 14) <br />(see Box H), The driving force for water exchange <br />between a stream and its hyporheic zone is created <br />by the surface water flowing over rough stream- <br />beds, through pools and riffles, over cascades, and <br />around boulders and logs, Typically, the stream <br />enters the hyporheic zone at the downstream end <br />of pools and then flows beneath steep sections of <br />the stream (called riffles), returning to the stream <br />at the upstream end of the next pool (Figure 14A), <br />Stream water also may enter the hyporheic <br />zone upstream from channel meanders, causing <br />stream water to flow through a gravel bar before <br />reentering the channel downstream (Figure 14B), <br /> <br /> <br />MOUNTAIN <br />V ALLEY <br /> <br />~* <br /> <br />-, <br /> <br />t;k:i~' ..- <br />;0\0 ".... <br />~'\.~ ..'" <br />,/}~: J <br /> <br /> <br />--~ <br />'-.: "'-":-Oirection of <br />local flow <br />,;;;, <br /> <br />", <br /> <br />, <br /> <br />'..., face <br />", I <br />.... <br />J <br /> <br />"" <br />0, / f <br />Irectlon 0 <br />regional flow <br /> <br />Figure 21, In mountailIous terrailI, groulId water call <br />discharge at the base of steep slopes (left side of valley), <br />at the edges offload plains (right side of valley), and to <br />the stream, <br /> <br />34 <br />