<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 />
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