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<br />
<br />
<br />age from a tributary aquifer, that
<br />water will be replenished during
<br />wetter years. The time that it takes
<br />to replenish that water could be sev-
<br />eral years, depending on how much
<br />water was depleted and how fast
<br />water enters the system when water
<br />is available again.
<br />A hydrograph generated using
<br />water levels between 1946 and 1983
<br />from a well tapping the South Platte
<br />alluvial aquifer near Greeley is
<br />shown below. Water levels at this
<br />location declined almost 10 feet
<br />between 1945 and 1955,. tf1t!lWasa
<br />period of time when ground water
<br />~ . ' , ' , . , ' . ' , ' , . , ' usage exploded with the installation
<br />. , ,.. . , ,. of many of the large production
<br />wells throughout this important
<br />agricultural region. Water levels
<br />have since leveled off, fluctuatii1.g.
<br />over a five-foot range between 26
<br />and 31 feet below ground surface.
<br />Even in times of drought, as indicat-
<br />ed by the drought index plot includ-
<br />ed wlth the hydrograph, water levels
<br />remained in the same range. Therelative stability of
<br />water levels in this alluvial aquifer during times of
<br />drought is due, in part, to the aquifer acting as a reser-
<br />voir for the stream system. It may also reflect that
<br />many of the large capacity wells tapping the aquifer
<br />have junior water rights and their use was probably
<br />curtailed. The relatively stable water levels during dry
<br />periods.would have benefited exempt wells.
<br />
<br />l ~ ,.. '" l ~ .... '" < v ,. ...
<br />
<br />,.. ,. .. J ,.. ,.. v " ,.. ^ v "
<br />
<br /><....~,....^_~<.... ,~^^~",.V^"^
<br />v .J < ",' v fractured- l ,. v " <
<br />~ , ... _ ^ ~ , '" ,. ~ 1 '"
<br />>>>,> bedrock <<..>>>
<br />
<br />...<"......;..
<br />"<v"
<br />...... .~n~~;;;,~~~;.t;,;.;j};;,>i~~ /' /'
<br />
<br />- - - - - - - - - - - - /,/' /
<br />- - Shale - -_ - - - ,.... _~ -......... ~ .
<br />- - - - - -NoFtow - - - ......-:.:;:;
<br />
<br />:,:'''':''
<br />
<br />,.,.......
<br />
<br />-'.'::.;..)=,'
<br />
<br />, "\ ~ J l " ." J <
<br />
<br />'" ^ ~ , '" ^ ., 1 ...
<br />
<br />Ground water in alluvial aquifers in the valleys and fractured crysfalline
<br />bedrock aquifers in the mountains are connected with surface water. In lay.
<br />er...d sedimentary sequences, the connection between groundwater and sur-
<br />face water may be poor when layers of shale separate the water bearing
<br />aquifers from the surface water.
<br />
<br />across the northeast corner of the state, this important
<br />aquifer holds an estimated8.3 million acre-feet of
<br />water in storage (or 2.7 x 10'2 gallons). By comparison,
<br />there is approximately 1.1 million acre-feet of surface-
<br />water storage capacity in the South Platte River water-
<br />shed.
<br />Although there is a tremendous volume of water
<br />in storage in the alluvial aquifer system, the ground-
<br />water rights are administered along with the surface-
<br />water rights. In times of
<br />drought, those holding junior
<br />water rights may be required
<br />to stop pumping their wells
<br />when stream flow cannot meet
<br />the demands of all owning
<br />water rights. This applies to all ::5:
<br />non-exempt wells that include
<br />most large.capacity commer-
<br />cial, municipal, and irrigation
<br />wells. Exempt wells that
<br />include most household and
<br />domestic wells.are exempt
<br />from this administration
<br />process and can continue to
<br />pump at permitted rates.
<br />An advantage to tributary
<br />water is that, since it is cormect-
<br />ed to surface water, it is renew-
<br />able. If a drought cycle results in
<br />large depletions of water in stor-
<br />
<br />r
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<br />
<br />Colorado GeoIogH:oI Survey ROCKfALl( Vol. 5, No. A
<br />
<br />-~
<br />
<br />-~- ----~~....:.-
<br />
<br />
<br />15
<br />
<br />7' 20. --.----
<br />co
<br />.J:l
<br />
<br />1 25
<br />~
<br />~
<br />.
<br />~ 30
<br />
<br />35
<br />
<br />19AO
<br />
<br />1960
<br />
<br />1950
<br />
<br />Waler level
<br />
<br />8 t
<br />
<br />d~
<br />..5
<br />.::
<br />co
<br />~
<br />o
<br />~
<br />o
<br />
<br />< 0
<br />
<br />. -A
<br />
<br />~
<br />.
<br />,...E
<br />. a
<br />00..
<br />
<br />-J
<br />
<br />1970
<br />
<br />1990
<br />
<br />1980
<br />
<br />Median Palmer Droughllndex
<br />
<br />This hydrograph from a well tapping the South Platte River alluvium near
<br />Brighton shows that water levels have been relatively stable, even in times of
<br />drought. The dr(>p in water levels between 1945 and 1955 occurred when
<br />many of the large-capacity irrigation wells first come on line.
<br />
<br />4}
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