BOARD01080

• Board Meeting Date: 1/27/2004
• Description: WSP Section - Native Species Trust Fund, Recommendations for FY 2004-05
• Board Meetings - Doc Type: Memo

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How Colorado Gels its Water

Colorado gels new water supplies I from only one source:
precipitation. in the form ofraln. hail. or snow. Colorado
gets all of its water from precipitation because there are no
major rivt:~ that flow Il'o,",[O Colorado.: There are severa]
major river basins. originaling in the Colorado Rockies.lhat
flow OUT oflhe state. providing water 10 much of the
soulhwestern Uniled States. and contributing to me
Missouri and Mississippi rivers as ..veIl. Thus. Colorado
eams ils til]e as "the ~Iolhcr of Ri"'ers:'

AlIhough Ihe main source ofColorado's water supplies is
precipitation. Coloradans typically do nol use water
direclly in Ihe form of precipitation. Usually. walercomes
to Colorado as precipitation but is then slored in one of
five forms of usable water:

snowpack (SNl. used directly for recrealion. although
it also serves as a storage of water supplies:
streamflow (Sn, used for recreation. habitat. irrigalion
and municipal water supplies. as well as 10 meet
interstate compact obligalions:
reservoir water (RW). used simllar]y to streamflow:
soil moisture (S11). used for natural ..'egctation and
agriculture: and
groundwater (GW). used for irrigation and municipal
watersuppJies.

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Thus. some of the brief summer rains that fall in Colorado
will add liuk or no water 10 the usable water supply. Water
can also be stored as snowpack for months ~fore melting
10 become streamflow. then reservoir water or groundwater.

There are I\loO nalUral palhways by which waler from
precipitation hc:come a usable source of water supply:

Pathway #1
(esp.lowerelcv.)

Pathway #2
(esp.higherelcv.)

Precipitation

Precipitation

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S~1 GW

.
Snowpack
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~ ~ " "
ST RW SM GW

~
. .
ST RW

The fi~t pathway is that precipitation falls on Ihe ground
and becomes soil moisture (SM) and groundwaler (GW) 10
support \'egelation and other uses locally where il occurs.
A portion may also become streamflow (Sn and reservoir
waler(RW). This is the dominant pathway for all lower
elevalions of the state and for the higher elevations in the
summer season.

The second pathway is lhat precipitation falls as snow at
The amount of time il takes for precipitation 10 turn into a higher elevations in the winter sea.'>On to hc:come snow-
u_~atl]e fonn of water can vary greatly. Precipitation can pack (S1'"). and later becomes available as streamllow (Sn.
add losoil moisture or snowpack almost immediately. resen..oir water IRW). soil moisture tSMI and g.roundwater
However. there can ~ delays of several days or \loeeks (GW) during the following spring and summer. This is lhe
before precipitation adds to the water Ic...els in streams. primary pathway by which mountain snows provide
reservoirs. or groundwater aquifers. During those time surface water resources for the state. and results in peak
delays. some precipitation can be lost to t'\'aporation. streamflows occurring from April through July.

1:-.101 including anc1(~nl aquliers. such as In the Den..-er ba\in. which receive little or no recharge and are helng "mined."
I Well. OK. there's Little Snake R...'er. wbich starn in Wyoming. enters Color.llJo briefly lojoin the Yamra before lea..ing for Utah. The
Green Rher also SI.llt5 in Wyoming. nO\loS to Utah. then comes into Colorado bnetly to join the Yampa before leaVing the state again.

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