S7_11-15-04

• Basin: Statewide
• Title: SWSI Phase 1 Report - Section 7 Availability of Existing Water Supplies
• Date: 11/15/2004
• Author: CWCB
• SWSI - Doc Type: Final Report

Section 7
Availability of Existing Water Supplies
within its service area. Conjunctive use of available
surface water supplies would reduce this cost and,
more importantly, decrease the annual demand on
the aquifers by approximately 50 percent (Black and
Veatch 2004).
As water levels continue to decline, water pressure will
drop and the possibility exists that the saturated rocks
will no longer be able to support the weight of the
overlying strata. Compaction will occur and, if significant
enough, could lead to subsidence that propagates
upwards to the land surface. This phenomenon has been
seen in many urban areas where groundwater pumping
is concentrated and can lead to considerable damage to
existing streets, buildings, and infrastructure.
The available supply in the Denver Basin bedrock
aquifers is further governed by the legal availability of the
water. The legal availability is determined in part by the
location in the basin and in part by the well age.
Approximately the eastern half of the Denver Basin
aquifers are part of one of four designated basins
(Kiowa-Bijou, Lost Creek, Upper Big Sandy, and Upper
Black Squirrel). In the western half of the Denver Basin,
wells that have been permitted since 1973 and do not
have an affect on the overlying surface streams are
considered non-tributary and have been allowed to
withdraw 1 percent of the water per year based on how
much water is underlying the land owned or controlled by
the appropriator, thus providing for at least a 100-year
life for the aquifer.
7.2.3 Designated Groundwater Basins
Designated basin groundwater is located in eight
specified areas in eastern Colorado, as shown in
Figure 7-5. Designated basin groundwater is
administered by the Colorado Groundwater Commission,
with daily management typically given to the Ground
Water Management District or districts within the basin.
Rules governing usage differ by basin but typically
distinguish between tributary and non-tributary aquifers,
if both are present, and permit usage based on aquifer
volume within an allowed radius and a specified annual
rate of aquifer depletion.
7.2.3.1 Designated Basins Other Than the High
Plains
There are six designated basins in this category,
including four that comprise the eastern part of the
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Denver Basin geologic region (Lost Creek, Kiowa-Bijou,
Upper Big Sandy, and Upper Black Squirrel) and two
that exist elsewhere within the lower South Platte Basin
(Camp Creek, Upper Crow Creek).
The alluvial aquifer in the Lost Creek, Kiowa-Bijou, and
Upper Black Squirrel designated basins has been
determined by the State Engineer to be
overappropriated and, therefore, no new large capacity
well permits will be granted.
The remaining aquifers in these designated basins,
including the alluvial aquifer in the Upper Big Sandy,
Camp Creek, and Upper Crow Creek, the bedrock
aquifers within the Denver Basin region (Dawson,
Denver, Arapahoe, and Laramie-Fox Hills), plus Camp
Creek, and parts of Upper Crow Creek. In these areas,
groundwater is subject to appropriation by high capacity
wells provided the appropriation does not unreasonably
impair existing water rights. The Colorado Groundwater
Commission determines whether a proposed new well
will cause an unreasonable impairment of existing rights.
7.2.3.2 High Plains Aquifer
The High Plains aquifer exists in the eastern portion of
the state. It consists of the Ogallala aquifer, which
extends from Texas to South Dakota, plus the overlying
alluvial deposits of the Republican River Basin. This
aquifer system is administered under the Northern and
Southern High Plains Designated Basin rules and
regulations. High capacity wells are allowed in both
designated basins, with wells in the Northern High Plains
designated basin being limited to a maximum allowable
pumping rate such that 40 percent of the water in storage
within the saturated materials can be depleted within
100 years.
It has been estimated that there is approximately
12.4 million AF of economically recoverable groundwater
in the Southern High Plains designated basin
(McLaughlin Water Engineers 2002). ~urrent
withdrawal rafi~s are approxim~tely 220,000 AFY,
leading to an estimated life of this porti~n ~f th~ High
Plain~ aquif~r ~f appr~ximat~ly 56 y~~r~. Water levels
have been declining in this basin at an average rate of
approximately 5.4 feet per year over the past 10 years.
In the Northern High Plains designated basin there was
an estimated 48 million AF of recoverable water in
storage (Woodward-Clyde 1966) before the onset of
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Sfvtewide Woter Supoly Initiofive
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