WSP01315

• File Number: 8057
• Description: Section D General Studies - State Water Plan
• State: CO
• Basin: Statewide
• Date: 6/23/1971
• Author: John E Moore
• Title: Integrating the Use of Ground Water Into Water Resource Planning
• Water Supply Pro - Doc Type: Report/Study

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area and to predict the effects of additional future development, For
example, the model was used to evaluate the redistribution of wells and
the location of favorable areas for new wells.

In the San Luis ~alley of south-central Colorado an analog model
was used to study a unique problem in a complex unconfined and confined
aquifer system, More than 2 billion acre-feet of water is stored in the
upper 6,000 feet of the aquifer. A model was first constructed for the
uppermost or unconfined aquifer, which ranges in thickness from 0 to 120
feet. That model simulated boundaries, storage, and transmissivity of
the aquifer, In addition, evapotranspiration was simulated by means
of current-limiting devices (transistors and diodes), The model was
used to predict the effects of a plan to salvage water being consumed
by nonbeneficial vegetation in a discharge area in the central part of
the valley by pumping a network of wells (Emery, 1970), The salvage
plan, which waS proposed by the Bureau of Reclamation, provides for the
construction of 129 wells to pump 84,000 acre-feet of water annually for
50 years. The model predicted the magnitude and areal extent of water-
level decline in the unconfined aquifer. The model analysis showed that
water-level declines ranged from 1 to 100 feet and that those declines
exceeding 10 feet would be confined mainly to the vicinity of water-
salvage wells. It reassured the local irrigators that the salvage
project would have little cr'no effect on water levels in the principal
irrigated areas. The first model was later expanded to include both the
unconfined and confined aquifer system, This model has been used to
describe the operation of the hydrologic system and to predict the
effects of increased pumping of wells on streamflow, aquifer head, and
storage.

Digital models provide another valuable tool for water-resource
planning that can be used to predict both quantity of flow and changes
in quality resulting from natural phenomena and man's activities. The
model is capable of predicting changes in ground-water storage and
effects on streamflo~.

A combination of the best features of an electric-analog and a
digital model was used in the Arkansas Valley of Colorado to define
the operation of a stream-aquifer system and to predict effects of
changes in water management. The results of these model studies have
been used for modifying water law, for developing ground-water supplies,
and for administrating water distribution.

The area modeled extends from Pueblo to the Kansas State line, a
distance of 150 miles (Moore and Wood, 1967). This reach of the valley
is underlain by an alluvial aquifer that OCcurs in unconsolidated sand
and gravel deposits, The aquifer ranges in thickness from 0 to more than
250 feet and eontains about 2 million acre-feet of water in storage, It
is hydraulically connected to the river, and the ground and surface
water constitute a common supply. The development of ground water for
irrigation has caused legal disputes between ground-water and surface-
water users because pumping the wells has reduced the flow of the

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