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
large-scale pumping that occurred starting in the 1970s.
At the time of the analysis, an estimated 160,000 acres
were irrigated by groundwater pumping. This number
grew rapidly to over 520,000 acres by 1975 and has
averaged approximately 550,000 acres since the mid-
1980s. The larger well production for irrigation has led to
declines in water levels of over 10 feet in large areas of
Phillips, Yuma, Kit Carson, and Cheyenne Counties
where the High Plains aquifer exists (CGS 2003). The
saturated thickness of the aquifer in this region is
commonly over 100 feet (CGS 2003).
7.3 Available Surface Water and
Alluvial Groundwater Supply in
Each Basin
Legally and physically available flows, as well as
naturalized flows, are summarized below at select
locations for each basin to the extent possible given the
available datasets. Naturalized flow is not calculated at
all locations by StateMod. Therefore, in some cases,
flows calculated for nearby locations were used in the
summaries presented here. Calculated naturalized and
physically available flows were not available for basins
without StateMod datasets (Arkansas, North Platte, and
South Platte). Alluvial groundwater supplies that are
considered tributary to the major river systems are also
summarized.
Historical flows at key gages in all river basins are
monitored by the SEO. This map, commonly referred to
as the "Snake Diagram" is a useful tool for illustrating the
volume of flows throughout the state. The snake diagram
is shown in Figure 7-6. It is important to note that the
snake diagram does not include consideration of
Colorado's commitments under compacts and decrees.
Therefore, only a portion of the flows that are shown are
available to Colorado.
There are numerous factors that may affect the physical
and/or legal availability of surface water supplies. Some
of the factors that are specific to individual basins are
listed in the basin subsections below. General factors
that must be considered when evaluating the availability
of supply are listed in Table 7-2. As can be seen in the
table, it is difficult to characterize supply availability
without stating which factors have or have not been
included in some fashion in the analysis.
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