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

Example yield curves for the Yampa River below Craig
are shown in Figure 7-1. Modeled demands for these
analyses follow typical monthly patterns of M&I use,
based on an analysis of monthly water demands from
several municipal water providers.
WatSIT also has an option for assuming agricultural
demand patterns, rather than M&I (i.e., assuming the
water is being used for agriculture rather than M&I). As
shown in Figure 7-1, for the Yampa River, assuming
agricultural patterns of use rather than M&I, results in a
small increase to the calculated firm yields. This increase
in firm yield is the result of greater agricultural demands
during the runoff period, allowing more direct diversions
during this period and less reliance on storage. Also
shown in Figure 7-1 is a yield curve corresponding to the
same set of assumptions as the original curve, except
that the criteria for firm yield are relaxed. For this curve,
some shortages (> 20 year return period) are accepted.
Small increases in firm yield (9,000 to 100,000 AFY) for
the same storage volume are predicted. These increases
may be more dramatic for different systems or for
accepting more frequent shortages (a shorter return
900,000
Section 7
Availability of Existing Water Supplies
period). Finally, it is expected that firm yields would
increase significantly if the storage water was used in a
conjunctive use project with non-tributary groundwater. In
other words, non-tributary groundwater could firm up
yields by supplementing shortages in surface water
supplies in dry years, pushing the yield curves upward.
7.2 Overview of Groundwater
Supplies and Availability
including Designated
Groundwater Basins and
Non-tributary Aquifers
Groundwater is present throughout the state. It is found
in a variety of aquifers, from unconsolidated sand and
gravel in the floodplains of the major rivers to bedrock
deposits buried deep below the surface. The key aquifers
in the state are located primarily in the unconsolidated
deposits. These include the alluvial aquifer systems of
the Arkansas, South Platte, Gunnison, Colorado, and
North Platte Rivers. In addition, there is a significant
aquifer located in unconsolidated deposits in the San
800,000
~ - ~ ~ _ _ _ _ _ _ _
700,000 ---------------f- ~-~-~ ~
600,000 ---------~ ----------------------------------------------
} / ~
LL ~
a 500,000 ----~- ~- ----------- M&I use
-a •
,d / - - Agricultural use
s
~ 400,000 - - - - _ - -
~ / ~ M&I use with shortages (22 year return period)
LL
---------------------------------------------------------
300,000 - -
~ Average Annual Available Flow = 1,030,000 AFY
200,000 -----------
Minimum Annual Available Flow = 298,000 AFY
Maximum Annual Available Flow = 1,717,000 AFY
100,000 -------------
500,000 1,000,000 1,500,000 2,000,000 2,500,000 3,000,000
Total Storage (AF)
Figure 7-1
Reservoir Yield Curve
Yampa River below Craig (1909-1999)
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S:\REPORT\WORD PROCESSING\REPORT\S7 11-10.04.DOC 7-.~