WSP05071

• File Number: 8146.400
• Description: Pueblo Dam - Reports
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 10/1/1994
• Author: US Geological Survey
• Title: Use of Frequency Analysis and the Extended Streamflow Prediction Procedure to Estimate Evacuation Dates for the Joint-Use Pool of Pueblo Reservoir Colorado
• Water Supply Pro - Doc Type: Report/Study

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TOTAL CAPACITY = 357.680 ACRE-FEET
EXCLUSIVE FLOOD-CONTROL POOL = 27,020 ACRE-FEET

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JOINT-USE POOL = 65,950 ACRE-FEET
(FIoock:onbol storage April 15-October 31; conservation storage November 1-Aprtl 14)

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CONSERVATION POOL = 234,350 ACRE-FEET

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DEAD AND INACTIVE
POOL = 30,360 ACRE-FEET

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NOT TO SCALE .

Figure 2. Cross-section schematic of Pueblo Reservoir storage-<:apacity pools.

Division No.2, State of Colorado; date of appropria-
tion November 10, 1987).]

After Pueblo Dam was completed in 1975, the
winter-water storage program was initiated by the
Southeastern Colorado Water Conservancy District, a
Colorado agency established to administer the Frying-
pan-Arkansas Project. During 1984, 1985, and 1987,
some winter-stored water was stored in the JUP
because the conservation pool was at full capacity. All
winter-stored water that was in the JUP was released
from Pueblo Reservoir prior to April 15; however, little
beneficial use was made of the released water because
the April 15 evacuation date generally is before the
crop-growing season in southeastern Colorado.

Recognizing the possibility for better manage-
ment of water resources, the Southeastern Colorado
Water Conservancy District began a study in 1988, in
cooperation with the U.S. Geological Survey, to deter-
mine if storage in the JUP of Pueblo Reservoir could be
extended beyond April 15 under certain hydrologic
conditions. Extension of the April 15 date by a few,
and as many as 30, days would improve management
of water resources for beneficial use and increase the
long-tenn yield of the JUP. Hereinafter, the study
described in this report will be referred to as the PRlUP
(Pueblo Reservoir JUP) study.

Purpose and Scope

The purpose of this report is to describe the
methods used in the PRlUP study and to discuss the
results. The methods that are described include (I) fre-
quency analysis of recorded daily mean (ROM) dis-
charges for selected streamflow-gaging stations
(stations) upstream and downstream from Pueblo Res-
ervoir (table I), and (2) implementation of the National
Weather Service's Extended Streamflow Prediction
(ESP) procedure (1\vedt and others, 1977; Day, 1985)
for the Arkansas River basin upstream from Pueblo
Reservoir. The report discusses how the results from
the frequency analysis and the ESP procedure can be
used to estimate evacuation dates for the JUP of Pueblo
Reservoir (that is, extend the April 15 evacuation date).

Because the flood-control storage capacity of
Pueblo Reservoir is based on a design flood that has a
recurrence interval of about 100 years, or a 0.01
exceedance probability (hereinafter referred to as EP)
(U.S. Army Corps of Engineers, 1977, p. 8-2), the
frequency analysis was done at this EP. Also, although
the study objective was to evaluate the likelihood of
using the JUP for additional conservation storage only
from April 15 through May 14 (April 15-May 14) (C.L.
Thomson, Southeastern Colorado Water Conservancy
District, and R.D. Kreiner, U.S. Army Corps of Engi-
neers, oral commun., 1989), all of April and May were

INTRODUCTION 3