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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DRAINAGE AREA, IN SQUARE MILES

stations (compare graphs for at-Canon City and near-
Pueblo stations in figure 7).

Adequacy of record length was further evaluated
by performing a frequency analysis for the at-Canon
City station for a 29-year period of record identical to
the period of record for the at-Portland station (table I).
This resulted in about a 25-percent increase in the
0.01 EP volume for the at-Canon City station (fig. 8).
Additionally, the effect of a single, very large discharge
on short and long periods of record was evaluated.
Record for water year 1942 was excluded from the
frequency analyses for the near-Pueblo and near-
Avondale stations; the April-May volume for water
year 1942 was about 50 percent larger than the next
largest April-May volume at each of these two stations
(Iable 2). Exclusion of water year 1942 from the longer
record at the near-Pueblo station had practically no
effecl on the 0.01 EP volume, but the exclusion from
the shorter record at the near-Avondale station resulted
jn about a 20-percent decrease in the 0.01 EP volume
(fig. 8).

Based on the analysis just described, the near-
Pueblo station was selected for use in the PRJUP study

Figure 8. Estimated April-May discharge volume at the 0.01 exceedance probability for selected stations
on the Ar1<ansas River.

to derive the 0.01 EP discharges flowing into Pueblo
Reservoir. Although the 79-year record at this station
seemed to be of adequate length for reliable frequency
analysis, several years (primarily during the 1980's)
that had large discharges (table 2) are not included in
the record for that station (table I). However, record
for those years is available for the at-Portland and
above-Pueblo stations (fig. I; table I); records for these
stations were used to extend the period of record for the
near-Pueblo station.

Frequency curves for the April-May discharge
volumes for Fountain Creek and the St. Charles River
are shown in figure 10; the ten largest recorded April-
May discharge volumes are listed in table 3. No sta-
tions with longer periods of record are available for
these tributaries to evaluate the adequacy of the record
length. However, the 0.0 I EP volume is not a substan-
tial extrapolation beyond the available data; therefore,
the record lengths for Fountain Creek and the
St. Charles River were considered adequate for the
frequency analysis of RDM discharges.

14 U.. 01 Fntquoncy Analysis and tho Exlended Streamllow PredictIon Procedure to Estlmato EvaeuaUon Dotos lor tho
Jolnt~U.. Pool of Pueblo Re'.Noir. Colorado