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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from low-elevation basins and partly by the shorter
periods of record. However, based on the available
data, the estimated 0.0 I EP discharges (fig. 13) are the
best possible; the estimates should improve and the
confidence limits should narrow as more data become
available (V.S. Interagency Advisory Committee on
Water Data, 1982, p. 23). The 0.01 EP discharges for
April IS-May 14, the maximum RDM discharges, and
the year of the maxima for Fountain Creek and the
SI. Charles River are listed in tables 5 and 6. The
om EP discharges for Fountain Creek and the SI.
Charles River (tables 5 and 6) generally are substan-
tially larger than the maximum RDM discharges,
except for a few days in April on the SI. Charles River.
Most of the maximum RDM discharges for these
streams also were recorded during 1942.

Perspective of Daily Mean Discharges
Recorded During April and May 1942

The data listed in tables 2-6 clearly indicate that
1942 was a year of exceptionally large discharge dur-
ing April and May on the Arkansas River downstream
from Canon City, on Fountain Creek, and on the
SI. Charles River. April 1942 also was one of the wet-
test months recorded in Colorado (Follansbee and Saw-
yer, 1948, p. 105). In the Purgatoire River basin, a
major tributary entering the Arkansas River about
80 mi downstream from Pueblo, the precipitation was
especially large from April 20 to 25 and resulted in a
major flood on the Purgatoire River; details of the flood
are described by Follansbee and Sawyer (1948,
p. 105-108). Establishment of April 15 as the date by
which the JVP of Pueblo Reservoir would need to be
completely evacuated of winter-stored water was
based, in part, on the April 23-24 flood on the Purga-
toire River (R.K. Livingston, V.S. Geological Survey,
written commun., 1988).
Data listed in table 2 indicate that the ] 942 April-
May discharge volume is the third largest on record for
the at-Canon City station and the largest on record for
the near-Pueblo and near-Avondale stations (as of
water year 1990). The frequency analyses for the
April-May volumes for these three stations (fig. 9)
indicate that: (I) For the at-Canon City station, the
] 942 volume has an EP of about 0.02; (2) for the near-
Pueblo station, the volume has an EP smaller than
0.005 (this also is indicated in fig. 11, which includes
the estimated discharges for water years 1976-90); and
(3) for the near-Avondale station, the volume has an EP
of about 0.01. To further analyz.e the 1942 discharges
at the near-Pueblo station, frequency analyses were
performed for RDM discharges on April 23 and 24

(fig. 14), which were the days of the largest RDM dis-
charges during April (table 4). The probability that
daily mean discharge on April 23 and 24 would be
equal to or larger than the RD M discharge on those
days during 1942 is substantially smaller than 0.01
(fig. 14).

For Fountain Creek and the SI. Charles River, the
1942 April-May volume is the largest on record for
both streams (table 3); for the SI. Charles River the'
1942 volume is almost twice as large as the second
largest volume (table 3). The EP's for the 1942 April-
May volumes are about 0.05 for Fountain Creek and
about 0.02 for the SI. Charles River (fig. 10). Fre-
quency analyses of RDM discharges for April 23 and
24, 1942, for the two tributaries are shown in figures 15
and 16. The probability that daily mean discharge on
April 23 and 24 would be equal to or larger than the
RDM discharge on those days during 1942 is about
0.015 for Fountain Creek and about 0.005 or smaller
for the SI. Charles River (figs. 15 and 16).

APPLICATION OF FREQUENCY-
ANALYSIS RESULTS TO ESTIMATE
EVACUATION DATES FOR THE JOINT.
USE POOL

Estimation of evacuation dates for the Pueblo
Reservoir]UP is made by using the 0.01 EP discharges
for the near-Pueblo station, Fountain Creek, and the
SI. Charles River (tables 4-6). Discharges for the near-
Pueblo station, which are the inflow to Pueblo Reser-
voir, are routed through Pueblo Reservoir and down-
stream to the at-Avondale station; discharges for
Fountain Creek and the 51. Charles River also are
routed downstream to the at-Avondale station to deter-
mine a total discharge at the station. To estimate the
evacuation dates, daily reservoir outflow was assumed
to be equal to daily reservoir inflow (the daily discharge
at the near-Pueblo station), except (I) when outflow
needs 10 be decreased to maintain the downstream
6,Ooo-ft3/s discharge criterion at the near-Avondale sta-
tion, or (2) when outflow can be increased because dis-
charge at the near-Avondale station would be less than
6,000 ft3/s and the JUP contains some previously
stored inflow. Data to estimate the evacuation date for
the JUP using the 0.01 EP discharges (tables 4-6) are
listed in table 7; diversions were not considered in the
estimation. The discharge-routing computations to
estimale evacualion dales for the JUP consisls of the
following steps:

26 U.e of Frequency Anelysl. end the Extended Streamflow PredIctIon Procedure to EstImate Evacuallon Date. tor tho
Joint-Use Pool of Pueblo Reservoir, Colorado