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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April 10

April 20

April 30

May 10

May 31

May 20

Figure 20. Sum 01 the estimated daily mean discharges at the 0.01 exceedance probability lor Fountain
Creek and the 51. Charles River.

stantial]y different from that shown in figure ]7, evac-
uation dates estimated from the relation in figure 17 are
considered reasonable. Although the evacuation dates
are clustered (figs. 17 and 19), a smooth trend in the
relation of the inflow volume to evacuation date was
assumed (fig. 17).

To apply the study results, only a forecast of the
April ]5-May 14 inflow volume to Pueblo Reservoir is
needed. The]UP evacuation date for the forecast
inflow volume then is estimated using figure 17. The
study results would be applied only in years in which
the conservation capacity of Pueblo Reservoir (fig. 2)
is fully utilized and the storage capacity of the JUP has
been used to provide additional conservation capacity.

Forecasts of April 15-May 14 inflow volume will
be made by the National Weather Service using the
ESP procedure (J. V. Bowman, National Weather Ser-
vice, written commun., June, 1989). The forecast of
inflow volume always is made at a 0.50 EP on the basis
of the cnrrent hydrologic conditions; the forecast vo]-
ume will vary for each year that the study results are
applied. In applying of the study results, it is important
that the two EPs, (I) the 0.50 EP of the forecast
April15-May 14 inflow volume with respect to the cur-
rent hydrologic conditions: and (2) the EP of the fore-
cast inflow volume with respect to historical inflow

volumes, are not confused. Knowledge of the EP of the
forecast inflow volume with respect to historical inflow
volumes is not needed to apply the study results. How-
ever, some knowledge of the magnitude and frequency
of historical April15-May 14 inflows (fig. 18) probably
would be beneficial in evaluating a forecast inflow vol-
ume. Inflow volumes were less than 60,000 acre-ft for
about 75 of the 94 years of record and exceeded
100,000 acre-ft in only 3 years (fig. 18).

An application of the study results implies that
some winter-stored water is contained in the]UP of
Pueb]o Reservoir: this water will need to be released by
the estimated evacuation date (fig. 17) for the current
April15-May 14 forecast of inflow volume. To aid in
estimating release rates for any winter-stored water, the
computations to estimate evacuation date for different
inflow volumes (lables 7 and 8) were used to estimate
maximum a1lowab]e storages in the JUP for different
forecasts of inflow volume (fig. 21). The dates by
which the JUP needs to be emptied were derived from
the assumed relation in figure] 7. The dates for the
maximum contents of the JUP were derived from the
evacuation-date estimations by (I) calculating the vol-
ume of discharge that could be released from reservoir
storage each day that daily mean discharge at the Avon-
dale slation was less than 6,000 ft3/s prior to the evac-

APPUCATION OF FREQUENCY-ANALYSIS RESULTS TO ESTIMATE EVACUATION DATES FOR THE JOINT-USE POOL 39