WSP04333

• File Number: 8141.400
• Description: Fryingpan-Arkansas Project - Reports
• State: CO
• Basin: Arkansas
• Water Division: 5
• Date: 1/1/1994
• Author: Gerhard Kuhn - USGS
• 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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Use of Frequency Analysis and the Extended
Streamflow Prediction Procedure to Estimate
Evacuation Dates for the Joint-Use Pool
of Pueblo Reservoir, Colorado

ByGerhard Kuhn andR.e. Nickless

Abstract

Part of the storage space of Pueblo Reservoir,
which is located on the Arkansas River in southeastern
Colorado, consists of a 65,950 acre-foot joint-use pool
(JUP). The JUP can be used to provide additional con-
servation capacity from November 1 to April 14. The
operating procedures for Pueblo Reservoir, however,
require that the JUP be completely evacuated by
April 15 and be used only for flood-control capacity
until November 1. During winter, the JUP primarily is
used to store water for agricultural uses. but because
April 15 is before the crop-growing season in south-
eastern Colorado, little beneficial use can be made of
the water released prior to April 15. The U.S. Geolog-
ical Survey completed a study during 1992, in
cooperation with the Southeastern Colorado Water
Conservancy District, to detennine if the JUP possibly
could be used for conservation storage for any number
of days from April 15 through May 14 under certain
hydrologic conditions.
The methods of the study were: (1) Frequency
analysis of recorded daily mean discharge data for
stations upstream and downstream from Pueblo Reser-
voir, and (2) implementation of the extended stream-
flow prediction (ESP) procedure for the Arkansas.
River basin upstream from the reservoir. The ESP
procedure was implemented by applying the opera-
tional capability of the National Weather Service River
Forecast System model, of which ESP is an integral
part. Estimated daily discharges were derived from the
frequency analysis for selected exceedance probabili-
ties (EP), including the O.oI EP that was used in design
of the flood-storage capacity of Pueblo Reservoir.
Discharges from the frequency analysis were routed
through the reservoir to estimate the evacuation date of
the JUP for different inflow volumes. A relation was
developed between the inflow volume and the JUP
evacuation date. To apply the study results, only a fore-
cast of the April 15-May 14 reservoirinflow for a given
year is needed; the forecast is made using the ESP

procedure. The JUP evacuation date then is estimated
from the relation between inflow volume and evacua-
tion date. The study results indicate that the evacuation
date can vary from April 23 for April15-May 14 inflow
volumes of about 169,000 acre-feet, to May 5 for
inflow volumes of about 20,000 acre-feet.

INTRODUCTION

Pueblo Reservoir, which is located on the Arkan-
sas River in southeastern Colorado (fig. 1), is the main
storage facility for the Fryingpan-Arkansas Project, a
multipurpose water development constructed by the
Bureau of Reclamation. The primary purpose of the
project is to bring surplus water from tributaries of the
Colorado River across the Continental Divide into the
Arkansas River basin to provide supplemental water
for agricultural, municipal, and other uses.

Pueblo Reservoir has a total capacity of about
357,680-acre-ft that includes a 65,950-acre-ft joint-use
pool, (U.S. Bureau of Reclamation, 1972, p. 4) (fig. 2),
When the conservation pool is at full capacity, the
joint-use pool (hereinafter referred to as JUP) can be
used to provide additional conservati.on capacity from
November 1 to Apri114. However, the current (1993)
operating procedures for Pueblo Reservoir require that
the JUP be evacuated by April 15 and be used only for
additional flood-control capacity until November 1
(U.S. Army Corps of Engineers, 1977).

A program implemented with the Fryingpan-
Arkansas Project is the winter-water storage program.
The purpose of this program is to enable downstream
agricultural water users to store water in Pueblo Reser-
voir from November 15 to March 15; the stored water
would be released during the following crop-growing
season. [A detailed description of this program is
beyond the scope of this report; additional description
is presented by Abbott (1985, p. 46, 54), by the U.S.
Bureau of Reclamation (1990, p. 15-20), and in the
storage decree (case 84CW 179, District Court. Water

Abstract 1