WSP06777

• File Number: 8281.980
• Description: Colorado River Studies and Investigations - Upper Gunnison/Uncompahgre Basin Water Study
• Basin: Gunnison
• Water Division: 4
• Date: 8/12/1987
• Title: Upper Gunnison-Uncompahgre Basin Study
• Water Supply Pro - Doc Type: Report/Study

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MEMORANDUM

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Study 80/iRD

Date:
To:
From:
Re:

August 18, 1987
Blaine Dwyer, CWRPDA
Chuck Brendecke, WBLA
Period of Record for Gunnison

Basin

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This memorandum outlines our rationa~for selecting a period ~~lCeeO(d~r~~~~--. .
the basin study. The memo is, hopefully, written in a form Si'mila..F:..:c.eG-.t.h.flt. .,__..__~j7
whieh will appear in Task Memorandum No. 5 and the study report. ''":._,~J....J.__ I
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STUDY PERIOD INFLOWS

The upper Gunnison-Uncompahgre basin model utilizes a common hydrologic
sequence of virgin flows for evaluation of all potential water development
plans. This 32 year long sequence of monthly inflows is derived from actual
streamflow records for the period 1952 through 1983, correeted for historic
depletions and flow regulation. In addition, virgin flows at several ungaged
sites have been derived synthetically, based, in part, on actual streamflow
records. The rationale for choosing this study period and the methods used to
develop virgin flow data are discussed in this section.

Selection of Study Period

The selection of the study period was based on considerations of hydrologic
representativeness and data availability. It is important that the hydrologic
charaeteristies of the study period be a representative sample of true basin
hydrology in order to avoid eoming to wrong conclusions as to the quantities of
water available for development. It is also important that the study period
contain critical dry periods so that minimum yields can be estimated.

Annual flow records for three representative gages in the basin were
reviewed to aS$ess long term hydrologic characteristics. These gages were: 1)
Taylor River at Almont <corrected for Taylor Park reservoir storage and
release), 2) Lake Fork at Gateview, and 3) flow below Crystal <CRSS estimated
virgin flows). Table contains annual flow data for these gages.

Average flows for the proposed 195Z-83 study period are slightly less than
the long terM averages at the three sites, although the difference is not
signifieant statistically. With one exception, the dry spells of duration 5
years or less all occur within the proposed study period. Based on these
observations the proposed study period exhibits the desired characteristics of
representativeness and contains the eritical dry periods.

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