9376

• UCREFRP Catalog Number: 9376
• Author: CH2MHill.
• Title: Duchesne River Hydrology and Water Availability Study.
• USFW Year: 1997.
• USFW - Doc Type: \
• Copyright Material: NO

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1,500 to 1,800 CFS in the other 3 years. The January 23,1995, letter stated that the lower
value would be a target flow for an average water year and the higher value would be for
an above-average water year. The duration for these modified flow recommendations is
not specified in-the March 9,1995, memorandum. The January 23,1995, letter recommends
that the events be a minimum of 2 weeks.
The preliminary flow recommendations from the USFWS are their best attempt without
more specific biological, and other types, of data. Results from future studies were
identified to be critical in determining and refining the preliminary flow recommendations
for the Duchesne River.
Comparison of Historic Randlett Flows to USFWS Preliminary
Recommended Flows
A comparison of the USFWS preliminary flow recommendations with historical flows at
Randlett was made to determine flow deficiencies that would have occurred over the period
of record (1912-1994).

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Analysis of the flow volume required to meet USFWS preliminary flow recommendations,
under a dry year scenario for the period of record, was accomplished by looking at the
yearly deficiencies in dry years. The flow volume needed does not necessarily equal the
cumulative difference for the entire year as shown in the table below. Most of the yearly
totals are influenced by the summer months of July, August, and September having higher
flows than the USFWS preliminary flow recommendations. These reduce the total yearly
deficiency. However, the critical amount required equals the total monthly deficiencies
during the period from October through May. This is the amount that would be needed in
storage, or result from reduced flows going into storage.
There are several years during the extended period of record from 1912-1994 when the
USFWS dry year preliminary flow recommendations were not met and would have
required additional water in the Duchesne River during some periods of these years. These
years include the early 1930x,1959-1961,1977-1980, and the period from 1989-1994. The
most critical period has been the recent drought years from 1989-1994, which coincides with
years the Bonneville Unit was essentially under full operation. This period was used to
determine the potential maximum amount of water that would be needed to meet the
USFWS dry year preliminary flow recommendations in any one year. For the period from
1989 to 1994, the flow needed monthly and annually to meet the USFWS preliminary flow
recommendations is shown below. Values in parentheses represent differences between
recommended and existing flows in the Duchesne River.
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