WSP04132

• File Number: 8200.760
• Description: Yampa River General
• State: CO
• Basin: Yampa/White
• Water Division: 6
• Date: 3/9/1994
• Author: CRWCD - Hydroshpere
• Title: Preliminary Biological Assessment Elkhead Reservoir Enlargement Project - March 9 1994
• Water Supply Pro - Doc Type: Report/Study

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USFWS - Flow Recommendations

In 1990, the Service published Phase II Flow Recommendations for the Yampa River
which included flow recommendations at Deerlodge Park "necessary for. aquatic resources.
recovery and maintenance." These flow recommendations were based on available biological
data on the habitat needs of the endangered fish and on the Section 7 Baseline flows at
Deerlodge Park produced by the HYDROSS model. The Recommended Flows were defined
as the HYDROSS modeled fifty percent exceedance values for the months August through
March and the "percentile which occurs naturally" for April through July. The U.S. Fish and
Wildlife Service Recommended Flows are shown in Table 2.

Table 2

U.S. Fish and Wildlife Service Flow Recommendations.

Month

Recommended Flow
(cfs)

April
May
June
July

Percentile which
occurs naturally
in any given
year.

August
September
October
November
December
January
February
March

364 (50% exc.)
254 (50% exc.)
339 (50% exc.)
385 (50% exc.)
327 (50% exc.)
327 (50% exc.)
373 (50% exc.)
659 (50% exc.)

Hydrosphere Yampa River Basin Model

In 1990 through 1993, Hydrosphere developed a hydrologic and water rights computer
model of the Yampa River in order to quantitatively evaluate various operational scenarios of
existing reservoirs and the utility of constructing new reservoirs at several potential sites in the
basin. The model represents the hydrology, water demands, reservoir operations, and water
rights administration of the basin on a monthly basis over a 53-year hydrologic study period
encompassing water years 1930 through 1982. This is the same study period used in previous
modeling work done by the Service to develop the Flow Recommendations for the recovery of
the endangered fishes. The period includes a wide range of hydrologic conditions, from
drought years to flood years, and permits an assessment of the long-term effects of changes in
water development and management.

As part of the Yampa River Basin Recommended Alternative Detailed Feasibility Study
("Feasibility Study"), the Hydrosphere model was used to make a comparison of flow regimes
on the Yampa River and Elkhead Creek with and without project development. Because of the
. ultimate need to compare post-project flow conditions to the Flow Recommendations provided
by the Service, and because the Flow Recommendation are based largely on the results of the
HYDROSS model, a comparison was made between Hydrosphere's pre-project (baseline)
model results and those produced by HYDROSS (Section 7 baseline).

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