7886

• UCREFRP Catalog Number: 7886
• Author: Hydrosphere Resource Consultants.
• Title: Yampa River Basin Recommended Alternative, Detailed Feasibility Study
• USFW Year: 1995.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

Reservoir Operating Studies
reservoir and reflects sedimentation which has occurred in the existing reservoir. Of this total
capacity, 3,722 of are assumed to be dead storage; this is the same as the existing reservoir.
The enlarged Elkhead Reservoir is assumed to fill under its existing water rights plus a
transferred California Park first-fill water right in the amount of 36,536 af. The California
Park water right is a conditional storage right held by the River District for a proposed project
further upstream in the Elkhead Creek basin. As a result of the California Park transfer, the
decreed storage rights at the enlarged Elkhead Reservoir total 50,236 af. As with Stagecoach
Reservoir discussed earlier, the "excess" decree capacity was assumed to be administered as a
refill right.

' Two important changes were made to reservoir operating assumptions in this scenario.
First, it was assumed that the 9,000 of industrial water supply contract pool in Stagecoach
Reservoir was moved into the enlarged Elkhead. This assumption reflects the fact that the 2040
demand projections show most increases in industrial water demands to occur in the Craig area
while most increases in municipal demand will occur in the Steamboat Springs area. The
transfer of the industrial contract to the enlarged Elkhead would free up that supply in
Stagecoach for additional municipal use in the upper part of the basin. As a result of this
assumed transfer, a total of 22,700 of of storage in the enlarged Elkhead Reservoir would be
allocated to existing municipal and industrial contracts and to dead storage, leaving 22,200 of
allocable to other future uses.
The second important change in reservoir operating assumptions was the adoption of a
flow support operation at the enlarged Elkhead Reservoir. This operation would seek to
enhance Yampa River mainstem flows in critical low flow periods by making releases from the
22,200 of unallocated pool in the enlarged reservoir. These releases would improve late season
low flow conditions in reaches designated as critical habitat for the endangered Colorado
squawfish and Humpback chub.
The timing and amount of such releases were assumed to be keyed to flow conditions at
Maybell; if flows at Maybell are less than a monthly target value and there is water available in
the 22,200 of unallocated pool, a release is made to bring flows at Maybell up to the target
level. Several target levels were investigated, including the preliminary flow recommendations
at Maybell. However, it was determined that releases to meet monthly targets equal to the flow
' recommendations would not provide as much flow enhancement supply in the late fall (the
water would be used up trying to meet the July target in most years) and would seriously
jeopardize the summer recreation potential at the enlarged reservoir. To some degree this
conclusion is an artifact of using a monthly model; nevertheless, a more modest set of monthly
targets intended to "feather" releases out over a longer period, was adopted. These targets are
displayed in Table 2-8. In actual operation these releases would probably be determined on a
daily basis.
Results
Water Deliveries
Shortages occur in 38 years of the 53 year study period. The average annual total
shortage is 1,588 of and the maximum annual total shortage is 15,721 af. These values are
basically the same as modeled demand shortages observed under future "without project"
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