BOARD01355

• Board Meeting Date: 5/19/2003
• Description: WSP Section - Colorado River Basin Issues - Coordinated Facilities Operations Study
• Board Meetings - Doc Type: Memo

Feasibility of New Tributary Storage Projects Below Shoshone

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Agenda Item 27 - Coordinated Facilities
May 19-20, 2003 Board Meeting
Page 8 of 12

supplying the 20,000 acre.feet release was shared among Green Mountain, Granby, Ruedi, Williams Fork and .
Wolford Mountain Reservoirs. Under this Modified :;'Coordinated Reservoir Augmentation Project,:.'. as
much of the 20,000 acre-feet was released from Green Mountain Reservoir as possible without releasing
flows through the turbine bypass and releasing the remainder of the 20,000 acre-feet from other reservoirs.
The study showed this alternative had the least impact on reservoir storage of all the alternatives investigated.

Feasibility of Efficiencies of Conveyance and Distribution Facilities Alternatives

Alternatives 3d, Re-analysis of Grand Valley Water Management Alternatives, and 3e, Analysis of GVrC
Water Management, were analyzed as components of Alternative la, Green Mountain Reservoir Operations.
This analysis focused on: (1) making the 20,000 acre-feet release to the IS-Mile Reach from Green Mountain
Reservoir and (2) the potential for replacing this 20,000 acre-feet in Green Mountain Reservoir by accruing
"savings" to the Historic Users Pool (HUP) through increased GVP and GVrC efficiency.

Analysis of this alternative indicated that diverting to storage under the Green Mountain refill priority was a
more efficient way to replace the 20,000 acre-feet supplied to the IS-Mile Reach than attempting to make this
replacement with reduced demand for releases from the Green Mountain HUP. Furthermore, based on the
analysis using StateMod and the Cl data set, there was limited reduced demand on the HUP as a result of
increased GVP efficiency. Therefore, it appears that this alternative would be a more efficient and effective
source of supply for making releases to the IS-Mile Reach during the late summer and early fall than for
releases during the spring peak flows,

The alternatives for building new tributary storage (Alternatives 4f, 4g, 4k, 4n and 40) are all costly, due
primarily to the limited physical supplies of water available from the tributaries and the need to depend on
pumping from the mainstem Colorado River to supply water to most of these proposed reservoirs. However,
since cost was the limiting factor, these new reservoir sites should be considered further if the reliability and
frequency to provide the 20,000 acre-feet of water from existing reservoirs is not sufficient to meet the
Programs needs. Particularly considering that water users need to construct new reservoir capacity to provide
the 10,825 acre.feet oflate summer and fall base flow releases for the Program. The economy of scale of
building a new reservoir to provide both the 10,825 acre-feet and the 20,000 acre-feet could make a new
tributary reservoir much more attractive. .

Feasibility of New Mainstem Storage Project

An additional engineering and economic feasibility investigation of the mainstem Webster Hill site was
completed in Technical Memorandum No. 4a (See Appendix E). The cost of reservoir storage at this site for
making the 20,000 acre-feet release to the IS-Mile Reach would be partially offset by the generation of
hydropower. Net capital costs per acre-foot of yield from the Webster Hill Reservoir would range from $29 to
$134/acre- foot of yield per year depending on the assumed value of hydropower produced at the site. Results
from this additional investigation further indicate that this site would likely be feasible if: (1) the necessary
right-of-way can be obtained at reasonable cost and (2) the U.s. Fish and Wildlife Service (Service) would
approve construction of a reservoir at the Webster Hill site. which would be located in the upper end of the
currentlv designated critical habitat.

The Webster Hill Reservoir would produce a firm yield of 20,000 to 40,000 acre-feet per year. It is important .
to emphasize that the 20,000 acre-feet release would be available from Webster Hill Reservoir even in dry
Flood Protection. Water Project Planning and Fjnance . Stream and Lake Protection
Water Supply Protection. CoI\Servation Planrring