WSP11761

• File Number: 8441.400
• Description: Colorado Big Thompson Project - Reports
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 4/1/1987
• Title: Joint-Use Reservoir and Green Mountain Exchange Projects - Summary Report
• Water Supply Pro - Doc Type: Report/Study

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for some 125 water-user organizations in Northeastern Colorado. Of the total Green Mountain

Reservoir capacity of about 154,000 af, 52,000 af is allocated for replacement of out-of-priority

diversions by the CBT Project. This enables the CBT. Project to divert water near Granby during

periods when flows would otherwise have to be bypassed to satisfy senior water rights. The

remaining capacity of Green Mountain Reservoir (approximately 100,000 af) is reserved for power

generation and beneficial uses in Western Colorado.

The collection system for the Roberts Tunnel includes Dillon Reservoir, completed in 1963,

on the Blue River upstream of Green Mountain Reservoir. Flows diverted from Dillon Reservoir

through the Roberts Tunnel .enter the North Fork of the South Platte River and the Metropolitan

Denver Water Supply. The water rights for the Roberts Tunnel Collection System are junior to those

of Green Mountain Reservoir.

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JOINT-USE RESERVOIR: The operational relationships between the, Dillon Reservoir-

Roberts Tunnel system and Green Mountain Reservoir have been prescribed in various federal court

decrees. As a result of these decrees, Dillon Reservoir can store water out-of-priority with respect

to Green Mountain Reservoir, subject to certain provisions. If Green Mountain Reservoir does not

fill during the spring runoff, water is released from Dillon Reservoir to Green Mountain Reservoir.

With permission of the Bureau of Reclamation, however, this obligation can be satisfied through a

water exchange. Water can be released from some other reservoir to replace water that otherwise

would have to be released from Dillon Reservoir.

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The Joint-Use Reservoir, one of two concepts investigated in this Study, would be dedicated

toward meeting such obligations. This new reservoir would be capable of providing about 30,000 af

of water per year, about half of which would be used to increase the water yield of Dillon Reservoir

and the remainder would be available for use in western Colorado.

GREEN MOUNTAIN EXCHANGE: The concept of the Green Mountain Exchange Project

recognizes Green Mountain Reservoir as a potential source of additional water supply to Dillon

Reservoir. Water would be pumped from Green Mountain Reservoir through 26 miles of pipeline to

Dillon Reservoir, which Is about 1100 feet higher in elevation. In addition, a Replacement

Reservoir(s) would be constructed to provide the replacement water for out-of-priority CBT Project

diversions and to supplement natural flows thereby meeting in-basin irrigation and municipal

demands. It (they) would also meet USBR water sales requirements that oould otherwise have been

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