WSP08813

• File Number: 8046
• Description: Section D General Studies - DSS
• State: CO
• Water Division: 1
• Date: 2/6/1996
• Author: George M Fosha
• Title: Colorado Decision Support System - 1997-2001 - 1332.2 CRDSS - Colorado Documentation - Denver Water ‎(Moffat Tunnel System and Dillon/Roberts Tunnel System)‎
• Water Supply Pro - Doc Type: Report/Study

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For the CROSS, the entire Williams Fork Collection System is modeled as a single node at
the west portal of the Gumlick Tunnel (WOlD 514603), with a tributary drainage area based on
the total area above Denver's collection facilities (13.9 square miles).

Williams Fork Reservoir (WOlD 5137091

Williams Fork Reservoir is located in the lower reaches of the Williams Fork River, about
upstream of its confluence with the Colorado River. According to information obtained from
Denver, the reservoir has a total storage capacity of 96,822 acre-feet, measured to the top of the
spillway gates. All of this storage is considered as active storage, i.e. no dead storage. The
reservoir has a stora;ge--decree for 93,637 acre-feet, adjudicated in 1937 with a priority date of
November 10, 1935. The reservoir is also included in a number of Denver's exchange decrees,
including: (11 an exchange for direct flow diversions at the Williams Fork Collection System and
the Fraser River Diversion Project (Moffat Tunnel) and (21 an exchange for all units of Denver's
system, including Dillon Reservoir and the Roberts Tunnel. Denver also obtained a more junior
storage right for Williams Fork Reservoir, which added power generation as a beneficial use of the
water. This right, which carries an appropriation date of October 9, 1956, can also be considered
as a re-fill right for the reservoir.

Denver operates a small hydroelectric generating facility, rated at three megawatts,
constructed on a secondary outlet from the reservoir. Depending upon the available pressure head
in the reservoir and the number of turbines in operation, the flow required for hydroelectric
generation ranges from about 100 cfs (one megawatt) to 280 cfs (three megawatts). Denver
obtained a decree for the Williams Fork Power Conduit (WOlD 511237) for 295 cfs with an
appropriation date of October 9, 1956.

In general, Williams Fork Reservoir is operated to provide replacement water to downstream
senior water rights on the Colorado River such that Denver's junior water rights at the Williams
Fork, Fraser River and Blue River diversion projects can continue to divert water, by exchange.
The water is diverted trans basin through the Moffat and Roberts tunnels, at times when the rights
would otherwise be out of priority. According to Denver personnel, there is not a formal operating
plan (rule curvel for reservoir. However, the reservoir is typically operated in the following manner:

111 Storage and releases are managed to allow the reservoir to fill without spilling by the end
of July (if the water is physically and legally available);

(21 Spills are minimized by controlled releases through the hydroelectric plant on the reservoir
outlet (see discussion below);

(31 Once the reservoir has achieved its maximum storage for the year, it is held at that level
until an administrative 'call' is initiated from the main stem (usually the call from the
Shoshone Power Rightl;

(41 When the call comes on, releases are made from the reservoir to replace on-going, out of
priority diversions at the Williams Fork, Fraser and Dillon/Roberts Tunnel diversions;

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