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UUl)(5;J4 DENVER WATER - DILLON RESERVOIR/ROBERTS TUNNEL SYSTEM The Denver Soard of Water Commissioners (Denver) operates Dillon Reservoir and the Harold D. Roberts Tunnel as primary features of its raw water collection and transmountain diversion system. Water diverted pursuant to the direct flow decree of the Roberts Tunnel, together with releases from storage in Dillon Reservoir is conveyed under the Continental Divide to the headwaters of the North Fork of the South Platte River on Colorado's eastern slope. The following discussion summarizes the key elements of the system operation. The Harold D. Roberts Tunnel (aka Montezuma Tunnell -"!: ..:--:: The Harold D. Roberts Tunnel (WDID 364684) diverts directly from Dillon Reservoir at a submerged inlet on the east side of the lake and extends about 23 miles to its point of delivery in the North Fork of the South Platte River. The tunnel has an estimated capacity of 788 cfs. In a March 10, 1952 adjudication, Denver obtained a direct flow water right for the tunnel in the amount of 788 cfs and an appropriation date of June 24, 1946 (Administration No. 35238.00000). Of this decreed amount, 468 cfs have been made absolute. On the Blue River, the Roberts Tunnel water right is junior to the storage rights of Green Mountain Reservoir and the direct flow rights of the senior portion (1929) of the Continental-Hoosier diversion project. Diversions through the tunnel are influenced by the downstream water rights for Green Mountain Reservoir, downstream "calls" from either the Shoshone Power Plant or the Cameo area water rights and the availability of water in other parts of Denver's system to replace out-of-priority diversions (Williams Fork Reservoir). Dillon Reservoir DiDon Reservoir (WDID 3645121 is located on the main stem of the Blue River and commands a drainage area of about 335 square miles, including the major tributaries of Ten Mile Creek and the Snake River. With the Roberts Tunnel, Dillon Reservoir is the major source of future raw water supplies for the City of Denver. According to information obtained from Denver, the reservoir has a total storage capacity at its normal high water line of 257,305 acre-feet of which 3,269 acre-feet represent dead storage. The active capacity is therefore 254,036 acre-feet. The reservoir has an absolute storage water right for, 252,678 acre-feet, adjudicated in 1952 with a priority date of June 24, 1946 (Administration No. 35238.00000). The outlet works from the reservoir is equipped with a hydroelectric generating facility, with a capacity of about 100 cfs. However, it generates power using only the releases that are made from the reservoir for other purposes. There is no direct flow right for the hydro operation. In the historic scheme of operations for Denver's western slope diversion projects, the Dillon/Roberts Tunnel system is the last supply used and is generally used to "top off" Denver's storage reservoirs in the South Platte River basin (Antero, Elevenmile and Cheeseman reservoirs). For this reason, very little water has been diverted through the Roberts Tunnel in wet runoff years (in the South Platte basin) and significant quantities have been diverted in dry years. According to Denver personnel, there is not a formal operating plan (rule curve) for the reservoir. However, the reservoir is tvoicallv operated in the following manner: 0-8