Exhibits 1-6 for Case 02CW038 - Laserfiche WebLink

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Cynthia F. Covell, Esq. July 17, 2002 Page 2 Flow Regime of the Gunnison River The flow regime of the Gunnison River changed with the construction of the Aspinall Unit in the late 1960's and the signing of the 1975 Taylor Park Reservoir Operation and Storage Exchange Agreement. Basically, the 1975 Exchange Agreement allows for the coordinated operation of Taylor Park Reservoir and the Aspinall Unit Reservoirs to stabilize the flows in the Taylor and Gunnison River for recreation, fishery, and other uses. Many of the aspects of the 1975 Exchange Agreement are incorporated into the decree in Case No. 86CW203. Therefore, the period of 1975 -2000 was utilized for the analysis of the historical flow regime at the Whitewater Course. The hydrology was analyzed for the period May through September, which is the time frame for the water rights application. The United States Geological Survey maintains the Gunnison River near Gunnison, Colorado streamflow gage. This gage has records available from 1910 to the present and is located approximately three - quarters of a mile upstream of the Whitewater Course as shown in Figure 1. The only major diversion between the Gunnison River near Gunnison gage and. the Whitewater Course is the "West Branch ". The West Branch conveys water through a local neighborhood until the majority of the water is diverted by Kelmel -Owens Number 1 Ditch and the remaining water flows in the West Branch back to the Gunnison River just downstream of the Whitewater Course as shown in Figure 1. The Kelmel -Owens Number 1 Ditch has decreed water rights for 74.25 cfs and diverts approximately 5,800 acre - feet/year. The historical flows diverted into the West Branch were not measured. Based on historical diversion records and personal observation of streamflows in the West Branch, the historical streamflow in the West Branch was estimated to average 50 cfs during the period May through September. The flows in the West Branch can vary from as little as 15 cfs to over 85 cfs; but for the purpose of this analysis, a constant rate of 50 cfs was utilized. Figure 3 is a flow duration curve developed using daily streamflows for the May- through- September period for the years 1975 -2000. As shown in Figure 3, the streamflows exceed 250 cfs 97 percent of the time and are greater than 2,000 cfs 20 percent of the time which results in the streamflows being within the design parameters of the Whitewater course 77 percent of the time. Because of the large variation in streamflow in the Gunnison River, the UGRWCD board decided to file the water right application based on bi- monthly time periods for the May- through- September period. After careful consideration of many factors, the UGRWCD Board selected the following water right flow rates: Figure 4 presents these flow rates relative to the maximum, average, and minimum flow during each bi- monthly period. Period Flow Rate cfs May 1 — May 15 570 May 16 - May 31 1,190 June 1 —June 15 1,460 June 16 — June 30 1,500 Jul 1 —July 15 1,100 July 16 — July 31 530 August 1 —August 15 460 Au ust 16 — August 31 390 September 1 — September 15 300 September 16 — September 30 270 Figure 4 presents these flow rates relative to the maximum, average, and minimum flow during each bi- monthly period.