Analysis of Colorado-Big Thompson Project Operation With Respect to East Slope Diversions and Non-Charge Deliveries

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evidently has been improved to slightly more than 400 cfs. The Dille Tunnel diversion facility was constructed so that sand in the river could be passed on downstream rather than being diverted into the tunnel. Because of this aspect of the diversion facility, a bypass of 40 to 50 cfs water is required at this structure. Horsetooth Reservoir has a total storage capacity of approximately 156,700 acre -feet at elevation 5,430 feet of which 149,700 acre -feet is active storage. It was constructed during 1946 -49 and became operational in January 1951. The principal outlet from Horsetooth Reservoir is the Charles Hansen Supply Canal which is used to deliver water to the Cache La Poudre and to the Poudre Valley Canal through a siphon across the Cache La Poudre. The Dixon Feeder Canal is another outlet from Horsetooth Reservoir. Project water is also delivered to Cache La Poudre for use in the North Poudre System. This water is diverted into the North Poudre Supply Canal through an exchange. Figure 2 is a sketch map portraying the east slope facilities of the C -BT Project that are important in this analysis. In addition, it shows the locations of the four gaging stations on the Big Thompson River that are important in this analysis. These are the gaging stations below Olympus Dam, at the canyon mouth near Drake, at Loveland, and at the river mouth near La Salle. The gaging station at the canyon mouth near Drake is below the Dille Tunnel diversion, but upstream from the 16 existing diversions on the Big Thompson River. The gaging station at Loveland is downstream from 12 of these diversions, and the gaging station at the river mouth is downstream from them all. East Slope Water Rights C -BT Project water rights allow diversions for project purposes from the Big Thompson River; the Cache La Poudre; three small tributaries of the Cache La Poudre that discharge directly into Horsetooth Reservoir; and Left Hand Creek, Dry Creek, and Boulder Creek. The Big Thompson River water rights provide for diversions at the Olympus and Dille Tunnels and storage in Carter Lake, Horsetooth Reservoir, and Boulder Reservoir. The Big Thompson River water rights for Carter Lake and Horsetooth Reservoir have effectively a 1933 priority. The Cache La Poudre water right is for diversions into the North Poudre Supply Canal and has effectively a 1943 priority. Table 1 provides additional data for Northern Colorado Water Conservancy District (NCWCD) east slope water rights. Historical Operation Table 2 shows the water brought over to the east slope through the Adams Tunnel from the start of its operation through 1998. The diversions averaged 207,300 acre -feet annually during this 52 -year period. Since most of the C -BT east slope facilities were operating by 1955, the demand for C -BT Project water should have been fully established by this time. The table shows that the Adams Tunnel diversions averaged 229,400 acre -feet annually during 1955 -98 and ranged from 159,900 acre -feet in 1983 to 315,900 acre -feet in 1964. During 1983 -98, the 7