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000381 Yampa River - Maybell Table 4 presents modeled monthly flows of the Yampa River at Mayben under baseline conditions. Figures 5a through 51 present monthly flow exceedance curves based on these modeled flows. Also shown in Figure 5 are flow exceedance curves produced from model scenarios run at a projected future demand level with and without construction of the proposed project. Future demand level model scenarios are further discussed below. Average monthly flows of the Yampa River at Maybell under baseline conditions range from a low of 115 cfs in September to a high of 5,632 cfs during the May runoff period. Occasionally, there are zero flow conditions predicted by the model at Mayben during the late summer and early fall. Howeyer, a minimum of 25 cfs is usually present downstream of the Mayben Canal as a result of leakage around the ditch headgate and return flows to the river. Leakage and return flows from the Mayben canal above the Maybell gage were not represented in the model. Table 5 presents the modeled 25th, 50th and 75th percentile flows at Maybell for the baseline condition. Table 5 Modeled Baseline Flows at Maybel1 (cfs) Month 25% exc. 50% exc. 75% exc. October 291 204 129 November 344 255 209 December 322 228 179 January 284 217 179 February 336 256 238 March 717 498 395 April 3,117 2,086 1,381 May 7,016 5,754 4,039 June 6,363 5,147 3,644 July 1,753 999 444 August 368 220 91 September 163 91 31 Anticipated Future Conditions Without Project The future demand scenario was defined in the Hydrosphere model by a projected demand level representing year 2040 conditions. Elkhead Reservoir was modeled with. a capacity of 13,700 af, as in the baseline scenario. All other modeling assumptions and operating rules were the same as those defined in the baseline scenario. The projected 2040 demand condition includes an additional consumptive water demand of approximately 38,000 af over conditions in the baseline scenario. Included in the 38,000 af demand increment is approximately 14,000 af of demand associated with future growth in municipal and agricultural water use. The remaining 24,000 af of demand is associated with construction of new thermal electric generation capacity at the Hayden and Craig stations, a new coal-gasificl,ltion plant, and new mining facilities. In most instances, these future depletions would be expected to occur using existing water diversion facilities and water rights. Some modeled future depletions may require consultation under Section 7 of the Endangered Species Act. 17 ,J....___1,