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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />llill9ti7 <br /> <br />Scoping Document I <br />Williams Fork Hydroelectric Project <br />FERC Project No. 2204 <br /> <br />4.1.2 Williams Fork Reservoir Existing Operations <br /> <br />Williams Fork Reservoir is a municipal water storage facility located on the <br />Williams Fork River approximately 2 miles upstream from the confluence with <br />the Colorado River near Parshall, Colorado. The reservoir provides replacement <br />water to meet downstream senior water rights requirements. replacing that <br />diverted by the Williams Fork Collection System. the Moffat Tunnel Collection <br />System, and the Roberts Tunnel Collection System. Williams Fork Reservoir is <br />operated for municipal water supply purposes and power generation is incidental <br />to the municipal water supply purpose of the reservoir. <br /> <br />To accomplish the purposes of the reservoir. Williams Fork Reservoir is operated <br />to ensure that it fills as much as possible. with the goal of filling every year. <br />Some of the main factors that affect the ability to fill the reservoir include: <br /> <br />I. The amount of runoff that occurs in a given year or a series of years; <br /> <br />2. The amount of releases required for water supply purposes; and <br /> <br />3. The length of time that downstream senior water rights are in priority. <br /> <br />As a result of the available runoff and downstream senior water rights, Williams <br />Fork Reservoir stores most water during the high spring runoff typically from <br />about mid-April through mid-July. Generally. during the remainder of the year <br />when streamflow is relatively low, the downstream senior right holders impose a <br />"call" on the Colorado River and its tributaries. At times when the reservoir can <br />no longer store streamflow, it is instead used as a replacement facility for Denver <br />Water's transmountain diversion projects. To enable Denver Water to continue <br />diverting at its other facilities, water stored during the spring runoff is released <br />from Williams Fork Reservoir in an amount equal to that diverted through Denver <br />Water's transmountain diversions. By this exchange method, Denver Water's <br />transmountain system can continue diverting. Water is released from Williams <br />Fork Reservoir to replace out-of-priority diversions at Dillon Reservoir and the <br />Roberts Tunnel. the Williams Fork Collection System and the Fraser Collection <br />System. Additionally, water stored in Williams Fork Reservoir is released in <br />substitution for water owed to Green Mountain Reservoir when Green Mountain <br />Reservoir does not fill due to diversions at Dillon Reservoir and the Roberts <br />Tunnel. As water is released for water supply purposes, Denver Water uses the <br />power facilities at the dam to generate as much power as is possible. This <br />replacement function for water supply purposes can occur in all months, with <br />most replacement occurring in July through March. <br /> <br />When snowpack data becomes available beginning in January. the Denver Water <br />staff makes initial calculations on the probability that Williams Fork Reservoir <br />will fill during the coming runoff season. Snowpack conditions are recorded and <br />tracked throughout the winter and spring. If calculations indicate that the <br />reservoir will likely fill and subsequently spill in the coming runoff season, then <br />water in addition to that needed solely for water supply purposes may be released <br /> <br />12 <br />