Laserfiche WebLink
<br />Executive Summary <br /> <br />Project contemplated draft, as converted to an instream flow right at Juniper Canyon, was <br />evaluated to characterize the impact on the annual hydrograph of the Yampa River. <br /> <br />The modeled influence of the Juniper instream flow right was to slightly modify the <br />annual temporal distributions of flow on the Yampa River. The instream flow right had the <br />effect of slightly increasing flows during the Jow flow fall and early winter months. <br />Augmentation releases for junior demands which were called out by the instream flow right (in <br />scenarios II through V) asserted an increased draw on basin reservoirs, which resulted in a <br />slight decrease in Juniper Canyon flows in the spring and early summer months when the <br />reservoirs filled. <br /> <br />Instream flow targets were modeled in two other locations on the Yampa River besides <br />Juniper Canyon. These instream targets were located immediately below Stagecoach Reservoir <br />and below the City of Craig. The Stagecoach target reflects current operating procedures of <br />the reservoir. The instream flow target (a constraint really) below Craig was modeled only in <br />Scenario V to help protect this river reach from the depletive effects of operating an exchange <br />out of Williams Fork Reservoir. No instream flow targets were modeled below Elkhead <br />Reservoir, Steamboat Lake or the Williams Fork Reservoir. <br /> <br />Model results from Scenarios I through V indicated relatively little variation between <br />development scenarios (III through V) with respect to instream flows in Juniper Canyon and <br />other mainstem reaches. Selection of the recommended development alternative was not <br />possible based on instream flow considerations alone. <br /> <br />Reservoir Fluctuations <br /> <br />The degree to which reservoir levels fluctuate has important biological and recreational <br />implications. The ability of a reservoir to act as a water supply for perimeter wetlands <br />depends greatly on seasonal rises and declines in the water surface elevation. In addition, <br />reservoir fish populations can be affected by the degree and frequency of reservoir operations. <br /> <br />There were relatively minor differences in reservoir fluctuations between the modeled <br />scenarios. Hence, as wit1:t the evaluation of instream flow predictions, it was not possible to <br />select the best water development project in the Yampa Basin based solely on the effects of <br />operations of reservoirs on fisheries and wetlands. Development of new reservoirs would <br />generally have more impact to existing wetlands than reservoir enlargements. <br /> <br />Project Costs <br /> <br />Preliminary cost estimates were generated for development of storage capacity at all five <br />candidate reservoir sites, although only the Elkhead and Stagecoach enlargements and the <br />Williams Fork project were modeled in the operating studies. These preliminary cost estimates <br />were intended to provide only comparative information between alternative projects. A greater <br />amount of information on physical characteristics was available for the Stagecoach and Elkhead <br />sites than the other sites. To allow comparison of projects on an equal basis, several <br />simplifying assumptions were applied to normalize cost estimating parameters. All estimated <br />costs reference the Engineering News Record Cost Construction Index No. 4777 (January, <br />1991). These figures were not intended to represent discrete, absolute numbers. <br /> <br />The preliminary cost estimate for the enlargement of Elkhead Reservoir was based on a <br />new reservoir with a total capacity 52,000 af; total costs of this dam raise and associated work <br />were estimated to be in the range of $15 - $20 million. The maximum reasonable reservoir <br />enlargement size at the existing Stagecoach Reservoir is 52,000 af and the preliminary costs of <br /> <br />S-23 <br />