Exhbits P-S; Rebuttal Report to Prehearing Statements

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? • Numerous similar structures that do not imPact 100-Year water surface elevations have been constructed in Colorado and other states. The 100-year water surface profile at the project site is partially controlled by backwater from the Highway 9 river crossing just downstream of the site. The 100-year water surface profile of the Blue River upstream of the Highway 9 crossing is controlled in part by the conveyance capacity of that crossing. Review of the FEMA flood insurance study for this reach suggests that backwater caused by the Highway 9 crossing propagates upstream during the 100-year flood event into at least part of the reach in which the proposed structures will be constructed. Preliminary review of hydraulic modeling conducted by Ecological Resources Consultants, Inc. for design of fish habitat just upstream of the Highway 9 crossing tends to reinforce this finding. The impact of this backwater will be to lessen the influence of river channel shape, roughness, irregularities, etc. on the 100-year water surface profile. Prior to construction, a floodplain permit will need to be obtained from the Town of Silverthorne. As part of the permit, it will need to be shown that the control structures will not cause a violation of floodplain regulations. Hydraulic modeling will be used to provide evidence of compliance. Brown and Caldwell has initiated the development of a more detailed design of the structures. If requested by CWCB, necessary design ? geometry of the control structures could be hydraulically modeled in advance of the permitting process to assure CWCB that floodplain regulations will not be violated. In order to model the reach of the Blue River potentially affected by the Silverthorne RICD, more detailed data on river channel geometry must be obtained. At present (June 29, 2005), flow in the Blue River at the project site was over 800 cfs, which is unsafe for wading and surveying. Currently, the flow in the Blue River at the site is dependent on precipitation runoff and Lake Dillon operations. Flows will need to decrease prior to surveying the site. It is uncertain when flows will reduce to levels safe for wading and surveying. However, it is likely that the survey can be conducted sometime in July or August when flows typically decrease. The question of adequate access was raised in the Prehearing Statement of CWCB. As indicated on the Plat Map for Riverview Subdivision, Filing No. 1 attached hereto as Exhibit P, Silverthorne is the owner the parcel delineated as Tract C which comprises the bed of the Blue River from the Highway 9 Bridge to I-70, except for a portion of the river bed, delineated as Tract D that is owned by the Buffalo Mountain Metropolitan District. As explained in the attached Rebuttal Testimony, Silverthorne is currently in active negotiations with that District for Silverthorne's ownership of Tract D. Also, as indicated on Exhibit P, there is an existing easement for pedestrian access all along the east bank of the Blue River along the Course. To the extent that additional rights of access are needed, Silverthorne is a municipality of the State of Colorado and, as such, is authorized by law to acquire such rights by consent or other lawful means, including by eminent domain. 10