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<br />n{'; I" ~ f) <br />.vv{)l~ <br /> <br />PROVISIONS FOR AURORA <br /> <br />The Strontia Springs proposal provides Aurora with a new diversion <br />point and Intake that is free of ice and sediment. The need for a <br />burled upstream conduit is also el iminated through provision of direct <br />access into the Rampart Tunnel by a short adlt from the intake. <br /> <br />The Upstream Dam and Joint Use of Rampart Tunnel alternatives <br />provide Aurora with a new diversion point in a reservoir formed by a <br />50-foot high dam upstream from its present diversion. A common intake <br />and tunnel from the intake to the entrance of Rampart Tunnel No.2 <br />wi i I be shared with Denver. The Upstream Dam alternative provides for <br />independent use of Rampart Tunnel No.2 by Aurora; whereas, the Joint <br />Use of Rampart Tunnel alternative provides for common usage of Rampart <br />Tunnel No.2. <br /> <br />The Chatfield, Harding, and Mouth of Canyon alternatives have no <br />provisions for Aurora. For Aurora to have an improved diversion point <br />and intake, new faci I ities would be required in the canyon. As a mini- <br />mum, it is considered that a new 50' high dam, intake, and tunnel would <br />be needed to del iver raw water to Rampart Tunnel No.2. This cost would <br />be approximately $25,000,000 and is included in the estimate. <br /> <br />DAM SAFETY <br /> <br />Pursuant to the Da~ Inspection Act, Public Law 92-367, the Chief <br />of Engineers issued the "Recommended Guidelines for Safety Inspection <br />of Dams." The proposed Strontia Springs dam and the alternatives were <br />reviewed for compliance. In accordance with the guidelines, the hazard <br />classification for a dam is based on the potential loss of life and <br />property. The magnitude of the design flood peak for a dam is based on <br />two conditions: (1) the size of the impoundment and the height of the <br />dam, and (2) the hazard classification. Under these guidelines, the <br />proposed dams at Strontia Springs and the Mouth of the Canyon should be <br />designed for safe passage of one-half the Probable Maximum Flood (PMF) <br />peak as the dams are of large size, being higher than 100 feet, and are <br />in a low hazard category. The remaining alternatives, where the height <br />of the dam is 50 feet or less, would be classified as smal I or inter- <br />mediate size dams. Therefore, the required design peak for the other <br />dams is a 100-year flood. Flood routing of the design peaks indicated <br />that some overtopping would occur during the design flood for al I dams, <br />except the Mouth of the Canyon and Chatfield. For the Mouth of the <br />Canyon alternative, the rockfil I dam requires a spi I Iway sized to carry <br />the flood peak without overtopping. <br /> <br />11 <br /> <br />