A 33-foot-diameter tunnel used to divert the river around the dam construction site was sealed, restoring flow to the river channel.Click here to enlarge imageDesign of the intake structure and rehabilitation of the overall river reach was aided by two separate physical models, one built and operated by Colorado State University (CSU) in Fort Collins and the other at USBR’s Hydraulics Laboratory in Denver. The full-scale, unit width model of the screens constructed by CSU was used to evaluate diversion capacity, sediment plugging tendencies and air-backwash effectiveness. A much larger scale model of the river reach by USBR was used to evaluate options for cofferdam regrading and overall reach geometry, and sediment transport characteristics.
The two physical models were complimented by computer-based numerical modeling using the BriStars sediment transport model and Flow3D, a computer-based three-dimensional hydraulic model. BriStars was used to evaluate both local and reach scale sediment movement for single event and long-term hydrology. Flow3D was used on a macro-scale to design a boatable bypass channel of naturalistic chutes and pools and to track sediment movement to assist in the design of sediment control structures. Flow3D was also used on a micro-scale to evaluate flow patterns and sediment movement through the intake screens.
Finished Product
Construction of the American River Intake Structure and channel were completed in late 2007. The bypass tunnel has been sealed and the river once again flows through the site. Revegetation will take several years and evidence of the dam project which started more than 40 years ago will always be visible. In place of the dam now stands a unique multi-use diversion facility that provides not only a reliable water supply but also provides for bypass of environmental base flows, fish and boat passage and whitewater recreation. The restored river enhances the appearance of the scarred dam construction site and new public access facilities open the area to recreation.WW
About the Authors: George Slovensky is a senior project engineer with WHPacific. and is based in the firm’s Lakewood, CO, office. He may be contacted at [email protected]. WHPacific, Inc. (www.whpacific.com) is owned by NANA Development Corp. of Anchorage, Alaska. The company provides a broad range of services including engineering, architecture, surveying and planning to commercial and governmental clients nationwide. Alan Stroppini is Design Branch Chief of the Mid-Pacific Regional Office of the USBR in Sacramento, CA.
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