Hydraulic Design of Dworshak Dam Diversion Facilities

The facilities used for river diversion, log passage, and migratory fish passage are described with respect to hydraulic problems and design criteria. Diversion was accomplished by use of a 40-ft diameter horse shoe-shaped tunnel, in conjunction with upstream and downstream cofferdams. The design of the tunnel entrance and exit channels and the concrete tunnel lining allow passage of the annual log drive. Tunnel closure involves a temporary gate at the upstream portal and a permanent concrete plug in the tunnel. Upstream migrating fish are prevented from directly entering the tunnel by a concrete sill across the exit channel. A fish trapping and loading structure to facilitate fish hauling is designed to operate alternately with a by-pass fish ladder to provide fish passage during construction.