Narrows II

Project required that a flow bypass system be constructed for the purpose of allowing the continuance of flow in the Yuba River while the Narrows II Powerhouse was shut-down for maintenance.

The project consisted of tunnel construction; furnishing and installing tunnel liner and junction, reinforced concrete bypass valve structure construction, powerhouse structural modifications, furnishing and installing bypass valve, guard valve, and turbine shutoff valve including operating and control equipment; testing; removal and disposal of waste materials; and final cleanup.

Tunnel work included drill & blast excavation of the bypass tunnel (120 ft long x 13 ft diameter horseshoe-shaped tunnel), construction of the bypass structure and discharge channel; supply and installation of 114” steel tunnel liner and a 90-degree tee connection to the existing penstock.

Construction of a 65-foot-deep access shaft near the upstream wall of the powerhouse to accommodate the wye branch to be installed in the existing steel lined power tunnel.

Other work included foundation excavation; construction of reinforced concrete bypass valve structure; structural modification of the existing powerhouse and installation of a 78-inch diameter fixed cone type bypass valve, a 78-inch diameter bonneted knife gate type guard valve, a 168-inch diameter butterfly type turbine shutoff valve, and a 168-inch by 186-inch by 138-inch wye branch.

Owner: Yuba County Water District