Olmsted Power Plant Penstock Condition Assessment and Replacement

The Olmsted Hydroelectric Power Plant was originally constructed in 1904 at the mouth of Provo Canyon in Utah, and has been in operation for over 100 years. The power plant is a key feature of the Central Utah Project and continuing the operation of the power plant and upstream penstocks is critical to maintaining the 429 cfs water right associated with the power plant that allows the Central Utah Water Conservancy District (District) to deliver water to customers located along the Wasatch Front. The power plant and penstocks have operated well beyond their useful life expectancy. In an effort to determine the most efficient future operation and management of the facility, the District completed a comprehensive condition assessment of the existing power plant and upstream conveyance system including: three 48-in. diameter and one 72-in. diameter riveted steel penstocks, a hydraulic regulating structure (pressure box) that provides approximately 325 ft of head for the power plant, a 900 foot long non-pressurized limestone rock tunnel, approximately 1,700 ft of existing 102-in. diameter concrete encased steel pipe, and an overflow cliff spillway structure. This paper summarizes the condition assessment and presents the recommendations for replacing the existing penstocks, pressurizing the existing rock tunnel, modifying the cliff spillway structure, and the hydraulic and surge considerations related to operation of the hydroelectric power plant. Since the Olmsted Power Plant was constructed in the early 1900s and design or as built drawings were not available, the evaluation included a three dimensional (3D) light detection and ranging (LiDAR) survey of the interior and exterior of the hydraulic structures, rock tunnel, and cliff spillway structure. The condition assessment evaluation resulted in a recommendation to replace the existing power house and penstocks with a new hydroelectric power plant and a new 84-in. diameter steel penstock. The pressure box was removed, the overflow elevation of the cliff spillway structure was increased, and the system was transitioned to downstream flow control at the power house to eliminate the unbalanced flow operation of the existing system. This paper provides a detailed discussion of key issues and project challenges associated with the rehabilitation and replacement of a historical power plant from the viewpoint of the Owner and the Engineer.