Thompson Falls Gate Inspection

The Thompson Falls Hydroelectric Project is located on the Clark Fork River in Sanders County, Montana. The project was originally constructed in 1915 and is owned, operated, and maintained by NorthWestern Energy of Butte, Montana. Schnabel Engineering was retained to complete the FERC Part 12 inspection and hands-on gate inspection of the project’s four spillway radial gates.

The facility’s main dam is a curved concrete gravity structure that features a 913-foot-long ogee spillway with an average height of 18 feet. Four 41-foot-wide by 18-foot-tall radial gates were installed along the crest of the dam after the construction of adjacent concrete piers to support the project’s gate trunnions and wire rope hoist equipment.

Schnabel’s SPRAT-certified engineers completed a detailed inspection of the gates, using rope-access techniques to closely inspect each of the four gates for weld defects, condition of the coating system, seal condition and serviceability, condition of the gate trunnions and their lubrication systems, lifting devices and attachments, and the mechanical and electrical components of the hoist equipment. Following the completion of the gate inspections, Schnabel completed a detailed Gate Inspection Report (GIR) in accordance with FERC guidelines, which culminated in an overall condition regarding the fitness of the gates for continued safe and reliable operation. In addition to the GIR, Schnabel completed the comprehensive FERC Part 12D Inspection and report for the project in 2021.