Nine Mile Dam Unit 1-2 Turbine Upgrade

Spokane River near Nine Mile Falls, WA: Multifaceted rehabilitation of 100+ year old dam. Replacement of 2 turbine/generator units, and upgrades to the forebay and tailrace.

Project Details

The rehabilitation of the Nine Mile HED put the versatility of Kuney Construction on display. The project involved heavy civil and marine construction efforts in the forebay and tailrace, combined with intricate mechanical and electrical work inside the powerhouse.

In the forebay, Kuney dewatered and refurbished the Unit 1 and 2 intake gates and slots, and dredged and removed a cofferdam cell. Tailrace work included the forming and placement of new pier extensions and a new tailrace deck allowing for operator access. Piers were drilled and anchored to the bedrock with new post-tension rock anchors. New tailrace stoplogs were fabricated and installed allowing for dewatering of the draft chest for the first time since 1908.

Inside the powerhouse, Kuney demolished over 2000 CY of concrete from the Unit 1 and 2 wetpits and original cast-in-place draft tubes. Concrete was removed to facilitate installation of new steel draft tubes which were assembled and suspended in position. Nearly 1000 CY of concrete was then placed around the draft tubes, and in the generator floor requiring elaborate forming systems, tight quality control and slow pour rates to monitor movement. After completion of the concrete placement, two new Seagull Weir American Hydro turbine units and 8.8 MW Hyundai local generator units were installed. New electrical components were also installed including panels, wiring, 15 KV switchgear, motor control center, transformers, plant controls, exciters and generator cabinets.

Project specs

  • Location: Nine Mile Falls, Washington on the Spokane River
  • Owner: Avista Utilities
  • Timeframe: 2014-2016
  • Size: Private (Over $10 Million)
  • Tailrace construction required dredging and sediment relocation to allow for pier rehabilitation and new steel stoplog installation.
  • Forebay construction completed within tight in-water work windows.
  • Sheet pile crane pad, and barge dock built under separate contract to facilitate construction and for owner's future use.