Blue Lake Expansion Project (Tunnels)

The City and Borough of Sitka said goodbye to dependence on imported diesel fuel with the raising of their Blue Lake Dam. The island community took a pro-active step toward securing its energy future when it approved a bond issue in 2012 to raise the 145-foot-tall concrete arch dam by 83 feet, which enabled generation of more hydroelectric power and eliminated their reliance on diesel as a backup fuel source.

Everything about the project posed access challenges, tunnels notwithstanding. One tunneling effort, from below the plunge pool into the left abutment was designed to assess current and future integrity of the rock abutment as the lake level and resulting head pressure on the dam rose. For this, subcontractor Blue Lake Tunnelers relied on our crane work to lower them and their equipment the 220 feet to the existing dam’s base. The new intake tunnel included a new 110 VF gate shaft since Blue Lake’s pristine water is the area’s drinking water supply as well as power source. Seasonal rising lake levels also mandated strict adherence to schedule as well as construction of a concrete plug in the intake during the area’s winter/rainy months. To protect the penstock from surge pressure (or water hammer) when the turbines need to shut down quickly, we also constructed a 414 LF adit tunnel and 360 VF surge shaft. The success of this project affects nearly everyone on Baranof Island.

Work on the Blue Lake project also appears in Dams & Reservoirs, Hydropower, Environmental and Marine categories.

Blue Lake Expansion Project (Tunnels)