Barnard Construction Co., Inc.

Owner:

City and Borough of Sitka

Scope Of Work

Following in the footsteps of their forefathers, residents of the City and Borough of Sitka voted nearly unanimously – 97 percent ‘Yes’ – to end their dependence on imported diesel fuel by raising their local Blue Lake Dam and adding a new 15 MW powerhouse to the system to produce more hydropower. The small island community took a pro-active step toward securing its energy future when it approved a bond issue in 2012 to further pursue a local source of energy. The additional water held back by raising the 145-foot-tall 1950s-era concrete arch dam by 83 feet feeds a new powerhouse equipped with three new 5.3 MW horizontal Francis turbines.

Barnard’s Team took on the challenges in late 2012. Raising the dam meant we had to deliver all equipment needed across the dam by crane because the dam is built into a steep, narrow canyon with zero access on one side. The powerhouse was constructed 2 miles downstream, on a site that posed excavation challenges of its own in solid rock. Getting the water to the turbines required construction of a 900 LF (274 m) new intake tunnel and concrete intake structure which involved 120 feet (36.5 meters) of vertical rock excavation on the shores of Blue Lake. In addition, Barnard constructed a 10-foot-diameter (3 m) surge shaft 360 vertical feet (110 vertical meters). Partnering with the City and Borough proved very beneficial to everyone. Regularly scheduled public tours of the jobsite led to understanding and cooperation, which proved essential during a temporary outage of the existing system to commission the new powerhouse and City drinking water system and decommission the old powerhouse.