225 20141125 DO SA 052 reduced

Barnard added 83 ft. onto the 145-ft.-tall, 1950s-era concrete arch dam built into a narrow slot canyon on Baranof Island to bring the dam to its maximum geotechnical height.

In an effort to eliminate their dependence on diesel fuel for additional power, the City and Borough of Sitka set out to expand its hydropower generation by raising the Blue Lake Dam and constructing a new powerhouse. The dam impounds the 3.25-mile-long Blue Lake Reservoir from which the area has been drawing most of its power for more than 50 years. The project included construction of a new ogee spillway with wing walls atop the dam extension and a new 15 MW hydroelectric powerhouse equipped with three 5.3 MW horizontal Francis turbine generators. Getting the water to the turbines required a new intake tunnel and concrete intake structure, which required significant vertical rock excavation on the shores of Blue Lake.

This project required in-water work with strict attention to the environment, given that Blue Lake contains some of the cleanest water in the U.S. and acts as the primary water resource for Sitka and the community at large. Water quality was never an issue throughout the duration of the project. The project included challenges inherent to construction in a remote location and throughout the continued operation of Sitka’s existing hydroelectric operations. Additionally, work was completed through a 65-day generation outage to commission the new intake, gatehouse, intake tunnel, penstock, and new powerhouse, which was completed 14 days ahead of schedule.


Location: Sitka, Alaska

Owner: City and Borough of Sitka, Alaska

Construction Manager: McMillen, LLC

Engineer: Hatch

Contract Type: Fixed Lump Sum & Fixed Unit Price

Status: Completed


  • 2016 Build America Grand Award
  • 2016 Marvin M. Black Partnering Excellence Merit Award
  • 350 CY of 27-ft.-tall by 36-ft.-long by 39-ft.-wide intake structure with two fixed trash racks and a 14,000-lb. bulkhead gate
  • 110 VF, 11-ft.-dia concrete/shotcrete-lined hard rock gate shaft
  • 212 CY 27-ft.-tall by 75-ft.-long by 12-ft.-wide gatehouse for a 28,000-lb. fixed-wheel gate
  • 414 LF, 10-ft. by 12-ft. horseshoe-shaped adit tunnel
  • 138 LF, 10-ft. by 13-ft. horseshoe-shaped drainage tunnel
  • Demolition of existing concrete on 120-ft. side spillway

83-ft. dam raise

500 LF of 8-ft.-dia. penstock

360 VF 11-ft.-dia. surge shaft

225 20141125 DO SA 023