Photo courtesy Natt McDougall Co. Natt McDougall Co. created a fish passage facility at Landsburg Dam in Ravensdale.

Natt McDougall Co. was the general contractor/ construction manager for a fish passage facility at Landsburg Dam, home to Seattle Public Utilities’ diversion dam and drinking water intake facilities in the Cedar River Watershed.

Fish passage through Landsburg Dam had been blocked since 1899, when the original dam was built. The new passage had to be built in 16 months, with no disruptions to the water treatment plant that provides 65 percent of Seattle’s drinking water, and in time for fish migration in the fall.

The work involved demolition of a massive dam wall, strengthening the dam with steel beam supports and installing a gate for the fish to pass through. Included was an innovative fish ladder, fish exit channel, fish screen and downstream passage gate to support the migration process.

The project also required construction of seven rock drop structures and a natural fish ladder to allow fish to migrate upstream over an 8-foot-diameter aqueduct pipe which crosses the river.

Natt McDougall had to secure 25 permits before construction could begin and work with a large number of oversight agencies on a rigorous daily water monitoring schedule. A system was built to transport dirty water into a holding area to be treated and dispersed into the forest, which also had to be protected.

The project was completed ahead of schedule and under budget with no injury time-loss days.