Best Small Project (under $10 million): Boundary Dam Spillway No. 1 TDG Modifications Removal
Boundary Dam is located in remote northeastern Washington and is one of the largest underground power generation dams in the nation, providing nearly half of the power generated by Seattle City Light (SCL). The structure features unique spillways cut into rock that are oriented so that water discharges from both sides, meeting in midair to dissipate the falling-water energy that would otherwise erode canyon walls.
The project goal was to mitigate impacts to local fish populations and minimize environmental impacts by removing total dissolved gas (TDG) modifications made in 2016 and to restore the spillway. Stainless steel roughness elements increased TDG in the river prior to this project, adversely impacting the fish population. These roughness elements also raised structural concerns when struck by debris.