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Dam Safety

Program overview

SPU is dedicated to ensuring that all dams are designed, constructed, operated, and maintained with your utmost safety in mind. SPU continually inspects, evaluates, and documents the design, construction, operation, maintenance, rehabilitation, and emergency preparedness for each dam.

The mission of the SPU Dam Safety Program is to ensure safe operation of the dams and the Cedar Moraine embankment owned by SPU. The program goal is to:

  • Comply with strict federal regulatory requirements.
  • Inspect, monitor, maintain and operate the dams to minimize the chances of loss of water supply or flooding downstream, and prevent these conditions from developing if possible.
  • Respond to dam emergencies by using rehearsed emergency action plans and other tools.
  • Develop emergency action plans in partnership with other agencies.
  • Ensure that the Tolt Dam and Lake Youngs Dam Failure Warning Systems are being operated and maintained appropriately.
  • Plan and invest in state of the art monitoring equipment to ensure safe dam operations, which allows the City to respond to emergency conditions.

Dam monitoring and emergency action plans

SPU has comprehensive dam safety, monitoring and surveillance equipment in place. Scientific instruments are installed to continuously monitor dam performance by measuring reservoir levels, groundwater within dams, and stream flows. Operation crews perform daily visual inspections on all dams and report unusual conditions and high instrument readings to dam engineers. Federal and state regulators work with our SPU staff to perform annual inspections to ensure safe operating conditions.

All our dams meet current engineering standards and are in compliance with state and federal regulations.

SPU has developed emergency action plans for each dam facility. These plans are updated on an annual basis, in partnership with local emergency management agencies, King County, the National Weather Service, and state and federal dam regulators.

Dam safety brochures

South Fork Tolt River Reservoir and Dam (pdf)
Lake Youngs Reservoir and Outlet Dam (pdf)

Related links

Cedar River Watershed (Seattle Public Utilities)
Tolt River Watershed (Seattle Public Utilities)
Take Winter By Storm! (Regional Public Information Network)
Howard Hanson Dam (U.S. Army Corps of Engineers)