Dam Safety
March 29, 2024
Yesterday Seattle Public Utilities (SPU) turned off the Tolt Dam Early Warning System sirens in Carnation while we investigate the cause of the unplanned siren sounding on March 27.
SPU has worked with King County Office of Emergency Management to ensure the community would be notified in the event of a dam emergency through Alert King County and the Wireless Emergency Alert System.
In addition, SPU is increasing daily inspections of the Tolt Dam and will continue its robust dam safety program which includes daily visual inspections and instrument readings by operators, dam safety quarterly inspections, periodic and annual evaluation and documentation of surveillance and monitoring, Federal Energy Regulatory Commission (FERC) annual inspections and independent consultant inspections every 5 years.
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 managed by SPU. The program goal is to:
- Comply with strict federal and state 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 surveillance and 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 high hazard 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.
Related links
Cedar River Watershed (Seattle Public Utilities)
Tolt River Watershed (Seattle Public Utilities)
Howard Hanson Dam (U.S. Army Corps of Engineers)
For more information about our Dam Safety Program, contact Taryn Sass at (206) 850-9737 or Taryn.sass2@seattle.gov.
For concerns about issues at the Lake Youngs facility or perimeter, please call the Lake Youngs desk at (206) 684-3933.
For emergency related questions, please contact your local emergency management agencies.