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South Fork Tolt River Reservoir and Dams

Seattle Public Utilities (SPU) owns and operates the Tolt Reservoir and Dam, located 16 miles upstream from the City of Carnation on the South Fork Tolt River. The reservoir stores 57,900 acre-ft of water to supply 30% of the drinking water for 1.3 million people in the metropolitan Seattle area.

The Federal Energy Regulatory Commission (FERC) regulates the 200-foot high earth-filled dam, and conducts annual safety inspections each year in conjunction with SPU’s own dam safety engineers. Every five years, specialty consultants also perform an independent comprehensive evaluation on the safety of the dam. These efforts ensure that the dam complies with federal dam safety regulations and engineering requirements to maintain safe operating conditions and engineering standards.

Warning system information

In the unlikely event of a dam failure, water from the reservoir may inundate the City of Carnation. To alert residents of such an event, SPU is working closely with the local government to maintain an advanced dam failure warning system. This system, now in its fifth generation, includes sophisticated monitoring instruments at the site, four cameras at strategic locations, and eight sirens along Tolt River Road and within the City of Carnation. The warning system is automated and monitored by operators in the SPU Operations Control Center 24 hours a day, 7 days a week. Sirens provide early flood warnings, and are tested every Wednesday at noon. These tests involve activating the sirens and playing pre-recorded audio messages.

What you can expect

Sirens produce three distinct pre-recorded messages. A loud high-pitch sound precedes each warning. Click below to listen to samples of each message:

  • Test message: Every Wednesday at noon, the warning system plays a test message. This ensures the system is operating as intended, and to maintain resident familiarity with the system. After the initial high-pitch sound, residents will hear the following message: “This is a test of the Tolt Dam Warning System. This is only a test.”
  • Dam failure message: In the event of a dam failure, sirens will alarm and produce the following message warning residents to evacuate the area: “The Tolt Dam has failed, evacuate the area immediately.”
  • All clear message: Once officials deem the area is safe for residents to return to their homes, sirens will sound the following message: “It is safe to return, the dam is secure.”

Local government has established contingency plans in the event of a dam failure. These plans specifically address public notification, evacuation and post-incident recovery efforts.

Be prepared

In the unlikely event of a dam failure, high water in the City limits may exceed a depth of 13 feet within a short period of time. Telephone lines will also be taxed, so contacting local governmental agencies is not recommended. Instead, Carnation residents should heed the siren warnings and follow the evacuation signs away from the inundation area. To prepare for this unlikely event, Carnation residents should visit the following City of Carnation websites:

For more information on how you and your family can prepare, respond, and recover from disasters, please visit King County’s Office of Emergency Management.

Partners in safety

Seattle Public Utilities (SPU) works with the following agencies and local governments in public communication and preparation of the Emergency Action Plan (EAP) for the South Fork Tolt River Reservoir and Dam:

  • City of Seattle
  • King County
  • City of Carnation
  • Snohomish County
  • Riverview School District
  • Eastside Fire and Rescue
  • Carnation / Duvall Police Department
  • National Weather Service

More information

For more information on evacuation routes, please contact:
City of Carnation
(425) 333-4192
www.carnationwa.gov

For further information on the Tolt Dam Warning System, please contact:
Daniel Huang (SPU)
(206) 233-2535
daniel.Huang@seattle.gov

South Fork Tolt River Reservoir and Dam brochure (pdf)