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About the Flood Warning System

About the Flood Warning System

King County, Washington

What is the purpose of the King County Flood Warning Program?

To warn residents and agencies of impending floodwaters on major rivers so they can take action and prepare themselves before serious flooding occurs. In most locations, the warning system provides at least 2 hours lead time before floodwaters reach damaging levels. This program does not take the place of individuals and local groups making their own flood disaster plans.

When does flooding and high water typically happen in King County?

Most commonly from November through February during periods of heavy rainfall or rapid snowmelt. Historically, King County rivers have flooded in every month but August.

How does the Flood Warning System operate?

When high water conditions are imminent, King County activates its Flood Warning Center. Operation of the Center is based on a four-phase warning system, issued independently for each river. The thresholds for each phase are based on river gages which measure the flow and stage (depth) of the major rivers in various locations. King County staff monitor the gages on a 24 hour basis, so that actions can be taken depending on river conditions.

What other information is available from the Flood Warning Center?

King County (KC) works closely with the National Weather Service to obtain forecast information used to make flood predictions. Close coordination occurs with the KC Office of Emergency Management, KC Roads, and other agencies to obtain up-to-date information about problems sites, road closures, evacuations and other emergency services. Coordination also occurs with the U.S. Army Corps of Engineers and Seattle Public Utilities regarding dam operations. Personnel at the Center are available to answer questions and help interpret gage readings during a flood event. Current river and flood information is always available through the phone menu system. Call the Flood Warning Center at: 206-296-8200 or 800-945-9263.

What can you do to avoid flood disasters?

Once a warning is issued by the National Weather Service or by King County, residents should prepare for flooding. Becoming familiar with the relationship between upstream gage readings and local flood characteristics can help you prepare your individual emergency plan. Read what you can do before, during and after a flood. Keep informed of changing river conditions and make early preparations in case of major flooding.

What does each phase mean?

Flood phases indicate the severity of flooding and guide King County’s response. Flood phases are issued independently for six major rivers. The thresholds for each phase are based on river gages which measure the flow and stage (depth) of the major rivers in various locations. Phase 1 is an internal alert to King County staff. Phase 2 indicates minor flooding in some areas. Phase 3 indicates moderate flooding in some areas. Phase 4 indicates major flooding in areas.

At Phase 1, County personnel are put on alert and preparations are made to open the Flood Warning Center. When a Phase 2 threshold is reached, the Center is opened. Staff at the Center monitor river gages and flood conditions around the clock and are available to take calls from the public. When a Phase 3 threshold is reached, investigation crews are sent out to monitor flood control facilities (such as levees). Flood Alerts are sent to anyone who has registered at Phase 2, 3 and 4.

King County provides funding to the United States Geological Survey to support the operation and maintenance of river and stream gages and related systems.

For questions about the King County Flood Warning System, please contact Ken Zweig, River and Floodplain Management Section.