Planned water releases from the Howard Hanson flood-control dam in the upper Green River watershed have brought the Green River Wednesday up to a Provisional Phase 3 flood alert level with predictions of a full Phase 3 alert by late Wednesday afternoon.
Moderate flooding is expected in rural lowland areas. Urban areas of the Green River Valley are generally protected by the levee system but be aware that flood conditions can change rapidly, according to the King County Flood Warning Center.
At 1:45 p.m. Wedneday, the Green River at Auburn was flowing at 8,300 cubic feet per second (CFS). A full Phase 3 alert goes out when the flow reaches 9,000 CFS. The flood stage had reached 61.52 feet.
A Phase 3 flood alert along the Green River could cause moderate flooding of varied depths upstream of Auburn and the lower Mill Creek basin. Portions of Southeast Green Valley Road and West Valley Road may overtop.
Flows are expected to reach or exceed 10,000 CFS between 3 and 5 p.m. Wednesday, according to the King County Flood Warning Center.
The National Weather Service reports that 4 to 7 inches of rain has fallen around the Green River basin to produce the large rise. The U.S. Army Corps of Engineers drains the reservoir behind the Howard Hanson Dam after the flood has peaked upstream.
The flood warning remains in effect from Wednesday to Saturday evening. According to the NWS, the river will rise after 3 p.m. Wednesday and crest near 10,764 CFS around 4 a.m. Thursday before falling.
At 9,000 CFS, the Green River will flood low areas of the Middle Green River Valley with water over Southeast Green Valley Road. Some backwater inundation is possible in lower Mill Creek Basin between Auburn and Kent.
At 5:30 a.m. Wednesday, the Green River at Auburn was flowing at 7,610 CFS, which exceeds the threshold of 7,000 CFS for a Phase 2 flood alert level on King County’s four-level flood phase system. At these flows, only minor flooding is expected to occur along portions of the Green River above Auburn without levees.
King County Flood Warning Center staff have been working ‘round the clock since 1:30 p.m. Tuesday, Feb. 21, to monitor this flood event, which is the result of extensive rainfall in the Cascade Range and foothills. Flood Warning Center staff will remain on duty throughout the duration of this flood event.
Updated information on flooding will also be posted on the King County website at www.kingcounty.gov, or via RPIN, the area’s regional website at http://www.rpin.org. A recorded flood-information hotline is also updated each hour for citizens wanting information in flood areas. The number is 206-296-8200 or 1-800-945-9263.
Citizens who need help interpreting flood information should call 206-296-4535 or 1-800-768-7932. Problems on county maintained roads can be reported by calling 206-296-8100 or 1-800-KC-ROADS.
An automated flood alert system is now available and provides real-time warning of potential high water on more than a half-dozen rivers. King County residents and business owners can sign up to receive King County Flood Alerts by visiting www.kingcounty.gov/flood, or by calling 206-263-3400 during regular business hours to register by phone. Messages of potential high flows on any of King County’s major river systems can be sent by phone, text or email.
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