The thousands of Green River Valley residents in communities such as Auburn, Kent, Renton and Tukwila will have an additional seven hours’ warning of possible flooding as a result of changes King County has made in how it monitors flows on the Green River.

In response to concerns about ongoing structural concerns at Howard Hanson Dam, King County Flood Warning Center staff will use water release data from the dam, rather than flows observed at a stream gage 30 miles downstream at Auburn, as the basis for their emergency response actions.

“It takes approximately seven hours for water that’s been released from Howard Hanson Dam to flow downstream to Auburn, so switching the data point to dam releases provides us with a significant amount of lead time to help those communities prepare for and respond to high water,” said County Executive Kurt Triplett.

“Measuring flows at Auburn has been our traditional yardstick on the Green River because that gage includes water from tributaries entering the river below the dam,” said King County Flood Control District Supervisor Julia Patterson, whose council district represents Green River Valley cities. “But without the dam’s full flood water storage capacity, it just makes good sense to provide as much early warning as possible of increased water releases from the dam.”

The heightened safety awareness is in response to restrictions on how much water the U.S. Army Corps of Engineers’ flood-control dam can hold in the upper Green River Valley.

The corps announced in February that storage capacity at the dam would be restricted until engineers could evaluate damage and complete repairs to the right flank of the flood-storage facility. The damage was discovered following the January 2009 flooding.

While the corps points out there is no immediate danger to people and property below the dam, there is an increased risk of flooding to the Green River Valley below the dam in the event of a major rainstorm or significant snowmelt because of the limited storage capacity.

Using water release data from dam is one of several immediate steps that have been taken to increase the safety of Green River Valley residents.

For example, the King County Flood Warning Center will open sooner than normal when significant rainfall is predicted, to closely monitor conditions on the Green River. Additional staff will be added to the Flood Warning Center to handle any increased work load.

King County’s Emergency Operation Center is coordinating with Auburn, Kent, Renton and Tukwila.