Army Corps warns of higher-than-average flows in the Green River

Those using the Green River Thursday through Saturday are advised that flows will be significantly higher than they have been over this past week, so caution is advised. This is due to water being released from Howard Hanson Dam. Outflows from the dam are expected to remain well below flood stage.

  • Friday, May 14, 2010 8:48pm
  • News

Those using the Green River Thursday through Saturday are advised that flows will be significantly higher than they have been over this past week, so caution is advised. This is due to water being released from Howard Hanson Dam. Outflows from the dam are expected to remain well below flood stage.

The following is the complete text of a U.S. Army Corps of Engineers media release:

The reservoir at Howard Hanson Dam reached an elevation above 1,167 feet above sea level May 9, allowing engineers to test the interim seepage barrier installed in November 2009 with additional reservoir volume. While the Corps brought the pool up above 1,167, outflow from the dam has been running at about 500 cubic feet per second, and now water managers must release significantly higher outflows to lower the pool back to elevation 1,167 by May 16.

Reservoir outflows increased significantly beginning late Wednesday and are expected to remain high through Saturday. During this period, releases from the dam are expected to be mostly in the range of 1,500 to 2,500 cfs. By Sunday, reservoir outflows will return to near the inflow rate, which is currently forecast to be about 1,200 cfs.

Those using the Green River through Saturday are advised that flows will be significantly higher than they have been over the past week, so caution is advised. Outflows are expected to remain well below flood stage.

During the conservation pool, the Corps has been testing and conducting in-depth investigations of the dam’s current effectiveness. During the fill, if there are any indications from readings or observations that the dam is behaving in any way not considered expected or normal, the reservoir level can be reduced appropriately.

Since April 21, when the reservoir reached the benchmark of 1,147 feet, the U.S. Army Corps of Engineers has conducted intensive monitoring, including scientists on the ground around the clock. Since early March, the Seattle District of the Corps has been slowly filling Howard Hanson Dam’s reservoir for its annual conservation pool.

Preliminary data from the testing results suggest that the grouted seepage barrier is reducing flow through the north abutment. However, this data is preliminary and should be considered provisional, as it has not been fully analyzed. During January 2009 flooding symptoms of internal erosion were observed, prompting an operational limitation of the dam at the headwaters of the Green River. This operational limitation raised the flood risk for those communities downstream to levels not seen for 50 years.

More in News

Black Diamond weighing budget, property tax

Public comment periods are set for Nov. 21 and Dec. 2.

Election wrap-up: King, Pierce voters disagree on statewide measures

The election hasn’t been certified as of yet, but the results are likely to remain how they are now.

Family finishes Tour du Mont Blanc

The Tour is a 110-mile hike through multiple European counties.

Spiketon Creek Bridge close to opening

The bridge was clsoed in the summer of 2018 after it was discovered a pillar had sunk into the ground below.

Enumclaw, Black Diamond police blotter | Oct. 29 – Nov. 6

A hit and run, sleeping in a car, and an escaped dog.

County recognizes Gamblin Motors

Oct. 29, 2019 was officially proclaimed Gamblin Motors Day in King County.

Local artists return for second Freestyle event

It’s an opportunity to watch artists create their work, and then even have a chance to buy it at the end.

Political activist Tim Eyman campaigns for Initiative 976 on Nov. 5 in downtown Bellevue. The initiative promised $30 car tabs while functionally eliminating the ability of agencies like Sound Transit to raise taxes for its projects. Photo by Aaron Kunkler
Election analysis: I-976 vote casts South King County against Seattle, Eastside

Preliminary precinct counts show support for the initiative split by region.

Vaping illness and vitamin E connected | Department of Health

A new study by the CDC found vitamin E acetate to be present in those who have been afflicted with the mysterious vaping lung illness.

Most Read