Tukwila Flood Watch Information

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Howard Hanson Dam Flood Watch Information

Background:

Following a record high level of water behind Howard Hanson Dam in January 2009, the U.S. Army Corps of Engineers became concerned after discovery of two depressions on the right abutment, increased water levels in groundwater monitoring wells, and the appearance of sediment-laden water entering the abutment drainage tunnel. These concerns compelled the Corps to limit the dam's operational capacity, in order to not put it at further risk. While the dam itself is not in immediate danger of failing, there is increased risk to downstream communities until seepage concerns with the right abutment have been resolved. The Corps of Engineers placed restrictions on flood storage and established an aggressive monitoring program, in addition to other risk reduction measures. Reduced flood storage capacity results in more frequent and larger volume releases during flood events, which could increase the probability that levees in the lower valley could be overtopped. Physical actions implemented to reduce risk include construction of a seepage barrier (grout curtain) and improvements to drainage in the abutment. Extensive coordination with local communities has occurred to aid emergency preparedness.

Project Status Update:

6/27/11

The following is a press release we recently received from the Army Corps of Engineers. It provides a good update on current conditions of the dam and what is in the works for this coming 2011/2012 flood season. Although things are progressing in a positive direction, we want to remind our citizens and businesses that the risk of flooding is still at 1 in 60. The Corps objective is to get back to the pre-event level of 1 in 144. These numbers will not change until the Corps is able to test the new measures this coming flood season. One might ask... do I need to keep my flood insurance? Since 2009 we have been recommending that potentially affected property owners obtain flood insurance. Our suggestion is that you wait until the Corps of Engineers reports they are "able to hold a flood pool as the dam was originally designed" before considering a change in your flood insurance coverage. If you have questions, please feel free to call our Emergency Management office at 206 971-8740.

Howard Hanson Dam reservoir at full summer pool, engineers running tests

Contact: Public Affairs Office (206) 764-3750

SEATTLE— The reservoir at Howard Hanson Dam has reached an elevation of 1,167 feet above sea level, allowing engineers, geologists and other scientists to run a battery of tests to gather more data on the right abutment drainage improvements that are completed and underway. At the end of testing, the Corps will share findings with national experts and will determine prior to this November if the dam can return to its authorized flood risk reduction operation.

The Corps is measuring seepage rates through the abutment, functionality of the new drains, as well as conducting other investigations during the next couple of weeks. That data then will be analyzed. The results of that data analysis will help determine paths forward for further interim measures, as well as any potential long-term repairs, to reduce the flood risk in the highly populated cities of Auburn, Kent, Renton and Tukwila and unincorporated King County.

“As construction on the drainage improvement work continues, all indications are that the new measures will perform as intended. Once the current improvement work has been fully completed, we will evaluate the effectiveness of those measures and determine if we will be able to hold a flood pool as the dam was originally designed,” said the Seattle District’s Dam Safety program manager, Rob Romocki. “We need to look at all the data from this summer’s conservation pool and analyze what we see before a decision can be made on how to safely operate the dam next flood season.”

While the reservoir level is being held steady throughout this testing, outflows from the dam will track reservoir inflows. As of this release, inflows and outflows are roughly 1,200 cubic feet per second. However, flows can change in a matter of hours, dependent upon weather, so caution is advised. Flows downstream of the dam are expected to remain well below flood stage.

More details and history about Howard Hanson Dam and the right abutment issue can be found at http://www.nws.usace.army.mil

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Flood Mitigation Photos

News Updates

12/13/10

Sandbag materials can now be picked up free of charge on a self-serve basis at the following location:

14000 Interurban Ave S (south of Foster Links Golf Course and just north of Grand Central Casino)

Help is available during regular business hours Monday - Friday, 7:00am to 3:00pm. You can call (206) 433-1860 between the hours of 7:00am and 3:00pm, Monday - Friday if you need help. Call (206) 571-4239 for after-hours flooding emergencies.

For more information please visit the King County Sandbag Distribution Website.

8/16/10

Howard Hanson Dam Risk To Be Cut In Half

Preliminary work on the Green River’s Howard Hanson dam will halve the upcoming winter’s risk of a Kent Valley flood — to one in 60 during a normal rainfall year, compared to the risk in 2009. This was the essence of a report from Army Corps of Engineers Seattle District Commander Col. Anthony Wright, during a press event Monday. Read the entire article...

5/13/10

Murray Delivers Funding For Howard Hanson Dam Fix

Today, U.S. Senator Patty Murray (D-WA), a senior member of the Senate Appropriations Committee, announced that she has secured $44 million in emergency funding for critical repairs to the Howard Hanson Dam. Murray included the funds, which will go to the Army Corps of Engineers, in the Fiscal Year 2010 Emergency Supplemental Appropriations bill. Read Entire Press Release...

4/30/10

Pool Level At Howard Hanson Dam Reaches 1,157-Foot Benchmark

The reservoir at Howard Hanson Dam will reach elevation 1,157 feet above sea level within the next 24 hours. 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. Read Entire Press Release...

4/22/10

Western Washington Lawmakers Push for Funding to Reduce Risk of Flooding in Green River Valley

Today, Senator Patty Murray, Senator Maria Cantwell, Congressman Adam Smith, Congressman Dave Reichert, Congressman Norm Dicks, Congressman Jim McDermott, Congressman Jay Inslee, Congressman Brian Baird and Congressman Rick Larsen sent a letter to Lieutenant General Robert Van Antwerp urging the U.S. Army Corps of Engineers to make unused funding available for short term fixes to protect the tens of thousands of residents and 95,000 jobs of the Green River Valley from catastrophic flooding while permanent fixes to the Howard Hanson Dam are underway. Read the Entire Press Release...

You may also view the entire letter sent from our Valley mayors to the Congressional Delegation. The letter was sent to Congressman Adam Smith and a list of other officials.

Mayor Haggerton's Flood Awareness Public Service Announcement