Tuesday, November 10, 2009

Howard Hanson dam flood maps: Lower flood risk, but we still recommend flood coverage

The U.S. Army Corps of Engineers has created several "inundation maps" showing possible areas of flooding -- and how much each would be underwater -- if the Corps has to release more water than usual from behind the weakened Howard Hanson dam.

The Corps, which had earlier put the odds of severe flooding as high as 1 in 3, now says that extensive work to strengthen the abutment has lowered those odds to 1 in 25. Further work this month should improve those odds.

There are four versions of the maps, projecting how things would look in the Green River Valley below the dam at each of four release levels:
-13,900 cubic feet per second
-17,600 cfs
-19,500 cfs
-and the worst case scenario: 25,000 cfs.

The yellow areas are light flooding -- 2-3 feet of water -- and the green areas are deeper: 6-10'. The lowland areas where water would pool more deeply than that are marked in shades of blue and light purple.

Hints for navigating the maps: Use the zoom tool (yes, the little magnifying glass) to get in close enough to see road names, streams, etc. You can zoom in quite a bit. (Zoom out by holding down your keyboard's CRTL button and clicking your mouse.)

If you need more detailed maps, click on this link and go to the "Large Format" versions of the maps. Even over a fast Internet connection, these large files can take a minute or more to load.

Although the flood risk is apparently lower than it was, our office is still recommending that people in the area get flood coverage. (We are the state of Washington's insurance regulatory agency.) The National Flood Insurance Program offers coverage for homes and businesses, although businesses will have to find other, private carriers for things like business-interruption coverage or large-value properties.

The federal flood coverage is sold through local brokers and agents, so check first with your regular agent. If they don't sell it -- and not all do -- you can get a list of local sellers through National Flood Insurance Program website or by calling them at 1-888-379-9531.

And don't put it off. The federal coverage doesn't take effect until 30 days after the policy is written.

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