Columbia River Flood Warning; What Does It Mean?

May 24, 2011

 

The NWS issued a long-awaited flood warning for the lower Columbia River this morning.  When I say “long-awaited”, I mean that we have been expecting minor spring flooding for a month or so now.  The river has been hovering around 16 feet at the Vancouver gauge, and will probably rise a foot to half a foot over the next few days.  Here’s a plot from the Northwest River Forecast Center, showing the flow over the past 10 days and the expected flow for the next 10 days:

Notice that there is no “surge” of water down into our area.  That’s because there is still lots of storage available higher up on the Columbia.  The largest dam, Grand Coulee, still has plenty of storage capability.  So the only event that would make the levels higher would be a sudden surge of higher water coming down the Willamette River.  I notice those reservoirs are all close to full.  We do have rain o the way later this week, but as of now none of it looks real heavy.

So what does a river level at 16-17 feet mean?  Not a whole lot.  No homes get flooded, but some paths, park benches, and farmland get inundated.  The river really needs to rise up to 20′ or so to start seeing “real” flooding.  Here’s part of the statement from the NWS:

EXPECT MINOR FLOODING OF SOME LOWLAND ACCESS ROADS NEAR THE RIVER ON SAUVIE ISLAND…AND ON THE WALKWAY NEAR DOWNTOWN VANCOUVER. THERE WILL BE SIGNIFICANT FLOODING ALONG  THE BANKS OF THE COLUMBIA RIVER THAT ARE COMMONLY USED FOR CAMPING SUCH AS ON GOVERNMENT ISLAND.

The last time this much water flowed through the Columbia River system was spring/early summer of 1997.  That year the river peaked twice around 19 feet at Vancouver…the first couple days of June and again the 3rd week of June.  I see there is high water even way up on the upper Snake River in eastern Idaho, and all that water has to work its way down the river system.  So you can plan on a very high river over the next 4 weeks but likely no big flooding unless we have an extraordinary rain event.  No camping on the Columbia River beaches this Memorial Day!

Chief Meteorologist Mark Nelsen