Flooding and the Pacific Northwest
USGS Hydrologist Tom Herrett gives us the skinny on the flooding in the Pacific Northwest and on how the USGS responds to such events.
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The Detective [read by Dave Hebert]
It was late on a Friday. I'd just decided to finish the day with a tall, stiff cup of chamomile tea when suddenly, there was a knock at my door.
"Who is it?" I demanded.
The Woman [read by Jenn LaVista]
"I just need some directions back to the interstate." [voice slightly muffled, as if through a door]
. . . a woman's voice replied.
"Heh—directions," I thought. "I got news for you, kid: We all need some direction. A light in the dark. Somewhere to turn when life turns you inside out."
Um, are you talking to me?"
. . . she said, as if she couldn't see me, as if we were talking through a closed door.
Well . . . we are talking through a closed door.
She saw right through me-my life was a closed door, and I was always the one stuck inside, always in the dark, always without a clue.
But . . . the sign out here says you're a detective.
Yeah, and I've never gathered a single scrap of info—I've swiped it all from the USGS Maps, Imagery, and Publications site. If I had a nickel for every time I went to usgs.gov, clicked on "Maps, Imagery, and Publications," and browsed, downloaded, and bought satellite imagery, fact sheets, historic maps, and more, I wouldn't be sitting in a crummy, two-bit podcast, talking to myself.
OK, the USGS. Thanks for the tip. I'm just going to go now and ask for directions at the gas station down the street.
So she walked out of my life, just like the rest of ‘em. And who could blame her?
She'd found what she needed: life's topographic map, the big, high-resolution picture, the open-file report to understanding. And I couldn't even remember where I put my teapot.
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"Jazz blues slease sax" by sofa sound
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Hello and welcome. You're listening to the USGS CoreCast, Episode 23, for December 2007. I'm Steve Sobieszczyk.
Phew . . . quite the weather we've been having out here in the Pacific Northwest recently. As most people around the country may have noticed, we got quite the storm here last week.
Keeping with our theme of timely and comprehensive coverage of major natural disasters, we're here today to discuss just how big the recent storm was, what the impact was concerning flooding and damage, and what it is the USGS does in response to similar storms and flooding. But first, a recap.
Last week, from Sunday, December 2, through Monday, December 3, a large storm system passed over the Pacific Northwest. It was essential two storms that were kind of butted together.
The first part of it that occurred on December 2 was primarily a wind storm, with wind gusts upward of 100 miles an hour along the Oregon Coast, including 129 miles per hour at Bay City, Oregon. Wind gusts along the Washington Coast were in the upper 70s to 80 miles per hour.
Just as the winds were abating, the second part of the storm followed on December 3, and this brought significant rainfall. On average, about 3-6 inches rain fell across much of Western Oregon and Washington, with some isolated areas getting upwards of 10 inches over that short period.
Both the Washington and Oregon governors declared states of emergency as the storms and flooding caused power outages and damage to major highways, including I-5 and Highway 101.
Now, monitoring flooding is nothing new to the USGS. Many of you are probably aware of the USGS streamgaging network. It is this streamgaging network that allows scientists, engineers, and emergency personnel to monitor streams and rivers, and to assess what type of risk that the flood will have on people and property.
To help put the recent storm and flooding into perspective, as well as describe the USGS response to the event, I'm joined by Hydrologist Tom Herrett. Tom is a Supervisory Hydrologist here in Oregon, and he's been working very close with Bob Kimbrough, who is the hydrologist up in Washington . . . who's monitoring the streams up there. So, thanks for joining me here today.
Glad to be here, Steve.
First off, can you describe where the major flooding occurred? Did all streams and rivers in the Pacific Northwest respond somewhat similarly, or was there a disparity in where the flooding actually occurred?
Primarily the flooding occurred in Southwest Washington and Northwest Oregon. If you were to draw a line from approximately Olympia, Washington, south through Centralia, Washington, and then down into the little town of Vernonia, Oregon, would give you an approximation of where the worst flooding occurred.
Now, for people who've been watching national news, there was a lot of emphasis put onto the flooding that came across I-5, where there was like 10 feet of water across the highway. I believe that was in Chehalis. There was also a discussion of Vernonia, where they actually had to fly people out. Can you give us a little perspective about what the conditions were like in those areas?
Sure. The Chehalis River was one of the basins that was hit the hardest on this last storm. To give some perspective, the Chehalis River near Doty had a peak discharge of approximately 51,900 cubic feet per second. The previous historic peak on that was in 1996 with a peak discharge of 28,900. This gaging station has a record of about 67 years. So this far exceeded anything we've had in the past 67 years.
The town of Vernonia, in Oregon, was hit pretty hard this past event. The town was also hit hard back in 1996 on that flood. In 2001 the USGS installed a gaging station just upstream from the town as part of a flood hazard warning system. We worked in conjunction with the National Weather Service, as far as locating the gage.
Since we only have a little bit of record on that site, since 2001, we can't get a really good handle on the recurrence interval of what happened up there. As you go further downstream, we have a gaging station closer to the mouth of the Nehalem River. That indicated about a 25-year flood event. But it appears that as you go further up into the basin the rainfall intensities were much higher.
Now, you've mentioned the 1996 flood a couple of times. In perspective of the Pacific Northwest, how comparable was this recent storm to previous floods in the area?
When you look back through the history books, as far as historic floods, the two most recent ones that stand out, you see 1964 and 1996 are two big events that covered big areas throughout the Pacific Northwest. And that was kind of the key thing for both those flood events compared to this one.
The most recent one we just had this past week was focused more along the western edge of Oregon and into Washington. While the 1964 and the 1996 events were more widespread throughout both Oregon and Washington.
So with all the flooding that was going on, what was the USGS response to the most recent event?
Well, we had staff monitoring the situation before the storm hit us. We rely very heavily on the National Weather Service for flood forecast information. And that tells us where we need to go in order to make sure our equipment is working properly and also to measure the high flow, so we can calibrate our rating curves that determine the discharge for any given stage of the river.
So, as the storm developed from Sunday into Monday, we had crews available and out in the field checking the gaging stations, making those high flow discharge measurements. And they'll be busy into January flagging and surveying high water marks in order to determine those peak discharges that we need.
Now, flooding, in general, is not something just common to the Pacific Northwest. It's experienced basically everywhere around the world and everywhere around the United States. So, if people wanted to know what was happening with streams and rivers around them, are there any resources you could recommend that they could check?
Steve, there are a couple of resources that the public can tie into to determine what's happening in any nearby stream or river. First one is . . . the USGS operates a network of approximately 7,500 gaging stations throughout the U.S. The vast majority of those sites have real-time information.
The second resource that the public can look at is flood forecast information provided by the National Weather Service. The National Weather Service provides flood warning information on numerous sites throughout the United States. Most of that information is provided to the Weather Service through the USGS streamgaging network.
So if you are trying to find out what's happening right now, on a current basis, the USGS would probably be your best bet to look at. But if you want to find out a forecast, then the National Weather Service is the place to go, and they can provide forecasted flows for major sites throughout the U.S.
Well, that's all the time we have today and all the questions. Thanks again for joining me, Tom.
You're more than welcome.
If you want to learn more about the USGS streamgaging network or USGS response to the flooding in the Pacific Northwest, check out the links in our show notes. As always, thanks for listening—we genuinely appreciate your support. If you have any questions, comments, or complaints send them to our e-mail, firstname.lastname@example.org.
Check back with us in a few weeks as we'll keep our feet firmly planted in water-related issues, as we discuss the science of dam removal and the impact on the downstream ecology.
This CoreCast is a product of the U.S. Geological Survey, Department of the Interior. Until next time, I'm Steve Sobieszczyk. Rock on!
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