USGS Multimedia Gallery: (Video)--USGS Activities During Missouri River Flooding 2011

Missouri River Flooding. Enhanced podcast 8/10/2011

Host: Rachael Hoagland

Interviewee: Richard Wilson, NEWSC Associate Director

RH: Welcome to Nebraskast where we talk to real USGS scientists about the important water-resources

work they are doing all over Nebraska. My name is Rachael Hoagland. I’m here with Rick Wilson. He is

the associate director for the USGS Nebraska Water Science Center. And we’re here to talk a little bit about

flooding that’s been going on here this summer. The images that you’re seeing are of our hydrologists and

our hydrologic technicians working on the river. Rick, what can you tell me about the flood that’s going on

on the Missouri (River)?

RW: This is a historic event in many ways, and the Missouri is a complicated system, and I’ll describe

that in a little bit, but the flood goes from the confluence at St. Louis up to Montana. That’s over 2,000

miles. So it started primarily in snow melt. This has been going on primarily in June and July of 2011. Now

it’s actually extending into August. The Missouri River is a complicated river and the reason is there are a

series of reservoirs on the mainstem channel, and that complicates the flow, that regulates the flow, and in a

lot of ways it protects downstream. What happened was the reservoirs filled up. There was so much runoff

and rainfall in the upper basin that filled the reservoirs and so that caused releases from the dams to go on

for months on end to evacuate the extra water.

Because of the high quantity, high volume of water, releases have been high. It’s flooded agricultural areas,

along the way. Fortunately, in that stretch of the river, there are levees that have protected much of the

infrastructure, but throughout the season we had breaks in levees. We had large areas inundated from

flooding because of that. We talk about the duration and magnitude of this flood. In historic terms, we don’t

really know what this event is compared to prior to dam construction. We think that it’s probably a 500-

year event, which is a very extreme event. Releases out of Gavins Point Dam, the most downstream

reservoir in the system, peaked at 160,000 cfs (cubic feet per second).

Typically in the winter releases from Gavins Point Dam can be about 20,000 cfs and in the summer

months, it’s approximately 40,000 cfs. So you can see we were four times the volume of water, and this

was a long duration, over 10 weeks in length. A normal flood occurs quickly, the water rises, it floods the

area. In this flood event, it’s as I just said, it’s over a 10-week period of time.

RH: What can you tell us about the USGS work that’s going on on the river in past weeks and coming into September?

RW: Well we want to know the volume of water because 1) with that information we can estimate how

high it is, and the stage, because that is how we predict flooding and how we respond to the flood event,

and 2) the velocity of the water. Velocity is critical because it causes scour. Scour is a phenomenon that

with high-velocity water, high-volume of water, it erodes critical structures, it erodes the bed of the river,

but also it can undermine bridges, water-intake structures, levees, and cause very serious problems. We

responded with a series of sonar device (surveys). One was called a multibeam echosounder that would

actually allow us to determine scour holes in critical infrastructure, including pipelines and transmission

towers.

Also, we used a tool called electromagnetic geophysics to do surveys of levees. Levees were a major

concern because they protected key infrastructure. We used this tool to determine the geologic properties,

the soil properties, and the underlying geology of levees that protected a coal power plant. We were able to

use this tool to survey almost 3 ½ miles of levee to determine areas of potential seepage, where seepage

could undermine the levee, or flow through the structure itself.

RH: As this water is moving, it’s also changing the bed of the river, is it not? Are you collecting data that

looks at how the bed of the river is changing as the water is moving through over such a long period of time?

RW: The Missouri River is a unique river. It’s a sand-bed river. This is not like a mountain stream which is

a hard rock surface which is stable. The Missouri changes, and the more water, the more scour we observe

or bed degradation. We used the sonar devices to make measurements to determine how the bed evolution

has occurred. So with that device, that will allow us to determine change. Also we used a technology where

we would take samples not only of the suspended sediment in the water itself – the amount of sediment in

the water column -- but also we were measuring bed load and that’s the amount of material that movies

along the bottom of the river bed. In these extreme events, in these high-flow events, that typically is a lot

of material that is being moved by the river.

RH: So flooding is probably going to continue for a handful more weeks so there’s still more data to be

collected, correct?

RW: Correct. I think we’ve dodged the bullet. As of Aug. 1, flow rates are now being reduced out of

Gavins Point Dam. By the end of September, they will be down to normal levels, 30,000 cfs. So as the flow

declines, additional surveys will be needed, additional monitoring will be needed, but the major concern

and the major problems, it looks like they have passed.

RH: Well, Rick, I’d like to thank you for taking the time to talk with me today.

RW: Thank you.