A once in 500-year flood event devastated Yellowstone National Park one year ago this month. A lot of infrastructure was destroyed – roads, bridges and buildings literally were swept into rivers.
Researchers have since studied the damage, hoping to learn lessons. This includes a specialized group of scientists who study civil infrastructure immediately in the wake of a disaster. Bret Lingwall, an associate professor at the South Dakota School of Mines and Calvin Tohm, who is a graduate student at the school, were at Yellowstone last year collecting data. They recently spoke with Wyoming Public Radio’s Caitlin Tan.
Editor’s note: This copy has been lightly edited for clarity and brevity.
Caitlin Tan: We're about one year since the flooding in Yellowstone. It sounds like you all were on the scene shortly after to collect data. Tell us about the day you got there and describe what everything looked like.
Calvin Tohm: I drove in from the Black Hills, and basically, as soon as I got off the interstate to start going towards Gardiner, Mont., that's pretty much when all the destruction started. It took me a couple hours longer than I was supposed to just because I had to stop when I was taking drone pictures and documenting some of the damages. The level of destruction – I had just never seen it before. So it was really astounding.
CTan: For those who aren't familiar with your research, maybe give us a little bit of an overview, and what the end goal was for the research.
Bret Lingwall: The National Science Foundation funds a number of extreme events, reconnaissance groups. These are groups of industry practitioners and faculty professor types like me, who, when an extreme event happens, the national steering committees meet and decide whether to mobilize to an event. In this case, the National Science Foundation funded GEER, the geotechnical extreme events reconnaissance organization, decided to mobilize and they selected two team leaders. You plan as much as you can in 24/48 hours. You collect as much information as you can from people who are already there. Most of the data we're collecting is geodetic data, which are essentially surveys. So we're using drones to collect aerial photos, which we can stitch together into three dimensional models. We also have LIDAR laser scanners, and we develop 3-D point clouds of damage areas as well.
What we're essentially getting is the topography, the shape, the morphology, of the damage. So be that a washed out bridge, or a landslide or a rock fall, or whatever the damage is. We're collecting what the surface looks like, then later researchers can come back and look at subsurface information. We also collect samples, we collect soil and rock samples to take back to the lab for laboratory testing and further analysis.
But you gotta get out there quickly. Because people who are in the local communities, they need to repair the bridge, or at least they need to do repair so they can get to the grocery store, they can get to the hospital. So we have to get out there quickly before a lot of the good information is covered up by repairs.
CTan: That makes sense. So, anecdotally, we all heard about the extensive damage. What were some of the results that you found?
CTohm: Well, Mother Nature can certainly be destructive. Some of the most damaging sites that we saw were on the outer bank of a river where your velocities were much higher. It would come into a curve, and that was where some of the most drastic erosion happened. It just ate away at that bank. So, we need to take into account how we design for that – armoring an embankment and around bridges and things like that.
BL: So for me, there are three big takeaways. There’s takeaways in the physical infrastructure and how we design our infrastructure and there are takeaways for policy. Then there's community resilience takeaways.
On the physical infrastructure side, we've got conclusions about the physical construction of bridges, and things like the wing walls, which protect abutments from erosion. Also, placement of bridges – giving plenty of room for the rivers to do what the river wants to do and move within its floodplain.
On the policy side, these events were yet another critical data point in the growing database of our knowledge. As a science and engineering community, we’re learning that the famous 100-year flood exceedance probability criteria for design is probably insufficient for the way our communities are constructed, and how they actually operate. Higher standards are likely required due to the increasing what we call ‘fragility of our communities.’ So the 100-year standard was selected many, many, many years ago. And we've learned a lot since then, and these floods were important data to contribute to the efforts that are underway in the various code and organizational committees across the country to raise the flood standards for infrastructure, instead of from 100-year to maybe 250, 500 or 700-year flood events. Because these are the events that are more damaging. There's just more losses than we probably want to tolerate as a community.
Then on the third leg of the findings, at least for me, was community resilience. One of the amazing things that I observed was the absolute resilience of the communities in Wyoming and Montana to floods.
I've been on a lot of reconnaissance after extreme events, and I've never seen communities pull together and just leap into action like I saw in Wyoming and Montana. Great lessons to other communities around the country.
It was just great to see how they addressed the washed out approaches to a bridge. Wyoming and Montana locals got their farm equipment, and they rebuilt the approaches before the Department of Transportation could get out there and do it for them. Why? Because they can do it. And they know how to do it. This was just awesome to see. It's a great example to communities around the country and the world of knowing what to do when extreme events happen, and knowing how to help one another as a community to just get things done, rather than sitting around and waiting. Awesome lessons.
CTan: Well, that's good to hear. So it sounds like some of your research could be used for future project planners in development going forward. Are there any areas specifically that come to mind right now that are particularly vulnerable that are on your radar?
BL: What's on our mind are the Black Hills of South Dakota and Wyoming because that's where we live. We know from Paleoflood data that the Black Hills are capable of producing just massive floods that can carry boulders the size of Volkswagens miles and miles and miles out onto the flats. Those floods have not been seen since the Black Hills were settled in South Dakota and Wyoming. However, the floods that are carrying these boulders out onto the prairies aren't terribly old, we know from the Paleoflood data. So there's great lessons to the communities and of the Black Hills on either side of the state line.
But really, when it comes to any community that is in a mountainous riverine environment where you have rivers, creeks and streams that seem small and tame on a year-to-year basis, but what a fury that can be unleashed in these extreme flood events. For the last 50-60 years, we built cabins closer and closer to these small, tame creeks, and all of a sudden, these creeks when they unleash, they can unleash powerfully and across our region be it the Black Hills, the foothills of the Wind River Range or the foothills of the Bighorns. We get so used to these streams, because in our lifetimes the small streams have been small little babbling brooks and we can do a little fly fishing and they seem so peaceful, but when these things get moving, just the sheer velocity and ferocity of the rivers can be quite staggering. It's a good reminder that this big, open river plane which are lovely to build on – people build ranches and farms and cabins – that that floodplain was placed by these large flood events that happen on geologic timescales quite frequently, but within human lifetimes, you might see only one every couple of generations, but they happen.
