Making Room for the River with Nature-Based Solutions, with Matt Chambers

Notable Quotes

• Vast scale of US levee infrastructure: “The estimates vary about how many levees there are … The US Army Corps of Engineers has in their portfolio something like 46,000 kilometers of levees. But then some recent academic studies have suggested that there’s upwards of 200,000 linear kilometers of levees on US rivers, and that is enough levees to wrap the Earth multiple times. It’s an incredible undertaking from an engineering perspective.” (9:15)
• Levees can create a false sense of security: “There’s no levee that can protect you against all floods. In a world where we have changing land use and a changing climate, our flood hazard, or our flood regimes, are changing. So, a levee that was built in the ’50s to protect against the flood regime at the time is no longer going to necessarily protect you against the flood regimes that are happening now … You can actually have escalating risk from investment in the land behind the levee as a consequence of the levee itself, which is a little bit counterintuitive. The levee is supposed to protect us; we feel safe; so we overinvest; and in effect, we become less safe.” (15:11)
• Benefit-cost analysis generally dictates decisionmaking by US Army Corps of Engineers: “The cost might be building a new levee, and benefits are reductions in the likelihood of experiencing flood damages—so, reductions in the likelihood that the levee gets overtopped, or that it fails geotechnically. That all gets calculated as a monetary value, and it goes in the benefit-cost ratio of your benefit-cost analysis.” (27:07)

Top of the Stack

• “Nature-Based Solutions for Leveed River Corridors” by Matthew L. Chambers, Charles B. van Rees, Brian P. Bledsoe, David Crane, Susana Ferreira, Damon M. Hall, Rod W. Lammers, Craig E. Landry, Donald R. Nelson, Matt Shudtz, and Burton C. Suedel
• Engineering with Nature podcast
• The Control of Nature by John McPhee
• An Indigenous Peoples’ History of the United States by Roxanne Dunbar-Ortiz
• The Gift of Good Land by Wendell Berry
• The Swamp: The Everglades, Florida, and the Politics of Paradise by Michael Grunwald

The Full Transcript

Margaret Walls: Hello, and welcome to Resources Radio, a weekly podcast from Resources for the Future. I'm your host, Margaret Walls. My guest today is Matthew Chambers. Matt is a researcher at the Institute for Resilient Infrastructure Systems, which is an interdisciplinary research center at the University of Georgia that focuses on the integration of natural and conventional infrastructure systems to strengthen resilience to flooding, sea level rise, drought, and other disruptions.

Matt is an engineer by training, and we're going to learn a little bit more about his background and his professional journey in a minute. I invited Matt on the show to talk about nature-based solutions to flooding and, in particular, about an article that he's a coauthor of that was published last year in the journal Anthropocene, which is called, "Nature-Based Solutions for Leveed River Corridors."

A lot of our big rivers in the United States have systems of levees all along them. Matt's going to tell us about that and about some new ideas about how to change some of these river systems so that they can work with nature, so to speak, rather than against it. These are some issues I do research on myself. I'm pretty passionate about this topic, so I am really looking forward to this conversation, and I hope you are, too. Stay with us.

Hello, Matt. Welcome to Resources Radio. Thanks so much for coming on the show.

Matt Chambers: Thank you for having me.

Margaret Walls: Matt, I’ve got to ask you—if you've listened to the podcast, you know this—I want to hear a little bit about your background and your personal journey. How did you get into this as an engineer and get into nature-based solutions to flooding problems? You can talk about how you got into engineering, then how you found your way to these issues.

Matt Chambers: Well, my path to engineering isn't all that interesting. I went to engineering school, but somewhere along the way I was doing a very traditional form of engineering. I'm a mechanical engineer by training, but somewhere along the way, I just wasn't that interested in the general engineering work and wanted to diversify into ecology. So, I started taking courses on plant biology and rangeland ecology, and I had this idea that I would go into a graduate program and find a way to merge them.

So, I applied to the Odum School of Ecology at the University of Georgia. As part of that process was introduced to Dr. Brian Bledsoe, who is an engineer, not an ecologist. And much like me, he had done mechanical engineering at Georgia Tech and had found a way to get into the world of ecological engineering and was the director of the Institute for Resilient Infrastructure Systems at the University of Georgia. Brian gave me an opportunity to work as an engineer for his institute. It's not a complete split, but you could think of it like a day job, while I do PhD work in a much more interdisciplinary space at the same time.

That's what I did for the past four years or so. My PhD work was in many respects focused on the numerical modeling of floodplain restoration and flood risk management: so, levee setbacks, as we'll get into it as part of that; also green infrastructure for coastal communities; and then, just general methods in the science of river restoration as a hydrologist or an engineer. That's part of that process. Now, I've begun to branch out into the economics of decisionmaking for infrastructure investments. In the federal case, of course, as many of your listeners will probably know, it's the benefit-cost analysis in the United States, at least.

Maybe I'm not quite done wandering in my research interests, but I'm certainly hooked. I've found a place where it's exciting every day in an interdisciplinary space. I like the elements of the ecology, the social sciences, the engineering, and the economics—all of it.

Margaret Walls: Very good. We're going to get into a little bit of all those things here. That's great.

I have to ask you to start, Matt, with giving our listeners a little bit of a background on what levees are and how many we have and so forth. First, tell us what exactly a levee is?

Matt Chambers: Levees are one of the primary types of flood-management infrastructure in the United States. For your international listeners, they might call them dikes, but effectively they're engineered embankments that run along the length of a river. You could imagine a giant earthen wall along the riverbank. Some engineers might take umbrage with that description, but effectively, if you wanted to have an image in your mind, you might think of it like that.

What they do is they prevent floodwater from inundating communities that live close to rivers. Naturally, we build our communities close to rivers for the economic benefits they provide—access to water, shipping, and agriculture—all the things that folks generally know intuitively. But in being so close to the river, there are also hazards from flooding, and we build these walls to protect us.

Margaret Walls: Okay. I didn't tell you this, Matt, but in the town I grew up in, my home backed up right to a levee. We always called it a “floodwall,” because in part of the town it was a concrete wall. But behind my house that I grew up in, it was an embankment on the Ohio River, actually. I never thought about it too much, but there was a huge flood there in 1937, and they built it after that.

Can you give us a little bit of statistics on how many there are, when were they built, who built them, and all that? Can you just give a little bit of background?

Matt Chambers: Totally. We have a fascinating history of levee-building in this country—at least, I think so, and for your infrastructure nerds out there, hopefully they will, as well. But the first ones, as far as I'm aware, were built by French settlers in the lower Mississippi River; so, think of New Orleans in the early colonial period.

In the latter parts of the nineteenth century, the US Army Corps of Engineers took on broader powers in their control and management of large waterways throughout the country. Their mission was navigability of those rivers for commerce, military operations, and then, later on after some huge floods happened, trying to ensure flood protection. There are always these two things that are in balance that are hard to wrap your mind around: it's flood protection, but it's also navigation in the United States, and the navigation part comes into it when you talk about long leveed corridors. I'll speak to that when I tell you some statistics.

Just imagine a scenario where the Corps of Engineers now wants to take these rivers that are difficult to navigate, like the Mississippi, the Missouri, and the Arkansas in the center of the country; and they want to transform them into pseudo-canals so that we can move agricultural products out and build the big communities that are places like St. Louis, New Orleans, and whatnot. That was the general mission.

The Corps is the primary builder a lot of times, but there's this mixed bag of authorities. There's local municipalities, and there's farmers, so we really have this quilted patchwork of levees all over the place in some of those watersheds like the Mississippi, but now also in central California and southern Florida. Since this time, the Corps has taken on bigger control of that process to try and just make sure that those rivers are navigable for long stretches and those communities have consistent flood protection.

The estimates vary about how many levees there are, but imagine a system of levees on, say, the Mississippi, that goes all the way from New Orleans up to southern Illinois, just continuously leveed; or along the Missouri River that goes from St. Louis all the way to South Dakota—so, huge and long corridors. The Corps has in their portfolio something like 46,000 kilometers of levees. But then some recent academic studies have suggested that there's upwards of 200,000 linear kilometers of levees on US rivers, and that is enough levees to wrap the Earth multiple times. It's an incredible undertaking from an engineering perspective.

Margaret Walls: That's amazing. I am not sure how many people know that. Tell us some of the good and the bad about levees, Matt. As you explained, they were built for a reason—to make rivers navigable, to protect communities from flooding—but they've created some problems. Can you talk about that a little bit?

Matt Chambers: Yeah, let me give you actually a little bit more background that's fun that feeds into answering the question of the good and the bad. In the late nineteenth century, the Corps had this internal debate, and it was super intense. It was: do we engineer our rivers with a multitude of different structures and approaches like levees, dams, channelization, all sorts of different approaches; or do we try to come up with one sort of approach? And that was with bank stabilization and levees, and they called it the levees-only policy. Guess which side won?

Margaret Walls: I guess the levees-only policy.

Matt Chambers: The levees-only policy won, exactly. The thinking behind that—and this gets into the good and the bad—is if you stabilize the banks for these long river corridors, and you build levees close to the river along the banks for a continuous corridor, then when floods come through, you funnel that water between the levees, and it erodes the bed of the river more substantially than it erodes the banks, because you've armored them with bank stabilization and levees. You're trying to fix the river in its place.

So, if you flush out whatever's in the channel, then you get rid of all the habitat complexity, the snags or little tree dams and whatnot that make navigation hard and you make the river more of a canal. It's probably horrifying to a lot of ecologists. It's somewhat of an elegant engineering solution, but the bad is that you destroy all that habitat complexity.

The Missouri River is a great example where it was this braided stream. There's lots of little channels moving down the river. It's this braiding pattern with channel bars and all sorts of different sediment deposition all throughout the river. If you channelize it in the way that's done with bank stabilization and levees, and you flush all that out, and you get this single, threaded, single-channel meandering stream … This is an incredible transformation of an ecosystem. And much of that transformation happened as part of this levees-only policy in the late nineteenth century, early twentieth century. Then, levee construction went hog wild with a bunch of dam construction and whatnot in the mid-twentieth century after a huge flood in 1927 proved that the levee-only policy was just not going to work.

The bad is obviously the environmental considerations that I've described just now. But another element of this is there's this constant interplay between what the local community wants in terms of flood protection, the type of levee they want, and what they can afford in terms of the non-federal cost shares that are associated with these projects, until you get inequities in the flood management that you have.

It's really a patchwork that's difficult to quantify, because if you don't let water spill out onto the floodplain, or you've built a big wall along it, you're just displacing floodwaters in different places. So, you need complicated numerical models to try and figure out where that water is going. And water that doesn’t inundate a floodplain and is protected, and some community is protected by that levee—that water could become water that's a hazard for someone else, primarily upstream or on an opposite bank. Those are some of the downsides of the approach that we've taken.

Margaret Walls: I want you to tell our listeners about what's called the “levee effect.” That's a term that gets used in the literature. What is the levee effect?

Matt Chambers: This one's fun. It's somewhat counterintuitive. The general idea is that if you build a levee, people may get a false sense of security about the protection it affords, and they may build or invest in the land that is protected by the levee under the assumption that they can start a life there. But there's no levee that can protect you against all floods. In a world where we have changing land use and a changing climate, our flood hazard, or our flood regimes, are changing. So, a levee that was built in the ’50s to protect against the flood regime at the time is no longer going to necessarily protect you against the flood regimes that are happening now.

The idea of the levee effect is that you can actually have escalating risk from investment in the land behind the levee as a consequence of the levee itself, which is a little bit counterintuitive. The levee is supposed to protect you, we feel safe, so we overinvest, and in effect, we become less safe.

Margaret Walls: Exactly. I think it's easy to understand it once you start talking about it.

Matt, I mentioned at the beginning we're talking about what are called nature-based solutions to flooding, and that you mentioned that you work both on riverine-environment issues and coastal issues. Tell us a little bit about what you mean. Step back and talk in general about, What do we mean by nature-based solutions, and what are some examples of that?

Matt Chambers: Sure. I feel like I've gotten myself in trouble lately with this one. There's lots of different definitions floating around, but there's a group called the International Union for Conservation of Nature, who your listeners might know. They have their own definition. Recently, in the literature, there's been some efforts to try and put quality control in what a nature-based solution is.

So, I try to keep their definition in my back pocket nowadays, and it goes something like this: It's actions to protect and sustainably manage and restore natural or modified ecosystems to address those social challenges that are before us at the moment, while both simultaneously providing well-being for everyone and for biodiversity. And I hope I didn't butcher that for those folks at the Union, but it sounds fairly general. It's hard to understand what that is.

But they have a series of criteria out there, which they use to judge what constitutes a nature-based solution and what doesn't. In that definition, I talk about sustainably managing a system, and that could be economic sustainability, ecological sustainability, social sustainability, and restoring ecosystems. In the case of a levee setback, you're moving a levee back from a river and you're trying to restore—some folks say restore; I might say rehabilitate—ecological structure and function of that ecosystem in the past before there was floodplain disconnection with the construction of the levee.

Examples that are commonly talked about in the literature and are hotly debated are planting trees—silviculture for climate mitigation. When we talk about a levee setback, it's a nature-based solution for infrastructure. That's a riverine scenario.

A coastal situation that's probably one of the more famous and popular ones that some of your listeners might know about are mangroves as a way of dissipating wave energy during storms on the coast. You might have a floodwall like you described earlier. Suppose you have a floodwall in South Florida, but then you also get some infrastructure service from a mangrove forest that is further out toward the coast from that floodwall, and it reduces the service demands of that floodwall. Maybe it doesn't have to be as tall or as stout, because you're getting this infrastructure service in terms of energy dissipation from the mangrove forest.

Margaret Walls: Let me ask you then to talk about levee setbacks a little bit, and especially this one, if you don't mind, that you talk about at length as a case study in that Anthropocene article that I mentioned. This is a setback on the Missouri River. There was a levee failure and a big flood in 2019, I believe. What happened, and how did that setback option end up being a preferred solution in that setting?

Matt Chambers: The central person involved in this case study, who’s also on the journal article, is Dave Crane, and he's a planner out in the Omaha branch. He works for the Army Corps of Engineers. This was one of his primary setbacks. I personally wasn't a designer on the setback. We're using this example nowadays to do a new setback that a general investigation study just opened up on recently.

But it's an interesting case study in the sense that that stretch of the river is continuously leveed, and many of those levees have failed repeatedly, like in the 1997 flood, the 2011 flood, or the 2019 flood. The politics of it are that there are local levee districts that are, basically, the owners of that levee system. They went to the Corps and said, "Please give us a new option. We're tired of being flooded out," and so, naturally, they considered a setback for it.

That setback was evaluated in a disaster-recovery program. It's called Public Law 84-99, and it's different from the general civil works process, which is much more involved and onerous and takes years and is quite expensive. It's an interesting scenario; it's almost luck of the draw in the sense that it was able to happen, because there's so much resistance to change. There's so much desire to maintain the status quo. It's just that this local community really wanted to try something different, and there were folks at the Corps that were progressive-minded and wanted to try something new.

So, as part of that disaster-recovery option, they said, "Well, what if we just throw in a setback as one of the alternatives to consider?" And the setback ended up being viable as part of the simplified benefit-cost analysis that is part of that Public Law 84-99 disaster-recovery program. This huge collaboration of folks got involved, from the Nature Conservancy to the Corps of Engineers, to the federal and state agencies in the area and the Natural Resources Conservation Service; and they were able to work with a number of landowners in the area to have them sell their land or sell easements and move the levee back from the river. That's something like a 1,000-acre setback, which is quite big by comparison to a lot of the setbacks out there. It's like our model at this moment of what is a large-scale levee setback and what it could be.

That project is fuel to our fire to try and do larger setbacks also in that area with the same group of folks, but preemptively, so we don't have to wait for another big flood to destroy the levees. There are obvious choices in that area of where we might do another one. The idea right now is to work with those exact same landowners that own a different levee system nearby, work through the general civil works process, and do a fully comprehensive benefit-cost analysis that includes not just the flood risk–management aspects of it, but also the ecosystem services and consideration for inequities in the distribution of flood risk benefits for that area. So, we're working through that process now as an applied research project.

Margaret Walls: That's great. Well, just give us a little bit more on the Corps, if you would, because you're talking about them a lot about this general civil works versus the disaster situation. Can you just give our listeners a sense of how the Corps makes decisions about projects, whether it be building a new levee or repairing one? So, why have they chosen this case to set this one back?

I know a little bit about the Corps. My sense is that they have some pretty strict guidelines and rules that limit their choices, and maybe nature-based solutions aren't disadvantaged relative to other options. I don't want to put words in your mouth, but tell us a little bit more about how that all works.

Matt Chambers: It's funny. The Corps has strict rules. They have principles. They have somewhat strict rules, but there's also flexibility. There's wiggle room in there. I would say this: There's this historical criticism of the Corps of being so inflexible and not trying anything, but it comes down to the people involved a lot of times. If you have folks that are excited to work with you or want to try new things, which honestly has been my experience with the Corps of today—my experience with the Corps of today is not what people have said is the Corps of the past, and they're skeptical but open to new ideas and how they might do infrastructure decisions.

That general process is the civil-works process or civil works–planning process, and the primary tool in that is benefit-cost analysis. With that, you calculate a benefit-cost ratio, which monetizes the different benefits and costs you might expect from a levee-improvement project. Cost might be constructing the new levee as part of a setback. You're building a new levee back from the river. You still have that gray infrastructure, but the floodwater that can inundate the floodplain riverward of the levee is a natural infrastructure service; it's part of why it's a nature-based solution, and you reduce the infrastructure service requirements of that levee.

So, the cost might be building a new levee like that, and benefits are reductions in the likelihood of experiencing flood damages—so, reductions in the likelihood that the levee gets overtopped, or that it fails geotechnically. That all gets calculated as a monetary value, and it goes in the benefit-cost ratio of your benefit-cost analysis.

But when I say that they're flexible, my experience is they'll do the benefit-cost ratio in the way that is required by their guidelines, but they'll also be open to doing experimental ones on the side. As long as you're completely transparent about how you calculate everything, at least there's consideration.

Our vision here is that we'll work with them and have access to data as part of their general process of benefit-cost analysis and try to find ways of improving it so that those benefits for the environment are captured, and some of the flood-risk elements and equitable elements are captured in it and work toward suggesting methodological changes in the benefit-cost analysis through example projects like this, and then we’re trying to work it vertically up through the chain of command at the core.

Margaret Walls: Matt, we could talk about this forever, but I think we're reaching the end of our time.

If you've listened, we want to end our episode with a regular feature we have called Top of the Stack, and I'm going to ask you to recommend something to our listeners—a book, a podcast, maybe a movie, an article; anything, really, that might've caught your attention lately. What's on the top of your stack?

Matt Chambers: Can I give more than one? Well, a podcast that folks might be interested in is the Engineering with Nature podcast that is part of the Engineering with Nature program from the Engineer Research and Development Center, which is the research arm of the Corps of Engineers. If you're interested in finding out what a more modern vision of what the Corps might become in the future, or maybe you're skeptical of what I've said about my experience with the Corps so far, you can listen to that and try to get some perspective on it. I think that right now is run by Jeff King, who's the program manager for Engineering with Nature.

And then, over the course of my PhD, I spent so much time just being in the weeds of how to do numerical modeling and methods of quantifying benefits. I was afraid of walking out into the world and not having this broader perspective of the bigger picture of why we do this work. So, I have a stack of classics that are related to this sort of thing. It might not be levee-specific, but it's more about how we get to where we are.

I have The Control of Nature, a John McPhee book, on my nightstand. It's an oldie. I got a new one a couple weeks ago. It's An Indigenous Peoples' History of the United States, which I believe is by Roxanne Dunbar-Ortiz. I hope I'm getting that right. As part of my world, you end up interacting with the Tribal Nations Technical Center for Expertise as part of the Corps, because there are so many Indigenous groups and nations that live in the watersheds that I'm working in.

Another oldie but goodie that we talk a lot about in the Institute for Resilient Infrastructure Systems is Wendell Berry's suite of books. The Gift of Good Land would be one. And then a new one that I'm thinking about as I try to learn more about South Florida is The Swamp. It's an oldie.

Margaret Walls: Thank you, Matt. I appreciate that. It's been really a pleasure having you on Resources Radio and talking about one of my favorite topics—nature-based solutions for climate resilience. Thank you so much for taking the time to come to the show.

Matt Chambers: All right. Thank you so much, Margaret. It's been a pleasure. Great to be here.

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