Drove the Chevy to the Levee and the Levee Was Dry
Dr. Jesse Reimink: [00:00:00] Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you. Chris, uh, you, you're just complaining about your only. Having two screens instead of three or four that you normally have. Your setup is a little bit, uh, is a little bit amiss over there. I hope you can bring your game and fight through it. [00:00:30] Those of us who have one screen on our setup, w hope that you can really grit your teeth and bear it and record with two screens in front of you only Chris.
Chris Bolhuis: So I, I gotta talk to you about something. So, after school today, I'm a, I'm a high school teacher, right? And I, I get this email about this kid, you know. So I go down to the principal's office, the assistant principal's office, and I walk into, in there and he's, luckily he's in there, so I'm like, Hey, what's going on with this kid? And I'm looking around as he's talking, cuz he was like, really jabbering. [00:01:00] And so I lost attention and I'm like, oh my God. He's got three screens around his desk. What? Does a high school assistant principal need with a NASA setup like I have, his is better than mine. It's not. It's not. Okay.
Dr. Jesse Reimink: You need you Chris, when we're recording. Podcast recording is serious business. You need many, many screens. It's basically like launching, you know, a SpaceX rocket. That's basically what we're doing here.
Chris Bolhuis: I need a screen for everything. Okay. I need a screen for [00:01:30] our script. I need a screen to look at you. And that's on the small
screen, by the way, that, that is the truth. And then I have another big screen to my right. So the, the script is on the left, your right dead center.
And then I have our garage band and other things that we record with on the right. And I like to, you know, levitate between all three and I, I just. Can't do that today. So I'm a little bit
Dr. Jesse Reimink: You're a little off. So if, uh, if Chris is off his game, we know why, uh, he's really struggling over there and, you know, we can all feel [00:02:00] bad for Chris with only two screens. So I
thought of
you.
Chris Bolhuis: torn up right now.
my recording room is torn up,
Dr. Jesse Reimink: I actually just thought of you, Chris, cuz just earlier this evening we were over at, one of my wife's colleagues, houses and they have this unbelievable log cabin, which you would very much appreciate.
You live in a log cabin, and you would've appreciated this. But what I really thought you would appreciate is they have a little, half bath on the main floor.
That their countertop is green River formation with fish fossils showing. And it made me [00:02:30] think of the time you and I were out there.
I don't know if we were in the Green River formation or the white mountain formation, but we were, we were splitting shale, what's that?
Chris Bolhuis: Florescent.
Dr. Jesse Reimink: The floor set. And we were looking for insect fossils and I found a little spider fossil,
Chris Bolhuis: I
found a mosquito.
Dr. Jesse Reimink: You found a mosquito. It was so good. An ant. I think we both found a little ant or something like that.
It was so good. That was really fun. It wasn't Green
Chris Bolhuis: and then her little friend Brian didn't find anything and he was very upset about that.
Dr. Jesse Reimink: Yeah. that was a [00:03:00] fun trip that we went on. And that, that was the one time I, well, you know this about me. I'm not like naturally inclined to paleontology. Like many fossils don't get me super excited. I don't really know why, cuz they're really interesting.
But I just don't get as excited, like give me a big garnet any day over a trilobyte fossil. But this one was really fun, like finding spiders and ants and little mosquitoes. That was actually kind of fun. Fossil collecting.
Chris Bolhuis: Well, I'm surprised a log cabin near the DC area, like that's not
Dr. Jesse Reimink: [00:03:30] Pennsylvania. Now this is out in the woods in Pennsylvania, Southeastern Pennsylvania, out in the woods. 10 acres, 12 acres. Beautiful.
Chris Bolhuis: Nice.
Dr. Jesse Reimink: So Chris, today in, uh, what is this third, I guess in the line of our sort of streams mini-series that we got going on here, we're talking about levies, and this is one that you pitched.
So why don't you give us the pitch for levies here.
Chris Bolhuis: I don't know. Levees are super important, first of all, and I have spent a lot of time driving [00:04:00] along levees, walking my dog along levees cuz I, you know, I spend my time, early April every year. In Mississippi and Louisiana and so that whole part of the Mississippi Rivers levied and they're, it's enormous.
And so they have bike paths along the top of crushed limestone paths and all that kind of stuff, and dog parks along the levee. It's just so, I don't know. I spent a lot of time there and it's, it's an important topic.
Dr. Jesse Reimink: You and I were together on a levee about a year and a bit ago at the AGU conference in Louisiana
Chris Bolhuis: Good
Dr. Jesse Reimink: there, [00:04:30] right. We were walking around the levee there with the aquarium and having a coffee and maybe had a beer or something like that. But yeah, so those of you that don't know, let's just define the levee right up front, right?
It
is basically a barrier. On the side of a stream and stream is a very general term. In Geology Stream is a sort of a river or a creek. Anything of any size is stream, like flowing. Water is a stream
Chris Bolhuis: Confined to a channel. Yep.
Dr. Jesse Reimink: confined to a channel and the levies are on the sides of the channel often, and we're gonna discuss [00:05:00] what these are, but they're kind of the embankments that, that keep the water in the channel
more or less.
Is that
accurate,
Chris?
Chris Bolhuis: absolutely. And there are two kinds of levees. There are natural levees and then there are artificial levees. So let's talk about the natural levies first, and then we'll get into the artificial or man-made and why we do that, and the pros and cons and all that. That's kind of where we're gonna go
Dr. Jesse Reimink: And let me interrupt you real quick there, Chris, and say, We're gonna talk about sort of generally what they are, how they're constructed broadly. [00:05:30] Then the pros. And geologically the cons of this cuz it really relates to how streams function. And then we're gonna kind of point some future looking discussion about like possible solutions or solutions that are being implemented out there in the real world to combat some of the cons that we're gonna discuss here.
So you said, lead us off, sorry for interrupting there, but natural and artificial two categories. What do we, what do we got?
Chris Bolhuis: Let's talk about the natural levies first. So this is like an earthen embankment that [00:06:00] parallels the channel. It's right next to the river channel itself. And so if you envision like a, a somewhat of a V-shaped, you know, channel shaped to the stream, there will be a pile of sediment on each side of the river that parallels that, that channel.
Okay, now I wanna talk about why that happens. So if this is hard because we have to like kind of paint a picture. So help me out with this, okay, Jesse. But when a river rises, you have an event. Okay. a cloud burst, a, you know, lots of snow [00:06:30] melt, whatever. Right. We got, we have an event where the river's swollen.
It's really, really thick, so it's about ready to spill out over its embankment.
So the river at this stage
is moving
Dr. Jesse Reimink: so let me just think about this a minute. If you're looking like, kind of as a cross section of the stream, you have the little U-shape thing where the water always is. That's the channel. And then this big flat thing on the side that we call the floodplain, where when it gets to flood stage, when the river breaks over its channel and is flooding, it's on this flat, broad [00:07:00] plane that is on either side of the embankment.
That's what we're kind of talking about here. so sorry. Go when it rises out and breaks out of its channel and flood stage is where we're
Chris Bolhuis: Well, first let me, let me get everybody to the point where it's not quite flooded yet, but it's just about to, so the river is really full. It's as full as it can be, and in that situation you have a high discharge, you have the stream is really ripping, right? It's moving fast. So it's moving a lot of sediment, a lot of sand, a lot of gravel, and so on.
as soon as it rises up just a little [00:07:30] bit more and it starts to spill out over the channel, Out onto the floodplain. It goes from being very deep to very, very shallow. just at that one spot where it's on each side of the bank, it is just built out. It's, let's say it's an inch deep, right?
Well, the friction from that shallow water slows the river down right there, only there, and whenever a river slows down, deposition is the rule. So it deposits on each side of its own bank. A little layer of sand and [00:08:00] gravel. basically that's the start of a levy. Every time a river floods, it builds up this pile of sediment adjacent to the banks so it builds up its own levy system according to its own flood dynamics.
Dr. Jesse Reimink: Yes, that's right. So, Yeah, absolutely. So like the frequency of flooding, the increase in river rate during the flood stage. So I e how much, how big of boulders can it transport downstream? How big of sediment can it transport [00:08:30] downstream? And then what gets dumped off in the levy? Like all those factor into the size that the levy will be relative to the size of the channel and the size of the floodplain, and whether it's meandering and et cetera, et cetera.
So there's a lot of natural natural variables that go into the size of a, a natural levy on the banks, but I think you described that really well. So if we go back to my sort of cross-section thing where we've got this U-shaped cutout, think of a broad flat floodplain with a U-shaped cutout in the middle.
That's where the river always is, the channel. What you were describing is we got little [00:09:00] bumps on the edge of the channel that go up above the floodplain. These are the levies that are higher than the floodplain around it. and right next to the channel typically. Or
very close to the
channel.
Chris Bolhuis: we often, you know, there are oftentimes roads and trails and so on adjacent to the levees or right next to the levees actually. those sometimes are maintained, right? if you have a road for instance, that is right adjacent to the levee, that road will be coated then in an event with sand and or gravel.
And then they have to [00:09:30] come off and they gotta brush it aside or sometimes snowplow it off the road. You know, I've seen this where I live along the Grand River, um, many times, especially in the spring when this thing floods over, that road is coded with six to eight inches of just really, really, beautifully colored sand that then has to be moved off to the side.
So just look at rivers from now on and you'll look at 'em a little bit differently. if it doesn't have a manmade artificial levee, they will have their own natural levee system of sand and or [00:10:00] gravel adjacent to the river channel.
Dr. Jesse Reimink: And that's a great segue, Chris, into artificial levies because we have a lot of artificial levies in the us uh, in, in the world because most of the time those rivers are not at flood stage. So we build our infrastructure, we build our civilization often around rivers. They're great places. They're beautiful, they're functional for a lot of reasons.
We build them around rivers and most of the time it's not flood stage. And so we build our stuff usually near the flood zone or on the floodplain, right? [00:10:30] and then therefore when it floods, we're like, oh crap, we don't want that. So we build up the levy, natural levy and build it up bigger or just make a new levee.
And that's the artificial levee.
Chris Bolhuis: So basically what you're saying is we have built some of our infrastructure on the floodplain of the river. we can't, we just can't have that. And so, you know, we build it, we build up this earth and mound. Most of the time it's just sand or dirt. Okay. Usually it's just like filter. [00:11:00] Sometimes they're concrete.
Um, you know, various materials can be brought into like kind of hem, the river in. Right? That's what we're trying to
do.
Dr. Jesse Reimink: yeah, so I mean this is a, a kind of harken it brought me back to our dams episode where we were talking about dams. this sort of impressive statistics here that
Chris Bolhuis: Which by the way, was another really good idea by me. Okay. Just saying that, you know, in fact, it was such a good idea that we had to do two episodes on dams and we almost broke up on the first dam episode. Oh, man, you really pissed me off. I'm,
Dr. Jesse Reimink: [00:11:30] You're getting all, you're getting
really pissed off at me again, aren't you right now just thinking about it. Oh my goodness. Well, anyway, so at Moral the story, Chris is always right and dams are pretty interesting. So are levees. Here's some stats for you, Chris. So the US Army Corps of Engineers is generally responsible for many of these levees there, 6,890 levy systems in the us.
That the US Army Corps of Engineers is responsible for, that's almost [00:12:00] 25,000 miles of levy. I mean, a ton of those are on the Mississippi River drainage system or the Missouri River. you know, the big major rivers, they're, they're heavily levied. the average age, and this is really what made me think of our dams up, so the average age of the levees are 59 years old.
And
Chris Bolhuis: Which by the way, is younger than me, but I'm gonna beat you to the punch. Okay? I know you're gonna say something about that.
Dr. Jesse Reimink: so
your average
Chris Bolhuis: a minute, wait a minute, No, I said that wrong. Damn it. They're older than
Dr. Jesse Reimink: older than you. Yes. You're, do you give yourself more credit, Chris? You're [00:12:30] not that old yet. Uh, if you are out there and you see a levee, you can think, wow, that is really old. it's even older than Chris Bullis. My God. It's super old.
the infrastructure bill that just passed in the us the US Army Corps of Engineers estimates that 21 billion is needed to improve. These things. And that's only about 15% of the known levies in the us. So anyways, this is like a huge infrastructure, um, issue or topic and potential issue.
And it's one that doesn't get any credit, you [00:13:00] know what I mean? Like it's one that we just don't think about until it becomes a really big problem. And we're gonna talk about some of those examples as we move through this.
Chris Bolhuis: the other thing that you left out of your stats there was that 97% of all levies are earth and embankments. It's just, it, it, that just basically means fill dirt, brought
in and just kind of stacked you know, adjacent to the river on both sides. usually they're on both sides, but that's the interesting thing too, is that they're not always on both sides of the river and they're not always equal heights, which [00:13:30] present some problems that we're gonna get into a little bit here in
Dr. Jesse Reimink: The other, the other, you know, 3% are concrete rock, steel, like all the things you'd kind of envision like building stuff out of, right? So building materials of various kinds. but earthen is the, it dominates. And that's a really interesting thing when we talk about well, we'll talk about the cons of, of levies or some problems as we go through it, but what are the pros?
Why do we build these things? Chris, like, let's start there. Maybe.
Chris Bolhuis: Good call. why in the world do we build levies? Because whenever you do something to a river, there are gonna be consequences to that, which are gonna be the cons, but, [00:14:00] you know, do serve a function. I mean, number one, I think is that they reduce flood frequency.
They don't prevent floods.
There's a quote, I don't know if I'm gonna get this right, but I'm gonna try. there are two kinds of levees, those that have failed and those that are going to fail. It's something along that line with levees. I think a, a city planner made that quote along the Missouri or the Mississippi, I can't recall.
But anyway, they reduce flood frequency. They reduce how often the river's gonna flood.
Dr. Jesse Reimink: Yeah. [00:14:30] And that's, I think that's something that is maybe not intuitive, we just need to explain just a little bit, is it's not, they don't really change the amount of water going through the river. They change whether the river breaches its channel or not. So you're just making the levy higher so that the river doesn't breach over the channel and make it and spill over into the floodplain and flood the floodplain.
So that's what we're talking about. Like it doesn't change rainstorm events or the amount of water going through the channel at all. it just
constrains it. So that's what you mean by
Chris Bolhuis: It just allows the river build higher and higher before it floods out over its [00:15:00] embankment. the other thing is too, that goes kind of along with the Meandering River episode we had a while back, is that it keeps shipping lanes.
Consistent, right? We can't just have river changing and eroding, you know, the cut bank and point bar dynamic that streams have and just doing its own thing. We we're kind of trying to hem the river in and keep the shipping lanes and, and roads and so on consistent.
Dr. Jesse Reimink: and then the other thing that they provide is they stop or slow the erosion along the banks, along the stream [00:15:30] banks, and all of these things kind of factor together. So, reducing flood frequency, keeping consistent shipping lanes and slowing or stopping the erosion along the stream.
Banks. Really what we're doing is we're protecting our societal infrastructure. That's kind of the goal here. And there's a couple,
Chris Bolhuis: And why is that important? go ahead Jesse, and say why that's important then, because you have some interesting stats here that kind of back this up,
Dr. Jesse Reimink: Yeah, I, again, these sort of, uh, Chris, this was a fun episode to put together because it's sort of mind blowing statistics. [00:16:00] 17 million people in the US alone live or work behind a levy. That blew me away. I, I would've never guessed it was that much. They live or work in a floodplain that is protected by a levee, that's what that actually means, right?
So behind a levee, you're, you're in an area that would flood frequently, were it not for the levee right next door. they protect 2.3 trillion of property, 4,500 schools with over 2 million students in them. And like, you know, obviously a ton of industry [00:16:30] and city centers and some of the famous ones that we have heard about recently, new Orleans is a, great example of a levee system that failed, w catastrophic results.
So, a lot of prose to levies, right? we sort of. For historical and modern reasons, build our infrastructure around rivers that are mandarin, they're big rivers, big shipping lanes, all this stuff. and they are protecting that infrastructure. So there are good, valid reasons to build levies.
Chris Bolhuis: so I have a thought, okay, because I do an exercise with my upper level [00:17:00] smart kid Geology students, right? And I give them this situation. I. I give 'em a situation where I have a meandering river let's say it's maybe 20, 25 miles of river section, and you have two towns one is on the, upstream side of this river, and one is on the downstream side.
and the upstream city floods all the time. The downstream city does not, and problem I give them is, all right, we'll solve the problem, I draw it on the board. I show them where the cities are, show 'em the position of the Mandarin River, [00:17:30] solve the problem.
and I just give 'em a few rules. Obviously you can't move the towns and you, you know, you have to deal with the situation as is and what can you do, right? Your, your solution is, I can build dams. I can maybe re-channel the river, reroute the river,
right? And I can levy the river and they have to support their reasoning with, alright, well everything that you do is gonna have consequences, whether it's building a dam.
And we talked about that a long time ago. And so on the consequence of doing this, so almost [00:18:00] always my students choose to levy the river.
that parallels what engineers do. I mean that's been our solution to dealing with rivers. That flood
we just like to levy 'em. So that offers then a good segue into, well, alright, we painted a good picture of why we do that and the pros to it, which are, they're not to be neglected.
These are, these are upsides. What are the cons? What are the downsides to Levin River? Cuz there are consequences.[00:18:30]
Dr. Jesse Reimink: I think the first con here, Chris, is a bit of a counterintuitive one perhaps, is that, often levees will increase flooding upstream from the levees. So although it protects flooding downstream, it creates more flooding upstream. Why?
Chris Bolhuis: let's think about that. Is that counterintuitive? Because to my students it is. You know, you think about, wait a minute. Um, why would you get flooding upstream from where the levies begin?
Dr. Jesse Reimink: And I think it is a bit counterintuitive cuz the instinct would be to say, oh, well, it creates flooding [00:19:00] downstream, probably. Which, it might do that as well. But, this instance is, is upstream, the upstream effect. Why does that happen? What do you say to your students, Chris, when they're like, eh, Mr.
Bois, what? I don't get it. What's going on? Why, why is this not, why is it working this way?
Chris Bolhuis: I think I have a good analogy for it. I always say, well, it's a traffic jam when you go from five lanes of freeway down to one. Then you get backed up. Right? isn't that what happens when you levy a river? And they're still though? They're like, whoa, ah, why? Well, [00:19:30] if you didn't have the levies there, what would the river do?
Right? the river would just spill out over its banks. Flood. The flood plane, you know, let's think about that a second. Let's let that soak in the flood plane. Okay? And you're distributing this massive amount of water then over a broad area, but not when you levy the river. Now you're confining it in, you're pinching it into this narrow channel, and you're causing the water then to kind of back up [00:20:00] much like a traffic jam on a, busy freeway during rush hour.
Dr. Jesse Reimink: Yeah, and I think it's really important to consider and remember that all of these streams have this branching upstream network, right? So as you go upstream, the streams get smaller and smaller but they're all connected, they're all interconnected. And this is a really important concept that although the, the river.
Is flowing downstream. All the water, you know, any individual water particle we talked about in the streams episode, how you can only step in one river once and then it's gone. It's not the same river anymore. all that applies. But the [00:20:30] physics of how the water moves through the system are ma, it's like a house plumbing system, right?
Like if you clog up one side of it, It affects the other parts of the house plumbing system. It's k they're all this kind of interconnected pathway. So I like the traffic jam analogy, Chris, that you put some construction, it's construction season here in Pennsylvania, so there's construction all over the place and, uh, yeah, there's always traffic backups when there's, you know, a few people working on one side of the highway that close down one tiny little bit of lane for half a mile and it's backed up for miles and miles and miles on the backside.
[00:21:00] So, good analogy.
Chris Bolhuis: I've driven so many times, countless times down the floodplain of the Mississippi River, and that floodplain can be five or six miles wide on one side alone. not to speak of the other side as well. So think about that a second, five or six miles wide.
On one side, that's a lot of water that can be distributed and spread out over that broad flat plane.
that now you're confining into the channel. So it's gonna back it up.
Dr. Jesse Reimink: that brings up a really interesting point because this, this sort of dual side to the river. We [00:21:30] talked about stream meanders and how, you know, one side is cutting faster and another important point that we talked about is how. when a river comes out of a bend, the water is directed, not straight down the river anymore, but kind of to the other side of the bank.
So it's if, if it's a left her hand turn. So if the river is turning from the left side and bending back to the right, the river is gonna be directed to the right side of the river and gonna hit the right side and embankment on the next turn. And this brings up an interesting [00:22:00] point that not. All levies.
You made it earlier. Not all levies are the same height on other side of the river. And that affects the river current. And, especially in places like, where there's perhaps a state boundary on one side of the river, in another state, on another side of river in two different jurisdictions, you know, they could get into fights about the size of the leving, who's directing water to which side of the river and who's doing more damage.
I mean, it reminds me of, of, um, It reminds me of like wave breaks along the beach where, you know, if somebody [00:22:30] puts a, a big, uh, concrete barrier up, it directs all the wave energy to their neighbors and their neighbors get a lot more erosion. It's kind of the same debate here on either
Chris Bolhuis: That's right. It is very similar to that for sure. For sure. so that's one serious downside is flooding upstream from when the levies begin. Right. But are others, and let's get into those a little bit. The other one is that, let's think about what the concept of a floodplain is, right?
It's a broad, flat plane that is meant to flood. and so what [00:23:00] levies do is they disconnect the river. From its own floodplain. so in other words, in in Geology and like Fluvial geomorphologists, is a really annoying and fancy term for just a river guy, you know,
let's, our, our
good friend Andy
is AFL likes to say I'm a Fluvial.
Geomorphologist.
I'm, uh,
Dr. Jesse Reimink: likes to put his pinky in the air while he is having a beer and call him sofa. Fluvial.
Geomorphologist. Yeah.
Chris Bolhuis: But. They like to say that these levees then, if you don't allow the river to flood, and you know when [00:23:30] a river's flooding like this, we already established that it's ripping, it's moving really fast, right? So it's carrying a lot of sediment.
When it floods, it spreads that sediment out over the floodplain and they call it the gift of the river, which is a really appropriate term because it is, it's very, very, Fertile soil, then that's being distributed out across the floodplain for, so agriculture is a great use for floodplain,
Dr. Jesse Reimink: it's why it's such good cropland. It's why when we were talking to Andrew Alden, he brought up that the Grand River used [00:24:00] to flow through Hudsonville, Michigan, and that's why it's such great farmland there is cuz you know, it was sitting on the floodplain of the ancient.
Grand River, the glacial, grand River system. And so, we're gonna come back to this point, this gift of the River Point. So let's like store that in our memory banks. Cause we're
gonna come back to that point when we, when we talk about solutions here.
Chris Bolhuis: Yeah. So Jesse, before you go on to that, I know where you're going cuz I know your little mind there. Um, I, I also wanna talk about another con, which I think is a serious con.
When rivers flood and it's spread out way out over this [00:24:30] broad flat floodplain, you're allowing water then to seep in and then recharge the water table below. So we're allowing, we're talking about groundwater recharge by flooded rivers. What? You don't get that. When you're not allowing the river to flood, we're just getting it through this channel and bringing it downstream and, and eventually to the oceans, cuz that's the ultimate destination of rivers.
So groundwater recharge
Dr. Jesse Reimink: let me make a point on that because I think when you picture, at least when I picture, a levy or [00:25:00] when I picture a stream, you know, I'm usually picturing something relatively small with a floodplain that's not that big. But really, you know, what we're kind of talking about here is, is picture the Mississippi River with five miles of floodplain on one side and five miles on the other.
that's the scale of groundwater recharge that we're kind of talking about, where this is super, super duper important. and you're not just flushing all that water downstream as fast as possible with the levees. Funneling it down, but you let it seep out and percolate in as it [00:25:30] spreads out over 10 horizontal miles from the river.
That's, that's a massive amount of recharge. So two last cons here. I think, well, three really, and, and the third one kind of leads into our solutions here, but, um, I don't know if this is counterintuitive or not, but actually the duration of flood events is increased with levies because it's harder for the water to get back into the channel and therefore out of the region.
And I, I think that kind
Chris Bolhuis: Hold on, I gotta interrupt you a second. That is because, all levies will [00:26:00] either flood, the river will rise above the levy that you built, or they will fail. And then because a levy keeps the water hemmed in, it's also gonna keep it hemmed out. Right.
It's not gonna let it back in. Is that what you're saying?
Dr. Jesse Reimink: Yeah, so you, you, once the water breaks through the levy, it, won't get back into the channel and it'll kind of prolong the flooding event longer than it that na it naturally would have been, let's say. and the other point here, and then Chris, you can lead us into the solutions here.
The, the last point is an interesting one [00:26:30] and it kind of, we talked about this with dams, is that when you levy the river, the river breaks out into its floodplain and then can't get back in. And what is, what's another, there's another effect here, though. There's another sort of, it's a long-term stream evolution effect. I, I,
don't know Chris, I don't know how to explain it.
Chris Bolhuis: Well, I'm sorry, but the teacher side comes outta me in this because I want to ask the question to our listeners like, what do you think another consequence could be? Right? Because you're talking about river that's. would be at flood stage. So it's ripping, it's moving, it's [00:27:00] fast, and it's moving a ton of sediment down slope, right?
But we're not allowing it to flood, so we're depriving the floodplain of its gift. So where does all the sediment go? What's the consequence not allowing that sediment to be spread out over the floodplain? So my young sage, I'm gonna let you handle the answer to that question, but I did wanna pose it.
Dr. Jesse Reimink: Well, there's two. I think there's two ways I would, at least my mind goes to answering this question. The first is, okay, there's not [00:27:30] sediment being deposited in the floodplain, so maybe the floodplain is subsiding. Which it is, like if you're not adding sediment to the floodplain, the floodplain subsides and kind of sinks down a little bit.
The other thing is that you have more sediment in the river channel. So the river channel goes up, like sediment is deposited in the bed of the river in the. Actually the bed level of the river raises up. And so you have this kind of duality thing, this kind of teeter-totter going on where the floodplain is sinking and the river channel is raising, which means to keep the river [00:28:00] within the channel.
We need to build our levies higher, which means the river channel gets higher and higher and we need to keep building our levies higher. And then you have this thing where you get in New Orleans is a big problem where you have this inversion where the river channel is actually higher than.
The floodplain outside of the levy, which creates as we've seen catastrophe at times. Because
Chris, the last
Chris Bolhuis: sink in.
you just said that the bottom of the river is higher than its own floodplain because of this situation. And that's a really [00:28:30] powerful thing to let sink in a second. That's a problem. You know
Dr. Jesse Reimink: You can see why it would be a big problem. Right.
you know, we've seen this happen catastrophically recently in the US and elsewhere, and this is the last con is that large floods, break levies, In 2019, this was a really recent example, right? The Missouri River flooded it. It didn't actually rain that much at the site of the flooding.
All the rain happened upstream up in Minnesota and way up in the upper reaches. But massive amounts of [00:29:00] rain in these small tributary streams. They all get aggregated together. in 2019, the Missouri River breached a hundred levies, inundated 1.2 million acres of flooding and damaged a ton of infrastructure.
One of the, levy systems was breached in seven locations, in one sort of levy system along the way. And I think this leads us nicely into some potential solutions, cuz I think the solutions are almost as interesting as, You know, the problem [00:29:30] itself there, there's some really interesting geoscience in these solutions, right?
So, Chris, I mean, we could spend a long time talking about these solutions. I'm sure you did deep dive and gotten some rabbit holes with these solutions. I kind of did the same thing and, uh, you out a few that were kind of interesting, but I don't know what, what struck you about some of these, uh, solutions?
Chris Bolhuis: Well, I think the one that is the most appealing makes sense to talk about first, at least for me anyway. and that's idea of setback levies, where you take 'em and, and you kind of like,[00:30:00] well you do exactly what it sounds like. You set the levee back a bit from the river, you are allowing it then to flood out. A little bit anyway. It depends upon, you know, what you have to work with, right? But you're allowing it to flood out onto the floodplain, seep down in, you're kind of spreading that out. You're widening the channel. And giving it a chance to do its thing. So that's, an appealing alternative. I, you know, I don't know.
It's not always feasible, right? Because if you have infrastructure that does [00:30:30] not allow that, I mean, you either have to relocate the infrastructure, which that's always our last alternative, or our last like, okay, let's do that. That's just not a viable solution in some cases.
Dr. Jesse Reimink: And I, I think there's a good example of this. It was finished in 2021 along the Missouri River. Part of this reach that, flooded in 2019 where, you know, there's been a setback where the, the levy system is being set back along one section of the river and it's reconnecting a thousand acres of floodplain.
is an issue that is is not without [00:31:00] controversy because you have to go and you have to say, Hey, person who owns the farm here that's behind a levy? Oh, tomorrow you're not gonna be behind the levy anymore. You're gonna be in the floodplain. Like, you can see how that's a problem in a potentially contentious issue.
Right. this particular instance, there is a lot of state forest and, Um, federal land that was part of that. So it's a little bit easier, but it's a pretty good test of how well do these work on large river systems that are prone to flooding like the Missouri River system. And so I think there's gonna be some exciting data that comes out of [00:31:30] some of these tests.
I think for me, Chris, one interesting aspect was, was the idea of notching levies. And so, you know, if you think
Chris Bolhuis: Oh, so are you talking about spillways then? Is
Dr. Jesse Reimink: Yeah. Yeah, like, like, cutting. And, you know, we're picturing and we've, we've been describing levies as like a continuous hill of sediment along the river channel. And instead of just having a continuous hill, you just kind of make a notch somewhere so that when the flood happens, it can kind of get out and you can control how much it gets [00:32:00] out.
And so you can kind of control, quote unquote, the flooding in a way and allow the river to replenish the floodplain sort of as much as you want at that particular time. So maybe when it's, not a high crop season. in a flood happens, you can let it out and replenish the river.
And if it, it is gonna flood during crop season where you really can't afford that, then you don't let it flood through the notch. And so we can kind of. Tune the levy system a little bit to our, our desires, which it seemed interesting to me for certain
scenarios at
Chris Bolhuis: I've seen these [00:32:30] firsthand, actually, along the Ohio River.
Um, so my son and I have gone to Cincinnati Bengals games.
You know, we, we've gone to a game every year since he was like four years old, and. Walking along the Ohio River there on the Kentucky side, that's usually where I, I've seen the, um, the notches that are cutting it.
And it is it's so obvious, you know, you have this huge levy, it's enormous. And then there are these slats cutting it. And they put these like steel, flat steel [00:33:00] sheets across the slat so that if they wanna let the water out or let the water into the river, whatever's going on, they have these notches where they can remove the, the slats and therefore you have a notch in the levy system.
It's really kind of a cool idea.
Yep.
Dr. Jesse Reimink: I, I, like that idea that that had some appeal to me. Um, you sent a, a link, Chris, and we'll put this in the show notes if you wanna see some amazing graphics about levies as we kind of wrap up here, where levies get placed, how they protect streams. There's, [00:33:30] an article about Mark Mount Carmel, Illinois.
that, really shows some really cool graphics on the border of Illinois and Indiana, where the Wabash River is being levied in sort of potential outcomes here, and the differences in peak water flows with levies and without levies. Like there's some really interesting geoscience in here, of shows some of the potential solutions that people are testing out.
So I just, I don't know, Chris, this, shocked me, this astonished me. Levies are so important, very underappreciated for our [00:34:00] society, and we need to learn more about levies and there's some really interesting tests going on as we speak about, compromises between the natural river system and a river with infrastructure around it that we really can't afford to have flooding all the time.
So,
Chris Bolhuis: that's right. That's interesting that you say, you know, that, that levies are kind of like not appreciated and, kind of undervalued or not really thought of a lot and that's interesting because it's our go-to. That's how we deal with rivers. More often than not, that's what we do, [00:34:30] is we levy the river.
So,
Dr. Jesse Reimink: I mean, Chris, but it's like everything in geoscience. We're just so undervalued. We're underappreciated. I mean, I don't get paid enough. You don't get paid enough. We're not appreciated. We are not celebrated when we walk down the highway. People aren't
throwing us parades. Like, what's up with that? I mean, we really
should be getting all
Chris Bolhuis: We're, trying to change that one person at a
time. Jesse. Hey. But I know you don't like it when I pitch an idea on the show, but I'm gonna pitch an idea for a future episode here, which
Dr. Jesse Reimink: Especially Chris. The reason I don't like it is [00:35:00] cuz you always say, Jesse, I'm always right. Just say you trust me,
Chris Bolhuis: Well, okay, so just trust me here. Just trust me. We need to do an episode on the human impact of flooding. You know, we touched on it here that, the Mississippi and the Missouri have had, numerous hundred year floods in the last decade, right? and sure, climate change plays a role in this, but, but so do we. Not in the way of climate change, but in the things that we build, have played a role in how often rivers [00:35:30] flood their
Dr. Jesse Reimink: Yeah, you, you know what? I think we should do? You know what I think we should do for that? We should, we should go interview a state, hydrogeologist who thinks about this for a particular area and, you know, models what a hundred year, a thousand year flood will look like. I think that'd be a really interesting conversation with somebody who's sort of an expert at modeling these types of things.
Cuz I
I think some of the things that they, they do is really, really impressive and, and frankly, a little bit beyond me. Because it gets complicated trying to think about these things. But I agree with you. I [00:36:00] think that's a super interesting point.
and something that's underappreciated and shows the
sort of breadth that geoscience matters a lot.
Chris Bolhuis: we, we are really good friends with a Fluvial geomorphologist,
but you know, I think you're right. We should hire a true expert.
To come on
Dr. Jesse Reimink: Let's, let's go to the, we don't wanna mess around with Fluvial. Geomorphologists. Oh my goodness. Oh, goodness. Hey, that's, I think that's a wrap for levies. Chris, this is super interesting.
good episode. Oh [00:36:30] gosh. You're
okay. Every once in a while you. Come up with
some good
idea.
You're on a roll. You're one for one. Just crushing it over there. Just crushing it. Hey, if you wanna learn all the basics of geoscience with audio discussions with us and all the images you need in a mobile online platform, go to camp Geo geo.camp courses.com. It's the first link in your show notes.
That's Chris and I have produced basically all the content that we teach in our intro to Geology classes. at the college [00:37:00] level, or the high school AP level, basically, first link in your show notes. Go there, check it out. Let us know what you think. You can go to our website, planet geo cast.com.
There you can subscribe. Support us. We always appreciate that and find our own episodes. And if you're on a podcast platform, just leave us a rating and review. We really appreciate it.
Chris Bolhuis: Cheers.
