Stanford [00:00:13]:
The whole idea for this podcast really emerged out of conversations I've had over the years with today's guest. In these conversations, I'm hoping to capture the insights of senior subject matter specialists in river mechanics, sediment transport, and fluvial geomorphology, mainly trying to reproduce some of the informal conversations that have been so formative to me over the years. And when I imagine these informal, insight dense conversations that have formed the way I think about river processes over the last couple decades, conversations that I wanted.

Stanford [00:00:40]:
To share, it is remarkable how many.

Stanford [00:00:42]:
Of those conversations have been with David Biednharn. Those of us who know David beat sometimes call him the Yoda of physical river processes, mainly because he generates lessons and aphorisms about how rivers work faster than we can take them in, though this may be the first he's hearing about that. David's worked at the core for 36 years at the district division and laboratory level, and he ran a private firm for another eight. He's worked on rivers at every scale. He's widely recognized as one of the go to experts on Mississippi process and morphology, but he's also worked on degraded streams and unraveling ditches across the southeast. But his role now at the coarse coastal and hydraulics lab in Vicksburg, Mississippi, is largely to mentor a new generation of river scientists. And, well, I kind of feel like that's great for those lucky early career engineers who get to work in his hallway, but what about the rest of us? So I wanted to try to see if we could get some of that mentoring to scale, to see if we could make one of these informal chats with David that been so influential to so many of us, out to others who don't happen to be co located with him. My name is Stanford Gibson. I'm the sediment specialist at the Corps of Engineers Hydrologic Engineering center and on the HSC Raas team. And this is the inaugural RSM River Mechanics podcast, a conversation with David Beaton Hart.

Stanford [00:02:02]:
David Beaton Hart, thanks for joining us today. I've heard you say that there are no cookbooks in river engineering. What do you mean by that?

David [00:02:10]:
Well, first off, thanks for having me here today, Stanford. But yeah, I think that, you know, as engineers, we go to school and we learn how to work from cookbooks sometimes. We have a lot of equations. We have go to lookup tables that we can design the concrete beam. And so when we move into river engineering, we sort of take that. We're going to have those same lookup tables and equations that are absolute. And we have these cookbook approaches that we can apply to our streams. And in most cases, that just doesn't work or the equations or the lookup tables don't exist, or they're really just more for guidance. And I think we get into trouble with that sometimes because people, particularly engineers, we're looking for that, you know, absolute path to follow, and we run into trouble with that sometimes. And I sort of equate this. Back when I first got married 47 years ago, I found the most beautiful girl I've ever found in my whole life. Married her. And I said, man, this is great. And then I gave her my mother's recipe for shrimp gumbo.

Stanford [00:03:21]:
That never goes poorly.

David [00:03:22]:
No, it started out bad. And so Linda told me, took the recipe, and she made the gumbo, and it was good, but it really wasn't as good as my mom's. So being young and dumb and inexperienced in married life, I told her it wasn't as good as my mom's, and that didn't go over well at all. And she grabbed the recipe and was handwritten in my mom's handwriting, and she throws it in my face, and she says, look at this. So I look at it, and it says, take two pounds of shrimp, tablespoon of salt. And then there was this cryptic phrase that said, a pinch of crushed red pepper, more or less until it tastes right. And she said, what does that mean? I said, I have no idea. But the whole point of that is that is kind of the way our river engineering guidance is. My wife, at that time was an inexperienced cook, and she now makes excellent gumbo and other things as well. But she didn't have the experience to take what my mother said is a pinch of red pepper, more or less until it tastes right and make it work. By the same token, I could take that recipe and give it to Bobby Flay, you know, the great chef.

Stanford [00:04:45]:
Right?

David [00:04:46]:
He didn't know my mother, and he would know how to make that sing. And he might not even use red pepper, and he might use something completely. He might use something completely different because of his experience. So he could take that recipe or that cookbook, and he could make it work. But without the experience, you can't do it. It's exactly the same thing in river engineering. We have a lot of good procedures and guidance that's out there and the corps, other agencies that help us with our river engineering designs. But we have to temper that with experience. And unfortunately, this is another thing that I think about a lot, is that it takes a long time to develop engineers or scientists into really functional performing river engineers and geomorphologists. We can take them out of school and we can put them to work with running models or doing analysis with data, and they can do the computations and run the models or run the analysis. But it's that interpretation of those results that is where it really becomes a factor of gaining more experience. And to get the experience, you've got to have projects to work on, and that's key. I was lucky when I first came to work for the corps. We had a lot of projects that I got thrown into, and I worry today, and I see it a lot in the core districts, that they may not have a lot of projects to get involved with. And if you've just had the book learning and the classes and you don't apply them and you don't apply them to a lot of different situations, it's hard to develop that expertise. So that's what I mean by the cookbook.

Stanford [00:06:36]:
One of the things that I think about this is that I feel like engineering tends to attract real type, a equation type people.

David [00:06:42]:
Sure. Right.

Stanford [00:06:43]:
And that we are used to like performing on equations in school. Like, I think about my daughter. My daughter's going to be an engineer. She just loves the math and she loves that she has a right answer at the end. And in some ways, if someone comes through that kind of pipeline and ends up in river engineering, we're kind of used to the right answer. But river engineering has this artistic. It's more of a craft.

David [00:07:06]:
It is.

Stanford [00:07:07]:
And a skill than a set of equations. And if you think about the history of craft, people don't learn a craft in a classroom. People learn a craft through an apprenticeship or through being mentored and just getting.

David [00:07:21]:
Reps. Yeah, you mentioned that. It makes me think when I started with the core, with the Vicksburg district back in the seventies, and I was in the hydraulics branch and we were hiring a lot of engineers at that time. We were very busy, and it was a booming period in the seventies and early eighties, and we would hire engineers right out of school. And it's like you said that, you know, we come out of school as engineers, we're ready to run the equations, everything's nice. And I, you know, cut and dry. But what we found is just within hydraulics. And most of what we were doing in hydraulics was maybe pure hydraulics at that time. I was doing a lot of sediment and geomorphology type things, but most, most of us were just doing hydrology, hydraulics and we found that after about a year or two, most, maybe 50% to 70% of the engineers we hired were looking to go somewhere else because they were wanting to go to design branch or geotech branch, somewhere where they were actually doing more computations. And they had more. They had more boundaries that they could work with. Whereas in hydraulics, even in just running straight hydraulics and hydrology type of projects, there was so much subjectivity in what we do. And as you said, the craft. And that's just in hydraulics. And when you bring in geomorphology and sediment transport, it exponentially gets worse.

Stanford [00:08:50]:
Craftier.

David [00:08:50]:
Yeah, craftier. That's a better way to say it. And so we find a lot of these guys and gals would move on to the design branch or geotech or something like that. And it's even more so when you, like I say, when you move into geomorphology and river engineering, it's. I like your word, craftier.

Stanford [00:09:08]:
That's one of the things that's good. One of the ways that I tell people about is, you know, if you're. If you're building a structure, well, you're going to get the materials off of a truck, and they're going to be predictable. And so you can have a cookbook that tells you how to do that. But like river engineering or even geotech, it's more like playing poker. You get dealt a hand of cards, and it might be a lousy hand of cards, but, like a good poker player knows how to play a lousy hand of cards. And I think that some people get tired of having to play lousy hands of cards.

David [00:09:40]:
Well, I think we always have lousy hands. Sometimes the data sets, it does seem like we're, you know, we're. We're always asking for three more cards.

Stanford [00:09:48]:
Three more cards. Just give me three. Yeah, that's right. So, David, when I started with the corps, or even like, you know, in my first ten years, whenever I would talk to kind of senior river mechanics or river engineering people, they would always say things like, oh, yeah, you know, we learned in the demonstration project, or, you know, back in the demonstration project, and it's like there's this great history of something called the Demonstration Project. And I never actually got around to just asking, what are you talking about? What was this demonstration project? Why was it so important? So let's just start with this, because I know this is one of the kind of big rocks in your career. What was the demonstration project?

David [00:10:29]:
Okay, the demonstration project you're talking about is the. It was the Vicksburg district project called Demonstration Erosion Control Project. It started in 1985. It really. I kind of saw it as a. As an outgrowth of what we call the section 32 program, which was a nationwide core program that was under the stream bank erosion control evaluation demonstration project. It was, I think, section 32 was the public law, and that was a nationwide project where the corps was able to go out and test different stabilization techniques, trying to come up with more cost effective, innovative type structures, in contrast to just doing a complete rip rap blanket right bank toe to top of the bank. And so a lot of the districts had bigger. It was several of the districts. Vicksburg was one that had a large share of that project. So when I first went to work with the corps, I was working with Brian Winkley, who was sort of my mentor at the time. And we were involved with the section 32 program, and we were able to build a lot of different structures and working with other districts as well. But it was a really good program where a lot was learned about some of the techniques that we take for granted today, like longitudinal stone toe protection. A lot was learned in that section 32 program about that. The problem with the section 32 program was it was funded through the seventies, and by the time we constructed a lot of this, it was the late seventies, 78, 79, and then we had to turn around and write a report to Congress in 1981. And then it ended. So there was just a short time frame of monitoring. So here's all these structures out on the ground, and we didn't get a chance to monitor them completely. So the section 32 program ended, and at that time, the congressman from Mississippi was a guy named Jamie Whitten, and he had been in Congress for about 100 years. South we like to keep our congressmen around for a long time.

Stanford [00:12:38]:
Yeah, if they're good at it, why change?

David [00:12:40]:
That's right. As long as they bring home a lot of the bacon. But he came up with a demonstration erosion control project in 1985, that it was centered on six watersheds in north Mississippi. And it was interesting that he actually told us that one of the purposes was he wanted to keep the sediment in the hills. These streams were up in what we call the Los hills of Mississippi, and all the sediment washes downstream into the alluvial valley. Old alluvial valley we call the delta streams. Clogs them up, it fills up wetlands, navigation, flood control channels. So he said, let's keep the sediment in the hills.

Stanford [00:13:20]:
Keep it in the hills.

David [00:13:21]:
Keep it in the hills.

Stanford [00:13:23]:
That's a great way of branding.

David [00:13:26]:
So we had this program, and it was really heavily funded in 1985. And I remember I was in hydraulics at the time and was the lead hydraulic engineer on it and said, all right, david, you got $6 million in a year. You better go find some places to build things.

Stanford [00:13:43]:
So that's not a current $6 million either.

David [00:13:47]:
No, no, we're talking about 6 million back then. So I had. How old were you? Oh, how old was. Yeah. Oh, gosh, I'm just 30.

Stanford [00:13:55]:
Okay.

David [00:13:55]:
I don't know. And I. So, luckily, through the section 32 program, I was somewhat familiar with a lot of these streams and had worked on a lot of these structures. So first thing we did is we got in a helicopter and I started flying all over these streams, looking for head cutting and nick points in the streams, because I figured that one of the first things we need to do was stop a lot of this degradation. These streams, most of them had been channelized back in the pre seventy's time period, sixties back, even, some of them back as far as the 1920s, mostly by local drainage districts and others not necessarily the core. And so we had a lot of head cutting, and just the streams were just unraveling.

Stanford [00:14:38]:
Can you just describe what a head cut is just for a moment?

David [00:14:40]:
So basically, when you. In these streams, which were channelized, we took meandering streams. I say we. I wasn't the one.

Stanford [00:14:48]:
Right, right. The big team.

David [00:14:50]:
The big team would take these meandering streams and make a series of meander cutoffs and straighten the streams, which would increase the slope. And so that would be an oversteepened slope for the sediment delivery for that stream. And it would start to scour the bed and erode the bed. And as it does, that oversteeping zone migrates upstream toward the head of the watershed. So we call that head cutting. At least that's the way I've always thought about it, is cutting toward the head of the watershed.

Stanford [00:15:20]:
And in like, an unconsolidated river, that'll happen kind of gradually.

David [00:15:24]:
Correct.

Stanford [00:15:24]:
But in the Mississippi lust hills, like, you'll actually propagate a waterfall, right?

David [00:15:29]:
Yeah. Well, what happens is, just like you said, if you've got a sand bed channel, which a lot of these were, that slope will just elongate and then propagate upstream. But if it encounters resistant or fairly resistant materials, clay outcrops, it'll form those overfalls, those waterfalls you're talking about. And we call those Nick points, or it may be a long zone of nick points. We call that a nick zone. And then it just keeps moving upstream and as it goes upstream the beds are lowered. In some cases these streams lowered 20ft.

Stanford [00:16:04]:
Oh my goodness.

David [00:16:04]:
Yeah. And when you lower the bed, you know, 20ft, the banks are now steeper and higher and we have mass failures due to gravity. And, you know, these streams, you know, 100% increases in width and it's just devastating to the, to the channels. Then all that sediment has to go somewhere and it's going downstream somewhere. Usually you don't want it.

Stanford [00:16:26]:
Right. We as an agency, either in our reservoirs or in our navigation channels or.

David [00:16:30]:
Something like that, and we spend taxpayers money to handle it there, right.

Stanford [00:16:34]:
So you get out in a helicopter and we're kind of going Nick point hunting.

David [00:16:39]:
Yeah, I never thought about it as Nick point hunting. Stanford, you have a really good way of coining things. But it was interesting. The one of the first streams I flew over, we saw this really nasty looking head cutting zone with these overfalls. Some of them were like six, 7ft high. Oh my goodness. So we land the helicopter in the field, get out and we look at it. I said, man, this, we got a site we can put some grade control in here to stop this head cutting. So we need to find out, you know, whose land this in because we want to come back on the ground later. So we saw a house off to the side. So we land there and walk up to the door and this old man answers the door and I told him who I was. I'm working with the corps of engineers and we'd seen some erosion over in the stream behind his field and wanted to know if we could go over there sometime and look at it, you know, when we come back on the ground. And he said, yes, sir, you can. He said, by the way, my name is Paul Whitten. Jamie Whitten, the congressman is my cousin. So I'm thinking, what are the odds of just landing a helicopter in the middle of Mississippi and you land in the congressman's cousin's backyard?

Stanford [00:17:53]:
Well, I guess it depends on how much land the congressman, the probability is correlated with how much land he owns, I guess.

David [00:18:00]:
Right, right. Needless to say, we put a lot of work on that area, that particular stream, but it needed it and so that's what we did.

Stanford [00:18:07]:
And how many structures got put in the ground during the demonstration project?

David [00:18:11]:
Oh, gosh. Stanford, I.

Stanford [00:18:12]:
The order of magnitude, tens, hundreds, hundreds.

David [00:18:16]:
Hundreds of grade control structures which were in stream structures to control the head cutting and stop that from, keep the beds from continuing to lower and gosh, and then bank stabilization, extreme bank stabilization, most of which was longitudinal stone toe type of structures. We did some hard points, we experimented with some other type of features. I'm gonna guess hundreds of miles of that.

Stanford [00:18:47]:
Hundreds of miles of longitudinal stone till.

David [00:18:48]:
Yes, a lot.

Stanford [00:18:49]:
So let me make sure I, let me make sure I understand the terminology. When you're talking about grade control, that's like a small check dam or something that is perpendicular to the flow, and you're trying to, you put in several of those to help the river dissipate its energy so it doesn't push these big nick points up. And we're talking about bank protection. That's something kind of along parallel to flow that's kind of at the base of the bank that will, or along up the bank that helps keep the bank from sloughing it.

David [00:19:20]:
Right? So. Yes, that's exactly right. The grade controls, as you said, are like a check down. They're really. This is the beaten horn view of them. It's kind of maybe not universally accepted.

Stanford [00:19:32]:
I'll accept it.

David [00:19:33]:
Yeah. Okay. It is in this room today. In this room.

Stanford [00:19:36]:
It's universally accepted.

David [00:19:37]:
Yeah. But I think a great control kind of working two ways. One is that you're putting a hard point in the, the bed of the channel, something that the river can't erode through. So it could be rip rap, it could be concrete, it could be car bodies, which has happened not recently, that's called Detroit detrap. But I mean, something that resists the erosion and stops that erosion from migrating upstream. The other way we use them is maybe build a structure and build the bed up and create a backwater, which takes some of the energy out of the stream. And so, and a lot of times the great controls are some combination of both of those. And, but they're really primarily focused on stopping that head cutting from moving through the system, but they also provide some bank stability. You know, when you have serious meander migration, they're not going to stop that completely. But just by nature of stopping the degradation from going upstream and exacerbating the bank instabilities, you're stopping that. So you're improving things that way, but you're also maybe getting some sediment to deposit in some of the local areas of erosion, so you get some benefit there as well. But if you've got serious bank erosion issues like you're talking about, you know, the stream banks are eroding, they're getting into a road or a bridge or some other feature that's important that we.

Stanford [00:21:02]:
Save or a farmer is literally losing land because it's falling into the.

David [00:21:08]:
Then you can actually come right in and protect that bank. And there's a lot of different ways we can do that. We can use an armor type of structure placed along the stream bank. That would be stone toes, riprap armors. It could be any number of type of structures you could think of. There's hundreds of different techniques out there. Or it could be some indirect methods, maybe like dikes, Bendway, weir type structures. There's a lot of different things, but the. But the primary goal is to stop that bank from migrating, and that's a little bit different from the grade control.

Stanford [00:21:43]:
Can you just make sure we understand the difference between a direct method and an indirect method? A direct method actually puts heavy stuff in the way of the flow so that the flow still attacks the bank. But there's something armoring there. An indirect method redirects the flow somehow.

David [00:22:06]:
That's exactly right. Armor type method is you're now placing something along the bank that resists those erosive forces and shear stress and velocity that's attacking the bank. The indirect methods, sometimes we call that redirected, just as you said. It might be like a dike structure that goes out from the bank, maybe perpendicular or angled upstream or downstream, depending on what you want. And their purpose is to actually redirect the attack of the flow coming into the bank and maybe reduce those velocities as they attack the bank. And there's. When you get into that field of bank stabilization, there's a lot of experience needed to select the appropriate type of structure. And that's a key thing, is, what is the appropriate type of structure for a particular erosion problem? And there's no one answer there. There's a lot of different structures are suitable in different places, and some places they're not suitable.

Stanford [00:23:12]:
So when I first joined the river engineering committee, Meg Jonas was on the committee. And one of the things Meg would say maybe twice a year is we learn so much from the demonstration project, and it's all being forgotten because the people who worked on it are retiring. And so I guess one of the things I always wondered is, what did we learn from the demonstration project? This is one of our chances to capture some of that. What are some of the kind of the big ideas that came out of that?

David [00:23:40]:
Well, I think she was saying that it's being forgotten. Thinking about me and some other people who've forgotten it, literally forgot. We can't remember. But going back to the demonstration program, it was a demonstration program. So it gave us a lot of flexibility to try things just like the section 32 program. But within the demonstration program, we decided early on that we weren't going to just look at demonstrating specific stabilization features like longitudinal stone tow or Benue Weir, but we were going to try to look at the system. And how could we demonstrate a systems approach looking at watersheds? And that gets exponentially more complicated, as you know. So that was when we first started naively, I said, okay, we've had six watersheds. And I said, well, we're going to look at each of these and treat them differently, and then we'll be able to see how they each respond and, you know, and we can make comparisons. Well, that didn't work. For one thing, we had, you know, we did have a high level of funding and we had to execute. So that meant we had to build a lot of structures. So as it turned out, we didn't have a perfect laboratory experiment out there.

Stanford [00:25:04]:
No one wants to be the control group that doesn't work.

David [00:25:06]:
Right, exactly.

Stanford [00:25:08]:
Maybe the congressman's brother, not the congressman's.

David [00:25:11]:
Nephew or a cousin. No, that wasn't going to happen. But we did try to keep that concept of looking at the system as part of it. We were looking at, we knew we had to go in and get the bed of these streams stabilized with grade control. That was one of the first things. And then we tried to start addressing some of these other issues. Now, one of the key things, a common theme in most all of these demonstration watersheds was that they had the erosion, the degradation migrating upstream and the excessive sediment delivery coming downstream, either into reservoir boundaries or some of our flood control reservoirs or into some wetland areas or some flood control channels. So the idea was, let's go up and do source control. Let's attack the sources of the sediment and stop the delivery of that sediment down to these sink areas. And it's a concept we call now sources, pathways and sinks and the, but you look at that source of the sediment and how it's moved through the pathways or the channels to wherever it ultimately ends up. And that sounds like it's nice and easy to say sources, pathways and sinks. But when you get on the ground and you've done this and you know that it's not simple because the way that sediment moves from a source through a channel system is dependent on a lot of factors. You know, the size of the sediment, the energy of the channel, and then where it ultimately settles out. So all sediment ain't equal.

Stanford [00:26:53]:
That's right.

David [00:26:54]:
And so we, we found out that we could go up in the watershed and do a lot of stabilization of some of these stream banks that were mostly coarser, coarse sands and gravels. And the benefit of that 40 miles downstream in a reservoir boundary, we may not see the benefit of stopping that source of sediment or preventing that from eroding. We may not see a benefit from that for hundreds of years because it takes that long for that to work downstream. Whereas if it's finer material, some of the finer sands and silts and clays that are moving rapidly through the channel system and then dropping out in that reservoir boundary, if we control those sources and stop that erosion, the reservoir downstream may realize that reduction in sediment load pretty quickly. Yeah, and that sounds, again, really easy, but it's very difficult because as you know, this all stream banks, the variability of the materials and everything, it makes it very difficult to apply sometimes. But that's the concept that we try to look at and that's something we learned a lot about in the demonstration project, is how to. How to think about how that sediment travels from those sources down to the sinks. Now quantifying that is really difficult. We can, qualitatively we could assess it, but quantifying it gets difficult. But that's one of the bigger things we learned. And as part of that, another thing that I learned from the demonstration project is that even if we're looking at local projects and a lot of times in the corps, we will be charged with addressing a local bank erosion problem or a local meander restoration of one or two meander bins or something like this, very local in nature. And we'll fail to weave that local project into the bigger channel system. And that's a real problem because we need to. We need to think about how our local project is going to affect the stream upstream and downstream, and also how the system is going to affect our local project. The problem there is rarely, if we have a local project, do we have the time and the authority and the money to do a complete upstream or downstream. We can't do a complete system study and we probably don't have the funds or the authority if we do have a system problem to fix it. If we've got, if we've got, we're trying to protect a bridge and we find out we've got a head cutting coming up of, you know, the beds gonna lower five or 6ft in the next ten years, we probably don't have funds or authority to fix that, but we can at least let the sponsor, whoever we're working with. Know that, hey, look, there's no sense spending money on this bridge right now. Cause you're gonna lose the whole thing.

Stanford [00:29:52]:
If you don't address this downstream. Outside of our realm of authority.

David [00:29:57]:
Right outside the footprint of your local project. And you have to think more broadly. And so that's a big thing that I think we learned from the project. But it's, again, sometimes difficult to apply.

Stanford [00:30:09]:
All right, let me see if I can summarize three themes here. First, I think one of the first David Beethenhearn ideas that I internalized was that you always have to look at more than the project scale. When we're talking about sediment. And this is on brand because this is a regional sediment management podcast. And you taught me about regional sediment management before I even know about the program. But the idea is that a lot of times our projects fail. Because the sediment forcings are either coming from upstream or downstream or project boundary. And we have to be thinking about how sediment transports on this watershed scale. And how these forcings are interacting outside of the landowner. And this one bank that's eroding. What is the systemic thing that's causing that? Then? Maybe the second thing, and this has actually become one of my heuristics for just thinking about any problem is what are the sources, pathways and sinks? It's like a sediment budget, but it's more dynamic than a sediment budget. Because you're asking, you know, where, where's are the sources of the sediment and where's it ending up? But also like, how's it getting there? And what's the time scale at which it's getting there?

David [00:31:15]:
Absolutely.

Stanford [00:31:16]:
And then the timescale is. And this is one of the things that I really got from you early in my career, is you have to think about the time scale in terms of wash load and bed material load. Because the wash load, that'll happen almost instantly. The bed material load could take decades or centuries.

David [00:31:31]:
Absolutely.

Stanford [00:31:32]:
And so if you do a lot of bed material load protection, you might be doing, doing a lot of good, but it won't even show up in your career. And then the third thing that I heard was that on this demonstration project, you have to make sure that you take care of the grade before you take care of the banks. That if you just go in and protect the banks, but the grade is still unstable, the bank protection is. It's not going to work.

David [00:31:57]:
Yeah. And that's a key process and a way to think about. As you were talking, I thought about a number of different things as usual, you get me thinking, but we're still applying this. Just recently we were working with Memphis district and I was working with Jack Kilgore and some of his group from environmental lab. And it's the same thing. We're looking at streams, and it was a restoration project. And again, we were looking at, these were streams that were degrading. And we said, well, the first things we got to do is get these beds stabilized. And then, and a lot of these are pretty straight channels. And one of the things that we'd like to do is once we get the bed stabilized, let that system settle down a little bit, then maybe we can come in and do some more bioengineering type of applications using more vegetation. It costs less, it's more environmentally acceptable. Whereas if we don't get that bede settled down, we couldn't go in there under the natural conditions and expect purely vegetative techniques to work there, whereas we might be able to do that. And we get the gray control. And the gray control can actually provide in some of these streams which are kind of devoid of a habitat, whatever, you're providing some different structure you've got. You can put a riffle type of structure in with the rock. You have a pool riffle, different habitat, which I'm really out of my, my wheelhouse when I talk about that. But when I work with the biologist and people like Jack Kilgore and others, they can tell me what they are looking for. And then as engineering geomorphologists, we can then try to make that happen. So that's the type of thing. The other thing I thought about is you were talking is that when we do these local projects, we often think we're doing good. But if we meandering is one that just comes to mind, I see it happening all over the country and we're trying to do good. You know, we're remandering streams that were straightened. And the idea is that apparently, you know, God loves meandering channels, but doesn't like the straight ones. And. But, you know, sometimes straight channels may be stable geomorphically, and we miss that concept, I think, of an application that I was not involved with. You mentioned the River Stabilization committee, which is a committee the corps has of experts that go and look at projects for the districts. There was one, I won't mention names, but it was a mitigation project on a stream where I guess they had done some work around a highway or something. So for mitigation, they went in and did some restoration work. So they, they took a stream that was fairly straight, gravel, sand bed channel and remandered it, made it a very sinuous channel. And they put root wads for bank stabilization and so they cut the slope in half and a year later it failed because it just filled up with sand. And our river stabilization committee went up and looked at it and as soon as they looked at it, everybody on the committee said there's no way that could ever.

Stanford [00:35:14]:
There's no way. Yeah.

David [00:35:15]:
And everybody knew that. But this group that had done this, you know, had training but just didn't have experience. Again, it comes back to this experience problem and they thought we're going to put that meandering channel there and it just wasn't appropriate. The other thing I think about sometimes is if we take streams and we start remiandering them, we're flattening the slope. So we're probably storing sediment. So what's happening downstream of the remandering section? Are we going to sediment star of that reach? Are we going to create a backwater upstream of that meandering reach? All these things have to be thought about and that's the key thing about looking at the system, not just the footprint of your project. And so those are things that come to mind.

Stanford [00:35:59]:
One of the things I think about that is sometimes we think the motivation of the project will save us morphologically. Like in the bad old days, we straightened streams and that wreaked havoc because you could straighten a localized part of the system and then the effects like propagate upstream and downstream. And so now I feel like sometimes we think, well, because it's for restoration, it'll be okay.

David [00:36:21]:
It must be good.

Stanford [00:36:22]:
We'll go in and remiander it. It's something a stream that has had 100 years to reach a quasi equilibrium with its new straightened state. Now we're going to go in and remiander it, but because it's for restoration it won't be a problem. But it's actually the equal and opposite problem. And so you do have to think about how, what is the current sediment continuity? How is this doubling of the slope going to change that continuity? And then what kind of problems would that cause upstream and downstream? And maybe we don't, maybe we put in meanders but we don't double the slope. Maybe we have to be less aggressive with our meanders.

David [00:36:56]:
And the key term you used there was sediment continuity.

Stanford [00:36:59]:
That's right.

David [00:36:59]:
And I know that's a key part of your world for sure, and mine too. And a lot of times we don't really use that concept correctly and it's ignored in a lot of these projects, but it's critical, and that's why a lot of these projects fail.

Stanford [00:37:20]:
On the topic of why projects fail, we've talked about several things, not accounting for the sediment continuity, not thinking about how it is situated in the regional context. But you also have some thoughts about how there are kind of equal and opposite extremes of restoration approaches that can both lead to failures. So what are these kind of equal and opposite extremes that you see as people try to engineer rivers that both sometimes give you pause?

David [00:37:51]:
Well, I've seen this a lot in the last 20 or 30 years. And even when I first started, you know, we were, when we would do streamline stabilization, it was, okay, we're going to put a rip rap armor and we're going to go from the top bank down to the bank toe and we're going to rock the whole bank.

Stanford [00:38:10]:
The corps was here.

David [00:38:12]:
We're the core. We're here to help. And that was sort of our benchmark civilization technique. And there are, there are absolutely applications that require that just recently was involved with one. I mean, when you're protecting a bridge and you've got something that has to be protected, can't be allowed to fail at all, you better make sure you stabilize that whole bank. And so there's an absolutely, there's a place for that type of full bank armor, and it's absolutely necessary. On the other end of the spectrum is, are areas where maybe the erosion is not going to take out a bridge or the failure of the bank is not going to be that catastrophic. The world's not going to end, and the bank erosion is not that aggressive. This is my view. There are a lot of vegetative, purely vegetative techniques that could be, we'll say bioengineering, but when I'm saying that, I'm saying vegetation only, you know, no rock. No rock. And a lot of times when we talk about bioengineering, it really is a hybrid type of structure. I'll talk about that in a minute. But so there's really good applications and applicability for purely vegetative bioengineering techniques. And if we can do that, that's absolutely what we need to do. The problem is, to me, it's like, I think of this in the bell curve world, that those two extremes, the full riprap armor on one end of the tail of the bell curve, and then the purely vegetative bioengineering represents the other tail. Now I don't know if that's two standard deviations off the mean or what, but it's a tail. Those are not the most common stabilization applications we have.

Stanford [00:40:07]:
At least they're not the most common that work. Right?

David [00:40:10]:
Yeah. Thank you. That's the whole point. In between those, there's this gulf of projects that, and most of the ones that we get involved with the core are really going to be pretty severe erosion projects. You know, we've got 20 foot high banks. Erosion rates are 3410ft per year. And you're going to have to have some structure in there and you can then do some hybridization structures like longitudinal stone toe and do vegetative work above that. And, but the problem is we have these, these two extreme groups. Sometimes you got the rock hounds on the right and the veg hounds on the left that, you know, all they see is every, every project is going to be fixed with either the full bank rock or the vegetation. And that's just not the way it should be. And so, so you can't just take vegetation bioengineering alone and apply it to most projects. There are places where it will work, but most of the places I get involved with, it's not going to be successful.

Stanford [00:41:16]:
Right.

David [00:41:16]:
But the point would be if you can use the rock and use as little amount of the stone as you have to, if you can use the vegetation to provide some of that additional stabilization. So maybe you can get by with, you know, two tons per foot of a stone toe versus five tons because you're gonna, you're gonna get some vegetation to help you because, you know, mother nature and vegetation can, can really provide some benefit to you by itself. It may not work in most of these cases, but I see that as a problem. I see that happening a lot, that people latch on to a technique and it's like they're a hammer and the whole world's a nail to them.

Stanford [00:41:57]:
Yeah.

David [00:41:58]:
And they come and they want to push their technique on you. And these techniques, there's a place for all of them, but they're not universally applicable everywhere and that's the key thing. And then understanding how to select the appropriate stabilization technique is a really important part of our design process.

Stanford [00:42:21]:
One of the things I feel like I've learned from you and Chris Herring and David May is we have to be really careful of ideology in this particular aspect because I think that it could be really easy to become a, well, rock's the only thing that works, person or a, you know, the core used to do rock, but now we do vegetation person. Right. Like, and there are just some, there's some basic math that has to be involved, but also we want to be as green as we can, and rock often is very bad for habitat.

David [00:42:52]:
Right.

Stanford [00:42:53]:
And so this idea that a good modern project, we'll do the math and the physics to figure out what materials actually are going to resist the forces or redirect the forces, and then we'll accentuate that with modern bioengineering as much as possible to add additional strength and of course the habitat. And that's where most of our projects fall. That's kind of been a really helpful framework for me.

David [00:43:17]:
You mentioned something a while ago made me think Stanford in restoration and applying different techniques. I see this a lot, and it always sort of bothers me that we're restoring streams and we talk about, we all know, restoration. There's different types and there's pure restoration, taking it back to some previous condition or maybe just doing some rehabilitation type work, trying to improve things. But we're often criticized in the core because we're using stone. We're the rock hounds. We want to stabilize everything with stone. So then you have this group that's okay, well, we're going to restore the streams and we're going to use vegetation and we're going to use stone and root wads, and all of a sudden it's like, that's just fine. And. But the problem is that if that technique works, you've stopped that meander from ever meandering again.

Stanford [00:44:19]:
Yeah, right.

David [00:44:19]:
I, and no matter what you do, whether you, whether you stop that erosion with root wads or rip rap, the stream bank doesn't know it. It just knows it ain't moving anymore. And we've taken away a major degree of freedom from the stream geomorphically. It's never going to meander again. And to me, that is probably more devastating than just about anything we do to streams. And so as a consequence, I'm very hesitant about just willy nilly jumping in and stabilizing streams. And speaking of someone who's probably responsible for putting more rock in streams than most of us, but I have more caution about it, and I don't think we should go in and do bank stabilization in streams unless it's absolutely necessary. Because once you have decided that you're going to stabilize a meander on a stream, you've bought it, it's yours. And if you've got a local bank that you're going to protect, you're going to protect the farmers bank, the highway or whatever. More than likely, you're not going to just have to protect that bank. You're going to have to go to the meander upstream or the meander downstream. So now you may be moving beyond your initial project boundary.

Stanford [00:45:43]:
That's interesting. It sounds to me like you're saying that we have this continuum between rock and vegetation, and there's often a debate of how are we going to stabilize this bank. Should we use vegetation, should we use rock? Or is it some sort of hybrid method? But null hypothesis should be do we have to stabilize this bank or is there a way to live with this river and let the river be the river?

David [00:46:06]:
Right. Whenever you do a stream bank stabilization project, you have to think about several things, is always a no work alternative. What happens if we don't do anything? Okay, the streams don't take out the water treatment plant. The other option is we can move the water treatment plant and it has to be something to think about, move the facility. And that in some cases is the preferred solution. The other is move the stream. Yeah, sometimes we have to move the stream and, but that comes with potential responses we have to think about. And the third is stabilize the stream and protect the stream. And that's, but when you, in all of those, if you move the facility, that's usually, you know, morphologically not going to be a big deal for the stream. If you move the stream, you've got some issues to consider, and if you stabilize the stream, you've got some morphological issues to consider. So that's, that's sort of the thought process I go through and I think about, and now that we're talking about stabilization, I, I think about the three e's. Okay. Whenever we.

Stanford [00:47:18]:
I haven't heard the three e's.

David [00:47:19]:
I just made it up right now. No, no, I didn't.

Stanford [00:47:24]:
No, I wouldn't believe that.

David [00:47:26]:
Yeah, I know. No, I think when we do stabilization, any kind of, any kind of project, it has to be economically feasible, have to be able to afford it, it has to be environmentally feasible and it has to be effective. And sometimes we really try to focus on low cost and we can, I can think of projects where we've tried to go as low cost as possible and if we really get a cheap project and it may even be environmentally great, we go in with pure vegetation. But if it doesn't work, then what's the use? And so that's the way I have to think about it. You want to think about those three e's and it has to meet them all. You know, we want to be an effective and stop. And maybe if it's stream bank civilization. We want to stop that erosion. And how can we stop it but also be environmentally, you know, responsible. But also not bust the bank.

Stanford [00:48:33]:
That's right.

David [00:48:33]:
And so how do we weave all those three together? And that's kind of the thought process I go to.

Stanford [00:48:44]:
So I could literally talk to David for hours. And I know that because I did. So we split this conversation into two episodes. The rest of the conversation as the final episode of season one. Because it hits some themes that wrap up this project really nicely.

Stanford [00:48:57]:
And we may have to talk to.

Stanford [00:48:58]:
Him again in the future. Because as soon as we stopped recording. I immediately thought of five more things I wanted to talk to him about. So go ahead and subscribe to this feed. Because we have a great lineup of these conversations for you. Including an excellent conversation with Molly Wood. Up next. Molly oversees the US Geological Survey sediment data program. And is just an endless source of insight. Really fun and helpful conversation. We're also posting some bonus content. Video shorts of clips and cuts from these conversations. So bookmark the website in the description. And check out the HCC sediment YouTube channel throughout the run of this podcast. This podcast was funded by the regional Sediment management program of the Corps of Engineers. And is part of their tech transfer initiative portfolio called RSMU. We also received funding from the Corps Flood and Coastal Storm Damage Reduction R and D program. And the H agency set program. These are informal conversations. And the views expressed do not necessarily reflect the positions. Of the US Army Corps of Engineers, their partners, or the offices or centers of the guests or host Mike Loretto edited this episode and wrote the music for the season. Thanks for tuning in to episode one.