Stanford [00:00:13]: Sometime late in 2020, when we were all in the early days of COVID I got an email from my friend Calvin Creech with a spammy sounding subject line that read something like have you seen this? But I opened the email anyways and honestly I couldnt believe I hadnt seen it. The email included early drone footage of a canyon that was more than 80 meters deep and several kilometers long, but it was only a few months old. It was the riococa, one of the large Amazon headwater rivers in eastern Ecuador. Nothing in my morphological imagination could concoct a process story to explain this massive erosion event, but in retrospect, I dont feel that bad that I couldnt figure out what caused this erosion, because nothing quite like this has happened in the anthropocene. The Rio coca regressive erosion may be the morphological event of my generation, but because it happened in February 2020, it never cracked a single news cycle. And even most geomorphologists and river scientists I talk to still haven't heard about it. So in this special bonus episode, we're. Stanford [00:01:12]: Going to fix that. Stanford [00:01:14]: I'm talking to two ecuadorian engineers who have been at the center of the Riococa story from the beginning. Pablo Espinosa Gerano is the lead of the studies, design, and monitoring division of the Special Riococa Commission that's part of the Corporation Electrica de Ecuador, Ecuador's energy corporation, which we will just call select. Pedro David Berea Crespo is the morphological modeler who's been working for this select special commission from the beginning and is an excellent project engineer with a broad understanding of the processes and timeline. Pablo did his graduate work at the University of Illinois, Urbana, and Pedro did his Adelph. And there's just no one better than. Stanford [00:01:49]: These two guys to tell this story from a robot mechanics point of view. Stanford [00:01:52]: Just a note, whenever a podcast has multiple guests, it can be difficult to distinguish the voices. So Pedro is the first to speak, and Pablo's voice follows shortly. I'm Stanford Gibson, the sediment transport specialist at the US Army Corps of Engineers Hydrologic Engineering center. And on this episode of the RSM River Mechanics podcast, I talked to Pablo Espinosa Heron and Pedro David Barrea Crespo about more sediment erosion than most of us can even imagine. A conversation about the Rio Coca. Stanford [00:02:24]: Pedro and Pablo, welcome to the podcast. Pedro [00:02:26]: Thank you very much for having us. Pablo [00:02:28]: Thanks, Stanford. It's an honor for us. Stanford [00:02:31]: So can you describe the San Rafael waterfall before 2020? Pedro [00:02:36]: So the San Rafael waterfall was really one of the key side visit points in Ecuador. So it was actually like, advertised internationally along with the Galapagos island, which is also like one of the spots to visit here in Ecuador. Stanford [00:02:52]: Right. Pedro [00:02:53]: So the San Rafael Falls was one of them. Stanford [00:02:56]: So I'm planning to take my family here to Ecuador for a vacation this summer. And the guidebook I have has the San Rafael waterfall on it. How many people would visit it in a year? Pablo [00:03:08]: I would say tens of thousands per year. Stanford [00:03:10]: Tens of thousands would visit it. Pablo [00:03:12]: 20,000 visitors per year. Stanford [00:03:14]: And how big was it? Pedro [00:03:16]: So it was impressive. It was like 150 meters tall. Stanford [00:03:21]: 150 meters tall. That's like 450ft, right? Pablo [00:03:25]: Basically, yeah. Stanford [00:03:26]: Right. Pablo [00:03:26]: Yeah. Pedro [00:03:27]: Our audience is like in the us unit, so. Stanford [00:03:32]: Sorry, we're using a better unit system here. Yeah. Okay. So a lot of things happened in February and March 2020. That's when Covid kind of erupted, which is probably the only reason this didn't hit the news. But what happened in February 2020, the. Pablo [00:03:50]: Water of the Coca river, because the San Rafael waterfall is the Coca river, started to find a way near to the left bank of the waterfall. And it started a piping process and it ended in the failure of the waterfall. So the waterfall collapsed. The whole water started to get beneath this lava dam, which is formed. And right now, after that, we saw the riverbed 150 meters below this arch. That was the former waterfall. Stanford [00:04:28]: So the waterfall was just a very thin sliver of basalt, basically. And it wasn't continuous all the way down. And so the water found a pathway under the dam and just failed it. The water level dropped 150 meters. Pedro [00:04:45]: Yeah. So maybe a little bit of a context. Stanford [00:04:48]: Yeah, please, where we are. Tell us a little bit about Reventador. Pedro [00:04:52]: Yeah, so the area we're talking about is in the Amazon region. It's like right at the edge where the Amazon starts. And so there's like this active volcano there that is called the Reventador volcano. Stanford [00:05:07]: I just think that's the best volcano name ever. We were just there and it erupted. Pablo [00:05:14]: It always owners hear his name. Stanford [00:05:18]: What does Rventador mean? Pedro [00:05:20]: Yeah, it means like blasting volcano. So that is exactly like the actual translation as Reventador. So the reventador volcano is sited really close to the Coca river, which is one of our major rivers here in Ecuador. That actually drives the whole geomorphology of the area. The volcano is. Is like the key player in all of the problems that unravel after the collapse of the waterfall. So historically, this volcano erupted and one of these lava flows that came out of those eruptions, they basically closed the rivers. One of those lava flow down the river. And that triggered a process of sedimentation upstream of this, of this lava dam that eventually with time got filled with sediment and also due to some volcanic processes along the way that fill this reservoir. So to say it was completely filled with sediment. So the riverbed aggraded and then, yeah, you get like this, 150 meters, fall right downstream of this, of this lava dam. Stanford [00:06:33]: So you have this giant lava dam, 150 meters and it's completely full of different kinds of volcanic sediment. The preventive door actually avalanched into it and you have debris flows. You know, it's as if you had a reservoir, but the reservoir has been there like maybe 19,000 years. So even though the reservoir is huge, it's entirely full of sediment. And then you have the world's largest dam removal. Basically what happened? What was the first few months like? Pedro [00:07:02]: Actually there needs to be a bit of more context. Stanford [00:07:05]: That's right. Pedro [00:07:06]: What type of infrastructure we have over there. Stanford [00:07:09]: Yes. Pedro [00:07:09]: So the site, in spite being near a volcano, one of the largest rivers here in Ecuador. We have a major part of our key infrastructure placed in that site. This infrastructure actually comprises of oil pipes, electrical transmission lines, pumping stations for the oil and also like the largest hydroelectric project here in Ecuador. Stanford [00:07:39]: So because this is a really thin corridor, it's the main road between the Amazon region and Quito. All the oil pipelines go through. All the electrical pipelines go through. But Pablo, what is this thing that's 20 km upstream of the lava dam? Pablo [00:07:55]: So we have the intake for the biggest power plant in Ecuador. It basically gives us 30% of the electrical demand of the whole country, which is big for us. It's a 1500 megawatts power plant. The first month after the collapse, the regressive erosion process started at a very high rate. Basically it advanced 8 km in the first six months, which suggested at that time, suggested us that we will lose, or we would lose the intake in one and a half year. Stanford [00:08:37]: So you have 20 km upstream of this failed lava dam, you have a power plant that produces 30% of Ecuador's power. Pablo [00:08:46]: Yes. Not the power plant, intake for the power plant. The intake. And then the intake takes the water from the coca river to the power plant through a 25 kilometer tunnel. So if we lose the intake, we will have the power plant without water. Stanford [00:09:02]: Right. Pablo [00:09:02]: So useless. Stanford [00:09:03]: So it's a mandatory part of the power plant. Pablo [00:09:06]: Of course. Stanford [00:09:06]: Totally 20 km upstream. And in the first few months you have what we call regressive erosion or essentially a head cut goes 8 km upstream. Pablo [00:09:17]: Yeah, but it's not like just a. I mean, it's 150 meters, right. So no structure could face these kind of heads. Stanford [00:09:29]: That's right. So just to give a little context for people who might be listening, we've talked about headcuts in a couple of these episodes. David Beat talked about headcuts and we talked about some really dramatic headcuts in Mississippi that are like two people tall. So we're talking about like a six meter head cut or something like that. And those are big headcuts. And this is like a discontinuity, works its way upstream and causes erosion. The reason we're using this term regressive erosion is because it's just a different scale. Can you maybe draw the picture for us of what it looks like out there? Pablo [00:10:03]: It looks like the Grand Canyon. Pedro [00:10:06]: Yeah, that is exactly what I was gonna say. Basically like the Grand Canyon of Ecuador. What is. Pablo [00:10:14]: Yes, because of the, like the nature of these sediments, like sand and gravels and other non consolidated materials. So the riverbed is decreasing their level. And of course the slopes are really unstable and the valley has widened it a lot. Stanford [00:10:34]: So what's the widest the valley has gotten? Pedro [00:10:37]: So as Pablo mentioned, so the river is not only incising it, but once incising starts, then the banks get unstable. That's right, they get unstable and they collapse into the river course. And so then the river flashes all that's the sediment downstream. And that causes like the valley to widen dramatically. I would say like in the more critical zone, the biological, the width of the valley has widened about, I don't know, maybe 500 meters, 600 meters. Stanford [00:11:10]: That's right. I mean, it looks close to a kilometer in some places. We'll run some of these clips with some images so that people can get a sense of it. But if you try to imagine eight football fields, whether american football or real football, wide, 150 meters deep. So we talked about the first few months, what's the status now? How far has the headcut moved and how much sediment in total has been eroded? Pablo [00:11:34]: The headcut or the erosion from, as we call it here in Ecuador, has advanced 12 km. Stanford [00:11:43]: Approximately twelve of the 20. Pablo [00:11:45]: Yeah, twelve of the 20. So we are just 8 km away, which if you compare the rates, it's 1st 8 km in six months and then two and a half years the other 4 km. So the rate has decreased dramatically, which is good for us. Yes, it's very good for the country and for us. For like XleC, which is the electrical company of Ecuador. And the amount of sediment that has. Pedro [00:12:15]: Been eroded is 200 million, 250 million sediment have been released. Stanford [00:12:24]: So in 250, you know, if you use a density of like 1400 or something like that. Stanford [00:12:29]: We're talking about 300 to 350 million tons. Pablo [00:12:34]: Yes. Stanford [00:12:34]: Okay. So a few episodes ago, I talked to Chris Nygaard, who's actually here with us right now. About the srs. The sediment retention structure. That's holding all of the sediment that has come down off of Mount St. Helens. That holds 200 million tons of sediment. So the Rio coca has essentially eroded twice as much of that in the last three years. Pablo [00:12:59]: Yeah, basically that is like the biggest quantity effect of this process. But we have had major infrastructure damages as well. The oil pipes, they are very important for the country. Because we are an oil producer country. And the road is closed since December last year. And also communities and lands. And the environmental damage is serious as well. Stanford [00:13:27]: For example, the road is the main way to get from Quito to the Amazon. Now you have. Pablo [00:13:32]: It's the fastest way to get to the north of the Amazon. Stanford [00:13:34]: And so now you have to go around. How much time does that add to. Pablo [00:13:37]: That trip before the waterfall collapse. To get to this important city. That is called Lago Agrio. In the eastern north part of Ecuador. It would take like 3 hours from Quito. And right now it's more than probably 10 hours and hours. Pedro [00:13:53]: Due to the unraveling of the headquarters and the regressive erosion. The power plant, which is the largest one here in Ecuador. Faces basically two problems. Stanford [00:14:01]: Yes. Pedro [00:14:02]: So the first one, as you guys were discussing it earlier. Is related to the fact that the headquarters might reach the intake structure, the power plant. And so. And then it could be undermined. Stanford [00:14:15]: That's right. Pedro [00:14:16]: I basically the diversion structure that is constructed there could be undermined. And the other problem is that basically 40 km downstream of the former side of the waterfall. Is where the outflow of the power plant is. Stanford [00:14:31]: This can be hard for people to visualize. And so what you have to understand is there's a big bend in the Rio Coca here. Which is why it's a great place for hydroelectric. Because you intake upstream of the waterfall. It goes through the mountain. It generates the electricity. And then the outlet is downstream of the waterfall. Which is a great design for hydroelectric. But it exposes it to both of these problems. Right, right. Pedro [00:14:54]: And so, yeah, the second problem is related to the fact that this whole release of sediment. So this pulse of sediment is traveling downstream. And if it has the potential to reach the outflow location. And actually increase the bed levels of the river in such manner that the turbine water from the power plant cannot be discharged back into the river. Stanford [00:15:18]: So you have the inlet upstream, which could be affected by the erosion, and you have the outlet downstream, which could be buried by the deposition, essentially, for the project that produces 30% of Ecuador's power, correct? Pablo [00:15:32]: Yeah. In a very, like, easy way to put it, is we have two major problems, the Chronicle and the acute problem. Yes, and the chronicle problem is the deposition. And the acute problem is to save the intake, to prevent the intake to be taken by the head. Stanford [00:15:49]: So if the Rio coca was to go to the doctor, the doctor would say, you have to take care of the erosion right now, but you also have to make some healthy eating habits because you've got this chronic problem that's going to come to get you later. Pablo [00:16:03]: And both of these problems can kill you for sure. Stanford [00:16:06]: For sure. Yes, yes. So you mentioned that the regressive erosion has slowed down. When we first heard of this problem, we thought, there's no way to stop that, but it has slowed down. Why did the river slow down? Pedro [00:16:21]: Due to the configuration of the geological strata of the river, you can find some sections that are harder to erode than others. So all the sediment that was released during the first months, it was really like really loose, fine sediment that was. Stanford [00:16:41]: Really easy to erode those first few kilometers. Where did that sediment come from? Pedro [00:16:46]: Well, that sediment basically stems from the activity of the avalanche. Stanford [00:16:53]: It's just avalanche. So it's just like loose, unconsolidated, and really easy to erode. Pedro [00:16:58]: The reventador events that created all this sediment is comparable to what happened with the St. Helens. Pablo [00:17:06]: Mountain Helens. Pedro [00:17:07]: Mountain Helens, exactly. So it basically was a sequence of flank failures of the Reventador volcano that created all this whole mass of sediment that basically clogged the river course and created all this sedimentation upstream of the dam. Stanford [00:17:29]: So if you look at the Raventador volcano in like a Tahoe map or Google Earth, it's not a symmetrical volcano. You can actually see where a large part of it has sloughed off towards the river. And it's just all that really loose avalanche stuff that was first, that eroded through first. But then what did it get to that slowed it down? Pedro [00:17:45]: Well, basically, there's not like one of these flank failures of end. Stanford [00:17:51]: Yeah. Pedro [00:17:51]: Historically, those flank failures probably happen more than twice. Stanford [00:17:56]: Okay. Stanford [00:17:56]: Yeah. Pedro [00:17:57]: So you get really all deposits that with time, get consolidated. Stanford [00:18:01]: Okay. Pedro [00:18:02]: And those deposits have helped slowing down the regressive erosion progress upstream. Stanford [00:18:08]: So earlier avalanches that had been consolidated and had a little bit more strength to them. Pedro [00:18:13]: Exactly. Stanford [00:18:14]: And then on the back end of. Stanford [00:18:15]: The reventador, it's been sending down these debris flows which essentially like natural grade control, right? Pedro [00:18:23]: Yeah. So the volcano is very active. Yeah, it's very active and it keeps sending out material and material, materials. So we were lucky in our last visits. We used time for that to see an actual eruption of the volcano. Stanford [00:18:40]: That's right, yeah. It's very impressive. So there is evidence in the historical record of lava dams breaking. We already mentioned the Grand Canyons, but kind of the most famous eroded lava dams are in the Grand Canyon. You can see the evidence that they were there, that they actually backed up the Grand Canyon. The Grand Canyon filled with sediment, they eroded and it was very similar. But this happened in geologic time. Stanford [00:19:07]: The idea that this would happen in. Stanford [00:19:09]: Historical time, four years after you built a dam, it's hard for me to imagine. I've been on the record to say if I was the project engineer, this is into failure mode. I would have evaluated what are the. Pablo [00:19:19]: Chances to lose your dam in like 50 year lifespan of a project. Yeah. Of this project. If the waterfall is there for 19,000. Stanford [00:19:33]: Years, you can actually compute those odds. But the waterfall wasn't static. Stanford [00:19:38]: There was some evidence that the waterfall was changing. Stanford [00:19:41]: Can you tell us a little bit about that? Pedro [00:19:42]: Geological studies have been carried out. Yeah, carried out around the waterfall and its history. And what they tell us that initially the waterfall was actually taller. It wasn't just 150 meters, but it was taller than that, maybe twice, twice as tall. Stanford [00:19:59]: And we were surprised by this because when we were in the field, we actually saw, because you can see the whole stratigraphy, because the whole wall is bare now. And you can see alluvial deposits well above the pre collapse elevation. So it was moving in time, you know, not human time, but in geologic time. Pedro [00:20:17]: Right, yeah, yeah. And as you mentioned, that evidence of that are like alluvial layers that you can see at different levels. Stanford [00:20:27]: Yeah, yeah. Pedro [00:20:28]: So, yeah. That is also related to the activity, which is very active. Stanford [00:20:34]: Yeah. Stanford [00:20:36]: So the location of the erosion front has been nonlinear. In fact, it stalled for a couple years when it hit this debris flow. But the actual volume of sediment eroded has been pretty linear. It's been pretty constant. What accounts for that difference? The river has slowed down the upward erosion and even the downward erosion. But you're still getting lots of sediment eroded downstream. Pedro [00:21:04]: Well, I think it comes to the fact that the nature of the sediment is being released. So what's being released constantly is this fine sediment right now. And what's being held back is basically, like the bulk of the. Of the sediment that was released, that is not fine. Right. So coarse material is traveling downstream, but. But in, like in another timescale that the fine sediment. Stanford [00:21:32]: Yeah. Pablo [00:21:33]: Also the erosion front is not progressing towards the intake, but the riverbed is still decreasing. The riverbed level, it's always lower and lower. And that's why we have so many landslides in the valley. Stanford [00:21:50]: And then the landslides, what are they doing? Pedro [00:21:54]: They are just adding more sediment to the system. Basically. Stanford [00:22:00]: It's not moving upstream as fast, but it's moving down and out. Yes. We call this the channel evolution model. Right. Is that we've never seen it so dramatically, but you get a base level change, you get erosion and then you just keep moving outward. Our colleague Paul Boyd, who's here with us too, he likes to say that it erodes to the skylights. Pablo [00:22:23]: Really? Stanford [00:22:24]: It does it daylight with the valley, the canyon. Yeah. Pedro [00:22:27]: And that is also like a problem for all the tributaries that joined the river in its course. So this erosion like it is not only related to the Coca river, but also to the tributaries. I mean, this is propagating option of those tributarian courses as well. Pablo [00:22:45]: And the erosion in the tributary is dramatic as well. Yeah, I mean, they have contributed with million tons of sediment and it's basically the same material as the Coca river. Stanford [00:22:56]: So what's the tributary that's eroded the most? Pablo [00:22:59]: I think it's the Montana. We've lost two bridges there. Stanford [00:23:04]: And so it's really the tributary erosion that's taken out the roads. If just the Petrophena was the regressive erosion event, it would be the biggest erosion event I'd ever seen. I think that's really critical to think about, how base level change doesn't just affect the main channel, but it'll spread out almost like an octopus, because all of the tributaries are going to have to return to that grade. Pablo [00:23:30]: Yes, yes. And we have seen like a couple, like waterfalls. Minor, of course, is not as big as the former San Rafael, but waterfalls like 20, 30 meters that last for a couple weeks and then it starts eroding. So, for example, the Piedrafina was. It was like, formed this water for like 20 meters and it was just a couple weeks. And then you lost the bridge, you lost the road, you lost like the. Everything there. Pedro [00:24:02]: Yeah. And during the early days when the erosion just started, they were planning to place the pipe somewhere else. Stanford [00:24:11]: The oil pipes. Pedro [00:24:12]: The oil pipes that run like along the river. They were planning to place them elsewhere, but really close to the former location. But they didn't realize that this erosion, as you say, was going to propagate through the tributaries. And so once that, I mean, they did replace the pipes with another pipeline, like, just right next to the former one, and then that one got damaged due to the propagation of the erosion. So they just decided to move the whole pipe. Stanford [00:24:45]: Now the pipelines go over the mountain. They just go over the mountain totally away from the. Stanford [00:24:48]: Yeah. Pablo [00:24:49]: And they have to be, like, very quick in those repairing actions because they are millions of oil barrels without being, like, pump and then transport to the coast and then sold overseas. Stanford [00:25:03]: So you can't be out of production for any amount of time. Yeah. And then there's also the environmental challenge of pipelines eroding. I guess one question that I have is, we've never seen anything like this, a generational event. One of the things I like to say is Mount St. Helens was the generational morphological event of the last generation. This is the morphological event of our generation. By watching this happen at such a grand scale, are there things that we can learn about normal rivers and how normal rivers work? Are there transferable lessons? Pedro [00:25:38]: Beware of volcanic environments. Stanford [00:25:42]: Volcanic environments are very dynamic. Pedro [00:25:45]: That is a real big problem here in Ecuador, because the whole city of Quito, which is the capital of Ecuador, is placed in this volcanic environment. It is surrounded by volcanoes, and the riverbeds actually run through similar environments of that of the Koka river. So it could potentially be a big problem here in Quito as well. I mean, you get some really steep slopes in the, in the. In the river. You know, they were like tributaries as well. And, like, at the end of those tributaries, like, at the end reach of those tributaries, they get really steep. That is a fact of, of that. This is also volcanic environment. Stanford [00:26:27]: Yeah. Pedro [00:26:28]: And, yeah, luckily, I mean, the discharges of these rivers are not even comparable to the discharge of the coca. Stanford [00:26:35]: The coca. Pedro [00:26:36]: So that, I think that is what. What has been holding things here together. Stanford [00:26:42]: One of the things that I learned, I just learned this week is that downstream, in the depositional zone, we saw a lot of bank failures. And that didn't make any sense to me because I thought, oh, it makes sense in the upstream that you're going to erode, and with the channel evolution model, you're going to induce bank failures. But that downstream, when you're depositing, it seems like it would protect the toe. You would get less avalanches, less bank failures. But a couple of the folks we were with, Chris Nygaard and Amy east, said, oh, no, we see this all the time in depositional environments, because when you overload a channel, the channel fills and the river starts going back and forth across the full floodplain to try to find itself and ends up impinged against the bank, and you actually get more landslides in a regressively depositional environment. That's something I've never seen, because I've never seen it in this aggressive manner. But I think that's something that's transferable to actual rivers. Pablo [00:27:35]: Yeah, I mean, it's a very dynamic process, like, like you said, and I would like to say not to be, like, so confident about whatever you do, you can do more. There's never, like, so much redundancy. I mean, for example, we have had, like, small periods where the erosion front or the headcut stopped, like, for like, a month or a couple months. Stanford [00:27:59]: Yeah. Pablo [00:27:59]: So we said, okay, we should be okay by now. And then we have to start all over again from zero, from scratch. To do some protection works. As many things you can do, the better. Stanford [00:28:14]: Yeah, I think that's the biggest thing that I've learned. The way that I sometimes have thought about it is that base level is destiny. That water is so powerful that if you change the base level, the river will take its original grade. It might take shorter time or it might take longer time, but eventually, base level is destiny. The river will find the new grade, and it doesn't need to be a flood. One of the interesting things is that I don't think that it's necessarily the. Stanford [00:28:42]: Biggest flows that are doing the erosion. Stanford [00:28:44]: It's more time above threshold that if you get these moderate flows, a few moderate flows, because the slope is so steep, do more work than one big flow. And so those are some of the things that, on that theme of don't underestimate the river is when you change base level so much, you can't necessarily trust your intuition about what the river will do. Pedro [00:29:07]: Yeah, totally. And that is, like, one of the main problems we're facing is how to predict whether, if it's going to reach or not the infrastructure that we need to protect. Stanford [00:29:21]: Because, Pedro, you've developed unbelievably good numerical models of this. You've developed an excellent Delft 3D numerical model that's just about as good as the model can be. But we're outside of the realm of things that have happened before, and so we have to interpret that cautiously as well. Pedro [00:29:38]: Yeah. So we're, like, at the edge of the knowledge. Stanford [00:29:43]: That's right. Pablo [00:29:44]: State of the art. Stanford [00:29:46]: Well, Pedro and Pablo you have an excellent team here and we've just been delighted to be involved and it is the event of our generation, and I just really appreciate you taking some time to tell everyone about it. Pablo [00:29:59]: Thank you very much. Pedro [00:29:59]: Thank you very much, Stanford. We really appreciate also the whole team, the whole USA team that is working here with us. And yeah, you bring a whole lot of experience and that has really helped us as well. Thank you very much. Stanford [00:30:13]: Thanks a lot. Pablo [00:30:14]: It's an honor for us to have you here, like every six months, let's say, and learn from you, of course, and learn from what you have to say about it. And, I mean, we have to win. We have to save the intake. Pedro [00:30:32]: Yeah. Stanford [00:30:33]: All right. Well, thanks a lot, guys. Pedro [00:30:34]: Thank you. Stanford [00:30:37]: I really appreciate Pablo and Pedro coming onto the podcast and talking to us about the science of their system. While some of the other guest names on this podcast might be more recognizable, the work that Pedro and Pablo are doing with the rest of the special commission team puts them in rare company. The scale, scope, scrutiny and stakes of Select's day to day morphological decisions are historic. They are practicing the principles of our discipline in an unprecedented moment in morphological history, and I really appreciate them sharing some of what theyve learned. Of all the episodes weve recorded, the processes in this episode may be the most difficult to visualize from an audio format. So I will be combining some of the clips of this conversation with some footage from the Rio Coco regressive erosion and posting them to the podcast website. The links to that website and other videos from previous episodes are in the podcast. Notes we have one episode left in this season, so well be back in a couple weeks with the second part of my conversation with Doctor David Beatnharten. These are informal conversations, and the views expressed by the host and guests do not necessarily reflect the positions of the US Army Corps of Engineers, the corporation Electrica del Ecuador, or any of their offices or partners. Michael Loretto mixed this episode and wrote the music for this season. Thanks for listening. Pablo [00:31:50]: The. Stanford [00:31:59]: Channel.