Hey Reddit! I work as a civil in dam safety many many states away. I also happen to work in failure modes and risk assessments of dams.
This is not a professional report, These claims are speculative and are only meant as a theory for understanding. Information was gathered from the internet and local county pages. Riverflow data from USGS. Use this information at your own discretion please.
**IMMINENT FAILURE DEFENITION:** ***A dam emergency has caused conditions that may lead to a dam failure. This does not mean the dam will fail for certain, but it means that everyone should prepare for it. Essentially, imminent failure is the last emergency action term used before FAILURE.***
Quick Facts:
Constructed: 1910
Dam Type: Hollow Concrete Dam (Amberson style)
Current Ownership: Blue Earth County
Nameplate Energy Generation: 5.5 Megawatts (2-3,000 homes)
Generation Maximum Flow Capacity: 1200 CFS (cubic feet per second)
Maximum Spillway Capacity: Unknown, but has successfully passed 43,000 CFS in history. I conservatively assume that the dam was designed to pass at least 40,000 CFS.
Blue Earth River 100-year Flood: \~35,000 CFS (cubic Feet per Second)
Flood of Record (largest flood the dam has ever seen): \~43,000 CFS in 1965 (this is a 500-year flood)
Current Max Flow (June 23-24th 2024): 35,000 CFS
**Theory on Dam Failure (SPECULATION from news, experience, and past dam failures):**
It appears that the blue river from USGS data is currently flowing at \~35,000 CFS. This should not be an issue for the dam, as it has seen such flows before. However, it appears that woody debris has built up and blocked the tainter gates (the radial spillway gates) and reduced the amount of water they can pass.
Debris has traditionally been low on this river, and trash has been removed at rapian by hand rake or by excavator. In large flood events, however, large quantities of debris will suddenly overwhelm a river. I am not aware of upstream debris booms, or other catchment techniques that are utilized, but there is not a modern or automated debris removal system capable of large debris inflows. Debris blocking spillway channels can cause their effective flow discharge to decrease by anywhere from 5-50% (sometimes more), especially for these relatively shallow tainter gates at Rapidan. Meaning the dam in a debris blocked state may have only been capable of passing 20k CFS. An insignificant amount of water can be passed through the powerhouse, so relieving pressure through the powerhouse is not an option.
In addition, the reservoir behind rapidan is not very large, and cannot “absorb” an incoming flood very well. Therefore, blockage in the spillway caused the water level of the reservoir to rise quickly. This may have happened so quickly that operators did not have sufficient time to respond. We're talking hours perhaps even minutes based on inflow. Water levels raised, and water breached the left levy, and quickly eroded and cut a channel.
From news observations it appears that the left abutment (the dam's left foundation) is founded and wedged in competent rock and may hold, but we will see how things play out. What’s most important at this point in time is that the left abutment holds and stays wedged into the rock. The right abutment appears to be in fine condition.
This was most likely a preventable disaster. This flood event occurred over multiple days, and measures could have been taken to prevent the buildup of debris. I think that an over-the-weekend flood and perhaps some negligence caused the owner to not be prepared for the clearing of debris, and it overwhelmed the project quickly.
I send my best wishes to those in the immediate area. Please follow evacuation orders and stick to them, in the case of a dam failure there could be a very large inflow and flood.
....
EDIT: Best guess at root cause based on available information:
There was an upstream debris boom that failed located under the glacier road bridge. There was only one boom that I am aware of, and the cable or anchor must have given out. That would technically be the root cause of this dam emergency.
100 year flood event -> debris buildup at upstream boom (under bridge) -> debris boom failure from loading -> severe blockage of the tainter gates limiting flow -> water level raised above left abutment height -> erosion of left abutment into channel.
Having been to rapidan Dam a lot there’s a highway bridge a few hundred feet upstream. Along that bridge’s supports there’s a large cable and bouys for catching debris. I was at the dam the day before and there were tons of trees being held by that cable. Judging by that big dip at 9-10 pm in the flow I’d say the cable broke and blocked the gates. In 2019 during the spring melt there was another large flood. That flood flooded the power house with 8 feet of water. Though with that flood they had some equipment out to remove the trees. So who knows. I believe the dam is rated for about 50,000 CFS
ah thank you! so the debris boom failed leading to spillway blockage. **Debris boom failure was therefore the first root cause.** and 50k cfs rating seems about right! slowly gathering more info so I appreciate the insight.
Ive been looking at some studies you might find interesting. Theres a long history of scouring and apron damage at this Dam. [2021-Rapidan-Dam-Repair-Feasibility-Study\_Nov\_2021\_Final (blueearthcountymn.gov)](https://www.blueearthcountymn.gov/DocumentCenter/View/6959/2021-Rapidan-Dam-Repair-Feasibility-Study_Nov_2021_Final) Apparently the designed spillway capacity ranges from 41.900 CFS to 105,000 CFS.
This another older study by the Army Corp [091055.pdf (mn.gov)](https://www.lrl.mn.gov/docs/2009/mandated/091055.pdf)
I’m just fascinated by this. I’d always visit this dam as a kid. I’d made some comments when they did the study’s a few years ago. Never did I think this would ever happen. I’d love to hear your thoughts on those studies if you have the time!
I took a glance today, some interesting information. Something that is worth noting is the dam is keyed into the surrounding bedrock, which is a very positive factor for resilience to failure at this point. So the left abutment is pretty robust in my opinion.
Absolutely fascinating reading and rather awesome that you found these studies.
Many thanks indeed for helping me to understand the dam site and make sense of the dramatic video yesterday of the floods cutting through the left side of the bank.
Is there any reason why they don't try to pull some of the debris out at this time? If you had a crane on the other side, you could at least pull the logs out.
Thank you for your professional insight, worth sorting by new for.
I see from Wikipedia that [this dam was already being considered for removal by the county in 2021 and 2022](https://en.wikipedia.org/wiki/Rapidan_Dam); assuming the left thrust block remains intact and survives this emergency, will demolition be the best option moving forward?
Based on the rough recover cost (at least 5 million) and the income it generates (low in comparison), its unlikely it will be restored. I would assume removal at this point but you never know.
I'm sure this isn't news to you but I just found the water gage graph immediately downstream:
https://waterdata.usgs.gov/monitoring-location/05320000/#parameterCode=00060&period=P30D&showMedian=false
I assume the current peak is the bank failure, and a total structure failure would be higher still, so hasn't (yet) taken place
I think there's more to this..lack of maintenance and modifications made to the dams original design played a large part. (not an engineer)
Needle gate bays were sealed off with concrete in 2017 ( the reason there's no water flowing from the two bays on the right) = dimished flow rate.
Sluice tunnels sealed with concrete in 2017 after sluice gate problems -> reservoir fills with silt -> no reservoir capacity to absorb rush of water due to silting -> 100 year flood event -> debris buildup at upstream boom -> debris boom failure -> blockage of tainter gates limiting flow -> water level raised above left abutment height ->erosion of left abutment into channel.
https://www.blueearthcountymn.gov/DocumentCenter/View/6959/2021-Rapidan-Dam-Repair-Feasibility-Study_Nov_2021_Final
In this video, I believe the water is eroding what was previously the bank next to the dam, which will lead to the dam failing. That’s why it’s imminent and not post-collapse.
It gives a lot more context looking at this area on the aerial imagery and Google Street View:
https://www.google.com/maps/@44.0924321,-94.1091493,236m/data=!3m1!1e3?entry=ttu
That pile of metal on the right of the video was a small power substation for the dam. The breach took out a large sheet metal barn, too, long gone. Water is flowing south to north.
If you click on the Rapidan Dam Park object there's 320 photos of the area before all this happened. There's even pictures of the substation, which is the area where the water is carving a new canyon.
it's the best dam store by a dam site!
I've been there a ton of times. Very good pie that gets written about in travel articles now and again. Hope the building survives.
Yes, this is a picture of the damn from the downstream side:
https://bloximages.chicago2.vip.townnews.com/mankatofreepress.com/content/tncms/assets/v3/editorial/8/cc/8ccdae3c-f7f7-11ec-b7dd-4f053dd7a527/62bccc9947b0d.image.jpg
So the spillway over the damn is basically running full and/or partially clogged by the trees and debris we see pushed up against it in OPs image. The water behind the damn backed up, flooded, and is now spilling around the dam. The water found a low spot/weak point to erode before it ran overtop of the dam itself.
There was water overflowing the dam last night/early morning. Water was flowing into the parking lot and in the transformer. Then it just started scouring the earth
Also not an expert but I think the problem is when the bank next to the dam erodes far enough, the dam won’t be able to hold itself up once the bank isn’t there to support it
The problem is that the erosion weakens the side of the dam. As it erodes into the soft earth and carved a new canyon the side of the dam is exposed to fast moving water which will damage it and can result in an eventual collapse of the whole dam.
The dam is 100 years old and has been damaged by flooding this last decade. It hasn't produced power since 2019.
Lots of sandbags and prep going on in town in case it falls fully.
This is incorrect. The dam supplied power to 600 homes, which is how several of the off-duty power station workers initially became aware of the situation.
The dam itself hasn't generated power.
Xcel energy (the owner of the dam) had a substation there that transported power, but it had been washed away since causing that outage
https://en.m.wikipedia.org/wiki/Rapidan_Dam
Non functional since 2019/2020
Much like filing your taxes, power plants file their energy production: https://www.eia.gov/beta/electricity/data/browser/#/plant/52054
Looks like COVID killed the dam.
There's a pretty good overview of the dam and options the pros and cons of removing ($82 million) versus repairing the dam ($15 million) after the flood in 2019 at [https://storymaps.arcgis.com/stories/807ea2c6ad90422ba97e8f3a1db9bafb](https://storymaps.arcgis.com/stories/807ea2c6ad90422ba97e8f3a1db9bafb) , though that decision is moot at this point.
I understand the decision is moot now, but I am curious what was decided in 2022.
I lived in Cannon Falls when we had to make a similar decision to take out our dam and return the falls. The state of Minnesota made the decision easy by funding removal, but making the city responsible for upkeep if citizens wanted to keep the dam. It was removed.
> I am curious what was decided in 2022
"it would cost at least $15.1 million to repair the dam... Removing the dam was estimated to cost at a minimum of $65.2 million... Ultimately, since both options had significant costs, neither were implemented."
https://www.cbsnews.com/minnesota/news/what-is-the-history-of-the-rapidan-dam-in-southern-minnesota/
You know that explains why I never heard anything else about that study. They did lots of outreach and released some study’s but then I heard nothing. Didn’t know they just completely abandoned it…. It seems the cable barrier holding the logs back broke around 9-9:30 last night
Some short term, but who knows if it would have been sufficient for this crazy of an event. Not to mention that even if the correct plan was chosen in 2022, the odds of having the funding in place, any environmental reviews and/or citizen hearings completed, contract awarding, construction company availability, just doesn't make it seem all that likely
It's honestly impressive work on the part of the dam's designers that this failure so close to an anchor point of the dam structure hasn't resulted in the immediate breach and failure of the dam itself.
It's because this dam wasn't designed in the way you are implying. It wasn't anchored to the abutments in a way that transfers the load to them. It is a gravity dam which means it was designed to resist the loads independently of any contribution from the abutments.
Despite this, it is likely the dam structure will ultimately fail due to erosion at the base and the dynamic forces of the water.
While it looks like a gravity dam, it’s technically a hollow concrete dam so it does transfer loads to the abutments. So the left thrust block is a load bearing piece of the dam.
Sorry I hate correcting people but I am a structural engineer on dams so I had to mention something hahaha
I actually have structural dam experience too :). The fact it's a hollow concrete dam doesn't mean it's not a gravity dam. Hollow dams used to be constructed to give a wider base to increase the moment that resists tipping failure, while saving on concrete. With this construction, it can still be heavy enough per unit length of width to not slide. I'm also intriuged at how you think the abutments count as thrust blocks with a flat dam geometry - the wall literally can't thrust into them like an arch would as the hydorstatic force is perpendicular and in line with the blocks. To shift the load to the abutment would require the transfer of massive lateral across-stream tensile loads and these dams aren't typically reinforced in that direction, if at all.
If you find any material for this dam that contradicts what I've said I'm happy to be proven wrong, but I really don't think it's possible. I'm not trying to be a dick haha I'm genuinely curious if there's a gap in my knowledge here. Obviously all this goes out to the window if it turns out it is reinforced, but with all the news articles flooding google it's not particularly easy to find construction detail 😉.
I love knowledge sharing on Reddit so no beef! I think you’re totally right and I have to rescind my comment here, as hollow dams do totally resist through gravity and moment resisting wide bases. like duh of course … it’s flat! Needed to take my arch dam hat off.
The dam was retrofitted and reinforced in the mid 80s as part of the refurbishment and return to service after the 1965 flood, so it does have that going for it. My perception was that it does have significant reinforcement to transfer load to the abutments, and I was examining the now very exposed (and honestly relatively robust looking) left abutment and jumping to a wrong conclusion. It was incorrect for me to call them thrust blocks as it’s absolutely not a transfer of load to the abutments like an arch.
All good, so do I! I was more just curious if there was some crazy dam design I'd never seen before.
And yep I'm definitely guilty of having been sucked into the arch dam work. They can be quite complex that you start overthinking everything else!
Great to chat to someone with some knowledge in this niche areat though.
It's not holding back a huge lake, just a higher portion of the river, so a full failure would not be as bad as one might assume based on the story. It's arguably a weir.
This. There's a ton of silt that makes up most of what's above the dam. If you wouldn't sink into the silt, you could easily walk across it above during normal water level periods. It's not like it's holding back a reservoir. It's a small river with a big dam that goes back to a small river. 100 years of silt buildup could have some unseen ecological damages though
Plus only about 20-15 feet is water. The rest is all sediment. (Though hazardous chemicals sediment). It’s basically a run of the river dam with two 600 CFS turbines
My dad did some work on a house that had been damaged by a flood. The houses around it were total losses, but this one was able to be repaired because when it became evident that the house was going flood, the owner plugged every drain left every tap wide open. The rationale was that the pressure of the water inside wouldn't allow dirty water to spill in. Everything would be wet, but at least they wouldn't have to scrap out all the mud and debris.
I have no idea if this is true, but I do wonder.
There's a restaurant in my area right on the Ohio that does this every flood season.
It works.
https://www.facebook.com/CQRiverside/videos/428176271812110/?_rdr
No one is surprised when infrastructure fails in this country.
It's when, not if. We all know, no one wants to pay.
The federal government will cover it after it fails. Why use state or local funds?
I work in Emergency Management for my state (not Minnesota) and we use federal and local funds to mitigate natural disasters. We focus on what could happen IF a disaster were to occur. Look into BRIC and FMA FEMA grant projects.
Removing a damn would be entirely private profit, it’s not like they hand everyone from the public works department a shovel and tell them to have at it.
We can't even get congress to approve congressional spending to fix bridges that have had failing grades attached to them by the Army Corps of Engineers.
I would love to have federal spending to ensure the construction and safety of every dam in this country, but clearly there's zero political appetite for it up to this point.
There are federal funds available for this type of thing but not 100%; most of those funds expect the state and county to chip in too.
Under a 'good'earmark system, the local congrsscritter talks with the county and state about what is needed to help and then gets an earmarkntondirect more funding to this specific job.
Many have already been identified. As part of my engineering degree, this was something that I had researched. Unfortunately, it's a lot more complicated than just "tear the dam down." Cost is a big factor, and a lot of people don't want to fund dam rehabilitation/removal projects because they're expensive. Even if dam removals are approved, there's lots of downstream and upstream effects that need to be considered and mitigated against, which takes a lot of time and money.
I do agree that we do need to start seriously taking a look at decommissioning older dams, for more reasons than just public safety, especially since these projects take so long to complete. But it's an uphill battle to get buy in from the general public and by extension, the politicians that ultimately approve the funding for these projects.
I know if they wanted to remove the dam they would have literal tens of thousands (if not more) truck loads of contaminated soil and sediment. Plus they would have to rebuilt a nearby bridge. About 68 million to remove it
sure, but, if you wait until the thing actually fails and causes a whole crisis, then you can request those sweet Federal Emergency funds to aid in the repair and avoid spending as much state money on it.
Too busy funding wars in other countries that already have free healthcare for their citizens. If it’s not making money for General Dynamics or Lockheed Martin, it’s just not important enough.
Isn't it interesting to see that the National Inventory of Dams noted that this dam is in "POOR" condition and it is 114 years old (commissioned in 1910). One wonders if something could have prevented all of this. Check out more information about the dam here: https://damsoftheworld.com/usa/minnesota/rapidan-dam
This may have potentially been prevented. However the reason for this is more so due to debris clogging the dam, causing water to move around the dam rather than through the dam.
we'd love to, almost the entire state is so wet that the land is struggling to actually take more water. Where I live in MN there is a random creek that has appeared that was just a wooded area before
Per the local news, when/if the dam fails, flood walls in Mankato will protect the city.
https://www.mankatofreepress.com/news/local_news/update-rapidan-dam-in-imminent-failure-condition-mankato-floodwalls-expected-to-handle-any-surge/article_411123d2-3235-11ef-bb62-6bf9d2baedaa.html
There had already been river flooding which caused the debris you see up by the dam. That debris blocked the outflow so that's why the water started overflowing the banks.
[There's already a report of the erosion beginning to eat into the ground directly under the foundation](https://www.cbsnews.com/minnesota/news/owners-of-rapidan-dam-store-evacuate-as-river-threatens-to-take-out-home/).
It's an old family home too. Truly awful situation.
The washout happened around 2-3AM when water began to overtop the dam. I believe that dip at 9PM was the debris collector upstream failing. Letting all of the logs block the spillway
I am looking at this horrified. There are rivers in south eastern Minnesota that are starting to overflow as well. Starting to worry about my drive down to my delivery locations. Thankfully the bridges along hwy 52 are pretty new as in at most 3 years old for most of them. Still this is becoming a problem in Minnesota. I didn't know Mankato was that bad though.
just because it hasnt failed structurally does not mean that it hasnt already failed.
Sure it has not catastrophically failed in that the reservoir is still being mainly held but the current failure is discharging a volume far beyond acceptable amounts.
patient is dead, but head is still attached.
I very strongly disagree. The patient has a severed artery and it's spraying. If you put the patient through a meat grinder all the blood will come out at once. So similar but different.
The best way I could describe it is the difference between having a 75 ft straight up wall of water crashing through everything in its path for the next 10 miles.
Or
Having 20 times the normal amount of water passing across that dam.
One is the Johnstown flood The other is a spillway opening.
It’s actually a wall of contaminated sludge that would slurp its way down to Mankato, not a wall of water… the damn dam is full of sediment and not water.
The river flows into the Minnesota River in Mankato, a college town of roughly 45,000 people. The Minnesota then flows north, where it will combine with the Mississippi River, just outside of Minneapolis.
It's amazing that when faced with the imminent collapse of hundreds of pieces of critical infrastructure like this one, the US has adopted a strict "fuck it" policy
Hey Reddit! I work as a civil in dam safety many many states away. I also happen to work in failure modes and risk assessments of dams. This is not a professional report, These claims are speculative and are only meant as a theory for understanding. Information was gathered from the internet and local county pages. Riverflow data from USGS. Use this information at your own discretion please. **IMMINENT FAILURE DEFENITION:** ***A dam emergency has caused conditions that may lead to a dam failure. This does not mean the dam will fail for certain, but it means that everyone should prepare for it. Essentially, imminent failure is the last emergency action term used before FAILURE.*** Quick Facts: Constructed: 1910 Dam Type: Hollow Concrete Dam (Amberson style) Current Ownership: Blue Earth County Nameplate Energy Generation: 5.5 Megawatts (2-3,000 homes) Generation Maximum Flow Capacity: 1200 CFS (cubic feet per second) Maximum Spillway Capacity: Unknown, but has successfully passed 43,000 CFS in history. I conservatively assume that the dam was designed to pass at least 40,000 CFS. Blue Earth River 100-year Flood: \~35,000 CFS (cubic Feet per Second) Flood of Record (largest flood the dam has ever seen): \~43,000 CFS in 1965 (this is a 500-year flood) Current Max Flow (June 23-24th 2024): 35,000 CFS **Theory on Dam Failure (SPECULATION from news, experience, and past dam failures):** It appears that the blue river from USGS data is currently flowing at \~35,000 CFS. This should not be an issue for the dam, as it has seen such flows before. However, it appears that woody debris has built up and blocked the tainter gates (the radial spillway gates) and reduced the amount of water they can pass. Debris has traditionally been low on this river, and trash has been removed at rapian by hand rake or by excavator. In large flood events, however, large quantities of debris will suddenly overwhelm a river. I am not aware of upstream debris booms, or other catchment techniques that are utilized, but there is not a modern or automated debris removal system capable of large debris inflows. Debris blocking spillway channels can cause their effective flow discharge to decrease by anywhere from 5-50% (sometimes more), especially for these relatively shallow tainter gates at Rapidan. Meaning the dam in a debris blocked state may have only been capable of passing 20k CFS. An insignificant amount of water can be passed through the powerhouse, so relieving pressure through the powerhouse is not an option. In addition, the reservoir behind rapidan is not very large, and cannot “absorb” an incoming flood very well. Therefore, blockage in the spillway caused the water level of the reservoir to rise quickly. This may have happened so quickly that operators did not have sufficient time to respond. We're talking hours perhaps even minutes based on inflow. Water levels raised, and water breached the left levy, and quickly eroded and cut a channel. From news observations it appears that the left abutment (the dam's left foundation) is founded and wedged in competent rock and may hold, but we will see how things play out. What’s most important at this point in time is that the left abutment holds and stays wedged into the rock. The right abutment appears to be in fine condition. This was most likely a preventable disaster. This flood event occurred over multiple days, and measures could have been taken to prevent the buildup of debris. I think that an over-the-weekend flood and perhaps some negligence caused the owner to not be prepared for the clearing of debris, and it overwhelmed the project quickly. I send my best wishes to those in the immediate area. Please follow evacuation orders and stick to them, in the case of a dam failure there could be a very large inflow and flood. .... EDIT: Best guess at root cause based on available information: There was an upstream debris boom that failed located under the glacier road bridge. There was only one boom that I am aware of, and the cable or anchor must have given out. That would technically be the root cause of this dam emergency. 100 year flood event -> debris buildup at upstream boom (under bridge) -> debris boom failure from loading -> severe blockage of the tainter gates limiting flow -> water level raised above left abutment height -> erosion of left abutment into channel.
Having been to rapidan Dam a lot there’s a highway bridge a few hundred feet upstream. Along that bridge’s supports there’s a large cable and bouys for catching debris. I was at the dam the day before and there were tons of trees being held by that cable. Judging by that big dip at 9-10 pm in the flow I’d say the cable broke and blocked the gates. In 2019 during the spring melt there was another large flood. That flood flooded the power house with 8 feet of water. Though with that flood they had some equipment out to remove the trees. So who knows. I believe the dam is rated for about 50,000 CFS
ah thank you! so the debris boom failed leading to spillway blockage. **Debris boom failure was therefore the first root cause.** and 50k cfs rating seems about right! slowly gathering more info so I appreciate the insight.
Ive been looking at some studies you might find interesting. Theres a long history of scouring and apron damage at this Dam. [2021-Rapidan-Dam-Repair-Feasibility-Study\_Nov\_2021\_Final (blueearthcountymn.gov)](https://www.blueearthcountymn.gov/DocumentCenter/View/6959/2021-Rapidan-Dam-Repair-Feasibility-Study_Nov_2021_Final) Apparently the designed spillway capacity ranges from 41.900 CFS to 105,000 CFS. This another older study by the Army Corp [091055.pdf (mn.gov)](https://www.lrl.mn.gov/docs/2009/mandated/091055.pdf)
That’s a fantastic find! Going to have to give that a read through
I’m just fascinated by this. I’d always visit this dam as a kid. I’d made some comments when they did the study’s a few years ago. Never did I think this would ever happen. I’d love to hear your thoughts on those studies if you have the time!
I took a glance today, some interesting information. Something that is worth noting is the dam is keyed into the surrounding bedrock, which is a very positive factor for resilience to failure at this point. So the left abutment is pretty robust in my opinion.
Absolutely fascinating reading and rather awesome that you found these studies. Many thanks indeed for helping me to understand the dam site and make sense of the dramatic video yesterday of the floods cutting through the left side of the bank.
Is there any reason why they don't try to pull some of the debris out at this time? If you had a crane on the other side, you could at least pull the logs out.
Approaching the project in any way is very dangerous, even an excavator on shore could be suddenly in danger if the dam were to break.
Where is there safe ground to put a crane at this point?
I find it so satisfying to match data to real world events.
Thank you for your professional insight, worth sorting by new for. I see from Wikipedia that [this dam was already being considered for removal by the county in 2021 and 2022](https://en.wikipedia.org/wiki/Rapidan_Dam); assuming the left thrust block remains intact and survives this emergency, will demolition be the best option moving forward?
Based on the rough recover cost (at least 5 million) and the income it generates (low in comparison), its unlikely it will be restored. I would assume removal at this point but you never know.
I'm sure this isn't news to you but I just found the water gage graph immediately downstream: https://waterdata.usgs.gov/monitoring-location/05320000/#parameterCode=00060&period=P30D&showMedian=false I assume the current peak is the bank failure, and a total structure failure would be higher still, so hasn't (yet) taken place
Truly an engineer's guess (not a report) when it begins with a disclaimer for liability. Fantastic info and thanks for offering your take on it
>This was most likely a preventable disaster. https://youtube.com/watch?v=yjfrJzdx7DA
Interesting, if this gets linked in the future, hopefully it won't be in a post-disaster thread.
This is why I can’t quit Reddit. A dam fine comment and dam fine insight.
I think there's more to this..lack of maintenance and modifications made to the dams original design played a large part. (not an engineer) Needle gate bays were sealed off with concrete in 2017 ( the reason there's no water flowing from the two bays on the right) = dimished flow rate. Sluice tunnels sealed with concrete in 2017 after sluice gate problems -> reservoir fills with silt -> no reservoir capacity to absorb rush of water due to silting -> 100 year flood event -> debris buildup at upstream boom -> debris boom failure -> blockage of tainter gates limiting flow -> water level raised above left abutment height ->erosion of left abutment into channel. https://www.blueearthcountymn.gov/DocumentCenter/View/6959/2021-Rapidan-Dam-Repair-Feasibility-Study_Nov_2021_Final
>Current Max Flow (August 23-24th 2024): 35,000 CFS Unless you're prognosticating, probably should edit those dates.
You are correct! Thank you, fixed
I read this in Brady's voice from Practical Engineering
Yes, I would like to subscribe to DamFacts
Quit writing essays on Reddit and get back to work. Our dam infrastructure is near beyond repair....
honestly, fair.
I don’t just make sure it’s safe….I make sure it’s *dam* safe.
In this video, I believe the water is eroding what was previously the bank next to the dam, which will lead to the dam failing. That’s why it’s imminent and not post-collapse.
It gives a lot more context looking at this area on the aerial imagery and Google Street View: https://www.google.com/maps/@44.0924321,-94.1091493,236m/data=!3m1!1e3?entry=ttu That pile of metal on the right of the video was a small power substation for the dam. The breach took out a large sheet metal barn, too, long gone. Water is flowing south to north. If you click on the Rapidan Dam Park object there's 320 photos of the area before all this happened. There's even pictures of the substation, which is the area where the water is carving a new canyon.
Wow, it looks like the spillway is the entire length of the dam and is already overflowed by 10 feet.
They’ll have to rename that cafe.
it's the best dam store by a dam site! I've been there a ton of times. Very good pie that gets written about in travel articles now and again. Hope the building survives.
Reminds me of the Dam Bait Store where I used to buy fishing gear.. or the Dam Deli where I had a Dam Footlong hot dog… memories 🎶
Where can I get some Dam bait?
I’m your dam guide!
To the Did Drop Inn?
Rapidan Rapids Cafe ought to sum it up nicely
They have plans to relocate nearby and rebuild, the new cafe will be called Dam Son.
Unless it’s called That Damn Dam, in which case…hilariously prescient.
“Temporarily closed”. I admire their optimism.
Minnesota Nice in action.
They're just relocating a bit downriver.
Yes but is the cafe open?
4.7 stars. I wanna go
Kayaks for hire.
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That entire region is incredibly interesting, geologically. https://en.m.wikipedia.org/wiki/Glacial_River_Warren
>geologically. Important to add this qualifier.
Water always wins
Grand Canyon says yep.
I hope the dam cafe survives.
Me too. I love the dam cafe.
But if the dam doesn't it'll just be the cafe, right?
Yes, this is a picture of the damn from the downstream side: https://bloximages.chicago2.vip.townnews.com/mankatofreepress.com/content/tncms/assets/v3/editorial/8/cc/8ccdae3c-f7f7-11ec-b7dd-4f053dd7a527/62bccc9947b0d.image.jpg So the spillway over the damn is basically running full and/or partially clogged by the trees and debris we see pushed up against it in OPs image. The water behind the damn backed up, flooded, and is now spilling around the dam. The water found a low spot/weak point to erode before it ran overtop of the dam itself.
There was water overflowing the dam last night/early morning. Water was flowing into the parking lot and in the transformer. Then it just started scouring the earth
They closed the park right when I now want to visit!
Trust me. You don’t want to visit right now.
Quick, somebody call /r/post10 !!!
I'm afraid it's a bit too late for that. It's in the process of unclogging itself
Ah yes, the water took a nice little detour *around* the dam. Title makes more sense now. I do believe that failure is imminent indeed.
Yea the damn hasn't failed technically but the supporting infrastructure has certainly passed the imminent failure point
Water, uh, finds a way.
Malcom was right.
The front fell off.
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Also not an expert but I think the problem is when the bank next to the dam erodes far enough, the dam won’t be able to hold itself up once the bank isn’t there to support it
The problem is that the erosion weakens the side of the dam. As it erodes into the soft earth and carved a new canyon the side of the dam is exposed to fast moving water which will damage it and can result in an eventual collapse of the whole dam.
Lake Delton residents seen nodding
The dam is 100 years old and has been damaged by flooding this last decade. It hasn't produced power since 2019. Lots of sandbags and prep going on in town in case it falls fully.
This substation served a nearby town called Lake Crystal. I’m not sure that’s true.
No, the floods in the last 10 years took the station out of commission in 2019
Crystal Lake?…oh shit
Ch ch ch ah ah ah
The dam doesn’t produce but the substation is still active infrastructure
*was*
Yeah 600 costumer are without power currently due to this
Those poor costumers. Where will they larp now?
My buddy who lives in Good Thunder lost power, presumably because of that dam and station going down.
This is incorrect. The dam supplied power to 600 homes, which is how several of the off-duty power station workers initially became aware of the situation.
The dam itself hasn't generated power. Xcel energy (the owner of the dam) had a substation there that transported power, but it had been washed away since causing that outage https://en.m.wikipedia.org/wiki/Rapidan_Dam Non functional since 2019/2020
Much like filing your taxes, power plants file their energy production: https://www.eia.gov/beta/electricity/data/browser/#/plant/52054 Looks like COVID killed the dam.
Damn. Who knew dams could get sick.
Mustn't have been any dam operators to spare for <7 MW.
In its hey day it could power 2,000 or so homes
There's a pretty good overview of the dam and options the pros and cons of removing ($82 million) versus repairing the dam ($15 million) after the flood in 2019 at [https://storymaps.arcgis.com/stories/807ea2c6ad90422ba97e8f3a1db9bafb](https://storymaps.arcgis.com/stories/807ea2c6ad90422ba97e8f3a1db9bafb) , though that decision is moot at this point.
I understand the decision is moot now, but I am curious what was decided in 2022. I lived in Cannon Falls when we had to make a similar decision to take out our dam and return the falls. The state of Minnesota made the decision easy by funding removal, but making the city responsible for upkeep if citizens wanted to keep the dam. It was removed.
> I am curious what was decided in 2022 "it would cost at least $15.1 million to repair the dam... Removing the dam was estimated to cost at a minimum of $65.2 million... Ultimately, since both options had significant costs, neither were implemented." https://www.cbsnews.com/minnesota/news/what-is-the-history-of-the-rapidan-dam-in-southern-minnesota/
Ah, the classic "do nothing" and hope someone else'll be in charge then solution.
"do nothing" when one of the first lines in that report is "doing nothing is no longer a long-term solution"
I'm not 🇺🇸 but fuck, do I often wish that kicking the can so blatantly was illegal in any jurisdiction.
It really sucks that the majority of people don't realize that "Do nothing" IS a decision, a real decision, that has real consequences.
Guess that "someone else" may also apply to mother nature.
You know that explains why I never heard anything else about that study. They did lots of outreach and released some study’s but then I heard nothing. Didn’t know they just completely abandoned it…. It seems the cable barrier holding the logs back broke around 9-9:30 last night
[https://www.youtube.com/watch?v=yjfrJzdx7DA](https://www.youtube.com/watch?v=yjfrJzdx7DA) The Onion predicts the future again!
I don’t think they ever came to concrete decision
It’s water over the bridge now.
The situation was fluid
There's always someone that undercuts the foundation of a good plan.
Blue Earth County was going to surrender control and it’s FERC license and put responsibility to the Minnesota DNR
I doubt either would have been completed in time
Either plan would have included some emergency short term maintenence.
Some short term, but who knows if it would have been sufficient for this crazy of an event. Not to mention that even if the correct plan was chosen in 2022, the odds of having the funding in place, any environmental reviews and/or citizen hearings completed, contract awarding, construction company availability, just doesn't make it seem all that likely
I know the plan to remove the dam would take 10 years alone
Good news is that the cost of removing is now zero
I think there might be some other... unseen costs to this method of removal
"This is Practical Engineering and today we're going to be looking at the failure of the Rapidan dam"
"Now, I dont normally do livestreams"
Oh you dirty dog.... saw that opportunity and went with it. Bravo.
It's honestly impressive work on the part of the dam's designers that this failure so close to an anchor point of the dam structure hasn't resulted in the immediate breach and failure of the dam itself.
The bank's designers on the other hand... smh.
Bankers ruin everything.
It's always the geotech's fault.
It seems to lack an emergency spillway. I would not pat the dam designers on the back. But it is also 100 years old.
It's because this dam wasn't designed in the way you are implying. It wasn't anchored to the abutments in a way that transfers the load to them. It is a gravity dam which means it was designed to resist the loads independently of any contribution from the abutments. Despite this, it is likely the dam structure will ultimately fail due to erosion at the base and the dynamic forces of the water.
While it looks like a gravity dam, it’s technically a hollow concrete dam so it does transfer loads to the abutments. So the left thrust block is a load bearing piece of the dam. Sorry I hate correcting people but I am a structural engineer on dams so I had to mention something hahaha
I actually have structural dam experience too :). The fact it's a hollow concrete dam doesn't mean it's not a gravity dam. Hollow dams used to be constructed to give a wider base to increase the moment that resists tipping failure, while saving on concrete. With this construction, it can still be heavy enough per unit length of width to not slide. I'm also intriuged at how you think the abutments count as thrust blocks with a flat dam geometry - the wall literally can't thrust into them like an arch would as the hydorstatic force is perpendicular and in line with the blocks. To shift the load to the abutment would require the transfer of massive lateral across-stream tensile loads and these dams aren't typically reinforced in that direction, if at all. If you find any material for this dam that contradicts what I've said I'm happy to be proven wrong, but I really don't think it's possible. I'm not trying to be a dick haha I'm genuinely curious if there's a gap in my knowledge here. Obviously all this goes out to the window if it turns out it is reinforced, but with all the news articles flooding google it's not particularly easy to find construction detail 😉.
I love knowledge sharing on Reddit so no beef! I think you’re totally right and I have to rescind my comment here, as hollow dams do totally resist through gravity and moment resisting wide bases. like duh of course … it’s flat! Needed to take my arch dam hat off. The dam was retrofitted and reinforced in the mid 80s as part of the refurbishment and return to service after the 1965 flood, so it does have that going for it. My perception was that it does have significant reinforcement to transfer load to the abutments, and I was examining the now very exposed (and honestly relatively robust looking) left abutment and jumping to a wrong conclusion. It was incorrect for me to call them thrust blocks as it’s absolutely not a transfer of load to the abutments like an arch.
That left abutment was replaced only a few years ago. Looking back when the dam was built there was nothing there holding that cliff
All good, so do I! I was more just curious if there was some crazy dam design I'd never seen before. And yep I'm definitely guilty of having been sucked into the arch dam work. They can be quite complex that you start overthinking everything else! Great to chat to someone with some knowledge in this niche areat though.
My friend live down stream from this and he said he's not in danger because he's in a more elevated place, but most of the town is fucked if it fails.
It's not holding back a huge lake, just a higher portion of the river, so a full failure would not be as bad as one might assume based on the story. It's arguably a weir.
Weir, new word to me. Had to look that one up.
Weir everywhere. (Google that one)
Username checks out
This. There's a ton of silt that makes up most of what's above the dam. If you wouldn't sink into the silt, you could easily walk across it above during normal water level periods. It's not like it's holding back a reservoir. It's a small river with a big dam that goes back to a small river. 100 years of silt buildup could have some unseen ecological damages though
Plus only about 20-15 feet is water. The rest is all sediment. (Though hazardous chemicals sediment). It’s basically a run of the river dam with two 600 CFS turbines
My dad did some work on a house that had been damaged by a flood. The houses around it were total losses, but this one was able to be repaired because when it became evident that the house was going flood, the owner plugged every drain left every tap wide open. The rationale was that the pressure of the water inside wouldn't allow dirty water to spill in. Everything would be wet, but at least they wouldn't have to scrap out all the mud and debris. I have no idea if this is true, but I do wonder.
There's a restaurant in my area right on the Ohio that does this every flood season. It works. https://www.facebook.com/CQRiverside/videos/428176271812110/?_rdr
What's hazardous in the sediment?
110 years of farm chemicals and fertilizer. 11 million cubic yards worth of sediment. Or 785,000 dump truck loads
His new riverside property might be worth more though.
Maybe it’s time to identify dams nationwide that are too old and maybe decommission them before something like this happens.
Yeah but that costs more than $0, so it’s a tough sell
“If it ain’t broke, don’t fix it!” Shocked Pikachu face when it breaks.
No one is surprised when infrastructure fails in this country. It's when, not if. We all know, no one wants to pay. The federal government will cover it after it fails. Why use state or local funds?
I work in Emergency Management for my state (not Minnesota) and we use federal and local funds to mitigate natural disasters. We focus on what could happen IF a disaster were to occur. Look into BRIC and FMA FEMA grant projects.
If there was a way to privatize and profit from dam removal politicians would be on it like hobos on ham sandwiches
Removing a damn would be entirely private profit, it’s not like they hand everyone from the public works department a shovel and tell them to have at it.
Would of cost about 68 million dollars and 10 years to remove it and make into river rapids
Looks like it's going to take $0 and about 24 hours to remove it and make it into river rapids.
We can't even get congress to approve congressional spending to fix bridges that have had failing grades attached to them by the Army Corps of Engineers. I would love to have federal spending to ensure the construction and safety of every dam in this country, but clearly there's zero political appetite for it up to this point.
There are federal funds available for this type of thing but not 100%; most of those funds expect the state and county to chip in too. Under a 'good'earmark system, the local congrsscritter talks with the county and state about what is needed to help and then gets an earmarkntondirect more funding to this specific job.
This literally already exists... its called the [National Inventory of Dams](https://nid.sec.usace.army.mil/#/)
Many have already been identified. As part of my engineering degree, this was something that I had researched. Unfortunately, it's a lot more complicated than just "tear the dam down." Cost is a big factor, and a lot of people don't want to fund dam rehabilitation/removal projects because they're expensive. Even if dam removals are approved, there's lots of downstream and upstream effects that need to be considered and mitigated against, which takes a lot of time and money. I do agree that we do need to start seriously taking a look at decommissioning older dams, for more reasons than just public safety, especially since these projects take so long to complete. But it's an uphill battle to get buy in from the general public and by extension, the politicians that ultimately approve the funding for these projects.
I know if they wanted to remove the dam they would have literal tens of thousands (if not more) truck loads of contaminated soil and sediment. Plus they would have to rebuilt a nearby bridge. About 68 million to remove it
sure, but, if you wait until the thing actually fails and causes a whole crisis, then you can request those sweet Federal Emergency funds to aid in the repair and avoid spending as much state money on it.
You mean like a [National Inventory of Dams](https://nid.sec.usace.army.mil/#/)?
That was done here, $15MM to fix and $65MM to remove. They decided on mother nature and insurance.
Too busy funding wars in other countries that already have free healthcare for their citizens. If it’s not making money for General Dynamics or Lockheed Martin, it’s just not important enough.
They have free healthcare because it's more expensive to not. To the tune of we get worse healthcare for 2x per capita cost.
Isn't it interesting to see that the National Inventory of Dams noted that this dam is in "POOR" condition and it is 114 years old (commissioned in 1910). One wonders if something could have prevented all of this. Check out more information about the dam here: https://damsoftheworld.com/usa/minnesota/rapidan-dam
This may have potentially been prevented. However the reason for this is more so due to debris clogging the dam, causing water to move around the dam rather than through the dam.
80% chance it’s imminent failing.
70% chance its gonna fail 100%
60% of the time it fails every time.
It's rained every day here for 2 weeks. Crazy how high the Mississippi has gotten near me. We are getting a massive spring flood in the summer.
So, uh... y'all need someone to take that extra water off your hands? /Colorado_basin
we'd love to, almost the entire state is so wet that the land is struggling to actually take more water. Where I live in MN there is a random creek that has appeared that was just a wooded area before
Mankato?
My fail in writing ...thanks for correcting
Mankato sounds like some place Pa would go to when Mary needs an eye doctor
Actually, Little House On The Prairie was based in Sleepy Eye, just to the west of Mankato.
Per the local news, when/if the dam fails, flood walls in Mankato will protect the city. https://www.mankatofreepress.com/news/local_news/update-rapidan-dam-in-imminent-failure-condition-mankato-floodwalls-expected-to-handle-any-surge/article_411123d2-3235-11ef-bb62-6bf9d2baedaa.html There had already been river flooding which caused the debris you see up by the dam. That debris blocked the outflow so that's why the water started overflowing the banks.
People have been calling to question the integrity of the flood walls as well though
Hmm, that doesn’t look good. *camera zooms out* HMMMM.
Mother earth always wins.
RIP white house. That home owner is fucked. Good bye 400k usd. His insurance will probably refuse payment
[There's already a report of the erosion beginning to eat into the ground directly under the foundation](https://www.cbsnews.com/minnesota/news/owners-of-rapidan-dam-store-evacuate-as-river-threatens-to-take-out-home/). It's an old family home too. Truly awful situation.
That's a lotta water
You can see when the soil washed out about [11PM on JUN 23 on the hydrograph](https://imgur.com/a/AfELh2t).
The washout happened around 2-3AM when water began to overtop the dam. I believe that dip at 9PM was the debris collector upstream failing. Letting all of the logs block the spillway
i believe this is past imminent lol
From what others have said, the actual dam is still intact but the land around it has failed.
Haha yep now it’s eminent.
Is there a live stream of this anywhere? No pun intended.
[here](https://www.keyc.com/livestream/)
Say it with me, "Deferred Maintenance."
I am looking at this horrified. There are rivers in south eastern Minnesota that are starting to overflow as well. Starting to worry about my drive down to my delivery locations. Thankfully the bridges along hwy 52 are pretty new as in at most 3 years old for most of them. Still this is becoming a problem in Minnesota. I didn't know Mankato was that bad though.
just because it hasnt failed structurally does not mean that it hasnt already failed. Sure it has not catastrophically failed in that the reservoir is still being mainly held but the current failure is discharging a volume far beyond acceptable amounts. patient is dead, but head is still attached.
I very strongly disagree. The patient has a severed artery and it's spraying. If you put the patient through a meat grinder all the blood will come out at once. So similar but different. The best way I could describe it is the difference between having a 75 ft straight up wall of water crashing through everything in its path for the next 10 miles. Or Having 20 times the normal amount of water passing across that dam. One is the Johnstown flood The other is a spillway opening.
It’s actually a wall of contaminated sludge that would slurp its way down to Mankato, not a wall of water… the damn dam is full of sediment and not water.
Wonder if the residents/owner of the house at the first bend down stream has packed up anything to move when/if failure occurs?
What is down stream? Terrible!
The river flows into the Minnesota River in Mankato, a college town of roughly 45,000 people. The Minnesota then flows north, where it will combine with the Mississippi River, just outside of Minneapolis.
I lived near there for twelve years. So sad!
The underpinning of the house is now showing. Poor family. 🌧️
It's amazing that when faced with the imminent collapse of hundreds of pieces of critical infrastructure like this one, the US has adopted a strict "fuck it" policy
If only they had more than 30 years of warning...
Enough money for war but no money to fix infastructure.
Lots more in similar condition in the states
The dam in "imminent failure condition" failed? The local government: *insert surprise Pikachu meme here*
Should they have opened the gates earlier to prevent this?
Logs blocked the gates
Minnesota prefers to have their infrastructure fail spectacularly
Hell of an opportunity for a local quarry to get some awesome advertising, dump a bunch of armor stones to save the house, put up a sign
We will just Built it Back, Better...
That's not imminent.
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I can see it standing whole in a slowly flowing river as the banks erode. Banks eroding does give the town some time to react.