A few times a week I surf on a "low head dam" It has a hydraulic controlled wing that adjusts the height and slope of the drop from tailwater to the run out. This way a perfect and surfable hydraulic jump is created which behaves much like an ocean wave. However sometimes the wave collapses and turns into a "keeper". We have ropes on hand to throw to anyone trapped and the level can be quickly adjusted by the controller to reform the wave and remove the keeper so it's fairly safe. It's still something to have a lot of respect for.
Pretty rad. What's the etiquette on the drop-in/surf time? And who built it/paid for it? Is it free?
Asking because I used to live near Bend, Oregon, which had a similar lowhead dam problem that they turned into a whitewater park with three separate channels of rapids. Love it when cities fund these sorts of things.
It's a really polite crew most of the time. We go one at a time. One from the left and then one from the right. Normally the etiquette is that you get 30 seconds. If you go much longer you get trash talked from the side and you have to try some kind of trick which will most likely end up with a wipe out
It's a privately built setup with a serious investment in the order of a million euro. A year pass costs us 440 euros. There are also day tickets available and there is a small bar for food and you can rent equipment.
I tried the link in a Firefox private tab on my mobile where I'm not logged into Instagram. You can view the video but it does try and convince you to log in as well.
are amazing: for many of these I don't think I would have considered them frightening at all from their appearance. Most of them look tiny, but these are all places where people were drowned by the current.
I live near a hydroelectric dam. Once when I was a kid, I was swimming near the floodgates. It was horridly frightening how unexpectedly suddenly the current got strong and started sucking me towards the gate, to which in my opinion I wasn't even that close. Inverse square law and all that. The immediate realization that if I don't start swimming away right now with every muscle I got I'd get sucked in startled me. I'd see nightmares for years involving water and dark holes I'd be unable to stop myself from flowing into.
I've experienced the same, it's truly the stuff of nightmares and I'm very very careful around water now. It's scary how quickly we can be overpowered.
A good complement on water education for adults is the well-known website: http://spotthedrowningchild.com/ Water is dangerous, pushing a little bit more education at each opportunity saves a lot of lives.
What puzzles me is why these areas are not marked on the shore with tall posts with signs saying: DANGER! STRONG CURRENTS! TURN BACK. Such signs should likely start like 150-200 yards upstream to warn boats and kayaks.
Indeed! According to that, The Dennett Dam drowned three people (between 2006 and 2009, so perhaps many more since it was built in 1933 and ruined in 1940). It's now been removed, and you can see when it's dry that it's about six feet tall:
My city removed a few low head dams near the center of the city over the last decade. We are still in the process of a major reworking of the sewer system (to the tune of a few billion dollars) to separate wastewater from storm water due to EPA regulations. Because untreated wastewater is no longer flowing into the rivers, one thing we found is that we didn't need so many low head dams to keep incision from occurring as much.
This improved our downtown as it allowed us to also alter the river channel and opening up some land to build new parks on. Paddle boaters can travel much further, and the river ecology is improving drastically.
Neat, which city? I live in Washington DC which is in a similar position, where an EPA consent decree to clean up the river and deal with old sewer overflow is driving lots of neat infrastructure and cleaning up the waterfronts rather dramatically. No low head dams that I’m aware of, however, though maybe there’s one on Rock Creek.
There’s a very dangerous low head dam in DC area just upstream of chain bridge. It is used to divert water for drinking. Fortunately clear warning signs on the water have prevented any recent fatalities, but there were a number in the past.
Bingo! I was not aware the 5th Ave. dam was used for cooling in the past. Most of my knowledge about the removal was talking to some people who worked on the project, and they mentioned water erosion (incision). I guess I added 2+2 and got 5.
This doesn’t entirely disambiguate OP’s sentence - he’s tying the lack of incision to no longer having untreated wastewater. Is that to say that treated wastewater would somehow cause incision, or just that the untreated wastewater increases volume and thus erosion?
Generally speaking events that overwhelm wastewater/stormwater combined systems are large storms, so if the decision is made to release untreated water you're probably releasing a lot of it all at once from whatever few outlets you have.
Maybe that's what causes incision? But hydrology isn't my area of expertise.
Thats important to know but in a low head dam you get sucked under and pinned.
This is very different from an exhausted swimmer, or the evolutionary dead end default state of just chilling in the water because their amoeba brain flipped off
When I was getting introduced to river kayaking safety basics, the instructor really emphasized the importance of staying away from these, or to start paddling like crazy if you can't avoid them so that you can get past the dangerous point. In whitewater, there are some sections where these can occur naturally as well when you have water falling off from a height of a few feet.
Yup, scary beasts. If you get sucked out of the kayak, the only way to escape those is to get rid of your life vest and try to catch the outflow deep underwater.
At least according to anecdotes.
This is terrible if not unresponsibly dangerous advice.
The top comment has a link to a database with cases of people drowning. The common pattern: if life vests were mentioned then those in the party who drowned were those who either took off their PFD or didn't wear one to start with.
Your best chance is to make it to the side of the river where the currents are less or nonexistent. A life vest increases your chances of making it there alive. Taking it off to dive down to some deep water outflow because somebody mentioned that stunt in some anecdote will get you killed for sure.
No! The only time that might a good advice is if you are stuck under water. Or otherwise exhausted all other possibilities and there's absolutely no hope to be rescued. Otherwise keep your life jacket on. For example the casualty in this [0] case would probably been alive still if he just waited for help instead.
In general, don't spread anecdotal safety advice. Someone might die.
Glad to see Grady’s channel get a mention on here. He, along with aVe, NileRed, Steve Mould, Big Clive, and Ben Kraznow are some of my favorite YouTube science creators.
Agreed, Grady does great work on his Practical Engineering channel. Other channels I appreciate are Smarter Every Day, The Action Lab, Veritasium, and Chubbyemu. What are others people would recommend?
My list of recommended Youtube subscriptions, built from over a decade of curation.
No Particular ordering within the categories.
(D) means possibly defunct, hasn’t uploaded in awhile.
A tier educational / edutainment
3Blue1Brown - High level math, explained simply with good animation.
Captain Disillusion - Visual Effect explainers
Everyday Astronauts - Deep dive rocket science explainers (also a mix of news and live streams)
Game Maker’s Toolkit - Video Game design breakdowns
Jay Foreman - Mostly humorous looks at maps, best in video sponsor spots on Youtube
Kurzgesagt - In a Nutshell - Animated with a board science focus
Mark Rober - Engineer tackles interesting projects
Mathologer - Long and novel math explainers
Minute Earth - Ecology focused animation
Minute Physics - Physics focused animation
Numberphile - Math and number based curiosities
PBS Infinite Series (D) - Math
Primer - Simulated economy and behavior
Rare Earth (D, likely to pick up after the pandemic?) - Stories from traveling around the world
SmarterEveryDay - Science meets engineering, often meets highspeed camera
Stand-up Maths - Humorous math
Steve Mould - Everyday life curios phenomena underlined by physics
Technology Connections - Deep dives into non-computer technology in your home
Tom Scott - Interestings things, places, and ideas
Veritasium - General science, slight physics focus
Scott Manley - deep dives into space news, kerbal space program
Good educational edutainment (but not quite A-tier by my personal preference)
Ben Eater - Computing projects made with low level electronic components.
Code Bullet - Coding Projects, often automating video games
Colin Furze - Crazy physical builds by an insane Brit
EngineerGuy (D) - engineering explainers
Jill Bearup - Fight choreography
Jordan Harrod - AI / Machine learning
LeiosOS - Various computer science
Linus Tech Tips - Computer projects and products mostly with a gaming focus
Lock Picking Lawyer - See every lock in existence get easily defeated by an expert
Noclip - Video Game Documentaries
Objectivity - Archived objects from science history
PBS Space Time - Astrophysics
People Make Games - Video Game Documentaries
Periodic Videos - Chemistry, and a deep dive into every element on the periodic table
Practical Engineering - Civil engineering
Primitive Technology (D) - Ancient techniques for building and crafting, relaxing
Scam Nation - Small scale magic tricks
Sebastian Lague - Coding Adventures
Simone Giertz - Previously queen of shitty robots, maker style projects
SingingBanana (D-ish, appears on numberphile mostly now) - Math
Sixty Symbols - Astrophysics explained by professors
Stuff Made Here - Engineering/crafting projects
Think Twice - Math animations
Tom Stanton - 3d printer powered home engineering projects
Vihart - math
vlogbrothers - Mixed in with nerdy vlogs are some gems of thought and introspection on our world
Zee Bashew - Animated D&D spells and more
BrainCraft - Human psychology
Computerphile - Computer Science concepts, explained
SciShow / SciShow Space - Science news
Video Essayists
Errant Signal - video games
Joseph Aderson - video games
Mathewmatosis - video games
Writing On Games - videogames
Every Frame A Painting (D) - movies
The Royal Ocean Film Society - movies
Just Write - movies and literature
Humor
Brian David Gilbert - Surreal skits
Casually Explained - Witty introspection on life
CrackerMilk - Short, weird, to the point
David Mitchell’s Soapbox (D) - British rants
Felix Colgrave - Animation, probably tied to drug use
Joel Haver - skits/animation
videogamedunky - video games
The Thought Emporium - does next level biology hacking (e.g. cured his own lactose intolerance through genetic engineering) and some physics
Applied Science - Great engineering, he built his own electron microscope for example. His video on the helium-disables-iPhones phenomenon was surprisingly more in-depth than the best writeups I'd read.
He works (worked?) at Formlabs, and seems to have access to some incredibly nice tools for machining, cutting, and forming all the various bits he designs.
While not mentioned in the videos, I'm guessing he also has the ability to ping some tough questions off people who would point him in the right direction quickly, but my guess is it's just a big passion and he's good at it.
"But, even though they pose little danger in the event of a breach, low head dams create a public safety issue that has caused more fatalities in the U.S. than all dam failures in the past 20 years."
Good article generally, but that's a super misleading statistic, or at least easily cherry picked to support a point. Dam failures in general are pretty rare, and fatal ones are even rarer.
Imagine if there was a bad but not Johnstown level fatal dam failure 25 years ago. You can tell two radically different stories if you choose to compare deaths over the last 20 years vs last 30.
The author's point would be more convincingly made if they talked about fatal dam failures over time and demonstrated that they had nothing up their sleeve before making that comparison.
Incidentally, you get naturally occurring keepers as well. I'm not privy to the full details but there was a drowning in the BWCA in 2002. AIUI somebody took a dip in a hydraulic below a falls along Horse Portage and wasn't able to escape. They went through too many times and could not be resuscitated. As I understand it, they were pulled out in an extremely risky and improvised rescue attempt, but it was too late for the victim.
I agree that comparing low head dams to dam failures is a weird comparison, so here’s a different one - on average about 10% of fatalities on moving water (ie rivers) are caused by low head dams (source: American Whitewater). That’s a lot.
As you note, hydraulic jumps occur naturally (and that’s what makes whitewater kayaking fun!), and deaths do occur on natural holes as well. Naturally occuring recirculating holes, however, are not as deadly as low head dams because they are rarely as uniform or as wide. There’s usually something that breaks up the flow or a place from which rescuers can reach the victim with a rope. Dams are typically wide and smoothly uniform across the width of the river leaving no place to escape.
Whitewater boaters (the people most likely to come across natual hydraulics) learn early how to distinguish the fun hydraulics from the scary ones. It’s usually inexperienced boaters that see the small drop of a low head dam and think it looks like a fun ride.
It's been twenty five years since I paddled it, but there was a weir on the river Dee that scared the hell out of me.
It was near the take out, but if you messed up and didn't break for the bank, you were going over it.
Paddling buddies said that if you messed up, the best bet was to gain as much speed as possible and try and get over and then through it. If you got caught by it though, you were likely to drown, as it was a keeper.
Yup. Indeed. A group I'm part of had a fatality in a canoe race back in 1991 because of exactly this. It happened in a channelized stretch of river where the dam stretched wall to wall.
The vertical eddy is called a "keeper" around here. The way to escape? Swim to the bottom of the river. Totally counterintuitive and hard in a panic situation.
His death led to some legislation here in Massachusetts about inspecting, marking, and, where feasible, removing these "roll dams."
It also led to race judges making sure racers do the portage and don't try to shoot the dam to save a few minutes.
> Or more commonly and much worse, these dams are abandoned by their owner and gradually fall into disrepair.
That turned into a catastrophic problem last year in Michigan. Heavy rains breached the Edenville Dam, and then the Sanford Dam downstream, on the Tittabawassee River. They're still cleaning up even now.
I like the simulation video at [1] which shows how a low head dam works in various conditions and how the risk can change dramatically depending on water flow, velocity, sediment levels or obstructions changing in a river. Note the hydraulic jump at 1:05.
Quite surprisingly, the incidence of deaths from whitewater kayaking and rafting is around 6 deaths per million participant days, compared to around 150 deaths per million participant days driving in cars[2].
It references this[1] which references this[2] which references this Kayaking paper[3] which says driving has a 152 fatality rate per million participant days if you assume 1 day = 100 miles. That references this[4] which says "The fatality rate per 100 million vehicle miles traveled (VMT)" is 1.52. If you assume 1 day = 100 miles, that means the fatality rate per 1 million days is 1.52. So there was a math error made in the Kayaking paper when they were doing unit conversion. They overestimated by 100x. That error then propagated to Wikidata.
Thanks for the investigate work! No wonder I was surprised with the figures from the kayaking paper.
I've updated Wikidata to deprecate the incorrect incidence rate from the kayaking paper, and replaced the incidence rate with more up-to-date data from the US BTS which puts it at 0.8 deaths per 100 million vehicle-miles in the US. Using the assumption from the kayaking paper of 100 miles/day being the average distance traveled by car, whitewater sports are therefore 7-8 times more likely to lead to death than traveling in a car.
New query showing more accurate incidence of death rates: https://w.wiki/3Src
USDOT says average motorist drives 13,500 miles/year, or roughly 37 miles per day[0]. So divide by another factor of 3 to get a more realistic comparison of death rates between whitewater kayaking and driving.
Those number's aren't that related to low head dams (most low head dams fatalities are swimmers, not whitewater kayakers or rafters or rec kayakers). While the mechanism behind low head dams (technical term hydrolic, informally called a 'hole') can directly or indirectly kill you, they're typically a natural feature in whitewater fatalities.
I know those numbers b/c it lets me tell my parents that whitewater kayaking isn't as dangerous as they think.
Never, ever, go over a low head dam in a kayak. The danger with them is that they do not kick you out like a normal hole. You go over, and if you don’t clear the hydraulic, you get pulled back in. Then it can hold your boat indefinitely as it drifts back and forth across the river. Then you pull your skirt and you are now a swimmer being recycled in a low head dam. Low head dams make swimmers out of boaters, and kill the swimmers. Do not ever go over one.
And rafting / kayaking is definitely a calculated risk. Skill is involved. Freak accidents can occur that just wouldn’t if you weren’t on the river, but if one is smart about it, it can be about as safe as any other recreational activity (skiing, boating, mountain biking). With friends trained in rescue and experience the safety margin goes up.
For others reading this, the danger depends on what kind of river you’re running, the temperature, and a ton of other factors. In a boat, you’re likely to die if you can’t roll the boat back up and you hit your head / get knocked out, or your boat gets trapped upside down. After you bail from the boat, you could get pinned or caught up in trees, pulled under big rocks that are undercut, trap your ankle in a rock (in shallow water), which then pushes your body underwater downstream, die from exposure / drowning (you wash down the river faster than anyone can get you and just give up the will to live because it’s too cold / you can’t stay above it anymore).
I did a similar calculation when deciding to learn to fly small planes (vs buying a motorcycle) - the accidental death rate is higher for both compared to driving a car - but pilot error is the cause of something like 90% of GA fatalities. But 40% or something of motorcycle fatalities are not the fault of the biker - he did everything right but someone else (or something else) got him.
Yes - and you have to be exceptionally discipled, but a huge part of the GA stuff you can control (by not flying in marginal conditions, not trying to extend your range, always using checklists, etc).
But you can do all that on a motorcycle and still get creamed.
It does require you to honestly assess your ability to say "no" when conditions aren't right.
Basically what I'm getting at is there are activities that are dangerous but some the danger comes from you and others the danger comes from outside forces/other people. (Sure, I guess you could argue that you could just not ride your bike when there's other people on the road, but that's not practical).
I love this guy's YouTube channel. The thing I admire most about him is his ability to explain something complex our counterintuitive in a way that empowers you instead of belittles you. It's something I try to do, but goddamn it is hard.
We had a major tragedy near my town because of this. 13 people died, also its mayor and many local officials. They organised "the last descent" before the river bed would be floded for the hydroelectric power plant.
https://www.nbcnews.com/news/amp/wbna25526342
My brother is a very avid fisherman - every time I call him, he seems to be out on a river or lake somewhere in western Massachusetts during the afternoon.
This article really struck me, so I shared this with him, along with the video of the Binghamton, NY Susquehanna River Dam accident, which is mentioned in this article. In a light tone I said to him "don't ask why I'm telling you this randomly now, but never go near a low head dam."
He quickly reminded me that I have a family member who died when I was young that drowned. I never knew the details - turns out it was a low-head dam.
It's easy to think that in modern society there aren't many almost unseeable risks like this lurking out in the world.
Back when I was a kid we would boogie board on one of those hydraulic jumps. If you were good you could stay up for several minutes at a time. It was somewhere in between the safe and dangerous examples he gave. No injuries or deaths, to my knowledge.
I appreciate the demonstrations he does for nearly every video. Also, there are so many engineering topics that sound boring, but are actually really interesting when you dig into them. The dangers of low-head dams is a great example of one of those topics.
Many of these structures have concrete channels downstream of the weir which means that the stopper/keeper/recirculating water is equally strong across the width of the river. It can also be extremely hard to swim with any sort of accuracy due to being constantly recirculated and not-very buoyant due to the entrained air.
There are other subtleties in 3D as well; some weirs form a downstream-pointing V when viewed from above the dam - these are generally considered safer as the currents will (generally) move you to the middle of the river and downstream where the water is more likely to be escapable - see [1].
Others can form an upstream-pointing V which has the opposite effect where the currents will move you towards the middle of the river but upstream back towards the stopper/keeper/hydraulic.
Interesting, I've never heard of weirs as being small before. The only weirs I've ever seen are large-scale flood control structures of the Sacramento River, and they're huge.
The catch being that you're submerged, being spun around in the currents and disoriented, and you have a very brief window to claw yourself along the riverbed.
I can't find the source but have seen reports where people have been caught in a weir, drowned, and remained spinning in the currents for a couple of days before they're eventually spat out by chance and the bodies are recovered. They've well earned the name "drowning machines".
I have no intention of going anywhere near one of these dams, if I can help it.
Low head dams like these don't generate a whole lot of power. Wikipedia's article says they generally generate <5MW of power; an individual wind turbine these days can deliver an equivalent amount of power.
Dams are also becoming less effective as climate change increases drought conditions in areas with dams.
Sure, but to saw timber, irrigate and grind seeds to not starve is also worth something.
Wind and solar have net negative energy output, meaning the cost of manufacturing the cells/turbine + the electronics, cables and batteries cost more energy than the hardware will generate in it's lifetime.
The tree is the best solar panel + battery and nature invented it, it made all the coal, oil and gas!
Beyond that only hydro and nuclear can help, and you cannot build, maintain or rescue a nuclear plant without dead trees.
So that leaves hydro, even with flooding and drought; it's the only stable "source of progress".
The reason you are getting downvoted is the phenomenon discussed here is independent of whether the dam creates energy or not. It has no bearing on whether you are pro or against hydro-electric power generation.
No the reason I'm getting downvoted is that people are toxic, because they don't even have an argument.
But it's ok I'm used to it and value karma the other way around; by design on this forum low karma is truth and high karma is toxic!
I'm aiming for the lowest karma possible, and I'm going to avoid the high karma people to the largest extent possible and when the HN database leaks everyone can see what's what.
They wont stop me from trying to have a discussion with people that actually have something to say.
EROEI is not calculated on the energy required to build and transport all the parts required (mining of the resources and the cat food for the cat of the operator of the truck in the mine etc.)
Everything except dead trees and hydro is completely stupid!
ERORI on oil has gone from 100/1 to 10/1 in 100 years.
What if the energy used to build and transport were to come from wind, solar and/or hydro? Does it stay stupid in your calculus?
Could you post some data and/or resources on where you’re getting your numbers? It sounds surprising and unlikely, because large wind turbines can generate a lot of energy over their lifetimes. Ivanpah solar generates about 850Gwh annually and has been running for 10 years, with many more on the horizon. You are sure 8500 Gwh is less that it took to construct? I’m curious about your claim and willing to hear the research. How are you calculating the energy inputs of manufacture? How are you calculating the lifetime outputs?
“A 2010 analysis of fifty separate studies found that the average wind turbine, over the course of its operational life, generated 20 times more energy than it took to produce. This level was “favourable” in comparison to fossil fuels, nuclear and solar power.”
And most importantly, is comparing energy in to energy out the right question to ask, and why? If energy in is renewable, then why would it matter how much it takes? With oil, return on investment isn’t even relevant to the question of whether it’s sustainable. We’re using up a non-renewable resource, and when it’s gone, it’s gone. The ratio of energy required to pull oil out of the ground compared to the energy it produces is a red herring.
Also what is the part about cat food about? Sorry I don’t get it. Are you suggesting everything needs to be accounted for up to and including cat food? Or is this a joke about over-accounting for things that aren’t directly related?
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A video of me surfing this wave.
https://www.instagram.com/reel/CPgfVHPlNJx/?utm_medium=copy_...