6 ms·

Acquaintance did some suburban kayaking and didn't see a 3ft drop (some kind of dam or culvert under a bridge) until too late. The fluid mechanics of that drop

Acquaintance did some suburban kayaking and didn't see a 3ft drop (some kind of dam or culvert under a bridge) until too late. The fluid mechanics of that drop are such that there is a vortex at the base that makes it difficult to get out. He was able to stand but just barely - scary to think how close a call that was in a pretty innocuous looking setting.

giraffe_lady 4y ago
Yeah those things are notorious for that. Place I grew up in had a lot of small rivers you could pretty much wade across most of the year. But you'd still hear of drownings every once in a while and if it wasn't a small child it was always someone going over a low head dam.
gonzo41 4y ago
That's called hydrolic lock. It kills experienced people all the time. Weir style dams are so subtle and dangerous.
AYBABTME 4y ago
I almost drowned on a beach without surveillance, jumping into the surf waist high, for fun, until suddenly the receding water pulled me just a few meters further away and now I couldn't touch the floor anymore, and was slowly being pulled further and further away from the beach. My girlfriend of the time was on the beach far enough away that she couldn't hear or grasp that I was struggling. By luck and after perhaps 10 minutes of fighting, I managed to move sideways and forward by persistence until I could touch the ground again and walk out. I was completely exhausted and I'm not sure how much longer I could have persisted like this. Just as I exited a few locals were arriving in haste for me. Apparently they had seen me struggling to come back. I'm guessing they had witnessed tragedies there before, because whereas my girlfriend hadn't picked up that I was in trouble, they had.
- scanny 4y ago
  Sounds like you encountered a "rip" [0]; usually letting it take you out and then swimming after the current eases is the safest thing to do. At school (Oceania) we get taught this as part of water safety, but I suppose it would be a foreign concept to many people, particularly those not living near the coast. [0] https://en.wikipedia.org/wiki/Rip_current https://en.wikipedia.org/wiki/Rip_current
  - anthomtb 4y ago
    Can confirm. My childhood in Colorado taught me nothing of rip currents. A few weeks on the east coast of Australia was quite the eye-opener.
  - vasco 4y ago
    I was taught to immediately start swimming parallel to the beach. Some rip tides can take you very far away very quickly, enough that nobody would be able to get to you without a boat, and that is if they were looking at you. Best advice is to swim parallel to the beach, while remaining calm and swiming at a pace you can hold. Do not sprint-swim due to fear.
    - danenania 4y ago
      Swimming parallel to the beach will get you out of it, but it could be a struggle depending on the width of the rip and the size of the waves. Getting past the break first is often easier since then you can swim parallel to the beach and away from the rip without having to deal with waves breaking on you.
- danenania 4y ago
  The key in surf is to never fight against the rip. While it can feel scary to get pulled out, remember that 99% of the time, it will end after you are pulled past the break, at which point you can swim laterally a bit and then go back in with help from the waves. Breaking waves naturally create alternating channels in the sand that either push you towards the shore or pull you back out to the break. The other 1% of the time is when you are close to the mouth of a bay or some other feature that creates a current independent of the dynamics in the surf zone. You'll know that's the case if the current stays strong after you're past the break. If it's too strong for you to swim against it, then you're in trouble and should start waving for help.
  - rozab 4y ago
    The good news is if you don't struggle against the current you should be able to stay afloat for a couple hours, long enough for help to arrive
    - ogre_battle 4y ago
      A couple hours in even moderately chilly water -- to include off the coast of California -- will give you hypothermia in an hour, often as little as 30 minutes. If you have to float for 2 hours without being able to get out you'll have a problem. Rip tides pull out, so let them pull you past the break then swim side to side. You shouldn't need more than 15-20 min to get past the worst of it, and can work laterally to inbound waves.
- jakogut 4y ago
  I watched numerous tourists do this in Cancun from our penthouse rental on vacation. In one case, a full-grown man was swept out approximately 100m and kept getting tugged and dashed by the waves as he fought them. A lifeguard kept whistling to him from shore and motioning to move perpendicular to the current to get back to shore, and he finally did. We also saw lifeguards retrieve a drowned child. They worked on him for about fifteen minutes in front of the parents before stopping, and the ambulance took him away. The beaches were marked with red flags as far as the eye could see, along with signs in English and Spanish clearly indicating that this meant swimming was prohibited, as it was unsafe. Many people paid no heed to the warnings.
- MrFantastic 4y ago
  If you aren't strong swimmer you should not play in ocean waves. If you don't know if you are a strong swimmer you are NOT. The ocean doesn't give a shit about your life.
  - dsfyu404ed 4y ago
    Why not just tell people never to swim? There are never "no waves" when you are at an ocean beach. These sorts of absolutist rules of thumb are of no benefit to anyone but the people offering them up. People will go swimming in the ocean and in all myriad of bays and estuaries that are more than capable of having enough surf to kill them depending on the weather. You just need to exercise good judgement about how much surf is too much.
  - alar44 4y ago
    That's just ridiculous. Most public beaches are perfectly safe.
    - ygjb 4y ago
      That's a lie that people tell themselves. It is fairly safe at most public beaches if: * you follow the posted signs for rules (e.g. where it's safe to dive, staying in marked areas), flags for current conditions * pay attention to weather conditions * know (roughly) when and how much of a change the tide will bring Unfortunately, a significant number of people don't follow the rules, or underestimate the risk. There is a reason many public beaches located within an urban center have lifeguards and patrols.
      - alar44 4y ago
        No, it’s true. Death by drowning in a riptide is a 100 people a year in the US. That’s almost literally nothing.
- whimsicalism 4y ago
  Interesting. I think they teach to not swim against rip currents in primary school now. I did not live near the coast
- xenadu02 4y ago
  Drowning doesn't look like drowning. The thing they show in movies or on TV is not what happens so most people have no clue when someone is in trouble. In some cases kids drown in pools while parents are not only present but looking right at them. In others like yours people wave and smile from the beach as the person in the surf is about to die. Mayo Clinic: https://www.youtube.com/watch?v=h0FH9b1LiwY https://www.youtube.com/watch?v=h0FH9b1LiwY WebMD Spot the Drowning Person: https://www.youtube.com/watch?v=beNheoRRdKk https://www.youtube.com/watch?v=beNheoRRdKk Another one is Bondi Beach - you can find episodes on YouTube. There are a bunch of examples of rescues and how little notice any of the people on the beach or other swimmers nearby give to people struggling.
  - PebblesRox 4y ago
    This interactive website lets you test your ability to spot drowning and develop a sense of what to watch out for - can you see which person in the wave pool is drowning before the lifeguard blows the whistle and jumps in? http://spotthedrowningchild.com/ http://spotthedrowningchild.com/
- dkarp 4y ago
  I used to live on a popular surfing beach in Australia. Every day people would see the surfers and think it was a good place to swim and get into trouble (In general, if you see surfers then it's a bad place to swim). Always swim near the lifeguard's tower and pay attention to the flags
  - bagels 4y ago
    Even without a rip, swimming where the surfers are is just going to get you knocked in the head by a board or yelled at.
  - Prcmaker 4y ago
    Yep! We used to ride the rip out on boards as it was easier than paddling through the waves. Dart across once you're out the back then catch a wave in.
giantg2 4y ago
Yep, we call those low head dams around here. It's like the roll under a big surf wave, but perpetual.
bombcar 4y ago
https://www.weather.gov/lmk/LowHeadDamPublicSafetyAwarenessMonth https://www.weather.gov/lmk/LowHeadDamPublicSafetyAwarenessM... Low head dams are the drowning machine, and they can look very safe and simple.
- james_pm 4y ago
  Practical Engineering discussed low head dams: https://www.youtube.com/watch?v=GVDpqphHhAE https://www.youtube.com/watch?v=GVDpqphHhAE
- hinkley 4y ago
  There's a lot of pressure to get rid of these things. Maybe not as much as there should be.
  - bombcar 4y ago
    Nobody really wants them anymore, it's just the cost of removal (and finding who is "responsible").
cafard 4y ago
Back in the 1980s, a number of soldiers drowned in the hydraulic below the dam at the Little Falls pumping station on the Potomac. One of Tufte's books (I think Envisioning Information) includes the illustration of the effect that The Washington Post published shortly after that.
el_nahual 4y ago
Those are called "weirs", and often known as drowning machines. Practical Engineering on youtube has a great video about them: https://www.youtube.com/watch?v=YkR79oDAgOg&vl=en https://www.youtube.com/watch?v=YkR79oDAgOg&vl=en
- DLwdTxdU6smHQA 4y ago
  The same guy has a video called "The Most Dangerous Dams" [length 8:43]. It seems so be less technical and more focused on the dangerous aspects. edit: link https://www.youtube.com/watch?v=GVDpqphHhAE https://www.youtube.com/watch?v=GVDpqphHhAE
jollyllama 4y ago
Yep. A couple of girls got killed in Pittsburgh a few years back. They were kayaking down the river and didn't realize a dam was ahead. People die all the time in nature for lack of preparedness because they don't know the environment they are getting into and they don't know their limitations. This also endangers rescuers.
- shagie 4y ago
  Practical Engineering has a video on the dangers of a lowhead dam - https://youtu.be/GVDpqphHhAE https://youtu.be/GVDpqphHhAE
  - psychphysic 4y ago
    What on Earth!? I just submitted Kyle Hills video on this early today to HN. What an eery coincidence. I hope it's not a bad omen that I keep coming across this topic today...
    - antipotoad 4y ago
      Seems about five others of us also linked his video in this thread :) Guess you’re experiencing the Baader-Meinhof effect, AKA the frequency illusion [1]. [1]: https://en.m.wikipedia.org/wiki/Frequency_illusion https://en.m.wikipedia.org/wiki/Frequency_illusion
      - shagie 4y ago
        It is interesting that Practical Engineering is an often-cited channel on HN. Not surprising, but rather a good indication of its content, quality, and value.
  - whymauri 4y ago
    I crossed a small dam solo hiking the Wichita Mountains. Not the one at Kite Trail on the Bison Trail Loop (Lost Lakes) which is wide and dry, but completely off trail since I had to get off trail to avoid bison. It was mossy with very little traction and I almost slipped. Brushed it off as an annoyance since I didn't get wet. Watched this video a year later and it made me think... how deep was that water, and was it really as calm as it seemed? Yikes.
codeduck 4y ago
weirs are drowning machines. Nothing more, nothing less.
antipotoad 4y ago
See this video from Practical Engineering, aptly titled ‘The Drowning Machine’: https://practical.engineering/blog/2019/3/16/drowning-machine-the-dangers-of-low-head-dams https://practical.engineering/blog/2019/3/16/drowning-machin...

giraffe_lady 4y ago

Yeah those things are notorious for that. Place I grew up in had a lot of small rivers you could pretty much wade across most of the year. But you'd still hear of drownings every once in a while and if it wasn't a small child it was always someone going over a low head dam.

gonzo41 4y ago

That's called hydrolic lock. It kills experienced people all the time. Weir style dams are so subtle and dangerous.

AYBABTME 4y ago

I almost drowned on a beach without surveillance, jumping into the surf waist high, for fun, until suddenly the receding water pulled me just a few meters further away and now I couldn't touch the floor anymore, and was slowly being pulled further and further away from the beach. My girlfriend of the time was on the beach far enough away that she couldn't hear or grasp that I was struggling. By luck and after perhaps 10 minutes of fighting, I managed to move sideways and forward by persistence until I could touch the ground again and walk out. I was completely exhausted and I'm not sure how much longer I could have persisted like this. Just as I exited a few locals were arriving in haste for me. Apparently they had seen me struggling to come back. I'm guessing they had witnessed tragedies there before, because whereas my girlfriend hadn't picked up that I was in trouble, they had.

scanny 4y ago
Sounds like you encountered a "rip" [0]; usually letting it take you out and then swimming after the current eases is the safest thing to do. At school (Oceania) we get taught this as part of water safety, but I suppose it would be a foreign concept to many people, particularly those not living near the coast. [0] https://en.wikipedia.org/wiki/Rip_current https://en.wikipedia.org/wiki/Rip_current
- anthomtb 4y ago
  Can confirm. My childhood in Colorado taught me nothing of rip currents. A few weeks on the east coast of Australia was quite the eye-opener.
- vasco 4y ago
  I was taught to immediately start swimming parallel to the beach. Some rip tides can take you very far away very quickly, enough that nobody would be able to get to you without a boat, and that is if they were looking at you. Best advice is to swim parallel to the beach, while remaining calm and swiming at a pace you can hold. Do not sprint-swim due to fear.
  - danenania 4y ago
    Swimming parallel to the beach will get you out of it, but it could be a struggle depending on the width of the rip and the size of the waves. Getting past the break first is often easier since then you can swim parallel to the beach and away from the rip without having to deal with waves breaking on you.
danenania 4y ago
The key in surf is to never fight against the rip. While it can feel scary to get pulled out, remember that 99% of the time, it will end after you are pulled past the break, at which point you can swim laterally a bit and then go back in with help from the waves. Breaking waves naturally create alternating channels in the sand that either push you towards the shore or pull you back out to the break. The other 1% of the time is when you are close to the mouth of a bay or some other feature that creates a current independent of the dynamics in the surf zone. You'll know that's the case if the current stays strong after you're past the break. If it's too strong for you to swim against it, then you're in trouble and should start waving for help.
- rozab 4y ago
  The good news is if you don't struggle against the current you should be able to stay afloat for a couple hours, long enough for help to arrive
  - ogre_battle 4y ago
    A couple hours in even moderately chilly water -- to include off the coast of California -- will give you hypothermia in an hour, often as little as 30 minutes. If you have to float for 2 hours without being able to get out you'll have a problem. Rip tides pull out, so let them pull you past the break then swim side to side. You shouldn't need more than 15-20 min to get past the worst of it, and can work laterally to inbound waves.
jakogut 4y ago
I watched numerous tourists do this in Cancun from our penthouse rental on vacation. In one case, a full-grown man was swept out approximately 100m and kept getting tugged and dashed by the waves as he fought them. A lifeguard kept whistling to him from shore and motioning to move perpendicular to the current to get back to shore, and he finally did. We also saw lifeguards retrieve a drowned child. They worked on him for about fifteen minutes in front of the parents before stopping, and the ambulance took him away. The beaches were marked with red flags as far as the eye could see, along with signs in English and Spanish clearly indicating that this meant swimming was prohibited, as it was unsafe. Many people paid no heed to the warnings.
MrFantastic 4y ago
If you aren't strong swimmer you should not play in ocean waves. If you don't know if you are a strong swimmer you are NOT. The ocean doesn't give a shit about your life.
- dsfyu404ed 4y ago
  Why not just tell people never to swim? There are never "no waves" when you are at an ocean beach. These sorts of absolutist rules of thumb are of no benefit to anyone but the people offering them up. People will go swimming in the ocean and in all myriad of bays and estuaries that are more than capable of having enough surf to kill them depending on the weather. You just need to exercise good judgement about how much surf is too much.
- alar44 4y ago
  That's just ridiculous. Most public beaches are perfectly safe.
  - ygjb 4y ago
    That's a lie that people tell themselves. It is fairly safe at most public beaches if: * you follow the posted signs for rules (e.g. where it's safe to dive, staying in marked areas), flags for current conditions * pay attention to weather conditions * know (roughly) when and how much of a change the tide will bring Unfortunately, a significant number of people don't follow the rules, or underestimate the risk. There is a reason many public beaches located within an urban center have lifeguards and patrols.
    - alar44 4y ago
      No, it’s true. Death by drowning in a riptide is a 100 people a year in the US. That’s almost literally nothing.
whimsicalism 4y ago
Interesting. I think they teach to not swim against rip currents in primary school now. I did not live near the coast
xenadu02 4y ago
Drowning doesn't look like drowning. The thing they show in movies or on TV is not what happens so most people have no clue when someone is in trouble. In some cases kids drown in pools while parents are not only present but looking right at them. In others like yours people wave and smile from the beach as the person in the surf is about to die. Mayo Clinic: https://www.youtube.com/watch?v=h0FH9b1LiwY https://www.youtube.com/watch?v=h0FH9b1LiwY WebMD Spot the Drowning Person: https://www.youtube.com/watch?v=beNheoRRdKk https://www.youtube.com/watch?v=beNheoRRdKk Another one is Bondi Beach - you can find episodes on YouTube. There are a bunch of examples of rescues and how little notice any of the people on the beach or other swimmers nearby give to people struggling.
- PebblesRox 4y ago
  This interactive website lets you test your ability to spot drowning and develop a sense of what to watch out for - can you see which person in the wave pool is drowning before the lifeguard blows the whistle and jumps in? http://spotthedrowningchild.com/ http://spotthedrowningchild.com/
dkarp 4y ago
I used to live on a popular surfing beach in Australia. Every day people would see the surfers and think it was a good place to swim and get into trouble (In general, if you see surfers then it's a bad place to swim). Always swim near the lifeguard's tower and pay attention to the flags
- bagels 4y ago
  Even without a rip, swimming where the surfers are is just going to get you knocked in the head by a board or yelled at.
- Prcmaker 4y ago
  Yep! We used to ride the rip out on boards as it was easier than paddling through the waves. Dart across once you're out the back then catch a wave in.

giantg2 4y ago

Yep, we call those low head dams around here. It's like the roll under a big surf wave, but perpetual.

bombcar 4y ago

https://www.weather.gov/lmk/LowHeadDamPublicSafetyAwarenessMonth https://www.weather.gov/lmk/LowHeadDamPublicSafetyAwarenessM... Low head dams are the drowning machine, and they can look very safe and simple.

james_pm 4y ago
Practical Engineering discussed low head dams: https://www.youtube.com/watch?v=GVDpqphHhAE https://www.youtube.com/watch?v=GVDpqphHhAE
hinkley 4y ago
There's a lot of pressure to get rid of these things. Maybe not as much as there should be.
- bombcar 4y ago
  Nobody really wants them anymore, it's just the cost of removal (and finding who is "responsible").

cafard 4y ago

Back in the 1980s, a number of soldiers drowned in the hydraulic below the dam at the Little Falls pumping station on the Potomac. One of Tufte's books (I think Envisioning Information) includes the illustration of the effect that The Washington Post published shortly after that.

el_nahual 4y ago

Those are called "weirs", and often known as drowning machines. Practical Engineering on youtube has a great video about them: https://www.youtube.com/watch?v=YkR79oDAgOg&vl=en https://www.youtube.com/watch?v=YkR79oDAgOg&vl=en

DLwdTxdU6smHQA 4y ago
The same guy has a video called "The Most Dangerous Dams" [length 8:43]. It seems so be less technical and more focused on the dangerous aspects. edit: link https://www.youtube.com/watch?v=GVDpqphHhAE https://www.youtube.com/watch?v=GVDpqphHhAE

jollyllama 4y ago

Yep. A couple of girls got killed in Pittsburgh a few years back. They were kayaking down the river and didn't realize a dam was ahead. People die all the time in nature for lack of preparedness because they don't know the environment they are getting into and they don't know their limitations. This also endangers rescuers.

shagie 4y ago
Practical Engineering has a video on the dangers of a lowhead dam - https://youtu.be/GVDpqphHhAE https://youtu.be/GVDpqphHhAE
- psychphysic 4y ago
  What on Earth!? I just submitted Kyle Hills video on this early today to HN. What an eery coincidence. I hope it's not a bad omen that I keep coming across this topic today...
  - antipotoad 4y ago
    Seems about five others of us also linked his video in this thread :) Guess you’re experiencing the Baader-Meinhof effect, AKA the frequency illusion [1]. [1]: https://en.m.wikipedia.org/wiki/Frequency_illusion https://en.m.wikipedia.org/wiki/Frequency_illusion
    - shagie 4y ago
      It is interesting that Practical Engineering is an often-cited channel on HN. Not surprising, but rather a good indication of its content, quality, and value.
- whymauri 4y ago
  I crossed a small dam solo hiking the Wichita Mountains. Not the one at Kite Trail on the Bison Trail Loop (Lost Lakes) which is wide and dry, but completely off trail since I had to get off trail to avoid bison. It was mossy with very little traction and I almost slipped. Brushed it off as an annoyance since I didn't get wet. Watched this video a year later and it made me think... how deep was that water, and was it really as calm as it seemed? Yikes.

codeduck 4y ago

weirs are drowning machines. Nothing more, nothing less.

antipotoad 4y ago

See this video from Practical Engineering, aptly titled ‘The Drowning Machine’: https://practical.engineering/blog/2019/3/16/drowning-machine-the-dangers-of-low-head-dams https://practical.engineering/blog/2019/3/16/drowning-machin...