Low Head Dams -- Danger

Discussion in 'Paddling' started by werewolf won, Apr 8, 2019.

  1. werewolf won

    werewolf won TANSTAAFL Supporter Bushcraft Friend

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    herr.jpg herr1.jpg
    These are a special kind of frequently fatal trap for a paddler. The picture is of a fish ladder, the steps are only about 18”, and the water is flowing faster than you could walk, but a fast sprinter might keep pace. If you canoe was three feet long these would be a nice scale model of a low head dam.

    The second picture shows the problem. The water from the top edge of the photo is traveling towards the bottom edge; the water at the bottom is going back up stream at the same speed it is traveling over the drop at. The water at the surface is traveling up stream—not flowing down the river. The water rolls over itself many times before getting to the bottom of the face of the drop and finally flushes downstream. In this case the out flow is almost 10 feet downstream—and this is a tiny drop.

    A dam as low as three foot tall with a moderate flow over it is more than sufficient to roll a canoe and it’s passengers over and over till the hull is so much flotsam and the passengers are drown.

    How do you deal with these? Avoid them is best; get out and carry around them. Be aware that anytime you see a straight line on a river it is a danger sign. It is a sign of a terrain change—might be a dam, a waterfall, or the start of rapids; always scout straight lines on unknown rivers. If you having to end up going over a low head dam do it with gusto, paddle hard and stay straight and don’t stop paddling until you are well down stream of it.

    If you screw up and end up parallel in the trough, lean downstream on a high brace, reach as far down stream as you can and put in an almighty powerful draw stroke to try to pull the bow up over the wave. The other thing to do is work your way to the edges of the dam where the water does flow out of the trough. And be thankful you’re in a canoe on your knees as it’s a good position for talking to your God.

    If you capsize and are getting turned over and over (window shading is the term white water folks call this – indistinguishable from a death roll as far as I’m concerned) Try reaching to the bottom where the water is flowing out, you might be flushed out. It also one of the few times shedding your PFD and being less buoyant might save you.
     
    Last edited: Apr 8, 2019
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  2. FreeMe

    FreeMe Guide

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    Also known as "maytagging".

    Here's one of our local hazards....

    [​IMG]

    Anyone attempting to run that is almost guaranteed to be caught in the undertow. Paddling up to it from below is also very dangerous. Someone attempting to paddle up and rescue a swimmer or boater caught in such recirculating water will find it difficult to impossible to escape the suck. This photo was taken at high spring flood flows. It looks a lot less threatening at lower flows, but is still a killer. If you ever find yourself involved in a rescue operation at such a site, be assured that you will need lots of rope and knowledge to pull it off and survive.

    edit: Another thing about escape.....
    WWW's comment about going deep to get below the recirculating water near the top is correct, in general. But this feature, in particular, has the added hazard of jagged rocks and debris hidden below, which are likely to snag and trap a swimmer.

    Short of executing a highly skilled rescue, there just isn't any good reason to risk running any such dam in common recreational paddlecraft (including whitewater kayaks). We had another below this one until a few years ago (it was replaced with a safer feature) that was the scene of too many drownings over the years. It looked much less dangerous than this one - which maybe was part of the problem.
     
    Last edited: Apr 8, 2019
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  3. stillman

    stillman Supporter Supporter Bushclass I

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    These don't look too dangerous to the unknowing eye. Thanks for the warning.
     
  4. werewolf won

    werewolf won TANSTAAFL Supporter Bushcraft Friend

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    That is part of what makes them so dangerous, they look pretty mundane.
     
  5. werewolf won

    werewolf won TANSTAAFL Supporter Bushcraft Friend

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    "But this feature, in particular, has the added hazard of jagged rocks and debris hidden below, which are likely to snag and trap a swimmer."


    Many if not all dams and waterfalls have that problem, they collect all kinds of debris that can be dangers. The feature that makes a dam or waterfall is usually rock, stone or concrete structure and they can easily become body traps too.
     
  6. JeffG

    JeffG Scout

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    Great article, and yes they are dangerous!
     
  7. badgerthehobo

    badgerthehobo Unathletic supporter Supporter Bushclass I

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    This is much appreciated. I’ve been getting back into canoeing/kayaking lately and a lot of the rivers out here have dams like this. I vote for a sticky. Or Pin. Whatever it’s called now, stick it at the top of the forum!
     
  8. M.Hatfield

    M.Hatfield Midnight Joker #42 Supporter

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    I remember kayaking a bit too close to one when I was younger. Not an experience I would like to repeat. :confused:
     
  9. FreeMe

    FreeMe Guide

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  10. werewolf won

    werewolf won TANSTAAFL Supporter Bushcraft Friend

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    The other nasty that catches and kills is the strainer. A strainer can be a lot of things but usually are trees that reach their branches into the water. Common when river’s flood their normal banks, but some river are lined with them year round too. The danger of a strainer is often the current will run right into them but unlike a rock or bridge abutment that will have an eddy and wave structure around it the strainer has nothing but lots of flexible structure just waiting to tangle your boat, equipment or your body up in.

    They can hold you under quit well just as is but combined with the common cold water in spring flood paddling adding hypothermia to the mix makes an already dangerous thing all that more deadly.
     
    Last edited: Apr 8, 2019
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  11. FreeMe

    FreeMe Guide

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    Sweeper/strainer on the left. As is often the case, that is also where the deep channel is, and where the current tries to push you. Notice the narrow safe path.

    2010_0513BoiseRiverMay20100085.JPG
     
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  12. Porkeater

    Porkeater Tracker

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    Several communities in my area have replaced low head dams with whitewater parks. It's a double win - danger reduced significantly and a fun place to play.
     
  13. werewolf won

    werewolf won TANSTAAFL Supporter Bushcraft Friend

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    It’s the current that washed away the soil from the roots and cause the tree to bend over and it is that same current that will want to push you that way. These are especially dangerous because they can form overnight on seemingly gently flowing rivers otherwise free from rapids and waterfalls.
     
  14. RavenLoon

    RavenLoon axology student Supporter

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    I was working with a guy on the Grand Rapids fish ladder on the old dam downtown Grand Rapids Michigan once many years ago. The dam is only a few feet high but the Grand River is very powerful and wide right there. He slipped and fell in. Even though he had on a life preserver he got caught in the vortex and would repeatedly get sucked down sometimes for several seconds, it seemed like over a minute at a time he was under. Luckily two fishermen in a boat were able to get close enough to grab him when he surfaced. He came very close to drowning. He was a good swimmer but he later said there was no way he could escape the vortex.
     
  15. FreeMe

    FreeMe Guide

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    That's a fact. The class 1 stretch in that photo has new such hazards every year.
     
  16. Boondocks70

    Boondocks70 Scout

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    Also worth mentioning, the reverse flow on the low side of the dam is often over-aerated. This causes a significant loss of bouyancy in any watercraft or PFD. Kinda like getting your boat or PFD to float on air.....won't work.
    Saw a video many years ago of a low-head dam rescue using a john-boat. As the boat got closer to the bottom edge of dam, you could see it riding noticeably lower in the water. Almost to the gunwales. Scary, scary stuff.
    WALK AROUND, DON'T DROWN.
     
  17. FreeMe

    FreeMe Guide

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    Thanks for bringing that up. Another difficulty piled on to the danger.
     
  18. werewolf won

    werewolf won TANSTAAFL Supporter Bushcraft Friend

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    Low head dam group rescue:
    You certainly can try a throw rope, but usually the victim is getting so tossed about if you don’t hit them right in the smacker they will not get the line. You might approach from downstream with a boat; again the victim might not even realize you are there. If the river is not too wide a line can be stretched across it and with a rescuer of each side walk the line right through the trough and snag the victim. You can tie a life vest between two lines and float that through the trough as well. If you have a long enough line you could paddle it across a river too wide to throw across naturally, this will also put people on both sides of the dam which you need.

    You could also swing a strong swimmer on a good line in from upstream, but that is really the realm of a very experienced team.
     
  19. FreeMe

    FreeMe Guide

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    Or you can attach a lead rope to a rescue craft approaching from below, and feed the line in so as to have a way to pull it back out of the boil, while someone riding the craft reaches for the victim. A common rescue craft is a "U" shaped inflatable with the open end facing the victim. Two canoes or kayaks can also be lashed together for an improvised craft, if time allows. (that assumes the swimmer isn't being violently recirculated, and in immediate danger of drowning)
     
  20. Forestree

    Forestree Treeforest Supporter Bushclass I Bushclass II

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    This is a great heads up as many folks would look at this as a fun challenge to go over in a boat. You don’t have to watch many YouTube videos to see how dangerous they can be. It wasn’t until I got trapped in a roller ( with pfd on) on the Nolichucky river for a short time that I learned to respect the force of water. That was the scariest moment I’ve ever had on the water....luckily i got spit out but haven’t forgotten it
     
  21. Porkeater

    Porkeater Tracker

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    That reminded me of this rescue:

     
  22. FreeMe

    FreeMe Guide

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    She's fortunate that she had enough buoyancy to stay above the froth. One benefit of inflatable craft.

    Speaking of aerated water - whitewater paddlers know this....not only does it reduce buoyancy, but it also reduces the effectiveness of paddles and oars. That's another reason you can get into trouble quickly, where it doesn't look that threatening to the untrained eye.
     
  23. Panzer

    Panzer Prepared Wanderer Supporter Bushclass I

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    more drowning deaths by low head damns then any other kind of boating accident here in Ohio. From what I have been told by fire river rescue
     
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  24. mongo1958

    mongo1958 Supporter Supporter

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    When water is heavily aerated, it is less dense, we don't float as well, even with a pfd.
     
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