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A lot of the fatal accidents in Yosemite National park come from people getting swept over waterfalls. Yes, the falls in Yosemite have fences and warning signs and yet people still ignore them.

If you were in a wilderness area and crossing a stream/river with a waterfall downstream of the crossing and there were no signs, how far above the waterfall should you cross?

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    Gut reaction- there is no one answer. It depends on depth, bottom composition, speed of current, how good your sense of balance is, and many other variables. – cobaltduck Nov 17 '16 at 18:21
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    If you are crossing by foot then how far up is mute. You walk straight across. How far up is for if you fall in and are carried by the current. – paparazzo Nov 17 '16 at 19:25
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    The incidents near Vernal Falls remind me of the saying, which I heard from a nuclear safety expert: You can make anything fool-proof, but nothing can be made damn-fool-proof. – ab2 ReinstateMonicaNow Nov 18 '16 at 2:42
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    As far as necessary, to find a safe crossing point. After that, your question becomes "How do I cross a river safely?" – Criggie Nov 18 '16 at 9:28
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The correct answer is as far upstream as you need to in order to swim/wade/jump across the stream and still provide the margin for error you are comfortable.

The problem answering the question in a more straight forward manner you have waterfalls like victoria falls (pictured below) that would almost certainly result in a fatal fall if you were to go over, but the chance of flushing over even when on the edge of the waterfall are low because of the depth and flow at the lip.

People bathing at the top of a waterfall

To Contrast here is huka falls, a waterfall that even hundreds of meters upstream you cannot safely cross because of the heavy currents and lack of exit points from the river.

enter image description here

In general you should avoid any water crossing with any meaningful current; unless you have whitewater experience or you can maintain your footing, shin deep or less, the entire time.

In an emergency type scenario ropes can be helpful to mitigate risks, but require careful application as they add complexity to a potentially dangerous situation. Again experience goes a long way.

Edit: I should probably add the Victoria falls is not actually travesable all the way across the lip, but was used as an extreme example of getting close to a lip of a waterfall in one location.

Source: I'm a whitewater enthusiast who has willingly gone over numerous waterfalls and navigated safely around even more using a variety of watercraft, swimming, wading etc.

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    low shin OK. high shin plus loose rock bad. this is based on little experience but I would be very careful about accidentally including a hard rule in an otherwise cautious answer. (Feel free to tell me I'm wrong, this just jumped out at me.) – djechlin Nov 18 '16 at 5:39
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    Just want to say that water in the second photo is beautiful! – NiCk Newman Nov 19 '16 at 9:28
  • "The correct answer is as far upstream as you need to in order to swim/wade/jump across the stream and still provide the margin for error you are comfortable." - that is not the answer, but the question... – AnoE Nov 19 '16 at 14:26
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    @djechlin I've fallen down a man-made feature in water that wasn't even over the soles of my shoes and I've held firm in water up to my neck while wearing floation. Mid shin is a general catch all guideline. I've done my best to provide a general case answer here when none was really available. Without these loose guidelines the answer becomes worthless except the cool pictures. – Glenn Nov 19 '16 at 20:44
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There are too many factors to consider to give anything like a precise answer.

I suggest a conservative rule of thumb for an average hiker, not a super athlete: if you can see or hear the waterfall and you cannot step or jump over the stream in one step or jump, you are too close.

If the waterfall is tiny, and/or the stream is shallow and slow, and/or there are some flat rocks in the stream this rule is too conservative.

Like everything else in TGO, the answer depends on judgement and the amount of risk a person is willing to take.

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    At least where I hike, that's far too conservative. Crossing a river that's 40 feet wide and 4 inches deep is not uncommon, and you can usually hear waterfalls from a mile or more away. – Mark Nov 17 '16 at 22:25
  • Where's that? 40 feet wide and 4 inches deep is not something I've ever seen. Rereading my answer, "and/or stream is shallow and slow" might cover your wide shallow river. But, I agree with your comment. – ab2 ReinstateMonicaNow Nov 17 '16 at 22:36
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    Lightning Creek in the Idaho Panhandle National Forest is a good example -- I've crossed it, moving slowly, without the water overtopping my boots. – Mark Nov 17 '16 at 22:42
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    12 metre wide and 1 dm deep is pretty common in Scandinavia. – gerrit Nov 18 '16 at 0:20
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    @gerrit You know how us Yanks are with metric... I thought that was the case but I wanted to make sure it wasn't a typo. In the States I see meters and centimeters fairly often. I haven't seen decimeters used since high school. – Erik Nov 23 '16 at 16:19
2

On pure math

ws = water speed
wd = width
ss = swimmer speed
us = how far upstream

us = wd * ws / ss

In reality the moving water will inhibit swimming speed compared to still water. Double that length might not be good enough.

If the water speed is slower than your swimming speed could angle upstream and swim straight across. But you rarely find slow water upstream from a water fall.

An average human can swim about 250 feet per minute. Throw a stick in the middle and measure how far it goes in a minute.

  • This doesn't take into account ferry angles (swimming upstream) which will drastically improve your ability to move across the current. Nor does it take into account other pertinent whitewater features like eddies, eddylines (whirlpools) etc, which may help or hurt your ability to move across. A stick thrown in may never reach the main current for estimation purposes. – Glenn Nov 17 '16 at 19:05
  • @Glenn Correct is does not account for all possibilities. It does cover you can swim at an angle. A ferry must ferry because the ferry dock is in a fixed location. Negative of ferry is you must swim further. If you cannot throw a stick to the middle then find a spot where you can. – paparazzo Nov 17 '16 at 19:14
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    You swimming speed is considerably too fast. I can't find a reference (academic or anecdotal) working out to over 200ft/min for swimmers who are trained enough to even measure it, and that's in a pool, without being burdened by hiking gear. I know short bursts of good speed are possible in kayaking gear, but swap the wetsuit boots for hiking boots and the bouyancy aid for a heavy rucksack and you'll struggle to swim at all until you've got rid of them, by which time you'll have been washed a long way downstream. – Chris H Nov 18 '16 at 9:51
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    @Paparazzi Same site: 2mph. I'm not sure how much to trust either of them (of course both could be right depending on your sample of people). A fair proportion of people "in a wilderness area" (to quote the Q) will be equipped like that, hence that bit. – Chris H Nov 18 '16 at 11:13
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    @ChrisH Should test yourself in a pool and then cut that in like 1/2 – paparazzo Nov 18 '16 at 11:18

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