I'm sure I must've posted this on BPL before (apologies!), but I'll add it to this thread:
About 30 years ago my boyfriend and I decided to backpack the Na Pali Coast trail in Kauai. I don't think we'd ever done anything beyond car camping up to that point. We were woefully inexperienced; I decided that we didn't need sleeping bags, so we just took thermarests and our tent, and I slept in my 50/50 poly/cotton sweats!!! However, I found that it actually rained a lot there, as in starting about 30 minutes after we left the trailhead. It continued all day, including while we were crossing the Hanakapiai stream near the beginning of the hike. We managed to cross without getting our feet wet by hopping rock to rock, and noticed a rope crossing, about which I thought to myself "if the rain makes the stream get higher, we can use that to cross on the way back."
Well, it rained all day and all night, we woke up with our tent in an inch of water, and decided to turn around and go back (still raining). By the time we got to the "stream", it was a raging torrent, probably several feet deep; you could not see most of the rope because it was covered with white water. Most of the large boulders in the stream could not be seen. We set up our tent and decided to wait, but after a couple of hours we were pretty cold, having all our clothing drenched (amazing how cold Hawaii can be when you're soaking wet and the sun is not out).
After a while we heard some other hikers outside the tent; they had somehow moved the rope up to higher ground, perhaps in collaboration with someone on the other side, so that it floated atop the water between two trees. They had also gotten another rope from a life preserver at the shore of the ocean (not really a beach at that time of year, just roaring ocean, as I recall around 30-50 yards downstream from the trail, so that you'd get washed out to sea if you floated down!) and were using it to tie around the waist/chest of the person crossing the stream. Folks on the shore would hold the end of that rope while the one crossing went hand over hand on the fixed rope. We watched for a while, getting more and more scared but also more and more cold, and finally went across ourselves, floating our bodies on the current and going hand over hand probably 10-15 yards or so across. I have never been so scared in my life, nor so exhilarated as when we made it across! One guy before us lost hold of the rope, but was pulled back to shore by the rope around his waist, and made it the 2nd time.
I learned a lot of lessons on that trip, mostly about stupid things never to do again! I also got a healthy respect for the power of water, which I'd only known theoretically from reading up till that point.
This is a picture I found on the web that looks sort of what it looked like at the start of the hike: