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The "Lech Fall" in Austria is a huge waterfall with a small peninsula on its inflow. This picture gives a nice overview:

Image of the "Lech Fall" in Füssen From Wikimedia

I was standing on that peninsula and experienced extremely strong changes of the water level. It rose that much, that half of the stony land was underwater in seconds! It randomly rose and fell (approximately every 5 minutes).

What causes these strong "tides"?

  • 2
    Possibly a dam or similar further upstream that releases after a certain amount of buildup? – Aravona Apr 28 '17 at 8:48
  • @Aravona Yep, good guess, also thought of that but it didn't quite make sense. Why would they constantly buffer and release that much water in such a random frequency? – OddDeer Apr 28 '17 at 8:56
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    Prob good to give a source for that photo, unless you took it of course, in which case I'm impressed! – user2766 Apr 28 '17 at 9:57
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    I wouldn't use the term tide when the cause can't be lunar. Changes in river level makes more sense. – Chris H Apr 28 '17 at 12:08
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    @ChrisH Thanks! I've changed the question accordingly. – OddDeer Apr 28 '17 at 13:57
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It looks a lot like there's a power station just downstream (photo), which can be seen on openstreetmap. I suspect that the power plant is being used to respond to peak loads for which hydro is very good. That whole stretch of river has several power stations and the flow through them will be coordinated to some extent. In particular there's a dam upstream of the falls.

TV pickup is a phenomenon where electricity demand spikes in the advertising breaks of popular TV programmes. It may be more of an issue in the UK than in some countries because of of the national obsession with tea-drinking and a significant fraction of the popoulation putting the kettle on at the same time but can account for surges in demand on the timescale you mention. It's also possible tht related to this you happened to be there at the right time for some sort of test/maintenance operation which resulted in opening/closing gates.

I'm slightly surprised that there aren't any warning signs telling people to stay out of the water as levels may change without warning. I've seen those before downstream of power stations.

  • We love a cuppa - we have similar issues in the UK during football matches with the water companies having to cope with hundreds of thousands of people suddenly flushing toilets. What a nation we are... – Aravona Apr 28 '17 at 14:23
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    @Aravona as I watch little TV and no football I can for once claim to not be part of the problem. For that matter I don't drink tea. But I promise I'm British really. – Chris H Apr 28 '17 at 15:07
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    Thanks for the answer Chris but I'm afraid that the power station is downstream of the "Lechfall". It flows in a north-north-easterly direction and crosses the German border, forming the Lechfall, a 12-metre-high (39 ft) waterfall; afterwards the river enters a narrow gorge (the Lechschlucht). Leaving the Alps, it enters the plains of the Allgäu at Füssen at an elevation of 790 metres (2,580 ft) in the German state of Bavaria, where it used to be the location of the boundary with Swabia. From Wikipedia. – OddDeer Apr 30 '17 at 5:52
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    The power station is downstream but the water control appears not to be. The German Wikipedia article Google translate - my German was barely enough to follow it - has more information but still not as much as I'd like. – Chris H Apr 30 '17 at 7:21
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    If you follow the Lech upstream in a satellite view, there is a channel that bears off south towards the road. You can see the water is emerging from underground and a building straddling the site. I assume this to be a turbine house for a run of river hydro scheme. Looking further upstream to Oberpinswang, you can see an intake where river level suddenly fall. While the spasmodic fluctuation you describe is odd, it may not be typical. It's possible it was due to maintenance measures on the day rather than a regular state of affairs. – Spagirl May 1 '17 at 22:43

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