Tuesday, 13 December 2016

Numbers, numbers

The Bodensee is pretty big. Being utterly lazy and looking on Wikipedia rather than doing a bit of GIS, the surface area of the lake is about 571 square kilometres. Approximately half the area of Dartmoor for the Devon reference. For someone who grew up thinking that Roadford Lake was pretty big (about 295 hectares), it's an impressive body of water.

I frequently find myself somewhat unsettled on an almost subliminal level to go dwn to the shoreline and discover that the tide has neither risen nor fallen. I'll get used to it. There are tidelines along the shore, a mix of decaying water plants and algae picked over by gulls, crows and Water Pipits, so there is a resemblance to the seashore. The lines mark the various windy periods and floods though, rather than any familiar ebb and flow.

There are water gauges at strategic points around the shore. Langenargen harbour has one which runs from the current level (somewhere over 3 metres) to 7 metres, with the notable floods of the past marked on it near the top. These are impressive enough just to look at as a red line on a board above the current lake level: the highest recorded flood was in 1871, reaching 6.91m - this level also carefully marked on the adjacent tourist information office wall. Then try and grasp the sheer volume of additional water present in the lake to reach that height! Even if you ignore the fact that the lake shore is rather flat and just run a 'cylinder' vertically upwards, trying to fit 3 metres of water onto half of Dartmoor is somewhat hard to comprehend.

Some fag-packet calculations (assuming my arithmetic is robust). When the water level in the lake reached 3m above what it is today, that works out to about 1,713,000,000 cubic metres of water. Some 685,200 Olympic-size swimming pools. Put more simply still, that's an awful lot of water. A;though the whole lake catchment is large, the major input of water to the lake is the Rhine: the river must have been an awe-inspiring sight, particularly at the Rhine Falls just below the lake's exit. At this point the river drops some 20m; spectacular at the quietest of times.

There it is folks, in black and yellow

And just to add weight to the tourist information office walls.

Langenargen harbour this morning.
For a post-script: the lake froze over on a number of occasions, the most recent being in 1963, when at least one brave chap apparently rode a horse across the lake. Given that you're crossing a body of water which reaches some 250m depth... well. Where is the dividing line between bravery and foolhardiness, I wonder? I also wonder what the horse thought about it?

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