Sunday, 23 August 2015

Hydrology - droughts, floods and sandbanks

Consider the following two photographs, both taken from the same point (at the estuary of the Jeziorka river, where it meets the Vistula). One was taken today - the other on 22 September 2012.

23 August 2015
22 September 2012
We'll have to wait a month to see whether the water levels in the Vistula fall to the same record low levels that they did three years ago, when the exposed riverbed yielded up historic artifacts, some dating back to the Swedish invasion of Poland in 1648.

While we wait, it is instructive to look at some satellite images of this very stretch of the Vistula over the years, courtesy of Google Earth. What's interesting is the way the sandbanks appear, disappear and shift over time. You can see the Jeziorka meeting the Vistula in the lower-middle of each pic. Sadly, there are no images of the floods of May/June 2010, nor of the drought of September 2012.

Image dated 3 April 2002

27 March 2007

23 July 2009

4 April 2011

1 May 2012

4 August 2013 - highest water in this sequence

11 March 2014 - lowest water in this sequence. Sandbank in second pic from top is visible.

4 October 2014
And so we have it - the river rises, the river falls, depending on the rain that falls in the mountains several hundred kilometers downstream. I will check back in a month's time - assuming the weather stays as dry as forecast - to see if that big sandbank has reappeared. In the meanwhile, don't place too much store on media panic. Nothing beats empiric observation of fact.

This time two years ago:
Radom air show - Part 1

This time three years ago:
Restricting passenger movement and safety

This time four years ago:
Seasonal fruit - eat it in bulk, while you can!

This time six years ago:
Russia-Polish 'unification', 1939-style

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