28 November 2013

The duck of Linz

In the City of Wien, the people still remember the greatest flood along Danube, from Regensburg to the Kingdom of Hungary. They still remember, despite it happened 500 years ago, and the chance it would happen again is very low. In July and August of 1501. the heaviest rainfall hit the forehill region of the Alps in Austria and Germany causing a flood never seen before. North from the Danube basin, along the Elbe and the Oder vast deluge flooded the lands, just like back in Noah’s age.

High water mark collection in Passau (photo: cruises.about.com)
By the Rathausplatz of Passau (formerly the Fichmarkt) there is a flood sign on an arcaded house in an unreachable height. It marks the 1501 flood drawn by the summed discharge confluence of the Inn and Danube rivers. This flood arrived in time of harvest. Due to the flooded croplands people could not harvest their crops, which led to famine.

In Hungary, this flood also devastated the Danubian floodplains. Monasteries built on the shore or on islands were swalloved by the river. This catastrophic event subsisted in the annales by the monastery clerks. In Bratislava (Pozsony, Pressburg) the water level had been risen up in one night and the Danube flooded the lower parts of the city with the main square leaving no chance for the inhabitants to escape. In this city alone 53 people died. It must have been a kind of flash-flood, when the water level is rising very quickly due to large amount of rain falling within a very short time.

This catastrophic flood indicates the beginning of a new era in climate. Since the end of the XV. century the weather progressively became more humid and cold in Central Europe, ending the dry and warm climate optimum which affected Europe’s climate since the 10th century.
High water mark in Linz, 1501 (ooegeschichte.at)
„Hiermit disen stain beczaichene stat 
 wie hoch die Dunaw geraichet hat 
 Das ist beschehen im Monet Augusti 
 bey Regirung Römischen Künig Maximiliani 
 Da von Cristi gepurde erganngen war 
 Tawsennt Funfhundert und ain Jar“

The duck of Linz photo: H. Strecker
Marking the height of the water levels is as old as mankind. These two flood marks are not only indicating the highest flood ever measured on The Danube, but in the mean time they are the oldest remaining ones. And of course it is not enough to mark the floods, you need to learn from them!

Not much remained from the islands and floodplains of Vienna

In Vienna they utilized the experience learnt from the 1501 flood when designing the city’s new river regulation plans. They formed an artificial island in the middle of the Danube with an unique shape. The Donauinsel is 21,1 kilometers long but only 70-210 meters wide. It separates the two Danube arms which became able to channel a record 14000 cubic meter discharge/second. Why 14000 cubic meters? Hydrologists calculated that the 1501 flood reached the level of 10,3 meters regarding the recent gauging station value on Reichbrücke in Vienna. This value is seven times more than the recent average discharge. To understand how much water had been in the river in 1501: the high water of 2002 had the discharge only 10000 cubic meters.

In Budapest they calculate the mean high water mark from the level of the 1876 icy flood. This mark is taken into consideration when implementing flood protection investments. They include one extra meter of course for more safety.  Only time will tell which city’s calculations are more foresighted.

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