Measuring the Babacai cliff

IN HUNGARIAN

Stupidity is contagious, especially on the internet, where people copy nonsense from each other. The question of the height of the Babakai rock on the Al-Dunan is like the same wrong answer in a school test example. We don't know who copied it from whom, but I think it's important to have at least one correct answer, so we're going to measure the Babacai rock, located near Coronini.  

"Babakai Rock used to be a 50-metre high cliff in the Danube, but since the construction of the Iron Gate power plant, only the top of the cliff has been sticking out of the river." 

Whether you read (the Hungarian) wikipedia or other online descriptions of the Lower Danube, the Babacai rock was 50 metres high before the construction of the Iron Gate power plant. The same descriptions estimate the height of the current cliff at 6-7 metres. This Jurassic limestone cliff, which in Turkish means grandfather (wise old man), still defines the image of the Danube, which narrows from two kilometres to 400 metres between Coronini and Golubac. Now imagine how a 15-storey cliff would define the Danube?

At 50 metres, the height would most closely resemble a telecommunications tower made of stone. Since it only rises six or seven metres above the Danube, it is easy to calculate that the Danube must have risen by 43 metres in 1972, when the Iron Gate I power station, located about 100 river kilometres from Babakai Rock (1,041 km), was completed. Except that the Iron Gate I power plant has caused a dam to rise 33 metres, up to 35 metres, and this value is decreasing as we move away from the dam upstream. If the Babacai rock had been somewhere around Ada Kaleh there would still have been 15-17 metres left instead of 6-7. It is therefore easy to see that a height of 50 metres is, to put it mildly, a baroque exaggeration.

But how can we determine the true height of the rock? 

We need a contemporary geological description of it, or if not at hand at least a picture to help us. Of course, it wouldn't hurt to have a scale next to the rock to give an indication of the true height. It would take a rare stroke of luck to find one, but for once we were lucky. The picture you want is available on the Hungaricana website: 

Judging by the style of the picture, it was undoubtedly taken before the creation of the reservoir. We still have the base of the cliff, where it could have been moored. It shows a tree braving the elements and, directly next to it, two "castaways", just the right scale. If we estimate their height at 1.7 to 1.8 metres, we can determine the height of the Babacai cliff for a given water level by a simple pair of ratios.

Based on this calculation, the height of the Babakai rock is between 14 and 15 metres.

If in doubt about the accuracy of the calculation, validation can be done with the towers of the castle of Golubac, located on almost the same river-kilometre section, which have been flooded by the Danube since the construction of the dam. 

Naturally, the rock appears lower at high tide and higher at low tide. That's no small feat; 4-5 storeys. But by no means 50 metres.

It would be nice if everyone corrected it for the next lesson! ;)

Translated with www.DeepL.com/Translator (free version)