It’s Europe’s second longest river flowing from the Black Forest to the Black Sea. But the Danube is much shorter than it was two centuries ago.
Human activity along the river has shrunk its length by 134 kilometers and made it 40% narrower in parts, a German study looking at the river’s sediment deposit shows.
The Bavarian State Office for the Environment made the announcement Tuesday in Augsburg, according to German news agency DPA.
These changes were caused by straightening, flood protection measures and dam construction.
Officially, the Danube is now 2,857 kilometers long. In the 19th century, the river was almost 3,000 kilometers long, a spokeswoman for the state office said.
The study will now investigate the negative consequences of the construction measures and propose countermeasures.
Under the mainly EU-funded project, 14 institutions from 9 countries bordering the Danube analyzed the sediment budget of the Danube for about 3 years.
The reason is that after construction work on the river, large quantities of the suspended matter transported by the water no longer arrive in the Danube Delta in eastern Romania.
It was once said that 40 to 60 million tons of suspended matter reached the Black Sea estuary every year. Now there are only 15 to 20 million tons.
Instead, the suspended matter is deposited along the river and thereby changes the course of the river.
“The first sediment balance of the Danube shows that a third of the river section is affected by sediment deposits, especially in front of the large hydropower plants,” the state office said. The sediment is then missing behind the dams at the power plants which often deepens the riverbed there.
To improve the sediment balance, the scientists propose various measures so that deposited particles can be carried away by the water. Examples of such measures are the removal of bank fortifications or modern hydroelectric plants with moving turbines.
Corrosion-reducing measures in agriculture could help to improve the sediment balance of the Danube, the study said.
The Danube is the second longest river in Europe, after the Volga.
It starts in Germany’s Black Forest and flows through Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova and Ukraine before draining into the Black Sea.
According to the Bavarian state authority, only a tenth of the Danube is still „in a near-natural state” today.