European rivers weave through million barriers

The number of barriers recorded in field was on average 2.5 times higher than in existing inventories.

Paris: More than 1.2 million barriers criss-cross Europe’s rivers — nearly twice as many as previously thought — threatening some of the world’s most diverse ecosystems, new research showed.

Although the rivers have been dammed, forded or bridged for centuries, there is a surprising lack of detailed databases of the continent’s waterways.

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Most only list barriers of a certain height, above 10 metres, for example, leaving hundreds of thousands of smaller water breaks undocumented.

In a pan-European initiative, scientists collated more than 120 data bases on European rivers and ran tests to ensure no barrier was repeated in the final tally.

They found 629,955 unique barrier records — a huge number demonstrating the extent to which human activity has influenced river ecosystems.

To compare the data with reality, the researchers then undertook a mammoth verification operation: they walked along more than 2,700 kilometres of European rivers, manually inputting any missing from records into the database.

The number of barriers recorded in field was on average 2.5 times higher than in existing inventories.

The authors said that while larger barriers such as hydroelectric dams often cause concern among conservationists, the presence of much smaller barriers such as weirs and sluices was a far more insidious threat to river ecosystems.

Dams above 15 metres in height, for example, account for fewer than one percent of artificial river barriers in Europe. More than 90 percent of the barriers are under 5 metres high.

Although large dams may draw the most attention, it is the small barriers that collectively do the most damage.