When do rivers run backwards?

In the former Soviet Union the direction of several rivers was diverted or even reversed to provide water for irrigation. Some of the rivers running into the Aral Sea were diverted northwards in a huge water management project to irrigate land north of the region. In some cases the direction of their flow was reversed. The result was that the Aral Sea began to dry up because no more river water flowed into it.

Sometimes the flow is reversed naturally, but this only happens in very large rivers, when very high tides overcome the normal river currents. In narrow parts of the river valley the water begins to pile up, and eventually a wave called a tidal bore passes back up the river, sometimes for a great distance.

Fact File:

Tidal bores happen in the Amazon in south America, where there is a bore as high as 4.5 metres. A smaller bore travels up the River Severn in England.


Picture Credit : Google