The River Severn begins as a trickle.
It is soon joined by another trickle. It’s about doubled in size, though you can’t really tell.
As it descends, more and more tributary rivers join. At each confluence (that’s the point where they join) the volume of water increases.
As the land opens out, the tributary valleys can be spotted on the hillsides.
At the town of Llanidloes, this…
…suddenly becomes this…
Entering from the right is the Afon Clywedog, bringing with it a sizeable volume of water.
With low banks at this point you might expect there to be a high risk of flooding but, although the Severn rises quickly when it rains, the Clywedog is very much under control.
At 72 metres this is the tallest concrete dam in the UK.
It was built in the 1960s, on the Afon Clywedog, to help control the River Severn downstream of their confluence, where the Severn moves into the flatter part of its long profile. Water is held back in the winter to prevent flooding and it is released in the summer to keep the Severn flowing during dry periods.
I visited at the end of the dry summer. You can see that a lot of water has been used and the reservoir now has plenty of space to store excess water over the winter.
A practical yet picturesque addition to the landscape.