Dry valley

A dry valley may develop on many kinds of permeable rock, such as limestone, chalk, sand stone and sandy terrains that do not regularly sustain surface water flow.

There are many examples of chalk dry valleys along the North and South Downs in Southern England.

Notably the National Trust-owned Devil's Dyke near Brighton covers some 200 acres (0.81 km2) of downland scarp, and includes the deepest dry valley in the world – created when melting water eroded the chalk downland to the permafrost layer after the last ice age.

The three-quarter mile long curved dry valley is around 700 feet (210 m) in height and attracts tourists with its views of Sussex, Hampshire and Kent.

A notable example is the valley of the River Manifold which is dry, except in spate, from Wetton south for several miles.