Winterbourne (stream)

A winterbourne is a stream or river that is dry during the summer months, a special case of an intermittent stream. Winterbourne is a British term derived from the Old English winterburna ("winter stream"). A winterbourne is sometimes simply called a bourne, from the Anglo-Saxon word for a stream flowing from a spring, although this term can also be used for all-year watercourses. Winterbournes generally form in areas where there is chalk (or other porous rock) downland adjacent to clay valleys or vales. When it rains, the porous chalk holds water in its aquifer and releases the water at a steady rate. During the dry season, the water table can fall below the level of the stream bed, causing it to dry up.

The use of chalk aquifers as a domestic water source in Britain has had the effect of turning many streams and rivers into artificial winterbournes. This effect is controversial, and local campaigns have often been successful in reducing aquifer abstraction and reversing the effect. For an example, see the River Pang in Berkshire.