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A winterbourne is a stream or river that is dry through the summer months. 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 water courses.
Winterbournes generally form in areas where there is chalk (or other porous rock) downland bordering clay valleys or vales. When it rains, the porous chalk holds water in its aquifer, releasing the water at a steady rate. During dry seasons the water table may fall below the level of the stream's bed, causing it to dry out.
Winterbournes occasionally give their names to settlements. Many of the UK's 'Winterbournes' are villages in Dorset, such as Winterbourne Abbas, Winterborne Monkton, Winterborne St Martin, Zelston, Houghton, Whitchurch, and Compton. In Wiltshire, north of Avebury there are the villages of Winterbourne Monkton and Winterbourne Bassett; and in South Gloucestershire there are the villages of Winterbourne and Winterbourne Down.
Exploitation of chalk aquifers as a domestic water source in Britain has had the effect of converting 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.
There is also a Winterbourne stream in an area of Lewes, East Sussex that is also called Winterbourne.