Are the dew ponds on the Wiltshire downs fed by dew and how old are they?
Dew ponds are actually fed by rainwater and they are normally situated in a slight depression so that there is a reasonable sized catchment area for rain. The amount of dew falling in a year is around half an inch whereas the rainfall will be between 30 and 40 inches a year. The water retention properties of the dew ponds lay in their making and the appreciation of the margins of the pond as a catchment area. The bottom layer of the pond was puddled chalk or clay, which was normally covered by straw, laid as it would have been on a thatched roof. This was then covered by a mixture of loose materials such as chalk rubble, sand, flints or gravel.
Most existing dew ponds date from the 19th or early 20th centuries, although a few may be 18th century. The only apparent ancient one is Oxenmere on Milk Hill on the downs to the north of the Vale of Pewsey. A Saxon charter of 825 refers to this pond as marking the boundary of Alton Priors, which it still does. It is possible that a pond has been here since that date but only if it has been cleaned out and its lining renewed every 100 to 200 years for Ralph Whitlock estimated that the life of a dew pond is 100 to 150 years.
The ponds were about eight feet deep and would often be fenced, with a small gap that nothing bigger than a sheep could get through. This saved the bottom of the pond being damaged by cattle. Dew pond makers tended to tour the country between September and April making up to 15 ponds, depending on their size. It would take four men about four weeks to construct a fair sized pond. Well known dew pond makers at the end of the 19th century were Charles White, Joel Cruse, Jabez Earley and Daniel Pearce of Imber. The decline of sheep on Salisbury Plain and the downs lessened the need for these ponds and it is believed that the last one in Wiltshire was made by the Smith family of West Lavington in 1938.
Little Imber on the Down: Salisbury Plain’s Ghost Village, by Rex Sawyer. Hobnob Press, 2001, 0946418 06 3
The Folklore of Wiltshire, by Ralph Whitlock. Batsford, 1976