The Dew Pond
The pond on the top of the hill in the old deer park by the Bradfield Road was always known as the Dew Pond. Dew pond is a traditional name for ponds found on high ground far from any protecting woods where there is no spring or stream and older ones have even been attributed to the work of Stone Age man. These ponds seldom dry up, even when springs in the valleys are reduced to a trickle, and provide water for animals and man on exposed high ground. It is not known whether the one here was actually constructed as a dew pond but it never seems to dry up even though the greater part of the spring-fed lake in the new park is now without water most of the time.
The traditional method of constructing a dew pond is to dig a hole somewhere where mist collects early on summer mornings. As with most old artificial ponds the bed is a layer of puddled clay but the secret of the dew pond is a layer of straw or reed between the clay liner and the compacted earth beneath. Once the clay is dry, the pond is filled by rain or artificial means and the theory is that it then retains its water even in the driest summers by virtue of the temperature difference between the surrounding land and the clay bed of the pond. During the day the land around the pond is warmed by the sun but the heat cannot get to the clay bed of the pond because of the insulating effect of the straw layer. When night falls the cooler clay condenses more moisture from the atmosphere and counteracts the evaporation during the day.
© 2019 Richard J Smith