Dewponds - how did they hold water on the chalk?

[Cherhill_Bill]

genuine question for the clever ones. dewponds. how did the old boys make a pond hold water up on the chalk, where every drop should drain straight through? we have a couple on our high ground, bone dry now, nobody maintains them, but they held water for the sheep for centuries up where theres no spring and no stream. lost art by the look of it. does anybody actually know how it was done?

[WiltsMuseum_Col]

A genuinely clever bit of old engineering, Bill. The name is a bit of a romance, it is not really dew that fills them, it is rain. The trick is the lining: puddled clay, sometimes over a layer of straw or chalk rubble, beaten until it is watertight, and made shallow and wide so the catchment is large. The straw, the story goes, insulated it so the cold of the night drew a little condensation too, hence dewpond. Mostly it was rain, caught and held on clay that has no business being up on chalk, carted up there on purpose. They stopped maintaining them when piped water and troughs came in, and a dewpond not puddled and not grazed cracks and drains and dies within a few years. Yours will have gone exactly that way. A made thing that only lived as long as someone kept making it.

[Larkhill_Geoff]

And worth saying, they were little worlds of their own, the dewponds, grand wildlife spots when they held water, newts and dragonflies miles from any other water. When they go dry, all of that goes with them. I miss them, ecologically. A whole small living thing on the top of a dry hill, kept alive by hand, and gone the moment the hand stopped.