Monday, July 18, 2011

Dew Ponds or Dieu Ponds

Dew or Dieu Pond

There is an air of mystery surrounding these small water storage ponds that dot the English countryside. They seemed to possess a magical ability to fill and retain water in the hills and higher elevations without a visible water source.  Even their name is a bit of a mystery.  Called "Dew Ponds" by some, they are also less frequently called "Dieu Ponds", "Fog Ponds", and "Mist Ponds".  Whatever their proper name, these small ponds are a fantastic Permaculture Project for collecting and storing water.

No one knows for sure when the Dew Ponds were first built in England, but according to folklore they were said to be filled by the nighttime dew (they are also known as "mist" or "fog" ponds for the same reason).  Others have said that they were filled with water sent by Dieu, French for God, himself.  These Dew Ponds were possibly being built as early as the first century A.D., and about 500 are still in existence in England today.  Most of these Dew Ponds still rarely run dry, even in the hottest summers of drought. 
A full Dew Pond
They were most likely created for watering livestock at the top of hills or in "high country" where no water source was readily available.  Historically construction of Dew Ponds were a closely held secret passed on only after years of apprenticeship or between fathers and sons.  While there was a mystical quality to the creation of these ponds, there are a number of sources from the late 1800's and early 1900's that describe their construction in a detailed manner. 

From the wikipedia article on Dew Ponds:
A Sussex farmer born in 1850 tells how he and his forefathers made dew ponds: “The requisite hole having been excavated, the chalk was laid down layer by layer, while a team of oxen harnessed to a heavy broad-wheeled cart was drawn round and round the cup shaped hole to grind the chalk to powder. Water was then thrown over the latter as work progressed, and after nearly a day of this process, the resultant mass of puddled chalk, which had been reduced to the consistency of thick cream, was smoothed out with the back of a shovel from the centre, the surface being left at last as smooth and even as a sheet of glass. A few days later, in the absence of frost or heavy rain, the chalk had become as hard as cement, and would stand for years without letting water through. This old method of making dew ponds seems to have died out when the oxen disappeared from the Sussex hills, but it is evident that the older ponds, many of which have stood for scores of years practically without repair, are still more watertight than most modern ones in which Portland cement has been employed.”

Dew Pond in South Downs, England

In more modern times, Dew Ponds are still built in a pretty similar manner.  There are so few people building these ponds now, and there are many variations on the theme, but the following is the best I could compile on how to build one.  Dew Ponds are dug where there is already a mini-catchment or a small depression, typically on the top or side of a hill.  They are typically anywhere from 3 to 30 feet in diameter, but up to 70 feet are not uncommon.  The ratio of width to heigth is 3 to 1 at a minimum, and the depth is usually no more than 3-4 feet.  The hole is then lined with straw or hay for insulation.  Then puddled clay or chalk (puddling is the process of adding water to clay or chalk, and pounding it down or otherwise compacting it until it is waterproof) is laid on top the straw.  Often soot or lime is added to the clay to deter earthworms from trying to burrow through the waterproof layer of puddled clay.  This is then covered with another layer of straw, then chalk and small stones.  If being used for animals, it is recommended that large stones are placed from the edges at the low side to provide access. Both the small and large stones are used to distribute the animal's weight and prevent a hoof from breaking the watertight seal.
So from the surface down, the layers would look something like this:
  • Water
  • Large Stones (weight distribution/protection)
  • Small Stones (weight distribution/protection)
  • Chalk or Clay (protection)
  • Straw (protection/insulation)
  • Puddled Clay or Puddled Chalk, possibly mixed with soot or lime (watertight layer)
  • Straw (insulation)
  • Earth
  • One cross-section illustration of a Dew Pond.

Research has shown that Dew Ponds are mainly filled with rainwater and only supplemented with water from dew.  Their small size and insulation keeps the pond cool which inhibits evaporation. Many ponds have one or more trees at the edge which also keeps down evaporation.

Dewpond on Ascension Island, Saint Helena
St. Helena is a territory of Britain
Dew Ponds are a great way to collect and store water.  Check out these other articles on collecting and storing water... all ways to cut back on irrigation needs:

2 comments:

  1. Looks interesting. May see where there could be a problem with mosquitoes with these unless you had some type of natural deterrant.

    ReplyDelete
  2. I would consider introducing Mosquitofish (http://en.wikipedia.org/wiki/Mosquitofish) to them if you live in an area that they are naturally found anyway or consider using Mosquito Dunks or other treatment of BT (http://en.wikipedia.org/wiki/Bacillus_thuringiensis).

    ReplyDelete