A dew pond is an artificial
pond
A pond is an area filled with water, either natural or artificial, that is smaller than a lake. Defining them to be less than in area, less than deep, and with less than 30% emergent vegetation helps in distinguishing their ecology from ...
usually sited on the top of a hill, intended for watering livestock. Dew ponds are used in areas where a natural supply of surface water may not be readily available. The name dew pond (sometimes cloud pond or mist pond) is first found in the ''Journal of the
Royal Agricultural Society'' in 1865. Despite the name, their primary source of water is believed to be rainfall rather than
dew
Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening due to condensation.
As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at wh ...
or
mist.
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Construction
![Mile Oak Dew Pond - geograph](https://upload.wikimedia.org/wikipedia/commons/3/36/Mile_Oak_Dew_Pond_-_geograph.org.uk_-_586363.jpg)
They are usually shallow, saucer-shaped and lined with puddled clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
, chalk
Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...
or marl on an insulating straw layer over a bottom layer of chalk or lime. To deter earthworms from their natural tendency of burrowing upwards, which in a short while would make the clay lining porous, a layer of soot would be incorporated or lime mixed with the clay.[Martin (1915: 84–85)] The clay is usually covered with straw to prevent cracking by the sun and a final layer of chalk rubble or broken stone to protect the lining from the hoofs of sheep or cattle. To retain more of the rainfall, the clay layer could be extended across the catchment area of the pond. If the pond's temperature is kept low, evaporation (a major water loss) may be significantly reduced, thus maintaining the collected rainwater. According to researcher Edward Martin, this may be attained by building the pond in a hollow, where cool air is likely to gather, or by keeping the surrounding grass long to enhance heat radiation.[Martin (1915: 133-135; 159)] As the water level in the basin falls, a well of cool, moist air tends to form over the surface, restricting evaporation.[Martin (1915: 160)]
A method of constructing the base layer using chalk puddle was described in ''The Field'' 14 December 1907.
A Sussex farmer born in 1850 tells how he and his forefathers made dew ponds:
The initial supply of water after construction has to be provided by the builders, using artificial means. A preferred method was to arrange to finish the excavation in winter, so that any fallen snow could be collected and heaped into the centre of the pond to await melting.
History
The mystery of dew ponds has drawn the interest of many historians and scientists, but until recent times there has been little agreement on their early origins. It was widely believed that the technique for building dew ponds has been understood from the earliest times, as Kipling
Joseph Rudyard Kipling ( ; 30 December 1865 – 18 January 1936)''The Times'', (London) 18 January 1936, p. 12. was an English novelist, short-story writer, poet, and journalist. He was born in British Raj, British India, which inspired much o ...
tells us in ''Puck of Pook's Hill
''Puck of Pook's Hill'' is a fantasy book by Rudyard Kipling, published in 1906, containing a series of short stories set in different periods of English history. It can count both as historical fantasy – since some of the stories told of ...
'': "…the Flint Men made the Dewpond under Chanctonbury Ring." The two Chanctonbury Hill
Chanctonbury Hill is an biological Site of Special Scientific Interest west of Steyning in West Sussex. Part of it is Chanctonbury Ring, an early Iron Age hillfort which contains two Romano-Celtic temples and which is a Scheduled Monument.
Thi ...
dew ponds were dated, from flint tool
A stone tool is, in the most general sense, any tool made either partially or entirely out of stone. Although stone tool-dependent societies and cultures still exist today, most stone tools are associated with prehistoric (particularly Stone Ag ...
s excavated nearby and similarity to other dated earthworks, to the neolithic period
The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several parts ...
. Landscape archaeology
Landscape archaeology, a sub-discipline of archaeology and archaeological theory, is the study of the ways in which people in the past constructed and used the environment around them. It is also known as archaeogeography (from the Greek "ancient ...
too seemed to demonstrate that they were used by the inhabitants of the nearby hill fort
A hillfort is a type of earthwork used as a fortified refuge or defended settlement, located to exploit a rise in elevation for defensive advantage. They are typically European and of the Bronze Age or Iron Age. Some were used in the post-Roma ...
(probably from an earlier date than that of the surviving late Bronze Age
The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second prin ...
structure) for watering cattle.[ A more prosaic assessment from ]Maud Cunnington
Maud Edith Cunnington (''née'' Pegge; 24 September 1869 – 28 February 1951) was a Welsh archaeologist, best known for her pioneering work on the some of the most important prehistoric sites of Salisbury Plain.
Early life, education, and m ...
, an archaeologist from Wiltshire, while not ruling out a prehistoric origin, describes such positive interpretations of the available evidence as no more than “flights of fancy”.
A strong claim to antiquity may, however, be made for at least one Wiltshire dew pond: A land deed dated 825 CE mentions Oxenmere () at Milk Hill, Wiltshire, showing that dew ponds were in use during the Saxon period.[ The parliamentary enclosures of the mid eighteenth to mid nineteenth centuries caused many new upland ponds to be made, as access to traditional sources of drinking water for livestock was cut off.] The suggestion has also been made that the nursery rhyme about Jack and Jill
"Jack and Jill" (sometimes "Jack and Gill", particularly in earlier versions) is a traditional English nursery rhyme. The Roud Folk Song Index classifies the commonest tune and its variations as number 10266, although it has been set to severa ...
may refer to collecting water from a dew pond at the top of a hill, rather than from a well.
The naturalist Gilbert White
Gilbert White FRS (18 July 1720 – 26 June 1793) was a " parson-naturalist", a pioneering English naturalist, ecologist, and ornithologist. He is best known for his ''Natural History and Antiquities of Selborne''.
Life
White was born on ...
, writing in 1788, noted that during extended periods of summer drought the artificial ponds on the downs above his native Selborne
Selborne is a village in Hampshire, England, south of Alton, and just within the northern boundary of the South Downs National Park. The village receives visitors because of its links with the naturalist Revd. Gilbert White, a pioneer of birdw ...
, Hampshire, retained their water, despite supplying flocks of sheep, while larger ponds in the valley below had dried up. In 1877 H. P. Slade observed that this was because the lower ponds have debris washed into them from surface water drainage, making them shallow, but the higher ones do not: the smaller volume of water is depleted more rapidly. Later observations demonstrated that during a night of favourable dew formation a typical increase in water level of some two or three inches was possible.[ However, there remains controversy about the means of replenishment of dew ponds. Experiments conducted in 1885 to determine the origin of the water found that dew forms not from dampness in the air but from moisture in the ground directly beneath the site of the condensation: dew, therefore, was ruled out as a source of replenishment.][ Other scientists have pointed out that the 1885 experiments failed to take into account the insulating effect of the straw and the cooling effect of the damp clay: the combined effect would be to keep the pond at a lower temperature than the surrounding earth and thus able to condense a disproportionate share of moisture.]
In turn these conclusions were disproved in the 1930s, when it was pointed out that the heat-retaining quality of water (its thermal capacity) was many times greater than that of earth, and therefore the air above a pond in summer would be the last place to attract condensation. The deciding factor, it was concluded, is the extent of the saucer-shaped basin extending beyond the pond itself: the large basin would collect more rainfall than a pond created without such a surrounding feature.
Dew ponds are still common on the downlands of southern England
England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
, the North Derbyshire and Staffordshire moorlands
Staffordshire Moorlands is a local government district in Staffordshire, England. Its council, Staffordshire Moorlands District Council, is based in Leek and is located between the city of Stoke-on-Trent and the Peak District National Park. The ...
and in Nottinghamshire
Nottinghamshire (; abbreviated Notts.) is a landlocked county in the East Midlands region of England, bordering South Yorkshire to the north-west, Lincolnshire to the east, Leicestershire to the south, and Derbyshire to the west. The trad ...
.
Measuring dew production
The first scientific experiments to measure and correlate the rate of dew deposit with evaporation were made by Harry Pool Slade of Aston Upthorpe
Aston Upthorpe is a village and civil parish about southeast of Didcot in South Oxfordshire. It was part of Berkshire until the 1974 boundary changes transferred it to Oxfordshire. The motion picture National Lampoon's European Vacation (1985 ...
, Berkshire, between June 1876 and February 1877, at a dew pond on Aston Upthorpe Downs (). Slade measured overnight dew deposit (by weighing cotton wool when dry and after overnight exposure), evaporation from copper pans beside the pond, the depletion of the pond, and relative humidity
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.
Humidity dep ...
. He found that on days with heavy overnight dewfall the level of water in the pond was not replenished but invariably diminished.[
]
In situ
''In situ'' (; often not italicized in English) is a Latin phrase that translates literally to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in ...
measurements of evaporation and condensation were taken at the Helmfleeth dew pond in Poppenbüll municipality (Eiderstedt Peninsula in Schleswig-Holstein, Germany) using meteorological measuring instruments and a floating evaporation pan after Brockamp & Werner (1970). These measurements proved the dew formation on the basis of temperature changes and the weather conditions. The Helmfleeth dew pond is part of the water supply for a marsh area and is still in use today.
Reproductions of historical dew ponds
In 2014, the traditional technique was verified by means of modern building material at reproductions of dew ponds in East Friesland. In this context, various techniques were tried in two terrestrial hollows. Commercially available PVC-film was used for the sealing and foam glass gravel for the insulation. The construction was carried out by craftsmen and the climatological analysis by Werner and Coldewey.
See also
* Air well (condenser)
An air well or aerial well is a structure or device that collects water by promoting the condensation of moisture from air. Designs for air wells are many and varied, but the simplest designs are completely passive, require no external energy s ...
* Rainwater harvesting
Rainwater harvesting (RWH) is the collection and storage of rain, rather than allowing it to run off. Rainwater is collected from a roof-like surface and redirected to a tank, cistern, deep pit (well, shaft, or borehole), aquifer, or a reservoir ...
References
Bibliography
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Journal articles
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Dewponds in specific locations
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Further reading
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External links
Articles
Building instructions from ''Popular Science''
''Wiltshire Community History'' information about Wiltshire dew ponds
Images
Dew pond images at Geograph
{{DEFAULTSORT:Dew Pond
Appropriate technology
Ecological techniques
Irrigation
Ponds
Water supply
Water conservation