dew pond

File:Mile Oak Dew Pond - geograph.org.uk - 586363.jpg, Sussex, showing layer of chalk rubble protecting the lining {{Coord|50.86192|-0.2367|format=dms}}]]File:Dew pond Oxteddle.jpg need regular repair. Oxteddle Bottom, Sussex {{Coord|50.87075|0.04112|format=dms}}]]

They are usually shallow, saucer-shaped and lined with puddled clay, chalk or marl on an insulating straw layer over a bottom layer of chalk or lime.{{cite book

| last = Brooks

| first = Alan

| author2 = Agate, Elizabeth

| title = Waterways and Wetlands

| publisher = British Trust for Conservation Volunteers

| year = 1976

| location = Doncaster

| url = https://archive.org/details/waterwayswetland0000broo

| isbn = 0-946752-30-3

| url-access = registration

}} 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{{cite book

| last = Johnson

| first = Walter

| title = Folk Memory Or the Continuity of British Archaeology

| publisher = Oxford University Press

| year = 1908

| location = Oxford, England

}} 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:

{{cquote|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.Martin (1915: 96)}}

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.Clutterbuck (1865: 273)

File:Dew pond west leake.jpg |date=2 June 2006}} Dew pond on hill above West Leake Nottinghamshire.
{{Coord|52.836462|-1.215963|format=dms}}]]File:Dewpond partly frozen - geograph.org.uk - 1143961.jpg ({{coord|53.22190|-1.6818|format=dms}}) dew pond pictured in winter]]

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 tells us in Puck of Pook's Hill: "…the Flint Men made the Dewpond under Chanctonbury Ring."{{cite book |last1=Kipling |first1=Rudyard |title=Puck of Pook's Hill |date=1900 |publisher=Macmillan |location=London |oclc=872301879}} The two Chanctonbury Hill dew ponds were dated, from flint tools excavated nearby and similarity to other dated earthworks, to the Neolithic period. Landscape archaeology too seemed to demonstrate that they were used by the inhabitants of the nearby hill fort (probably from an earlier date than that of the surviving late Bronze Age structure) for watering cattle.{{cite web

| title = Chanctonbury Ring

| work = Prehistory

| publisher = Steyning Museum

| year = 2005

| url = http://steyningmuseum.org.uk/chanctonbury.htm

| access-date = 14 April 2008

| archive-date = 27 August 2008

| archive-url = https://web.archive.org/web/20080827155811/http://www.steyningmuseum.org.uk/chanctonbury.htm

| url-status = dead

}} A more prosaic assessment from Maud Cunnington, 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”.{{cite book

| last = Cunnington

| first = Maud Elizabeth

| title = An Introduction to the Archæology of Wiltshire from the Earliest Times to the Pagan Saxons

| publisher = George Simpson and Co

| year = 1934

| location = Devizes, England

}}

A strong claim to antiquity may, however, be made for at least one Wiltshire dew pond: A land deed dated 825 CE mentions Oxenmere ({{Coord|51.375960|-1.848221 |format=dms}}) at Milk Hill, Wiltshire, showing that dew ponds were in use during the Saxon period.{{cite web

| title = Question: Dew ponds

| work = Wiltshire Community History

| publisher = Wiltshire Council

| url = https://apps.wiltshire.gov.uk/communityhistory/Question/Details/47

| date = 3 January 2003

| access-date = 25 May 2023

}} 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.{{cite book|last=Whitefield|first=Patrick|author-link=Patrick Whitefield|title=The Living Landscape: How to Read and Understand It|year=2009|publisher=Permanent Publications|location=East Meon, England|isbn=978-1-85623-043-8|page=265}} The suggestion has also been made that the nursery rhyme about Jack and Jill may refer to collecting water from a dew pond at the top of a hill, rather than from a well.{{cite book |last1=Talman |first1=Charles |title=Meteorology; the science of the atmosphere |date=1922 |publisher=P.F. Collier |location=New York |oclc=3299179 |page=353|chapter= Atmospheric byways}}{{cite journal |last1=Martin |first1=Edward A. |title=Dew-Ponds |journal=Antiquity |date=September 1930 |volume=4 |issue=15 |pages=347–351 |doi=10.1017/S0003598X00004932}}

The naturalist Gilbert White, writing in 1788, noted that during extended periods of summer drought the artificial ponds on the downs above his native Selborne, Hampshire, retained their water, despite supplying flocks of sheep, while larger ponds in the valley below had dried up.{{cite book

| last = White

| first = Gilbert

| author-link = Gilbert White

| title = The Natural History of Selborne

| publisher =Benjamin White and Son

| year = 1788

| location =London

}} 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.{{cite book |last1=Slade |first1=Harry Poole |title=A Short Practical Treatise on Dewponds |date=1877 |publisher=E. & F. N. Spon |location=London|oclc= 28513303}} 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.{{cite book

| last = Hubbard

| first = Arthur John

|author2=Hubbard, George

| title = Neolithic Dew Ponds and Cattleways

| publisher = Longman

| year = 1905

| location = London

}}

In 1919 architect George Hubbard, in a lecture at the Royal Institute of British Architects, described how he constructed a {{convert|100|ft|abbr=off|adj=on}}-square dew pond to demonstrate how to capture at night the large volume of water vapour contained in air warmed during the previous day. The lining of the pond incorporated 2,500 slabs of mica, {{convert|2|ft|abbr=off|adj=on}}-square and of {{convert|2|in|abbr=off|adj=on}} thickness, set in sand, pitch and asphalt, for insulation from the warm earth. After a rainless autumn night he found that, above the insulated slabs only, a thick layer of hoar frost had formed. As the morning progressed the frost melted to produce "hundreds, if not thousands, of gallons of water", but this rapidly dried out in the heat of the sun.{{cite news |title=Water without springs, rivers, or rain, construction of a dew-pond |work=The Times |issue=42015 |date=4 February 1919 |location=London |page=5}}

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.{{cite book

| last = Pugsley

| first = Alfred J

| title = Dewponds in Fable and Fact

| publisher =Country Life Ltd

| year = 1939

| location =London

|pages= 42–45

|oclc= 1628476}}

In 1979 naturalist Ralph Whitlock suggested an alternative origin of the name: after dismissing as "hopelessly wrong" the proposal that "dew" was a corruption of the French language d'eau ("water"), he described how the royal archives at Windsor Castle contained a reference to a certain "Mr Dew" as pond maker to King George III in Hampshire and Surrey. Thus, Dew became an eponym for the artificial downland pond.{{cite news |last1=Whitlock |first1=Ralph |title=The dew-pond myth |work=The Guardian Weekly |date=May 1989|issn=0959-3608}}

The first scientific experiments to measure and correlate the rate of dew deposit with evaporation were made by Harry Pool Slade of Aston Upthorpe, Berkshire, between June 1876 and February 1877, at a dew pond on Aston Upthorpe Downs ({{Coord|51|32|58|N|1|13|20|W|type:landmark_region:GB|display=inline}}). 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. He found that on days with heavy overnight dewfall the level of water in the pond was not replenished but invariably diminished.{{cite journal |last1=Scott |first1=R. H. |author1-link=Robert Henry Scott |title=Agricultural and Forest Meteorology |journal=Journal of the Royal Agricultural Society |date=1881 |volume=17 |page=66 |publisher=Royal Agricultural Society |location=London |quote=The idea that the so-called dew-ponds are really filled by dew has been satisfactorily disposed of by Mr. H. P. Slade.}}{{cite journal |last1=Gibson |first1=Herbert |title=The genesis and function of the dew-pond |journal=Journal of the Royal Society of Arts |date=5 August 1910 |volume=58 |issue=3011 |pages=847–849 |publisher=Royal Society of Arts |location=London|jstor=41339264 |quotation=[…] a thick mist arose from the pond […] and rolled away over the downs, leaving a strong dew deposition in its track.|url=http://www.jstor.org/stable/41339264}}

File:Tauteich Helmfleeth.jpg

In situ 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).{{cite journal|last1=Brockamp|first1=B.|last2=Werner|first2=J.|title=Ein weiterentwickeltes Verdunstungsmessgerät für Kleingewässer (als Beitrag zur hydrologischen Dekade der UNESCO)|journal=Meteorol. RDSCH.|date=1970|volume=23|issue=2|pages=53–56}} These measurements proved the dew formation on the basis of temperature changes and the weather conditions.{{cite journal|last1=Coldewey|first1=W. G.|last2=Werner|first2=J.|last3=Wallmeyer|first3=C.|last4=Fischer|first4=G.|title=Das Geheimnis der Himmelsteiche - Physikalische Grundlagen einer historischen Wasserversorgung im Küstenraum|journal=Schriften der DWHG|date=2012|volume=20|issue=2|pages=315–329}}{{cite journal|last1=Werner|first1=J.|last2=Coldewey|first2=W. G.|last3=Wallmeyer|first3=C.|last4=Fischer|first4=G.|title=Der Tauteich Helmfleeth im St. Johannis-Koog, Gemeinde Poppenbüll - Messungen und Berechnungen des Wasserhaushalts 2010|journal=Jahrbuch "Zwischen Eider und Wiedau 2013"|date=2013|pages=1–10}} The Helmfleeth dew pond is part of the water supply for a marsh area and is still in use today.{{cite journal|last1=Meier|first1=D.|last2=Coldewey|first2=W. G.|title=Wasserversorgung in den Nordseemarschen von der römischen Kaiserzeit bis zur frühen Neuzeit|journal=Schriften der DWHG|date=2012|volume=20|issue=1|pages=249–260}}

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.{{cite journal|last1=Werner|first1=J.|last2=Coldewey|first2=W. G.|last3=Wesche|first3=D.|last4=Schütte|first4=H.|last5=Schütte|first5=F.|last6=Fähnders|first6=H.|last7=Neumann|first7=R.|title=Studien der Wasserbilanz an zwei modernen Nachbauten historischer Tauteiche an der Nordseeküste|journal=Schriften der DWHG|date=2016|pages=349–369}}

Dew ponds are still common on the downlands of southern England, the North Derbyshire and Staffordshire moorlands, and in Nottinghamshire.

• Air well (condenser)
• Rainwater harvesting

{{Reflist}}

{{Commons category}}

• {{cite encyclopedia | title=Dewponds | encyclopedia=Standard Encyclopedia of Modern Agriculture | author=Blundell, E | year=1909}}
• {{cite book | title=Earthwork of England, Chapter 8, Dewponds | publisher=Macmillan | author=Allcroft, A. Hadrian | year=1908 | pages=265–286 | url = https://books.google.com/books?id=V8MsAAAAMAAJ&q=%22earthwork%20of%20england%22%20dew%20pond&pg=PA265}}
• {{cite journal | title=Prize Essay on Water Supply | author=Clutterbuck, J.C. 1865 vol. 1 pp. | journal=Journal of the Royal Agricultural Society of England | year=1865 | volume=1 2nd series | pages=271–287 | url = https://books.google.com/books?id=fOQMEXZ04eEC&q=clutterbuck%20prize%20essay%20Journal%20of%20the%20Royal%20Agricultural%20Society&pg=PA271}}
• {{cite book|last=Martin|first=Edward Alfred|title=Dew-ponds: history, observation, and experiment|year=1915|publisher=Werner Laurie|location=London|oclc=505154175 | url = https://archive.org/details/dewponds00martgoog|quote=Dew-ponds: history, observation, and experiment.}} (Note: link is 1907 ed.)
• {{cite book | author=Johnson, Walter | title=Folk-memory: or, The continuity of British archaeology | publisher=Oxford | year=1908 | location=Oxford | pages=[https://archive.org/details/folkmemoryorcon01johngoog/page/n305 295]–318 | url = https://archive.org/details/folkmemoryorcon01johngoog | quote=construction dew ponds. }}

• {{cite journal | title=Collection of Dew on Roofs | author=Beckett & Dufton | journal=Nature | volume=135 | issue=3419|date= May 11, 1935 | pages=798–9 | doi = 10.1038/135798b0 | s2cid=30099986 }}
• {{cite journal | title=The Great Dewpond Myth | author=Walford, E. | journal=Discovery |date=October 1924 | volume=V |page=245}}

• {{cite book | title=Downland Pathways | publisher=Methuen | author=Allcroft, A. Hadrian | year=1924}}
• {{cite book | title=The Downland Shepherds | publisher=Alan Sutton | author=Wills, Barclay | year=1989}}
• {{cite book | title=General View of Agriculture and Minerals of Derbyshire | url=https://archive.org/details/generalviewagri18britgoog | author-link=John Farey, Sr. | last=Farey | first=John | year=1811}}
• {{cite book | title=Some Dewponds in Dorset, Dorset County | publisher=Chronicle Office | author=Pope, A. | year=1912}}
• {{cite book | title=The Marlborough County | publisher=Oxford University Press | author=Brentnall & Carter | year=1932 |pages=57, 58}}
• {{cite book | title=The Spirit of the Downs | publisher=Methuen | author=Becket, Arthur | year=1949|edition=8th}}
• {{cite book | title=Sussex Geology | publisher=Arthur & Co | year=1932}}

• {{cite book | title=Dew harvest : to supplement drinking water sources in arid coastal belt of Kutch | publisher=Centre for Environment Education, Foundation Books | author=Sharan, Girja | year=2006 | location=New Delhi, Ahmedabad | url = https://books.google.com/books?id=r52bwys37WYC&q=dew+ponds&pg=PA78| isbn=9788175963269 }}
• {{cite book | title=Dewponds in fable and fact | publisher=Country Life Ltd | author=Pugsley, Alfred John | year=1939 | location=London}}
• {{cite book | title=Neolithic dew-ponds and cattle-ways | publisher=Longmans, Green and Co |author1=Hubbard, Arthur John |author2=George Hubbard | year=1905 | url = https://archive.org/details/neolithicdewpon00hubbgoog| quote=dew ponds. }}
• {{cite book | title=The Great Drought of 1976 | publisher=Hutchinson, Readers Union Group | author=Cox, Evelyn Cox | year=1978 }}

• [https://books.google.com/books?id=NioDAAAAMBAJ&dq=dew+ponds+POPULAR+SCIENCE&pg=PA109 Building instructions from Popular Science]
• [https://web.archive.org/web/20041214173046/http://www.geosciences.ou.edu/~bweaver/Ascension/dewpond.htm Article about dew ponds in Ascension Island]

• [https://www.geograph.org.uk/search.php?i=2534074&page=1 Dew pond images at Geograph]

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