A dew pond is an artificial pond 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. [1] Despite the name, their primary source of water is believed to be rainfall rather than dew or mist. [2] [3]
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. [5] 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 [6] or lime mixed with the clay. [7] The clay is usually covered with straw to prevent cracking by the sun [7] 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. [3] 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. [8] As the water level in the basin falls, a well of cool, moist air tends to form over the surface, restricting evaporation. [9]
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 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. [4]
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. [10]
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." [12] 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. [13] [14] 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”. [15]
A strong claim to antiquity may, however, be made for at least one Wiltshire dew pond: A land deed dated 825 CE mentions Oxenmere ( 51°22′33″N1°50′54″W / 51.375960°N 1.848221°W ) at Milk Hill, Wiltshire, showing that dew ponds were in use during the Saxon period. [15] [16] 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. [3] 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. [17] [18]
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. [19] 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. [20] 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. [13] 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. [6] 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. [13] 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. [21]
Dew ponds are still common on the downlands of southern England, the North Derbyshire and Staffordshire moorlands, and in Nottinghamshire.
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 ( 51°32′58″N1°13′20″W / 51.54944°N 1.22222°W ). 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. [20] [22] [23]
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). [24] These measurements proved the dew formation on the basis of temperature changes and the weather conditions. [25] [26] The Helmfleeth dew pond is part of the water supply for a marsh area and is still in use today. [27]
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. [28]
Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae.
Wiltshire is a ceremonial county in South West England. It borders Gloucestershire to the north, Oxfordshire to the north-east, Berkshire to the east, Hampshire to the south-east, Dorset to the south, and Somerset to the west. The largest settlement is Swindon, and Trowbridge is the county town.
Downland, chalkland, chalk downs or just downs are areas of open chalk hills, such as the North Downs. This term is used to describe the characteristic landscape in southern England where chalk is exposed at the surface. The name "downs" is derived from the Celtic word "dun", meaning "fort" or "fastness", though the original meaning would have been "hill", as early forts were commonly hillforts - compare Germanic "burg" (fort) and "berg" (mountain).
Salisbury Plain is a chalk plateau in southern England covering 300 square miles (780 km2). It is part of a system of chalk downlands throughout eastern and southern England formed by the rocks of the Chalk Group and largely lies within the county of Wiltshire, but stretches into Hampshire.
The Chiltern Hills or the Chilterns are a chalk escarpment in southern England, northwest of London, covering 660 square miles (1,700 km2) across Oxfordshire, Buckinghamshire, Hertfordshire, and Bedfordshire, stretching 45 miles (72 km) from Goring-on-Thames in the southwest to Hitchin in the northeast. The hills are 12 miles (19 km) at their widest.
The South Downs are a range of chalk hills in the south-eastern coastal counties of England that extends for about 260 sq mi (670 km2) across the south-eastern coastal counties of England from the Itchen valley of Hampshire in the west to Beachy Head, in the Eastbourne Downland Estate, East Sussex, in the east. The Downs are bounded on the northern side by a steep escarpment, from whose crest there are extensive views northwards across the Weald. The South Downs National Park forms a much larger area than the chalk range of the South Downs, and includes large parts of the Weald.
The North Downs are a ridge of chalk hills in south east England that stretch from Farnham in Surrey to the White Cliffs of Dover in Kent. Much of the North Downs comprises two Areas of Outstanding Natural Beauty (AONBs): the Surrey Hills and the Kent Downs. The North Downs Way National Trail runs along the North Downs from Farnham to Dover.
The Berkshire Downs are a range of chalk downland hills in southern England, part of the North Wessex Downs Area of Outstanding Natural Beauty. The Berkshire Downs are wholly within the traditional county of Berkshire, although split between the current ceremonial counties of Berkshire and Oxfordshire. The western parts of the downs are also known as the Lambourn Downs.
Dorset is a county in South West England on the English Channel coast. Covering an area of 2,653 square kilometres (1,024 sq mi); it borders Devon to the west, Somerset to the north-west, Wiltshire to the north-east, and Hampshire to the east. The great variation in its landscape owes much to the underlying geology, which includes an almost unbroken sequence of rocks from 200 to 40 million years ago (Mya) and superficial deposits from 2 Mya to the present. In general, the oldest rocks appear in the far west of the county, with the most recent (Eocene) in the far east. Jurassic rocks also underlie the Blackmore Vale and comprise much of the coastal cliff in the west and south of the county; although younger Cretaceous rocks crown some of the highpoints in the west, they are mainly to be found in the centre and east of the county.
Cranborne Chase is an area of central southern England, straddling the counties Dorset, Hampshire and Wiltshire. It is part of the Cranborne Chase and West Wiltshire Downs Area of Outstanding Natural Beauty (AONB).
The visible geology of Hampshire in southern England broadly comprises a folded succession of sedimentary rocks dating from the Cretaceous and Palaeogene periods – mostly gentle folding in the north, more complex folding along the south coast. The lower (early) Cretaceous rocks are sandstones and mudstones whilst those of the upper (late) Cretaceous are the various formations that comprise the Chalk Group and give rise to the county's downlands. Overlying these rocks are the less consolidated Palaeogene clays, sands, gravels and silts of the Lambeth, Thames and Bracklesham Groups which characterise the Hampshire Basin.
Bowerchalke is a village and civil parish in Wiltshire, England, about 9 miles (14 km) southwest of Salisbury. It is in the south of the county, about 1 mile (1.6 km) from the boundary with Dorset and 2 miles (3.2 km) from that with Hampshire. The parish includes the hamlets of Mead End, Misselfore and Woodminton.
Newtimber is a small village and civil parish in the Mid Sussex District of West Sussex, England. It is located north-west of Brighton. The parish also includes the hamlet of Saddlescombe. The parish lies almost wholly with the South Downs National Park, with the exception of a small section of the parish north of the B2117 road. The planning authority for Newtimber is therefore the South Downs National Park Authority (SDNPA), the statutory planning authority for the National Park area. The downland scarp, which includes Newtimber Hill, Newtimber Holt, Saddlescombe chalk quarry and Summer Down, is mostly part of the Beeding Hill to Newtimber Hill, designated Site of Special Scientific Interest.
A garden pond is a water feature constructed in a water garden or designed landscape, normally for aesthetic purposes, to provide wildlife habitat, or for swimming.
Ditchling Beacon is the highest point in East Sussex, England, with an elevation of 248 m (814 ft). It is south of Ditchling and to the north-east of Brighton. It is a large chalk hill with a particularly steep northern face, covered with open grassland and sheep-grazing areas. It is the third-highest point on the South Downs, behind Butser Hill and Crown Tegleaze.
Cranborne Chase and West Wiltshire Downs, marketed as the Cranborne Chase National Landscape, is an Area of Outstanding Natural Beauty (AONB) covering 379 square miles (980 km2) of Dorset, Hampshire, Somerset and Wiltshire. It is the sixth largest AONB in England.
Scratchbury Camp is the site of an Iron Age univallate hillfort on Scratchbury Hill, overlooking the Wylye valley about 1 km northeast of the village of Norton Bavant in Wiltshire, England. The fort covers an area of 37 acres (15 ha) and occupies the summit of the hill on the edge of Salisbury Plain, with its four-sided shape largely following the natural contours of the hill.
Marlborough White Horse, also called the Preshute White Horse, is a hill figure on Granham Hill, a fairly shallow slope of the downland above the hamlet of Preshute, southwest of Marlborough in the county of Wiltshire, England. Dating from 1804, it is one of several such white horses to be seen around Great Britain, and one of nine in Wiltshire.
Beeding Hill to Newtimber Hill is a 321 ha (790-acre) biological and geological Downland Site of Special Scientific Interest (SSSI) north of Shoreham-by-Sea in West Sussex. It is a Nature Conservation Review site, Grade 2, and it includes Devil's Dyke Geological Conservation Review site.
The surface of the county of Berkshire, England can be divided into three bands: the county's downlands, south and east of which the London Clay spans almost the whole county, and in the south-east corner sandy Palaeogene heath covers the London Clay. This is an oversimplification, because not everywhere have later layers been eroded away and because layers between the chalk and the London Clay survive in some places.
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}}: CS1 maint: numeric names: authors list (link)Dew-ponds: history, observation, and experiment.(Note: link is 1907 ed.)
construction dew ponds.
dew ponds.
