A leat (; also lete or leet, or millstream) is the name, common in the south and west of England and in

Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

, for an artificial

watercourse A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams a ...

or aqueduct dug into the ground, especially one supplying water to a

watermill A watermill or water mill is a mill that uses hydropower. It is a structure that uses a water wheel or water turbine to drive a mechanical process such as milling (grinding), rolling, or hammering. Such processes are needed in the production ...

or its mill pond. Other common uses for leats include delivery of water for

hydraulic mining Hydraulic mining is a form of mining that uses high-pressure jets of water to dislodge rock material or move sediment.Paul W. Thrush, ''A Dictionary of Mining, Mineral, and Related Terms'', US Bureau of Mines, 1968, p.560. In the placer mining of ...

and mineral concentration, for

irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has been devel ...

, to serve a

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

works or other industrial plant, and provision of drinking water to a farm or household or as a catchment cut-off to improve the yield of a

reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contr ...

. According to the ''

Oxford English Dictionary The ''Oxford English Dictionary'' (''OED'') is the first and foundational historical dictionary of the English language, published by Oxford University Press (OUP). It traces the historical development of the English language, providing a c ...

'', ''leat'' is

cognate In historical linguistics, cognates or lexical cognates are sets of words in different languages that have been inherited in direct descent from an etymological ancestor in a common parent language. Because language change can have radical ef ...

with ''let'' in the sense of "allow to pass through". Other names for the same thing include ''fleam'' (probably a leat supplying water to a mill that did not have a millpool). In parts of northern England, for example around

Sheffield Sheffield is a city in South Yorkshire, England, whose name derives from the River Sheaf which runs through it. The city serves as the administrative centre of the City of Sheffield. It is historically part of the West Riding of Yorkshire ...

, the equivalent word is ''goit''. In southern England, a leat used to supply water for

water-meadow A water-meadow (also water meadow or watermeadow) is an area of grassland subject to controlled irrigation to increase agricultural productivity. Water-meadows were mainly used in Europe from the 16th to the early 20th centuries. Working water- ...

irrigation is often called a ''carrier'', ''top carrier'', or ''main''.

Design and functions

Water mills

Leats generally start some distance (a few hundred yards, or perhaps several miles) above the mill or other destination, where an offtake or

sluice Sluice ( ) is a word for a channel controlled at its head by a movable gate which is called a sluice gate. A sluice gate is traditionally a wood or metal barrier sliding in grooves that are set in the sides of the waterway and can be considered ...

gate diverts a proportion of the water from a

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of ...

stream A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams ...

. A

weir A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of l ...

in the source stream often serves to provide a reservoir of water adequate for diversion. The leat then runs along the edge or side of the valley, at a shallower slope than the main stream. The gradient, together with the quality of the wetted surface of the leat, determines the flow rate. The flow rate may be calculated using the Manning formula. By the time it arrives at the water mill the difference in levels between the leat and the main stream is great enough to provide a useful

head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals ...

of water – several metres (perhaps 5 to 15 feet) for a watermill, or a metre or less (perhaps one to four feet) for the controlled irrigation of a

Water supply

Leats are used to increase the yield of a reservoir by trapping streams in nearby catchments by means of a contour leat. This captures part or all of the stream flow and transports it along the contour to the reservoir. Such leats are common around reservoirs in the uplands of Wales.

Mining

Leats were built to work

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...

, tin and

silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...

ores in mining areas of

Cornwall Cornwall (; kw, Kernow ) is a Historic counties of England, historic county and Ceremonial counties of England, ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people ...

Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devo ...

, the

Pennines The Pennines (), also known as the Pennine Chain or Pennine Hills, are a range of uplands running between three regions of Northern England: North West England on the west, North East England and Yorkshire and the Humber on the east. Common ...

and the

Leadhills Leadhills, originally settled for the accommodation of miners, is a village in South Lanarkshire, Scotland, WSW of Elvanfoot. The population in 1901 was 835. It was originally known as Waterhead. It is the second highest village in Scotland, ...

/ Wanlockhead area of Southern

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to ...

from the 17th century onwards. They were used to supply water for

hushing Hushing is an ancient and historic mining method using a flood or torrent of water to reveal mineral veins. The method was applied in several ways, both in prospecting for ores, and for their exploitation. Mineral veins are often hidden below ...

mineral deposits, washing ore and powering mills.

Use in Roman times

Leats were also used extensively by the Romans, and can still be seen at many sites, such as the Dolaucothi goldmines. They used the aqueducts to

prospect Prospect may refer to: General * Prospect (marketing), a marketing term describing a potential customer * Prospect (sports), any player whose rights are owned by a professional team, but who has yet to play a game for the team * Prospect (minin ...

for ores by sluicing away the overburden of soil to reveal the bedrock in a method known as

. They could then attack the ore veins by fire-setting, quench with water from a tank above the workings, and remove the debris with waves of water, a method still used in

. The water supply could then be used for washing the ore after crushing by simple machines also driven by water. The Romans also used them for supplying water to the bath-houses or

thermae In ancient Rome, (from Greek , "hot") and (from Greek ) were facilities for bathing. usually refers to the large imperial bath complexes, while were smaller-scale facilities, public or private, that existed in great numbers throughout ...

and to drive vertical water-wheels. Devonport leat 3

Dartmoor

There are many leats on Dartmoor, mostly constructed to provide power for mining activities, although some were also sources of drinking water. The courses of many Dartmoor leats may still be followed.Hawkings, D.J. (1987) ''Water from the moor'', Devon, Provides a full history of the leats which supplied Plymouth, England. Many such leats on the moor are marked on the 1:50000 and 1:25000

Ordnance Survey Ordnance Survey (OS) is the national mapping agency for Great Britain. The agency's name indicates its original military purpose (see ordnance and surveying), which was to map Scotland in the wake of the Jacobite rising of 1745. There was a ...

maps, such as that serving the now-defunct

Vitifer mine Birch Tor and Vitifer mine was a tin mine on Dartmoor, Devon, England. Located in the valley of the Redwater Brook, to the east of the B3212 Moretonhampstead to Princetown road, below the Warren House Inn, the mine was worked between the mid– ...

near the Warren House Inn. Notable leats include: * Drake's Leat, constructed in 1591 under the management of

Sir Francis Drake Sir Francis Drake ( – 28 January 1596) was an English explorer, sea captain, privateer, slave trader, naval officer, and politician. Drake is best known for his circumnavigation of the world in a single expedition, from 1577 to 158 ...

, as an agent of the Corporation of Plymouth, to carry water from Dartmoor to

Plymouth Plymouth () is a port city status in the United Kingdom, city and unitary authority in South West England. It is located on the south coast of Devon, approximately south-west of Exeter and south-west of London. It is bordered by Cornwall to ...

. * Devonport Leat constructed in the late 18th century to carry water to the expanding naval dockyard at Devonport (now a part of Plymouth).

References

External links

{{Rivers, streams and springs Aqueducts in the United Kingdom History of mining Hydraulic engineering Water management in mining cs:Náhon nrm:Bieu