Leat 65345 223290573 2008-07-03T12:34:30Z Lightbot 7178666 Units/dates/other A '''leat''' (also '''lete''' or '''leet''') is the name, common in the south and west of [[England]], for an artificial [[watercourse]], or [[aqueduct]], supplying water to a [[watermill]] or its mill pond. Leats may also deliver water for mineral washing and concentration, for irrigation, or to a dye or other industrial works. According to the ''[[Oxford English Dictionary]]'', "leat"' is [[cognate]] 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]], the equivalent word is ''goit''. In southern [[England]], a leat used to supply water for [[water-meadow]] irrigation is often called a ''carrier'', ''top carrier'', or ''main''. ==Functions== Leats generally start some distance (a few hundred yards, or perhaps several miles) above the mill or other destination, where an offtake or [[sluice]] gate diverts a proportion of the water from a [[river]] or [[stream]]. A [[weir]] 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 determines the flow rate together with the quality of the wetted surface of the leat. 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 [[hydraulic head|head]] of water &ndash; several metres (perhaps 5 to 15 feet) for a watermill, or a metre or less (perhaps one to four feet) for a water-meadow. ===Mining=== [[Image:Dolaucothimap2.jpg|thumb|320px|Map of the Roman gold mine]] [[Image:Aqueduct1.jpg|thumb|250px|left|The aqueducts at Dolaucothi]] In mining areas, leats were built to supply water for [[hushing]] mineral deposits, washing ore and powering mills. They were used extensively by the [[Ancient Rome|Romans]], and can still be seen at many sites, such as the [[Dolaucothi]] gold mines. They used the [[aqueduct]]s to prospect for ores by sluicing away the over burden of soil to reveal the bedrock in a method known as [[hushing]]. 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 [[hydraulic mining]]. The water supply could then be used for washing the ore after crushing using simple machines also driven by water. The Romans also used them for supplying water the bath-houses or [[thermae]] and drive vertical [[water wheels]]. Leats were built to work [[lead]], [[tin]] and [[silver]] ores in [[Wales]], [[Cornwall]], [[Devon]] and the [[Pennines]] during the 17th century and later. ==Dartmoor== *[[Drake's Leat]], constructed in 1591 under the management of [[Francis Drake|Sir Francis Drake]] as an agent of the Corporation of Plymouth to carry water from [[Dartmoor]] to [[Plymouth]]. [[Image:Devonport leat 6.jpg|thumb|200px|Devonport leat near Nun's cross farm]] [[Image:Devonport leat 3.jpg|thumb|left|200px|Devonport leat showing sluice gates]] *[[Devonport Leat]] constructed in the late 18th century to carry water to the expanding naval dockyard at [[Devonport, Devon|Devonport]] (now a part of Plymouth). *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 <ref>Robins, J. (1984) ''Follow the leat with John Robins : a series of walks along Dartmoor leats and a description of the mines some of them served'', John Robins, ISBN 0 9508030 0 6</ref><ref>Hawkings, D.J. (1987) ''Water from the moor'', Devon, ISBN 0 86114 788 X Describes a full history of the leats which supplied Plymouth, England.</ref> * Many leats used for tin mining are marked on the 1/50000 and 1/25000 [[Ordnance Survey]] maps, such as the leat serving the now defunct Vitifer mine near the [[Warren House Inn]]. ==References== {{Reflist}} ==See also== *[[Aqueducts]] *[[Dolaucothi]] *[[Flume]] *[[Roman aqueducts]] *[[Roman engineering]] *[[Roman mining]] [[Category:Bodies of water]] [[Category:Geography of England]] [[Category:Aqueducts in the United Kingdom]] [[Category:Watermills|*]] [[Category:History of mining]] {{topography-stub}} [[fr:Bief (sur un cours d'eau)]] [[nrm:Bieu]] [[wa:Bî]]