Dartmoor leats
Leats have been in use on Dartmoor since medieval times and were originally constructed to provide power for local industries, before later being used to channel Plymouth’s municipal water supply. Dartmoor Preservation Association volunteers have spent several years clearing gorse and scrub from the dry leats on Roborough Common so that Plymouth Leat and Devonport Leat are now clearly visible again.
The word ‘leat’ comes from the Old English word ‘gelaet’ meaning a conduit or a trench and is particularly common in the South West to describe the proliferation of manmade channels built to transport water. Waterwheels were an essential part of mining operations, providing power to drive stamps for crushing ore, bellows for the smelting furnaces and pumps. Early medieval blowing houses usually sourced their water as close as possible and short leats were often constructed to divert water from the nearest river to the operations site. However in later centuries, longer leats were constructed, such as the Grimstone and Sortridge Leat which still carries water from the River Walkham, west of Great Mis Tor, and was used to supply the waterwheels at Sortridge Consols, as well as a number of farms and houses. Powdermills gunpowder factory in Postbridge was one of the more unusual local mills to make use of a leat. It was built in 1844 to provide gunpowder to local tin mines and granite quarries and used waterwheels to power the grinding machinery until it closed about 1900. Leats from the River Walkham serviced various mills in Horrabridge from the 14th century until the 20th century. A leat still flows to the site of Phoenix Mill in Horrabridge which was used as a paper mill very briefly towards the end of the 18th century, and then later for fulling, leather and wool before it became a flour mill in the 20th century.
Plymouth Leat, also known as Drake’s Leat, was built between 1589 and 1591. Drake became Mayor of Plymouth in 1581 and was also a Member of Parliament when the Water Bill proposing a leat to supply water to Plymouth was presented to parliament in 1584, receiving royal assent the following year. The leat started under the present site of Burrator Reservoir, diverting water from the River Meavy and continuing for approximately 17 miles, following the contour lines to allow a steady flow along the leat to Plymouth. It was originally planned to provide water for naval and merchant shipping, as well as fire-fighting in Plymouth, although Drake also had a vested interest in helping to get the bill passed as he was granted a lease to build and work six mills along the leat, at a time when corn mills were extremely profitable.
Over time public 'conduits' were also constructed to supply water free of charge to the population; the sides of the leat were lined with stone or slate, and sections were roofed to prevent pollution. In the 1820s, reservoirs were built in Plymouth at Drake's Place and North Road and the city’s water supply system was considerably updated during the 19th century. When a dense snowfall during the ‘Great Storm’ of 1891 brought the leat to a standstill for several days it was obvious that an alternative solution needed to be found. The Plymouth Corporation Act of 1893 authorised the construction of a reservoir at Burrator Gorge and water ceased to flow along Drake’s leat in 1898.
In the 1790s Devonport was a separate town with a busy port and an increasing requirement for water. Plymouth was unwilling to share its water supply so a bill was lodged with Parliament proposing a new leat for Devonport which was approved in 1792, with the leat eventually being completed in 1801. Considerable engineering skill was employed in building the leat which starts just north of Wistman's Wood and takes water from the West Dart, Cowsic and Blackbrook rivers along aqueducts, a tunnel at Nun’s Cross and even a waterfall at Raddick Hill, using sluice gates, weirs and ‘bullseye’ stones to control the flow as required. The leat originally ran for 28 miles and terminated in a reservoir in the site of Devonport Park. More reservoirs were built around Devonport as the town expanded, then in 1878 a large one was built at Crownhill and water was piped from there into the town.
Devonport Leat now supplies a nearby waterworks site that distributes water as far away as Plymouth, Tavistock and surrounding areas, with excess water flowing into Burrator Reservoir via a waterfall. Remains of the continuing dry section, as well as sections of the dry Drake’s Leat can still be seen between Burrator and Plymouth, particularly between Yelverton and Clearbrook where the two leats run close to the cycle path. In addition to Devonport Leat, there are still a number of leats on Dartmoor that carry water, including Grimstone and Sortridge Leat, Wheal Friendship Leat, Wheal Jewell Leat, Hamlyn’s Leat, Holne Town Gutter and Gidleigh Leat.
Rosemary Best and Keith Ryan (Dartmoor Preservation Society)