Water Power - Devon, Tamarside

Before the early 19th century, reliable water supplies were scarce on the Devon bank of the Tamar, only a handful of narrow valleys containing unreliable streams cutting down through the western edge of Morwell Down. There is some evidence for tin stamping and smelting mills in the 17th and early 18th century in these valleys, such as those at Gutter Hole, Hatchwood and Impham, documented in early 18th century lease and estate maps in the Bedford Papers (DRO).

Small leats were brought from these valleys to feed tin and copper workings on the valley side, of at least early 18th century date, such as the two from the Impham valley northwards to Hatchwood/Ding-Dong tinwork; that from the Rubbytown valley to Hatchwood valley above Newbridge, and a short leat from Sheepridge to the early 18th century Providence Copper Work in Sheepridge Wood. A leat from Lobscombe above Morwellham may be much earlier as it seems to have fed a tinwork called Morwellham Parks, documented in 1566 and 1578.

The majority of these early leats were probably used for surface dressing of ore or possibly 'hushing' to remove overburden. Water power is however known to have been used underground in the Marquis Copper Work (later part of Bedford United Mine) as early as 1724, when the Bristol Copper Company installed a large water wheel in a chamber underground, pumping a shaft alongside it (Brooke 2001, 12). This is discussed on the Water Power home page. Its chamber is accessible off the south sides of the upper and lower adits, though it is partly filled with later deads.

Sufficient survives however to show that the wheel was supported in a frame of close-set upright timbers, let into slots cut in the rock and presumably braced at their extremities with short cross-timbers. This disinclination to support the wheel on the soft killas rock shows the miners' scorn for any strength it may have had. The vibration of a working wheel would have quickly dislodged it from its bearings.

It is interesting to note that underground wheels in the Harz mountains in Germany, a geologically similar area to the Tamar Valley, were also placed on timber frames, though of a different design (Balck 1999, 36).

Some of these also share the position of the Marquis wheel's associated shaft, immediately alongside the wheel. The water supply for the Marquis wheel was brought from the Rubbytown valley 1km to the north, and had probably already been laid out to serve earlier stamping mills at Gutterhole to the south. The leat survives as a terrace on the steep valley side and is cut by the nearby early 18th century Tavistock Copper Work, showing the leat to be earlier. The point at which it entered the Marquis Work is shown by a deep rock cutting, seen here just to the left of the upper level gunnis.

A longer leat of later 18th century or earlier date was also taken from the Rubbytown valley and carried northwards through Blanchdown Wood to augment the small stream in the Hele valley. Its course is shown on Brenton Symons' mining map of the Tavistock District of 1848, when it served the early workings on the Devon Great Consols Lode, while its collection pond and take-off from the Rubbytown Brook is shown in this extract from the foreground of an engraving of JMW Turner's painting 'Crossing The Brook' from 1812.

Augmentation of this type was occasionally used to increase the water available to a particular mine - a classic example is the use of water from Foxtor Mires near Princetown, carried seven miles to Brookwood near Buckfastleigh in the 1840s. An attempt to build a similar leat taking water from near Widecombe to serve Ashburton United Mines near Ashburton in 1832 ended in a lawsuit which successfully challenged 13th century mining law giving tin miners the right to obtain water wherever they needed it (Fiona O'Connor pers. comm.). This leat was never completed, perhaps explaining the mines' subsequent reliance on steam power.

The development of water power on the Devon bank of the Tamar was massively expanded in 1817, with the opening of the Tavistock Canal. This flowing body of water was brought through a 1½ mile long tunnel under Morwell Down, providing large quantities of power at a high level in the valley. Two leats were taken from the Lobscombe valley where the canal came out of the tunnel. The Gawton Leat was the shorter of the two, serving two 40ft diameter by 4ft breast wheels at George & Charlotte Mine (with an earlier one underground) before supplying an incline haulage wheel at New Quay Limekilns, installed in 1825-26.

An extension was made in 1852 to Bayly's Shaft at Gawton Mine where a 45ft by 4ft wheel pumped Gawton and Bedford Consols mines, also crushing their ores with a roller crusher. This leat is said to have leaked so badly that Gawton Mine eventually went over to steam power, although the leat continued in use as late as the early 20th century, powering a small-diameter wheel which drove Brunton calciners at Gawton Arsenic Works.

The second of these leats; later known as the Bedford United Leat was planned as early as 1803 but not built until 1828, serving a 40ft diameter wheel for pumping, hauling and crushing at Wheal Russell and two large diameter wheels for pumping and crushing on the adjoining Impham Mine.

One of these is shown here, on the Wheal Russell AMR section of c.1860 which shows workings on the Impham Lode. A smaller wheel was in use by the 1860s at the nearby Impham Brickworks, hauling clay to the surface from a shallow mine.

The leat was extended north of the Impham valley in 1842 to carry water to Bedford United Mine, where it drove two large diameter wheels in tandem for pumping, crushing and hauling. One of these is carved into a gravestone dated 1860 in Calstock Churchyard.

Just north of Impham valley the leat had to pass for some distance along the sheer cliff face beneath Chimney Rock. Parts are said to have been suspended from chains, while at least one supporting iron strap is known, driven horizontally into the rock. The engraving below shows a similar suspended launder being inspected by engineers, probably in North America.

After serving Bedford United Mine, the leat was brought southwards again at a lower level, crossing the A390 road just above New Bridge and supplying dressing floors and a large diameter pumping and stamping wheel at South Bedford Mine. This wheel is of interest as it also pumped a shaft of Old Gunnislake Mine across the river.

The flatrods crossed the river on an extraordinary timber trestle bridge, possibly replacing an earlier one referred to in the 1790s by John Swete in his diary (Gray & Rowe, eds. 1998). The tailrace fed a leat which was taken further south across the lower cliff faces below Chimney Rock on long timber legs, as can be seen in this 1920s photograph, taken from the Cornish bank just below Weir Head. This probably fed the large diameter pumping wheel at the mouth of the Impham Valley which appears on William George's gravestone.

The course of the upper leat is shown in blue dots on the photograph where it follows a precipitous route around the cliff face beneath Chimney Rock. This part was in use as late as 1930, serving a copper precipitation works at Bedford United Mine.

The Devon Great Consols leat system was commenced in the late 1840s when it was realised that this mine needed to harness the River Tamar for its power. Two leat systems were constructed, the first taking water from a new weir below Latchley and carrying it along the valleyside to a point just north-west of Blanchdown Farm. Here two pairs of gigantic water wheels 40ft diameter by 12ft breast turned, operating long flatrods to pump the principal shafts on the line of the lode on the hilltop to the north. The wheels were designed by Wheal Friendship's hydraulic engineer Nathaniel Smith and were set in motion in 1849. This date is carved into the keystone of one of the exit arches from the wheel pits, which survive in an incomplete state. An additional wheel operated a set of plunger pumps in the valley bottom near Blanchdown Farm, pumping fresh water from a leat up the hill to feed the second leat system.

This second system combined fresh and foul water (the latter pumped to surface from the mine), settling sediments out in large ponds at the top of the hill. It was largely used for ore dressing and passed water round the various centres of operations via a complex system of leats and reservoirs. This extract from the 1867 Bedford Estate Map shows part of the system around Wheal Josiah.

Ore dressing at Devon Great Consols is described in detail by RJ Stewart in his excellent book on the subject (Tamar Mining Press 2005) while he has recently completed a major book on the mine's history, to be published by the Trevithick Society. This is expected to become the standard work on the subject.
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