Mossy Moor Reservoir and Leats
According to Thomas Hammond's memoirs written in 1927, Mossy Moor Reservoir was constructed in about 1850 by Thomas Mason, the owner of Hebden Mill, to help maintain a constant supply of water to power the mill, and the available evidence supports his memory. The precise date of construction is uncertain. The reservoir does not appear on the 1853 OS map, with the survey being carried out between 1848 and 1850.
The moorland was at that time held jointly by the Trust Lords, and their agreement would have been required for such a construction, but the reports of the Barmaster, who looked after their interests, are incomplete for this period. There is, however, an entry in the Barmaster's records for May 1853: "Rec.d of Mr. Mason, Gargrave, Dam rent: 10s 0d". So evidence suggests that the reservoir was constructed between 1848 and May 1853. Mason continued to pay his rent to the Trust Lords until he was awarded that piece of land by the 1857 Enclosures.
The reservoir was built on a low-lying marshy area, with a catchment area of little more than 10 hectares, and so would have taken a long time to fill up, but would be quickly emptied.
When William Sigston Winn and Joseph Osborne leased the Manorial mineral rights in August 1853, they began by driving Top Level about 250 metres up Bolton Gill. Adjacent to this they constructed a dressing floor to process the ore. Lead ore dressing requires power to drive the ore crushers, and copious amounts of water to wash the crushings. The dressing floor was well above the level of the beck in Bolton Gill, and a reliable supply of water had to be sourced.
The solution involved considerable engineering and investment, but it resulted in the last word in reusable energy. Presumably by arrangement with Thomas Mason, they took advantage of Mossy Moor Reservoir by constructing a system of leats, or water channels, over 2.3 km long that extracted water from Bolton Gill just above the Engine Shaft that to feed it, and then returned it at a lower level to provide water for the dressing floor. A regular supply into the leat system was assured by constructing a compensation reservoir 400 metres further up the valley, called New Dam. Later, when Bolton Gill Engine Shaft was built, the leat system was extended to power a waterwheel on Bolton Haw Side which in turn provided power to the engine shaft. All the water eventually finished up back in Bolton Gill.
Both parties benefited from the arrangement. Thomas Mason had a reliable source of water topping up his reservoir, and Hebden Moor Mining Company had sufficient water to service their requirements.
In the above Google Earth image north is to the left. Bolton Gill engine shaft is on the left and Mossy Moor Reservoir is on the right. The top red line shows the path taken by the upper leat that carried water from Bolton Gill to the reservoir, and the mauve line shows the path taken by the leat carrying water from the reservoir outlet channel to the waterwheel and dressing floor. The lower blue line shows the leat that fed the waterwheel, and the upper blue line shows a short-cut from the upper leat to the waterwheel. The reason for the offset in the two lines is that it is thought that the waterwheel was moved. The orange line shows the tail race from the waterwheel returning the water to Bolton Gill via Bolton Haw Side Tunnel. From above the water wheel, the lower leat (mauve) divides into two. One drops water directly into the tailrace, and the other takes it round the corner to the engine shaft dressing floor.
A considerable amount of effort was put into developing the leat system, and much of it is still intact, and in many places obvious on the ground. Usually it was constructed as a slab-covered stone-walled channel. Occasionally, because of the topography, it was necessary to bury it, but it can still be traced as a natural line through the fields, and occasionally they just dug ditches. Almost all of it can still be followed without difficulty, although much of the section running along the valley to the crushing plant is no longer visible although enough of it remains to show the line it took. It is not obvious where this section turns into the valley.
It is not known for how long the leat system was in use, but only the top leat is marked on the mining company's 1866 map of its infrastructure.
According to B.J. Harker's account of Hebden written in 1869, the dam burst in 1855. According to Hammond's 1927 account, this caused considerable damage, washing away fences and damaging fences. It must have been repaired very quickly, as it was an important part of the mining infrastructure.
After the mines closed, the leat system fell into dis-use, and now has gaps. The only feed into the reservoir is now from upstream of the shallow valley in which it is contained. In 2002, a new channel was excavated at the north-east end of the dam to reduce the level and size of the reservoir.