The growth in mineral output that created Britain’s most important non-ferrous metal mining region was due to vertical exploitation of irregular, and erratic lodes within hard rock. This necessitated shaft mining and presented a continuous challenge in terms of depth and water drainage.

The driving of long drainage tunnels (adits) from the lowest suitable points in the topography was vigorously pursued from 1700 onwards. By the second half of the eighteenth century most established mines possessed adit systems.

The Great or County Adit was a venture headed by the Lemon and Williams families and drained the largest concentration of copper mines in the world. It was commenced in 1748. Its branching network eventually drained over 100 mines to an average depth of 80-100m and attained a length of over 65km. In 1839 it discharged around 66 million litres per day and had more steam engines pumping into its course than were used by the whole of continental Europe and America combined.

A high level of dissolved metal salts in this discharge gave rise to copper precipitation works and iron ochre works in the Bissoe Valley. Even when steam engines were introduced, adits remained cost-effective, especially in coastal locations such as at St Agnes where up to 100m of vertical ore-ground could be drained by using sea-level adits. In the deeply incised Tamar Valley Mining District this was even greater and an adit driven in the mid nineteenth century at Gunnislake Clitters mine met the ore-ground at a depth of 160m.

At Wheal Rose near St Agnes in 1725 the Newcomen engine was so costly that the adventurers decided to drive a 2.4km adit to alleviate the cost of carrying on firing it. By the time steam engines were adopted, the ore-ground above an adit was often exhausted.

We are all assured, that a large water-wheel engine, if water is plenty and cheap, is most effectual and steady for the purpose of draining our mines. (W Pryce, 1778)

Water had long been removed from mine workings by devices that employed manual, horse or water power. William Pryce, writing around 1760, records horse whims that drew 120 gallon (545 litres) barrels by the power of four horses. He writes The water-wheel with bobs is yet a more effectual engine, whose power is answerable to the diameter of the wheel and the sweep of the cranks fixed in the extremities of the axis.

Water wheels also provided power for winding machinery, stamping mills and a host of other appliances. There were hundreds in the region, often working on a seasonal basis, some through leats taken off streams further up the valley, but also through leats taken from reservoirs that would only allow effective working during the rainy months of winter and spring.