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The Great County Adit, sometimes called the County Adit, or the Great Adit was a system of interconnected 
The portal of the adit is in the Carnon Valley below the hamlet of
adit
An adit (from Latin ''aditus'', entrance) is an entrance to an underground mine which is horizontal or nearly horizontal, by which the mine can be entered, drained of water, ventilated, and minerals extracted at the lowest convenient level. Adit ...
s that helped drain water from the tin and copper mines in the Gwennap
Gwennap ( kw, Lannwenep (village), Pluw Wenep (parish)) is a village and civil parish in Cornwall, England. It is about five miles (8 km) southeast of Redruth. Hamlets of Burncoose, Comford, Coombe, Crofthandy, Cusgarne, Fernsplatt, Fr ...
area of Cornwall
Cornwall (; kw, Kernow ) is a historic county and ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people. Cornwall is bordered to the north and west by the Atlantic ...
, in the United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
. Construction started in 1748 and it eventually reached a length of over of a tunnel, providing drainage to over 100 mines at an average depth of .
The adit was the brainchild of John Williams (born 1714) of Scorrier
Scorrier is a village in Cornwall, England, United Kingdom. It is in the civil parish of St Day, about northeast of the centre of Redruth and southeast of the coast at Porthtowan, on the A30 road at the junction of the A3047 road that leads ...
who was the manager of Poldice mine
Poldice mine is a former metalliferous mine located in Poldice Valley in southwest Cornwall, England, United Kingdom. It is situated near the hamlet of Todpool, between the villages of Twelveheads and St Day, three miles (5 km) east of Re ...
. Although work was started in 1748, it did not reach Poldice mine until the late 1760s. By 1778 the adit had been extended past Wheal Busy to Wheal Peevor, and another branch, known as the Consols Adit was driven west in the 1770s and 80s to drain the Consolidated Mines
Consolidated Mines, also known as Great Consolidated mine, but most commonly called Consols or Great Consols was a metalliferous mine about a mile ESE of the village of St Day, Cornwall, England. Mainly active during the first half of the 19th ...
and United Mines. By 1792 a branch from Poldice extended to Wheal Unity.
The portal of the adit is in the Carnon Valley below the hamlet of Twelveheads
Twelveheads ( kw, Dewdhek Stamp) is a hamlet east of St Day in west Cornwall, England, United Kingdom.Ordnance Survey ''One-inch Map of Great Britain; Truro and Falmouth, sheet 190''. 1961 It lies in the parish of Chacewater, between Truro and ...
. In 1839, probably at its peak, it discharged over 14.5 million gallon
The gallon is a unit of volume in imperial units and United States customary units. Three different versions are in current use:
*the imperial gallon (imp gal), defined as , which is or was used in the United Kingdom, Ireland, Canada, Austr ...
s (66 million litre
The litre (international spelling) or liter (American English spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metre (m3 ...
s) of water per day into the Carnon River
The Carnon River ( kw, Avon Carnon) is a heavily polluted river in Cornwall, United Kingdom. It starts in Chacewater. Trewedna Water and River Kennall flow into the Carnon before it merges with Tallack's Creek to become Restronguet Creek, which ...
. At that time the adit had more steam engines pumping into it than were used by the whole of continental Europe and America combined.
The Carnon River empties into Restronguet Creek
Restronguet Creek is a tidal ria in south Cornwall, United Kingdom. It is a tributary of Carrick Roads, the estuary of the River Fal, and is situated approximately four miles (6.5 km) south of Truro and three miles (5 km) north o ...
(a tidal arm of the Carrick Roads
Carrick Roads ( kw, Dowr Carrek, meaning "rock anchorage") is the estuary of the River Fal on the south coast of Cornwall in England. It joins the English Channel at its southern end near Falmouth.
Geography
It is a large flooded valley, or ...
upstream from Falmouth). Major floods in the winter of 1876 caused large quantities of gangue
In mining, gangue () is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. It is thus distinct from overburden, which is the waste rock or materials overlying an ore or mineral body ...
and silt to be washed into the higher part of Restronguet Creek, permanently damaging navigational access to the upper quays at Devoran
Devoran ( kw, Deveryon) is a village in south Cornwall, England, United Kingdom. It is southwest of Truro at .Ordnance Survey: Landranger map sheet 204 ''Truro & Falmouth'' Formerly an ecclesiastical parish, Devoran is now in the civil par ...
.
Although all the mines served by the Great County Adit have closed and it is unmaintained, it still drains many of their underground workings today; in the summer of 1980 the flow was 500,000 gallons per day.Buckley, p.80
See also
*Mining in Cornwall
Mining in Cornwall and Devon, in the southwest of England, began in the early Bronze Age, around 2150 BC. Tin, and later copper, were the most commonly extracted metals. Some tin mining continued long after the mining of other metals had be ...
References
Sources
* * * History of Cornwall Mining in Cornwall History of mining in the United Kingdom Tin mines in England Industrial archaeological sites in Cornwall {{Cornwall-struct-stub