Carnon River

The Carnon River, a heavily polluted waterway in West Cornwall, rises north of Chacewater and drains the GwennapHamlet and civil parish in West Cornwall.Hamlet and civil parish in West Cornwall. historic mining district. Its tributaries include the Hicks Mill Stream near Bissoe, Trewedna Water near Perranwell Station and it merges with the River KennallRiver in south-west Cornwall. south of DevoranRural village in West Cornwall. to become Restronguet Creekm which flows into the Fal Estuary and Carrick Roads.

Deep alluvial deposits laid down in the Carnon River between the bridge on the old turnpike road and Devoran sustained the most important tin stream worksProcess for extracting tin from the mineral cassiterite. in Cornwall during the 18th century.

Geography

From its source near Chacewater, the river catchment drains many historic tin and copper mining sites. It is joined by the Hicks Mill Stream upstream of Bissoe, Trewedna Water near Perranwell StationMostly rural parish in West Cornwall. and it merges with the River Kennall south of Devoran to become Restronguet Creek, which flows into the Fal Estuary and Carrick Roads. The Great County AditSystem of underground tunnels that drained tin and copper mines between Redruth and Bissoe in west Cornwall., with its network of tunnels draining many mines, empties into the Carnon below the village of Twelveheads.

Between Bissoe and Devoran the Truro to Falmouth railway line crosses the river on a high viaduct that was built when the river was tidal. The viaduct also crossed the line of the Redruth and Chasewater Railway that followed the Carnon Valley between Twelveheads and Devoran is now part of the route of the coast-to-coast cycleway between Portreath on the north coast and Devoran.

History

The Carnon Valley has been a source of tin ore from prehistoric times but evidence of the tin industry from the early Bronze Age is scant. William Jory Henwood (1805–1875) described a discovery made in March 1823 when workers at the stream works uncovered a Bronze Age human skeleton in the tin–bearing sediment about 22 feet (7 m) below high water.^[1] Tin streaming is a basic method of extracting tin from river valleys where the mineral was so abundant that alluvial deposits from the river bed could be gathered and washed through running water leaving the heavy tin deposits behind. Alongside the tin, small amounts of gold were also found in the sediments and a large nugget found in 1808 is in the Royal Cornwall Museum collection.^[2]

The deep alluvial deposits laid down in the Carnon River between the bridge on the old turnpike road between Perranwell and Carnon Downs and Devoran sustained the most important tin stream works in Cornwall in the 18th century.^[3]

Pollution

The Carnon’s catchment drains the GwennapHamlet and civil parish in West Cornwall.Hamlet and civil parish in West Cornwall. area, now part of the Cornish Mining World Heritage Site, which was described in the 19th century as “the richest square mile anywhere on earth”. Over time, mining has polluted the entire length of the river and its tributaries. The Great County Adit has also contributed to its contamination with arsenic, iron, cadmium,nickel, copper and zinc.^[4] When the Wheal Jane mine near Bissoe closed in 1991, its de-watering pumps were removed, resulting in the release of acidic minewater from the Nangiles adit portal in January 1992. The Carnon and part of the Fal Estuary were heavily contaminated by millions of gallons of bright orange pollution. The clean-up was costly, involving constructing plant that became operational in 2000 to treat the minewater before it was discharged into the Carnon.^[5]