River Rheidol - Geography and Geology

Geography and Geology

The Rheidol rises in the headwaters of the Nant y Moch reservoir (52°27′32″N 3°50′06″W / 52.4590°N 3.8349°W / 52.4590; -3.8349 (River Rheidol (source))) on the western flanks of Plynlimon and then flows south through the village of Ponterwyd on the main Aberystwyth to Rhayader road. Continuing south-westwards, largely through Welsh Oak ancient woodlands in an increasingly deep valley the Rheidol joins with the Afon Mynach and veers westwards, the direction in which it continues for most of the rest of its course. At its confluence with the Mynach, it descends one of the most spectacular waterfalls in Wales at Pontarfynach (Devil's Bridge). Below these waterfalls, the river passes the abandoned workings of the Cwm Rheidol lead mine. This mine, together with numerous other metal mines in the valley, has been a source of extreme metal pollution of the river right down to the sea. Even when the mine was closed, a major blowout of water contained in an adit in the late 1960s coloured the whole river an ochre orange colour and greatly added to the concentrations of lead and zinc in the river. Management of the waters still draining from the mine is by the use of constructed wetlands. Previous management includes a limestone filter bed, installed in the 1960s, which is now redundant. The filter bed is still in place and can be seen from the road. The remainder of the meandering course of the river is through an ever-widening valley before discharging to the sea through Aberystwyth (52°24′26″N 4°05′23″W / 52.4071°N 4.0898°W / 52.4071; -4.0898 (River Rheidol (mouth))).