The River Rheidol is a river of mid Wales. The Rheidol catchment has an area of 246 square kilometres and an average rainfall of 1760 mm of which 1272 translates into river flow. It has an average flow of 9.657 m�/s at Llanbadarn Fawr and a maximum recorded flow of 145.285 m�/s on 17 December 1965. Note that the flow is regulated by a hydroelectric power scheme at Cwm Rheidol.
Geography and geology
The Rheidol rises in the headwaters of the Nant y Moch reservoir 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 ancient oak 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. The remainder of the meandering course of the river is through an ever-widening valley before discharging to the sea through Aberystwyth Harbour.
The catchment of the Rheidol is dominated by the western maritime exposure of this part of Wales. Rainfall levels are high and ecosystems reflect both high rainfall and the acidic nature of the underlying rocks. Upland Molinia spp. grassland is common growing on deep deposits of peat. Within the valleys, dense and ancient oak forests with rich understoreys of ferns, mosses and lichens are common. In the valley bottom, glacial and alluvial deposits have been worked by man into a relatively low intensive agriculture.
Economy and the human influence
Metal mining dominated the economy of the Rheidol valley for many centuries. This has now been replaced by farming (beef, dairy and sheep), forestry and tourism.
There are a number of tourist attractions in the Rheidol valley. These include the Devil's Bridge waterfalls where three bridges, each built over the previous, span the top of a most spectacular waterfall.
Between Devil's Bridge and Aberystwyth runs a narrow-gauge steam railway - the Vale of Rheidol Railway. This was originally built to ship metal ore from the mines but now provides a very popular tourist route into the top end of the Rheidol valley.