The River Elan rises on the vast moorlands south of the Plynlimon range and after uniting its waters with Claerwen, flows down into a wild, romantic valley to join the Wye River at Rhayader. Birmingham picked the Elan valley as the source of its water supply and built a series of great dams to form the lakes that are now a major tourist attraction. By the end of the 19th century the water engineers from Birmingham arrived and began the construction of the magnificent series of dams that ended in 1952 with the final dam across the Claerwen. It must be admitted that these grey walls of heavy stone seem to fit into the landscape and the lakes behind them are glorious when full to the brim after rain. The Claerwen alone is of concrete.
The earlier series of dams begun in 1892 and completed by 1907, after being formally opening by Edward VII in 1904. The first dam is Caban Coch, built at a narrow part of the valley, with impressive crags and tree-clad hill-sides all around. A fox once escaped the hounds by running half way up the centre of it. The dam impounds a lake of nearly 500-acres, and much of the water is allowed to flow for compensatory purposes in the Wye. Caban Coch becomes a show-piece after heavy rain in winter, when the whole face is covered with the overspill water.
At Garreg-Ddu a submerged causeway runs across the lake. All the water above this goes direct to Birmingham. As Birmingham has a scheme for running some of its waste water, after usage, into the River Trent, it can be claimed that water from these wild Welsh moorlands ends up in the North Sea. The topmost dam on the Elan is Craig Goch, enclosing over 200-acres. The highest part of the Elan Valley becomes wild, open and bare with the infant stream meandering over the peaty valley floor.
The great sheep-walks that surround the road leading eventually over to the steeply trenched valley of Cwm Ystwyth were originally in the possession of the monks of Strata Florida. Indeed the monks possessed most of this central moorland country by the gift of the Lord Rhys, the powerful Welsh ruler of South Wales in the 12-century. Like true Cistercians, they introduced sheep farming on a big scale. The present day farms of these hills are therefore the heirs of an old tradition.
The branch valley of the Claerwen was dammed after the Second World War. The dam was opened by Queen Elizabeth II. It is the largest of the dams and impounds a lake of over 600-acres. The farmhouse of Cerrig Coupla is placed immediately under the vast concrete wall, and the farmer goes about his business unaffected by the thought of the immense weight of water poised so near him.
The older farms in these valleys were of the ancient long-house pattern, with the quarters for animals at one end and the domestic quarters at the other. One of these long-house farms was dismantled when the Claerwen dam was constructed and re-erected in the National Folk Museum at St Fagan's, near Cardiff.