Rhayader, Powys

Part of the original plan for the Elan Valley reservoirs was Dol-y-Mynach, at the western end of Caban Coch reservoir in the lower Claerwen Valley. The plan, which envisaged three reservoirs in the Claerwen Valley, were shelved, and the bas of the never-completed Dol-y-Mynach dam still stands, though is submerged when the water level is high. In 1957 the Claerwen Dam was opened, providing far more capacity then the planned three reservoirs together.