The Elan Valley Reservoirs are a chain of man-made lakes in Wales, west of Rhayader, (also known as the "Welsh Lake District"), The reservoirs were constructed early in the 20th century to supply clean water to the Birmingham area. The dam at Craig Goch, the highest upstream of the series of dams in the Elan Valley, is often referred to as the 'top dam'. It is located at a height of 1040 feet (317m) above sea level. As with all the dams, work started with the arrival of the railway line at the site. In the case of the top dam the line had farthest to go and a rocky outcrop had to be blasted and dug through on the route to the site. Work on excavating the foundations for a secure base for the structure started in July 1897, some three years after the start of work on the lowest dam at Caban Coch. Craig Goch is seen by many as the most attractive of the dams, with an elegantly curved retaining wall and a series of arches carrying a narrow roadway across the top of the dam. It has a domed valve tower and the structure is typical of the 'Birmingham Baroque' style of much of the waterworks scheme. Part of James Mansergh's design proposals, dated July 1892, for the Elan Valley scheme are shown here. The Craig Goch top dam is on the right and the lowest dam at Caban Coch is on the left. The cross-section also illustrates the way in which the water above the level of the submerged dam (near the centre of the reservoir at left) in Caban Coch reservoir can be used as part of the supply for Birmingham drawn off at the Foel Tower just upstream of the submerged dam. Water below that level can only be used as compensation water to maintain the normal river flow downstream to the rivers Elan and Wye.
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