Chatterbox, 1906

by Various

ARD working Birmingham was getting short of water, and it certainly looked as though the time would soon come when there would be none to quench its thirst with. The wells and streams in the countryside had served their purpose splendidly while the city did not demand too much, but as the number of people increased, the number of taps increased too, and water was getting short.

In this unpleasant state of affairs, Mr. Mansergh, a well-known civil engineer, said that he knew where to get the water from. Forty years before, when travelling in South Wales, he had been struck by the suitability of the country for storing water in. The rivers Elan and Claerwen, he said, flowed through valleys which would make splendid natural reservoirs if only they were crossed by the necessary dams. The distance, it was true, would be seventy-three miles from Birmingham, but then it would be all down-hill, and so the water would flow of its own accord. The rivers Elan and Claerwen, in Brecon and Radnor, collect their waters from mountain streams over an area of seventy-one square miles. If preserved in reservoirs, this would supply one hundred and two millions of gallons a day. A certain proportion of this would, of course, be allowed to escape, as it would never do to stop the river Elan altogether. It is an important tributary to the Wye, and the city of Hereford would have had cause for complaint if its water supply had been interfered with.

Valley before Building the Dam.	A Sluice in the Dam.
Building the Pen-y-Gareg Dam.

The work was begun in 1894. Just below the point where the two rivers join, preparations were made for building the first dam. A stank, or wall of timber, was first constructed to turn the water of the river aside, and in the channel over which it had flowed, thus rendered dry, excavations were made for the foundations. When the wall had been raised to a height of thirty feet, with two large culverts or openings left in its lower part for the great water-pipes to pass through, the stream was again turned into its old course, through these openings, and the next part of the dam was begun. Thus in three sections the water-wall rose till a height of one hundred and twenty-two feet was reached, stretching six hundred feet at the top, to the sloping walls of the valley. As this dam will have to hold back five hundred acres of water, containing 7800 million gallons of water, its base has been made as wide as its height. The wall tapers to the top and is perpendicular towards the reservoir. It is formed of large blocks of granite called 'plums,' set in strong cement, and weighing many tons each. Over the top, when the reservoir is full, the flood water pours like a small Niagara. If we could launch a boat on the glittering surface of the reservoir, from the top of this dam, we should have to row for four and a half delightful miles, between the overshadowing sides of the valley, before we reached the next principal dam, at a place called Pen-y-gareg—so huge are these cups of water in Birmingham's service. On the way we should pass under the arches of a stone bridge, thirteen feet wide, stretching from side to side of the artificial lake. The archways spring from the top of a submerged dam, forty feet below the surface. And this was built because Birmingham, seventy-three miles away, is six hundred feet above the level of the sea. In constructing the long water-hill from the Welsh mountains down to the famous Warwickshire city, it was deemed necessary that the upper end should be one hundred and seventy feet higher than the lower end. Now at the point where the first dam was erected, the river-bed is only one hundred feet higher than the land on which Birmingham stands. Therefore, the starting point for the water was made farther up the valley at a spot seven hundred and seventy feet above sea-level (thus giving the necessary fall of one hundred and seventy feet), and just below that spot the sunken dam of which we have spoken was built across to hold back enough water when the main bulk had been used.

As our boat glides onward from under the shadow of the arch, we see near the eastern shore a strongly built stone tower. This stands over the mouth of the aqueduct (as the huge pipes are called which convey the water to Birmingham). The water flows into the tower through several large openings on all sides, and its entrance into the aqueduct is controlled by hydraulic machinery.

Bending to our oars again we follow the curves of the lake for about three miles, with the railway running close to the water's edge. It was laid by the engineers to assist them in this great undertaking. Then we come in sight of the Pen-y-gareg wall. This was built in the same manner as the first dam, though slightly different in design. At regular intervals all along the top, we see square openings like windows in an old castle. They are to admit light and air into a narrow passage left in the heart of the dam and stretching from end to end. It is only six and a half feet high and two and a half wide, so that two people, however obliging they might be, would have a difficulty in letting each other pass if they met half-way. But it is not a public passage, being only constructed for the purpose of admitting workmen to the valve tower, which regulates the flow of water into the lower reservoir.

Some mile and a half farther on we come to the third and last dam on the Elan River. It is called the Craig Gôch, and is the tallest of them all, rising one hundred and thirty-five feet from the river-bed. In order to build it a tunnel was driven through the hills on one side to carry the water past, the stream being guided into this tunnel by means of a concrete wall built a short distance from the scene of operations. The dam is built on a curve, the bow being towards the reservoir. It carries on its summit a handsome stone bridge with a public roadway less than ten feet wide between the parapets. To stand on this bridge and watch the flood water flow between its arches, to fall with a roar like thunder on its way to the lower reservoir, is very impressive. It is said that at times the water passes over the crest of the dam in a cascade eighteen to twenty inches deep. Thus the water is held back among the mountains in three huge steps, much as the water in a canal is banked up by the locks. On the river Claerwen three similar dams are being built.

While this work was going forward, another army of engineers was preparing the road to Birmingham. Hills had to be tunnelled through, valleys and rivers crossed by bridges, while syphons were used for passing under small streams and similar obstructions. One of the tunnels was no less than four and a half miles long, and another two and a half. They are, however, only six or seven feet in diameter, just large enough for workmen to enter for the purpose of doing repairs. The pipes for conveying the water are a little more than one yard across, and are capable of delivering twelve and a half million gallons per day. There is room on the road for six such pipes to be laid, so it is considered that Birmingham will not run short of water for at least a hundred years. It need hardly be pointed out that these pipes do not descend at one uniform grade throughout their journey of seventy-three miles, but any irregularity in their rise and fall is of little consequence so long as the end of that irregularity which is nearest Birmingham is at a lower level than the point at which it begins. Thus, for instance, if the pipes are to take a sudden dip to pass under a stream, they should not rise again on the other side to quite the same level. This dip is called a syphon, and in no way retards the natural flow of the water. There are many such 'ups and downs' between Radnor and Warwickshire; so many, indeed, that we might almost look upon the whole aqueduct as a syphon seventy-three miles long. Birmingham is the lower end, and water must flow to the lower level.