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pipes to the filter beds, which are situated at Llanforda, about half a mile nearer to Oswestry. The filters, of which there are at present three in number, are composed of sand and gravel, through which the water is made to pass at a rate which experience shews to give the best results. The filtered water is collected in a tank, and thence is drawn off as required for use in Liverpool. From Oswestry the water, now filtered, resumes its journey towards its destination, once more in pipes. They continue in unbroken line for eighteen miles, until they reach Oat Hill, near the village of Malpas, in Cheshire. Here again there is a small break-pressure tank, where the water comes into sight. From Oat Hill there is a length of eleven and a half miles of pipes, terminating in another tank on elevated ground at Cotebrook, between Tarporley and Delamere Forest. From this point there is another run of eleven miles of piping to Norton Hill, in Sutton Weaver, Cheshire, crossing under the River Weaver in Kingsley. In the neighbourhood of Norton there is no land high enough for the construction of a tank at the required level near to the surface, and consequently it became necessary to build a tank to a height of over one hundred feet above the ground line. Hence the Norton Tower—a prominent object to travellers between Liverpool and Crewe. From Norton Tower the line of pipes is continued to the Corporation reservoirs at Prescot, crossing under the Manchester Ship Canal and River Mersey through tunnels. Until a few weeks ago the Vyrnwy aqueduct ended at Prescot, eight miles from Liverpool, and the Vyrnwy water came to the city from Prescot through the old Rivington pipes. The pipes have now, as you are no doubt aware, been continued to Kensington, within the city.
I must describe a little more fully the difficulties encountered in crossing the River Mersey. It is obvious that to reach Liverpool from any part of North Wales the Mersey must be crossed somewhere and somehow. The conditions applicable to the carrying of a large aqueduct over or under the river are in many respects the same as for a railway, and we are all practically familiar with the difficulties of a railway journey between here and North Wales. In laying out the Vynrwy scheme the method of crossing the Mersey was necessarily an important factor. The position ultimately selected and shewn on the parliamentary plans was so chosen because of the facility with which pipes could be placed in the bed of the river ; the intention being that a trench or channel to contain the pipes should be formed by dredging or by hydraulic jets in the sand—a comparatively simple and inexpensive method of crossing such a waterway. Unfortunately, and most mistakenly, as I believe, this plan was opposed by persons interested in the navigation above Runcorn, and chiefly by the town of Warrington. Influenced by this opposition, the House of Commons put a clause in the Bill, according to which the depth of the aqueduct under the river was to be fixed by the Board of Trade. In due course the Board of Trade held an inquiry, and fixed the depth at such a level in relation to the river bed as to make the construction of a tunnel inevitable. Elaborate borings proved the existence of the sandstone rock at a depth of about seventy feet under the middle of the river, and overlying the bed of rock a bed of boulder clay, varying in thickness from twenty to fifty feet. Designs were prepared and a contract entered into for a tunnel to be made through this bed of clay. The work was not carried out, and I need only mention the fact that the contractors abandoned their undertaking after completing one shaft and about fifty feet of tunnel. New contractors undertook the task, but elected to construct the tunnel at a higher
level, through the beds of sand and gravel overlying the clay. They failed to carry out the whole of their contract, and it had to be completed as day work by the Corporation, under the direction of the engineer, Mr. G. F. Deacon. The approach to the tunnel is by means of a circular vertical shaft on the Cheshire side of the Mersey, 52 feet in depth by 9 feet 9 inches in internal diameter, lined with cast iron rings. On the Lancashire side is a similar shaft, but 59 feet in depth, and between these shafts a tunnel 9 feet internal diameter and eight hundred feet in length. The tunnel is lined with cast iron segments, built in position as the work advanced. As a matter of scientific interest the work is important, because it affords an example of successful tunnelling through an ever varying mixture of mud, sand, gravel, and shingle, full of water, with a big tidal river overhead. I should be venturing too far in the direction of technical engineering if I were to discuss the details here.
There is another portion of the aqueduct to which I must briefly refer, because of the scientific and general interest attaching to it. I have spoken of two tunnels near Oswestry. They are driven through a diversity of rocks, chiefly mountain limestone and silurian. When the rocks had been pierced, it became necessary for the engineers who were responsible for the work to consider to what extent the face of the rock should be protected, and the escape of water prevented by the insertion of linings. After a careful and thorough examination, they came to the conclusion that certain lengths, amounting in the aggregate to 1853 lineal yards, might be safely left unlined, the natural rock being shaped to form a smooth channel for the water. This conclusion was perfectly justified by the facts then disclosed and by experience; but about two years ago-long after the completion of the contracts, and after the water had been flowing through for a considerable time-attention was called to an outbreak of water near to a workman's cottage in the Morda valley, fully half a mile from any part of the aqueduct. No one would have suspected any connection between this outflow and the existence of the Llanforda tunnel, but the occupant of the cottage discovered that when there was no water flowing through the tunnel there was no water flowing into his kitchen, and that as soon as the Vyrnwy water was again turned on the flooding recommenced. This led to an inspection of the tunnels, and to the discovery that a considerable quantity of rock had fallen from the roof in the unlined parts, and had caused the water to back up in such a manner as to permit it to escape through fissures, which were above the normal water line. The examinations disclosed a number of such falls, and also disclosed the unexpected fact that the water was acting upon some of the rock in a very serious manner. It was ascertained by chemical analysis that the slaty rock, which was chiefly affected, contained about six per cent. of carbonate of lime and fine particles of iron pyrites. The water dissolved the carbonate of lime, and destroyed the coherence of the rock, leaving the slaty particles in a loose state of mud. This was the chief cause of disintegration, but Prof. Brown thought it was also, to some extent, due to the presence of the iron pyrites, which were oxidised by exposure to air and water, sulphate formed, and the limestone decomposed by some of the sulphuric acid, which partly disintegrated the rock.
Under these circumstances it became necessary to arrange at once for more lining, and this was a difficult as well as disagreeable business, involving the temporary stoppage of the supply from Lake Vyrnwy, and the putting down of extensive plant and rails for bringing the rock out and carrying bricks and mortar into the tunnels. However the task had to be faced, and the Water Committee were resolved that the work should be thoroughly done so that there might be no interruptions in the delivery of water in future years, when interruptions would be even more serious than now. A contract was entered into in 1892, under which the contractors were to have possession of the tunnels for three weeks out of every four, the fourth week being reserved for sending water through for storage at Oswestry and Prescot to supplement the Rivington and well-water in Liverpool. The lining of one of the tunnels (Llanforda) has been completed, and the second will be completed, so far as the invert is concerned, in about a fortnight. There will then only remain the arching in the second tunnel, and the Corporation will, it is hoped, be in a position to make full use of the first instalment of the new supply.
You will expect me to say something about the quality of the Vyrnwy water. This is a subject that suggests and includes many important scientific considerations-as to the effect on the composition of water of the physical characteristics of a watershed; as to the effects of storage in reservoirs of various depths; as to the influence of the bed of a reservoir on the quality of the water stored under varying temperatures, in summer and winter; as to the effect of sand filtration and exposure to light. On these and analogous questions a great deal of light has been thrown by recent investigations, chemical and biological. The Vyrnwy works have contributed to the solution of these problems to an extent which I cannot even indicate to-night.
It was always expected that, following experience elsewhere, the water would improve by storage, and this