Thirlmere Aqueduct
The Thirlmere Aqueduct is a 95.9-mile long pioneering section of water supply system built by the Manchester Corporation Water Works between 1890 and 1925.
In 1874 John Frederick Bateman advised Manchester Corporation that the increasing demand for water, then averaging 18,000,000 imperial gallons (82,000 m3) per day, would soon exhaust the available supply from Longdendale. His first recommendation was to source water from Ullswater, but it was eventually decided to seek powers to acquire Thirlmere and build a dam there. In the face of local opposition the project received Royal Assent in 1879. Under this act Manchester was granted priority of right to 25 imperial gallons (110 l) per person per day.
Also see Thirlmere Waterworks
1891 See Engineering 1891/12/11 for details of the ingenious self-acting stop valves, intended to close in the event of a burst downstream of the valve. They are butterfly valves, normally securely latched in the open position to allow free flow.
External weights suspended by chains from wheels on the valve spindle act to close the valve when the latch is released.
Release was effected by a flow-sensitive lever located in the bore of the valve. At the lower end of the lever was a circular paddle, positioned in the axis of the valve bore, making it subject to the force of the flowing water. The lever was weighted externally, by weights sufficient to prevent the lever being moved under normal flow.
In the event of the flow rate increasing due, say, to a leak downstream, the increased force on the paddle causes the lever to rotate, triggering release of the latch holding the butterfly disc closed. The flow required for activation could be set to any desired value by altering the external weights.
It was essential to prevent the valve closing quickly, as this would result in excessive pressurisation upstream, and cause water hammer. In order to limit and regulate the closing speed, as the valve disc spindle rotates, it winds a chain on a pulley, and this chain pulls a piston in a cylinder filled with glycerine. The discharge rate of the glycerine (from one side of the piston to the other) determines the rate of closure of the valve. The closing rate is required to gradually decrease as the disc moves nearer to vertical. This was achieved by having a 'quarter turn' plug cock in the line between the two sides of the cylinder, rotated by a rod from the chain pulley. The flow area through the cock gradually reduces as the chain pulley on the valve spindle rotates.
The glycerine-filled cylinder was used to reopen the butterfly valve, pressure being applied by a hand pump, served by a small reservoir of glycerine. Test figures showed a closing time of 45 seconds. 5 - 6 minutes were required to reset the valve.
Even with a slow closing speed, the upstream pressure would rise. To limit the pressure increase, the valve was equipped with a large air cushion vessel.
Note: One of these valves, made by Glenfield and Kennedy, is preserved at Manchester's Museum of Science and Industry. See photos here. See also Geograph photo here. Similar (but much larger) valves were later used on the Maentwrog hydro-electric scheme. See The Engineer 1928/11/02 for a detailed description of those valves.
1892 As built, there were 23 bridges carrying the aqueduct over rivers, streams and railways. There were also ten subways taking the pipes under railways. These included the River Ribble bridge (three spans, cast iron arches); Lune bridge (wrought iron, skew); Brownhouse Stream; Otter Geer bridge; Birklands; River Mint; River Sprint; Lupton Brook; River Wyre; River Darwen; River Brock; River Calder; Rawgill. [1]
The aqueduct from terminated in a new reservoir situated alongside an existing reservoir at Prestwich, 352 ft. 3 in. above datum and 4 miles from Manchester in a north-westerly direction. The existing reservoir, with a capacity of 20 million gallons, was constructed in 1867 for supplying the higher parts of Manchester, the water being conveyed in pipes from the Longdendale works. The new reservoir was built to the west of the existing reservoir, the western embankment being utilised as the eastern embankment of the new reservoir. It was of the same area, 4 acres, and had capacity for 21 million gallons.[2]
1893 'TAKING THIRLMERE WATER TO MANCHESTER.
Manchester is one of the most go-ahead of English cities, and at the present time it has as many irons in the fire as would fully occupy the attention Of a dozen lesser municipalities ....The Manchester water supply has been derived up to the present from the Longendale Valley, about 18 miles to the east of the city. About 20 years ago it began to appear, from the increased demand, that this source would soon become insufficient; it became necessary to look ahead, and the Corporation had their attention directed to other sources of supply. At first there were communications with Liverpool with a view to a joint scheme, but this ultimately fell to the ground, and each city has now carried out its own independent works. The Liverpool people finally adopted the plan of bringing their water from Wales. The source selected was on the River Vyrnwy, a tributary of the Severn; no lake existed, but one was brought into existence by means of a large dam. This lake submerged in its depths a village, a parish church with its burial ground, as well as a number of farms and houses. The water thus collected had to be carried about 75 miles through tunnels, pipes, and syphons, to Liverpool. This was the longest aqueduct that had up to that time been made, for the longest the Roman aqueducts, the Anio Nevus, constructed in the time of Claudius, extended only 62 miles. Both of these are now exceeded by the aqueduct front Thirlmere to Prestwich, which extends over a distance of 96 miles. Prestwich, where the reservoirs are, is 3 1/2 miles on the north of Manchester, so that the water has to be carried altogether about 100 miles. One of the reasons which led to the selection of Thirlmere in preference to the other lakes in Cumberland was the height of its surface above the sea level. This is given as 533 feet, and when the lake is increased in size, which it will be by means of a dam, 50 feet more will be added, making it 583 feet. Prestwich is 353 feet above the sea, which leaves 230 feet of a fall as a gravitating power to carry the water along the conduits. Thirlmere has neither villages nor mineral works of any kind on its banks from which pollution can come into its waters; and as the Corporation of Manchester is now the owner, not only of the lake, but also of the whole of the watershed, including the "mighty Helvellyn," it can prevent all encroachment in the future that would tend in any way to the deposition of deleterious matter. Under the Act of Parliament for the Thirlmere Water Supply, passed 1879, Manchester is empowered to supply towns or districts around the city, on the line of the aqueduct, with water, on certain conditions; one of which is that 25 gallons a day must be reserved for each inhabitant of Manchester.
Thirlmere is comparatively a small lake; it is only about 21 miles in length, and at its widest not above a quarter of a mile; it covers about 330 acres; the greatest depth is 112 feet. It has an exceedingly picturesque aspect, greatly due to the mighty Helvellyn, whose base rises from the southern end of the lake like a great buttress, while above, its peak stands supreme above the other rocky summits. Facing Helvellyn is the Eagle's Crag; at the northern end of the lake is the Raven's Crag, while, opposite the last, is the Great How, a beautifully-wooded hill, all of which are familiar studies of the artist. The great dam is being made at the north end of the lake, which is intended ultimately to raise the height of the water fifty feet above its present level, and which will increase its capacity to the extent of 80,000,000,000 gallons of water. This dam is the principal outward and visible work of the scheme; it is 800 feet in length, and its highest points, from foundation to summit, are about 100 feet; at the base it is 50 feet in width, and a bold, hollow curve reduces this to 20 feet on the top, which supports along the whole length a roadway of 16 feet, upon which vehicles will be able to pass. A discharging tunnel at the 20 feet height has been made, and at the same time another at 50 feet, so that when it necessary to increase the depth of the lake, the closing up of the 20 feet exit is all that will have to be done. The water supply is withdrawn from the lake at its upper, or south end, that being the end nearest to Manchester. At this point a round battlemented tower is all but finished, which will be known as the "Straining Well," where the water will have to pass through very fine strainers, so as to separate any tangible particles that may be floating in it. From this to Manchester there is little that is visible of the works. It is nearly all underground, but the amount of labour that has been expended on it may be comprehended when it is stated that there are 50 3/4 miles of tunnelling, the tunnels being 7 feet wide and 7 feet 9 inches in height, this being expected to carry the full supply of water that will be required. The largest work of this kind is the Dunmail Raise Tunnel, which is just over three miles in length; it begins at Thirlmere, where the water leaves the lake, and extends to near Grassmere. A great many small streams and valleys have to be crossed with the aqueduct, and this is accomplished by means of inverted siphons. The two largest rivers on the line are the Lune and Ribble. These are crossed by handsome bridges, with stone piers and iron girders, and are large enough to contain the pipes which will be required in the future.'[3]
1901 Second Pipeline. 'Tenders have been opened by the Waterworks Committee of the Manchester Corporation for the first section of the cast-iron pipes forming the second line of the Thirlmere aqueduct. The weight of the first section is 17,000 tons, rather more than one-fourth of the full quantity that will be required. Tenders for the remaining piping will be asked for shortly, and it is expected that the work of laying the pipes will begin about Whitsuntide. Probably three years will be spent completing the work. Shortly before the Council decided, upon the recommendation of the Waterworks Committee, to begin the laying of the second line of pipes the consumption of water within the area of greater Manchester was going up by leaps and bounds. In 1889 32,500.000 gallons of water were used, two and quarter millions more than in the previous year. At this time the city reached the high-water mark of its prosperity, and the prospect of the continuance of good trade imposed upon the Waterworks Committee the necessity of making ample provision to meet a continuance of the abnormal demand. Since 1899, however the consumption has remained practically stationary. If anything, curing the last twelve months it has shown a diminution, and this fact, indicating a suspension in the progress of industries of the city, has removed to some extent the anxieties of the Waterworks Committee. Now they are convinced they will have their new pipe ready in time to meet the increased demands arising from the normal growth of the city's demand for water.' [4]
1902 One of the automatic valves was activated by the fracture of a pipe close to the excavation for installation of the second pipeline: 'it was found that the whole weight of the water and of the pipe, which was laid on the slope of a hill, was unsupported, except by a pinnacle of rock which jutted up under its centre. The rest of the bed must have been soft ground. .... There was a small transverse crack visible just above the point of contact between the pipe and rock. The diameter of the pipe was 40 in.; length, 12 ft.; and the thickness of the metal, which was good cast iron, was l 3/8in. The head of water in the pipe was 270 ft. The joints were the usual leaded spigot and socket....'[5]
1911 A third pipeline was laid from Lake Thirlmere to Manchester, about 105 miles of aqueduct, divided into four main contracts.
A pumping station was built at Heaton Park Reservoir in 1954–1955 incorporating a large relief by Mitzi Cunliffe signed and dated 1955. The building materials and the reliefs are all symbolic of the achievement in bringing water from the Lake District to Manchester. The building was given grade II listing in 1988.
1948 'WORK on the second stage of the Haweswater Reservoir scheme — which will bring an extra 12,000,000 gallons of water daily to Manchester — has received final Ministry of Health sanction and will go ahead soon, it was announced to-day. Manchester's first supply direct from the Haweswater reservoir will come to the city in a main pipeline to be constructed at a cost of £6,000,000 between Garnett Bridge, near Kendal, and Heaton Park, Manchester. Hitherto, water from Haweswater has had to flow through the main Thirlmere aqueduct, at the rate of 13,000,000 gallons daily, so that when the new pipeline is complete the supply will be 25,000,000 gallons daily.' [6]
See Also
Sources of Information
- ↑ Engineering 1892/01/22
- ↑ Engineering 1892/02/05
- ↑ Newcastle Daily Chronicle - Thursday 31 August 1893
- ↑ Manchester Evening News - Thursday 31 January 1901
- ↑ [[Engineering 1902/10/24
- ↑ Manchester Evening News - Tuesday 17 February 1948