245 DESCRIPTION OF THE MANCHESTER WATER WORKS. BY MR. JOHN FREDERIC BATEMAN, OF LONDON. The works by which the city of Manchester and its suburbs are now supplied with water were originally designed in 1846, and were commenced in the autumn of 1848; and the water was first introduced into the city at the end of 1850. Previously to this date the water supply had been gathered from various sources : for some twenty years the greater portion had been obtained from a limited tract of gathering ground within a few miles of Manchester; a small additional quantity had recently been procured from a well sunk into the new red sandstone at Gorton ; and urgent deficiencies were made up by occasional supplies from the Ashton and Peak Forest Canals. The supply however was very inadequate and very impure. The present water supply is brought from the River Etherow, which divides the counties of Derby and Chester, deriving its supplies from the western slopes of the great chain of hills commonly called the backbone of England. A general plan showing the drainage area and the entire course of the works to Manchester is given in Fig. 2, Plate 84; and Fig. 3, Plate 85, is a longitudinal section along the line of the works. The drainage ground lies nearly midway between Manchester and Sheffield, and extends over about 19,000 acres. It rises in parts to an elevation of about 1800 feet above the level of the sea, and about 1200 or 1300 feet above the deep and romantic valley of Longdendale, in which the main collecting reservoirs are situated, as shown to a larger scale in the plan Fig. 1, Plate 83. The district consists of the shales and sandstones which constitute the lower portion of the coal series, the upper millstone grit forming the cap of the steep escarpments on each side, while the lower 24G MANCHEBTER WATER WORKS. millstone grit, which may be said to separate the coal measure shales from the limestone shales, is found in the bottom of the valley. The water yielded by this geological formation is some of the purest in the world, being equal in general character to the water of Loch Katrine which supplies Glasgow. The spring water is especially brilliant, highly aerated, containing little or no foreign matter, and varying from about It" to SgO of hardness according to Dr. Clark's scale, in which 1' of hardness is that corresponding to 1 grain of lime dissolved in 1 gallon of distilled water. The spring water is at all times most abundant, the district yielding much more than the usual quantity in proportion to the area from which the springs issue. The average rainfall is about 50 inches per annum, and the average amount of water which may be collected about 40 inches, the net produce of three or four consecutive dry years being about 33 inches in each year. This quantity if wholly stored would afford a gross supply of about 39 million gallons per day; from which a certain stipulated guaranteed quantity has to be given as compensation to the mills on the streams interfered with, amounting to nearly 13 million gallons per da,y on the average of every day in the year ; this leaves as the supply available for the city and its suburbs 26 million gallons per day. The quantity at present supplied is about 13 million gallons, so that there is water for double the population at the same rate of consumption. Pure and beautiful as all the water is in dry weather and when unaffected by recent rain, the river and most of the principal streams are coloured by peat in floods and wet weather, especially in the summer and autumn months of the year. These circumstances determined several of the more important arrangements of the works. The average quantity of pure uncoloured water was more than sufficient for the wants of the city, but the actual amount was sometimes less than required and at other times too much. A system of separation wst8 therefore adopted, by which the pure spring water, and the stream water when uncoloured, should either be taken direct to Manchester ; or, when there was more than was wanted for the daily supply of the city, should be stored in reservoirs MANCHESTER WATER WORKS. 247 set aspart for the storage of pure water. The turbid or coloured water, being the water of floods, was to be stored in reservoirs specially allotted for the purpose ; and after becoming comparatively pure by settlement and exposure to the atmosphere, it was either to be discharged into the river as compensation to the mills, or decanted off into the pure-water reservoirs for the supply of the city. The means adopted for carrying this object into effect were very simple and certain, and have proved perfectly successful. Each stream, whether large or small, separates itself by a simple arrangement, so that the pure water flows on direct to llanchester, or into the pure-water reservoirs, to be there stored for future use j and the turbid water flows into the turbid-water reservoirs or runs to waste down the river. In Fig. 4, Plate 86, is shown the manner in which the separation of the water is effected in a large stream, the Crowden Brook. A weir A A is erected across the stream, with a passage B for water within the masonry beneath the top. In front or on the down-stream edge of the weir, a narrow transverse slot C opens into the passage beneath. When the stream is small, as indicated by the lower water line D D, or rather when not swollen by rain, and the water consequently perfectly pure, it drops through the slot into the passage B beneath, which communicates with a conduit to convey the water to Nanchester or to the pure-water reservoirs. The slot C is constructed of such a width as to admit the whole stream, when it consists only of the pure water; but when the stream is swollen, as indicated by the upper water line EE, the velocity with which it passes over the weir is sufficient to carry it clear over the slot and down the face of the meir, into the ordinary river course or to the reservoirs for turbid water. Figs. 5 and 6 show the separating arrangement adapted to the case of a small stream, where the object is effected by a transverse slot C in a trough F crossing the pure-water conduit B. The water, when small in quantity and consequently pure, falling from an elevated ledge at the back of the slot, drops through the slot into the pure-water conduit B ; but overshoots the slot when the quantity is large, and is then carried by the trough I? in another direction. M2 248 MANCHESTER WATER WOR6S. The main impounding Reservoirs, shown in Fig. 1, Plate 83, are constructed in that beautiful part of the valley known as IJongdendale, and are five in number. Three of them, namely the Woodhead, Torside, and Rhodeswood reservoirs, are constructed along the course of the River Etherow in the main valley, which they occupy for about 5 miles in length. The other two, the Arnfield and Hollingworth reservoirs, are placed on tributary brooks. The highest, the Woodhead reservoir, is at a level of 790 feet above the sea. The point at which the water leaves the lowest or Rhodeswood reservoir to be conducted to ManChester is about 13 miles distant from the city. To this point also is conducted all the spring water and pure water collected by the various conduits constructed for the purpose ; and the joint volume of water is conveyed away by a common aqueduct” for the use of the city, as shown in Figs. 2 and 3. This aqueduct is principally a covered conduit. It has a fall of 5 feet per mile, and passes under the Mottram ridge by a tunnel of about 3000 yards length, Fig. 3, and terniiuatcs in a reservoir at Godley near Hyde, about 8 miles distant from Manchester and 314 feet above the centre of the city. From this reservoir the water is conducted by a single line of cast-iron pipes of 40 inches diameter to two service reservoirs at Denton, about 4 miles from Manchester and 163 feet above the centre of the city; the axerage fall of the pipes from Godley to Denton is 43 feet per mile. The Denton reservoirs are used for the service of the higher parts of the city, while the old Gorton reservoirs, the lowest of which is 77 feet lower in level, are employed for the supply of the lower parts; and a pipe of 30 inches diameter is now being laid direct from the Godley reservoir to supply distant localities and various elevated suburbs, such as Pendleton, Broughton, Cheetham Hill, and Newton. From the Denton reservoirs to llilanchester there is a line of pipes of 36 inches diameter; and a culvert of 4 feet diameter conveys a portion of the water to the old Gorton reservoirs, from which the lower parts of the city are supplied. From these latter reservoirs two pipes, of 24 and 18 inches diameter, convey the water to the city. * (In Fig. 1for “ Line of Plpes ” read “Line of Aqueduct.”) MANCHESTER WATER WORKS. 249 The total capacity of the five reservoirs in Longdendale is about 550 million cubic feet when full to the level of the overflow weirs, and their area about 400 acres. The heights of the embankments and the capacities of tho several reservoirs are given in the following Table :- _- -.