1850. 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



65 



near Cookham, is carried over the Thames by an aqueduct bridge about a 

 quarter of a mile above Maidenhead-bridge, keeps nearly close to the Great 

 Western Railway as far as Bull's-bridge, a length of 13 miles, and for 

 nearly 10 miles by the sides of the Grand Junction and Paddington canals, 

 passes under the Grand Junction Canal at West Drayton, and tvTice under 

 the Paddington Canal westward of the London and North-Westeru Railway ; 

 the aqueduct then continues through Willesden, under the Edgeware-road, 

 and on to West-end, Hampstead, where it terminates in a large basin. The 

 ■whole length from Mednunham to Hampstead basin is 33i| miles. 



Three large collecting and seUling reservoirs, for cases of drought, or of 

 the water being discoloured by land floods, are proposed in the line of the 

 aqueduct: one near Cookham, another near West Drayton, and the third, 

 of 77 acres, near Harrow. 



From the Hampstead basin, in which the water will stand 85 feet above 

 high water, it is to be raised by steam power (3,500 borse) into an elevated 

 reservoir, also at Hampstead, which is 250 feet above high water. From 

 this last reservoir large iron mains, extending in various directions on the 

 north side, and over Vauxhall-biidge to the south side of the river, will be 

 connected with and supply the mains and pipes in all the districts of the 

 present water companies, whose works are henceforth to belong to the com- 

 missioners of the new works, the shareholders of the old companies being 

 compensated by a fixed interest upon their capital. 



The inclination or fall in tlie surface of the water from Mednunham to the 

 Hampstead ba;in is calculated by Messrs. M'Clean and Stileman and Mr. 

 Blackwell, the projectors and engineers of the plan, to be sufficient for con- 

 veying from the river 200,000,000 gallons in 24 hours as far as West 

 Drayton, and 100,000,000 thence to Hampstead. This last being the quan- 

 tity supposed to be required for giving " an ample daily supply for the me- 

 tropolis," is stated to be at least double the present supply by all the com- 

 panies. 



The object of the large aqueduct as far as Drayton is to pass a quantity, 

 when there is surplus in the Thames, into the Grand Junction Canal, and 

 thence into a reservoir at Paddington, 85 feet above high water, whence it 

 will be conveyed into the sewers of London for the purpose of cleansing 

 them. The large addition for the purposes of sewerage would lead to an 

 increased expense if any of the schemes for pumping up the water after 

 passing through the sewers be adopted. 



The engineer's estimate is : — 



Works for bringing water from Henley to London, 



including compensation to millowners . . . . £1,000,000 

 Cost of plant for distribution, in addition to the 



plant of existing companies 1,OCO,000 



£2,000,000 

 And the annual expense as under: — 



Rentcharge, as compensation to proprietors of ex- 

 isting companies £127,500 



Cost of distribution, independently of interest of 



capita! for plant ' 100,000 



No. II. — The Mapkdurham Scheme. 



The other, or Metropolitan Water Supply Company, which has been 

 brought out during the last summer by Messrs. Gordon and Liddell, en- 

 gineers, proposes to take its supply from the river above Mapledurham lock, 

 which is five miles above the junction of the river Kennet, near Reading, or 

 17 miles (by water) above Mednunham (the Henley Company's point of 

 abstraction), in which distance there are five locks, the united lift or rise 24 

 feet above the Mednunham proposed level. An open cut or aqueduct, four 

 and a half miles long, is to convey the water from Mapledurham to Caver- 

 sham, where four reservoirs, together 100 acres, and 98 feet above high 

 water,* are to be formed for purifying the water upon Dr. Clarke's patent 

 process. Powerful steam-engines are to raise the water from these reser- 

 voirs through three iron pipes, each five feet diameter, carried across the 

 liver, and then into three smaller reservoirs, at one mile distance from the 

 Caversham reservoirs, and 35 miles from London, and at different levels, 

 corresponding with the levels of the three districts into which the engineers 

 suppose London to be divided — the northern or western district being taken 

 at 120 feet ; the centre district, which comprehends the City, at 70 feet; 

 and the south and east district at 10 feet above high water. The highest of 

 the small reservoirs is 233^ feet above high water mark, and the lowest 178-J 

 feet, the rnean lift being 100 feet, which will require 1,100 horse-power. 

 The water is conveyed from the small reservoirs by a continuation of the 

 three 5-feet pipes to the Great Western Railway, near Twyford, whence they 

 are laid by the side of the railway, and pass over the Thames at Maidenhead, 

 over the Grand Junction and under the Paddington Canals to near Worm- 

 wood Scrubs; here the high level pipe diverges, and passes under, and then 

 by the side of, the North- Western Railway to a reservoir at Primrose-hill 

 of 3J acres, and 169 feet above high w'ater. The other two pipes, for 

 the middle and eastern levels, continue from Wormwood Scrubs by the side 

 Of the Great Western Railway at Paddington, and thence along Westbourne- 

 terrace and Oxford-street into a reservoir in St. Giles's, of J acre area, 



* There is a want .of agrsement in the levels which have been obtained from the en- 

 gineers 



and 114 feet above high water. The third or lowest pipe crosses the 

 Thames at Waterloo-bridge into the southern district. The three great 

 mains, or town reservoirs, communicate with the pipes of the present com- 

 panies. 



The engineer's estimate for this scheme is — 



For works £1,200,000 



Annual working expenses 20,000 



We come now to consider the effects of the two plans upon the naviga- 

 tion of the river, and in doing so we do not think it right to confine ourselves 

 to what the parties profess as to the quantity they mean to abstract ; for if 

 the whole of London is to be supplied from one source there will be no sa- 

 tisfaction until the supply is ample and constant, whether the source be 

 Mapledurham or Henley; and parliament will naturally take this into con- 

 sideration, and give a preference, so far as quantity is concerned, to the plan 

 which has the greatest certainty in the above respect. 



The present supply by the water companies is stated, in a recent publica- 

 tion by Sir W. Clay, cliairman of the Grand Junction Company, to be 

 44,573,979 gallons per day ; so that the quantity has much increased since 

 1834. This has been caused partly by the increase of population, and partly 

 also by the greater supply to each house. Is it not probable that both the 

 above causes, and the demand for water for sewerage and other sanitary 

 purposes, will continue to operate so as to render it prudent to allow for 

 these in any great plan ; and to consider the effects which the greatest pro- 

 bable abstraction would be likely to have upon the navigation ? It is, how- 

 ever, to be noticed (and this was one of the objects in our describing the 

 main features in the two plans), that the Henley party propose their works 

 to be made at first for taking double the quantity calculated by the Maple- 

 durham Company ; and also that the Henley aqueduct, being chiefly open 

 can be enlarged — if ever this should be required — at less cost than the 

 Mapledurham, who have to raise their water to a mean height of 100 feet 

 and then pass it through 36 miles of close pipe. To increase the number 

 of pipes would add materially to the cost, and to double the quantity 

 through the same pipes would require an increase of power much beyond 

 the increase of the quantity. 



To compare in detail the merits of the two plans would require us to sur- 

 vey the lines, which your instructions would not warrant our doing ; but 

 having said thus much on what may be considered a superiority in the Hen- 

 ley scheme, it is but proper to add that the liability of an open canal to re- 

 ceive impurities into it, whatever care may be taken to prevent this, and also 

 to be partially impeded by ice, are objections to which the Mapledurham is 

 not subject ; and if the salubrity of the water be presumed to depend upon 

 its freedom from organic matter the Mapledurham source would appear to 

 be preferable, as in the seventeen miles between the points of abstraction, 

 Henley, Reading, Wargrave, and some villages drain into the river. On the 

 other side of the question, it is to be noticed that the Loddon and Kennet 

 join the Thames below Mapledurham and above Mednunham. 



We propose therefore to calculate on the abstraction of 100,000,000 

 gallons per twenty-four hours stated by the Henley project, which is exclu- 

 sive of their taking an equal quantity (except in times of drought) for sewer- 

 age, as has been stated. 



The termination of drought and commencement of surplus in the river, 

 with the works for regulating the additional discharge, should be determined 

 in a manner to be approved, and afterwards inspected and controlled by 

 you. 



Now, the effect which thq abstraction will have upon the navigation both 

 of the locked part above Teddington and the tidal part between Teddingtoii 

 and London, being dependent on the proportion which the part abstracted 

 bears to the whole of the river water, we have endeavoured by former mea- 

 surements taken by the late and present Mr. Rennie, by Mr. Simpson, and 

 now by Mr. Blackwell and ourselves, at dift'erent times, to ascertain the 

 natural discharge of the Thames during such a drought as not unfrequently 

 occurs. 



At Staines, the head of your district, we consider the quantity mav be 

 taken at from 350,000,000 to 400,000,000 gallons per 24 hours ; and at 

 Teddington (IS miles lower), in which space the Colne, Wev, Mole, and 

 Hog's Mill rivers join the Thames, at from 500,000,000 to 550,000,000: so 

 that, in round numbers, the abstraction near Staines will be one-fourth, and 

 at Teddington one-fifth, of the whole natural discbarge of the river. In 

 1846, a very dry time, it was oiily 248,000,000 near Staines by Mr. Leach's 

 measurements. 



As Mr. Blackwell made the river at Henley, during the shortest water of 

 this year, 345,000,000, it may be fairly supposed that at Mapledurham, 

 which is above the junction of the Kennet, it did not exceed 300,000,000; 

 so that the abstraction of 100,000,000 would be one-third of the whole 

 river during seasons of drought. This is more the business of the commis- 

 sioners of the upper districts ; but if the navigation in their portion of the 

 river be damaged, the effect upon the trade would he nearly the same as if 

 the evil were done in your own district. 



To enable us to judge as to the effect of the abstraction, correct sections 

 of the bed of the river, and of the depths and inclinations or slopes of the 

 water in the lengths likely to be affected, were imlispensable. We again 

 employed an engineer to complete the levels and sections from Staines to 

 Teddington, which he began in the spring, and Mr. Smith to assist us in the 



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