isso.l 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



261 



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4 



1 



1--150FJ- 



i^fiirit 



the dam is 8 feet wide at the top and 65 feet wide at the bottom, 

 vertical to the stream, with 

 occasional off-sets. The 

 lower or down side has a 

 curved face, so that the 

 water does not fall verti- 

 cally upon the apron at the 

 foot. In order to guaran- 

 tee the foot of the dam 

 against the undermining 

 action of the cataract, a 

 secondary dam has been 

 formed at a small distance 

 to retain a head of water 

 over the apron, so as to 

 break the force of the water 

 falling, upon it. On the 

 upside m the masonry of 

 the dam a slope in earth, 

 with an incline of 1 in 5, is 

 executed, extending 275 

 feet into tlie reservoir .at 

 the foot. The whole length 

 of the overfall is 251 feet. 



In the course of the pas- 

 sage from the fountain 

 reservoir above 11 tunnels 

 and 14 small bridges were 

 executed. At a pointcalled 

 Sing-Sing-Kill, there is, 

 moreover, a bridge travers- 

 ing a small stream of 88 

 feet opening, with a rise of 

 33 feet, of an elliptical 

 form. The bottom of the 

 ravine is 70 feet below the 

 underside of the key, so 

 that we may fairly ask 

 why the engineer should 

 have gone out of his way 

 to employ the most difficult 

 and expensive form of 

 arch, instead of at once 

 making it a semicircular 

 one? The bridge over the 

 Harlem River is, however, 

 the great boast of our ; 

 transatlantic bretliren. The i_ 

 height from the foundations 

 in the river to the top of 

 the work, is 150 feet; the 

 width across the top, 21 

 feet. The distance be- 

 tween the extremes of the 

 pipes is 1377; feet; for the 

 distance of 18 feet at each 

 end there is an inclination, 

 tlie rest is upon the le\ el. 

 The bottom of the pipes is 

 below the le\el of the 

 aqueduct, on the upper side 

 12i%th feet; on the lov»er 

 it i§ 10i%th feet. 



On the south side of the 

 rivtr there is an arch of 50 

 feet span; across the ri\er 

 there are eight arches of 

 80 feet span each; and on 

 the north side there are six 

 arches of 50 feet span 

 each; making in all 15 

 arches. We may justly 

 question the policy of the 

 engineer whohas burthened 

 the water supply with the 

 maintenance of these sy- 

 phon pipes for the sake of 

 saving, at most, 12^ feet of 

 additional masonry in the 

 piers. 





iS-F.t 



k 



There is a very important syphon in the Manhattan Valley, 

 whicli carries the water over a depression of 102 feet in the 

 deepest part. Provision is made for laying down four pipes, 5 feet 

 in diameter. Temporarily only two are fixed, which are sufficient 

 for the present demands of the city. 



The receiving reservoirs are skilfully constructed, with a depth 

 varying from 20 to 30 feet of water. The retaining walls are 

 executed partly in masonry towards tlie streets, with a batter of 

 1 in 3; the inside is of earth, puddled, and covered with dry 

 pitching, laid and dressed ofi' to a slope of Ig to 1. Tlie total 

 surface of these reservoirs is nearly 31 acres; their contents are 

 estimated at about 150,000,000 imperial gallons. 



The distributing reservoir is situated about two miles from the 

 receiving reservoirs. It is 420 feet square on the top, with about 

 3(i feet depth of water when full, and is calculated to hold about 

 20,000,000 gallons. 



The total cost of the aqueduct and the reservoirs was about 

 9,000,000 dollars, or 1,800,000/. sterling, without including the 

 pijies for the town supply. These latter, added to the above cost, 

 make the total expense incurred by the municipality for its water 

 supply amount to the sum of 12,000,000 dollars, or 2,400,000/. 

 nearly. 



Geo. R. Burnell. 



PURIFYING AND FILTERING WATER. 



On the Purifying and Filtering of targe bodies of Water for 

 supplying extensive and populous Towns. By James Henbekson, 

 C.E., Glasgow. 



Rain water, immediately after it has fallen, is generally consi- 

 dered the purest of all natural waters, and being the great sourc« 

 from which all streams and rivers are supplied and more easily 

 obtained in large quantities than spring water, it forms the best 

 supply for large and populous towns. But as the rains which fall 

 on the surface of the earth collect and flow from their various 

 sources into their different channels, and from thence into the 

 streams and rivers which convey them back again to the ocean, 

 they become impregnated with various earthy, mineral, and organic 

 substances. Vii'xih. many of these, owing to the great solvent 

 power which water possesses, it chemically combines; while with 

 others it forms only a mechanical mixture, the impurities being 

 simply held in suspension. These latter impurities, together witli 

 all insects, animalculae, &c., can be removed by a proper system of 

 filtration ; but those which are chemically combined with the water 

 cannot thus be separated. 



Tlie nature and quantity of the impurities in streams and rivers 

 depend on the nature of the contributing ground, and the state 

 of the weather; which causes, and more esiiecially the latter, pro- 

 duce great variations in their purity — the same stream or river 

 which, during a succession of fine weather, is comparatively pure, 

 becoming, during heavy floods, loaded with a large accumulation 

 of earthy and other impurities. This being the case, it is highly 

 essential, that before water is let on to a filter, it should be 

 impounded in a reservoir, so as to purify to a certain extent by 

 subsidence. 



V\ hen the stream which supplies the town is not large enough 

 to admit of giving a suflicient quantity at all seasons of the year, 

 the impounding of the waters becomes, of course, one of tlie main 

 principles of the system, in order to retain a sufficient supply in 

 storage when the run in the stream is deficient in dry summer 

 weather; but when the river is large enough at all seasons to give 

 an adequate supply, it still becomes highly essential fii-st to impound 

 its waters in a reservoir for the sake of subsidence; and the lai-ger 

 tliat reservoir can be obtained, so much the better. In some water- 

 works, where the supply is from a large river, the principle of 

 subsidence is particularly attended to, while in others the water is 

 taken directly from the river on to filter ; thus greatly increasing 

 the difficulty of supplying pure water to the inhabitants at all 

 seasons. Indeed, in all such water-works during heavy floods, 

 excejit where some peculiarly advantageous circumstances exist, 

 the supplying of the inhabitants with muddy water becomes 

 almost unavoidable, the filter bed in ashort time becoming so much 

 loaded with silt as to be incapable of passing a sufficient supply, 

 and to make up the deficiency the water has to be sent in as it 

 comes from the river. 



The impounding of the waters in large reservoirs, besides being 

 advantageous by allowing many of the impurities to subside, owing 

 to its thus being more exposed to the influence of the sun and air. 



