260 



THE CIVIL EXGINEER AND ARCHITECT'S JOURNAL. 



[August, 



water mill, established upon tlie Schuylkill, near Fairmount. A 

 (lam was thrown across the river Id'OO feet iouj^, so as to ileadeii its 

 velocity for a distance of six miles up the country, and to maintain 

 a constant depth of water at the dam of Hi feet. The dam itself 

 is inclined at an angle of 4J^ to the current. A canal for the 

 navigation is constructed 900 feet lonar, with two locks of 6 feet 

 fall each, o]>posite to the mill race. The mill race itself, in ordi- 

 nary states of the river, offers an opening of 68 feet wide hy 6 feet 

 high. It can be closed at the head, and an overflow sluice is 

 constructed to carry off the water in this case, without passing 

 through the wheels. The race is 419 feet long, by 110 feet wide, 

 and from 16 to 60 feet in de]ith. 



The engine-house is built for 8 wheels and pumps; each pump 

 lifts actually 530,000 gallons per 24. hours. It is calculated that 

 one gallon of water raises one other gallon into the reservoirs by 

 its action on the wheels; but this action appears to be considerably 

 exaggerated. The wheels are 16 feet diameter, by 15 feet in width, 

 and they make 13 revolutions in a minute; they are capable of 

 functioning even when there is 16 inches of water o\er the wheel. 

 The floods, indeed, are a serious inconvenience upon this river, for 

 they appear to cause the mills to lose 64 hours every month. The 

 pumps liave 6 feet stroke; the water is lifted 9'i feet into the 

 reservoir.s, through cast-iron pipes 16 inches diameter. The 

 reservoirs are situated at 102 feet above the low-water mark of 

 the Delawaie, and 56 feet above the average level of the streets of 

 Pliiladeli)hia. They are four in number, covering a surface of 6 

 acres, with a depth of 12ft. 3in., and they contain 22,000,000 

 gallons of water. The cost of constructing these reservoirs was 

 about 29,000/. sterling. Jn consequence, also, of the very intelli- 

 gent manner in which the engineers have availed themselves of 

 the natural power furnished by the river, the annual expenses 

 incurred to secure a supply of 3,122,644 gallons daily are only 

 about 2,800/. per annum. 



The Croton Aqueduct of New York is, however, the work upon 

 which the American engineers pride themselves the most; and it 

 must, injustice, be allowed to be an extraordinary work, although 

 far inferior to many of those we have hitherto considered. This 

 aqueduct was constructed at the expense of the city of New York, 

 under the control of a commission of the Common (-ouncil. The 

 preliminary surveys appear to have been made by Mr. David B. 

 Douglas, and the works were executed under the superintendence 

 of Mr. John B. Jervis. 



The Croton River takes its rise from a series of large ponds, or 

 lakes, the aggregate of whose surface areas is about 3800 acres, 

 which are principally situated in the county of Putnam, at a distance 

 of about 50 miles from the city of New York. The dam built for 

 the purpose of forming the fountain reservoir is situated about 

 38 miles from that town; and in the precise locality in question 

 the medium quantity of water flowing in the river is above 50,000,000 

 gallons in the 24 hours, whilst in seasons of drought it has never 

 been known to fall short of 27,000,000 gallons. 



The dam across the Croton is in this place raised 38 feet above 

 the level of the river in its natural state, and by this means it sets 

 back the water six miles up the country, forming the fountain 

 reservoir, whose surface is 400 acres. Excavations were made 

 wherever the shores assumed a gentle slope, so as to create a 

 minimum depth of water of at least 4^ feet. The available capa- 

 city of this reservoir, down to the level where the water would 

 flow off by tlie aqueduct, has been estimated to be equal to 600 

 million gallons. The height of 38 feet, quoted above, is the height 

 at which the aqueduct receives the water from the reservoir. The 

 surface of this fountain reservoir is 166^ feet above the mean 

 level of the tides at New York; the surface of the receiving reser- 

 voir on the island is 119 feet above the same level; so that the 

 total fall from the one to the other is 47^ feet. The distributing 

 reservoir is 1 15 feet above the mean level of the tides, and regulates 

 the height to which the water can be delivered in the city. 



The water is led from the fountain reservoir the whole length of 

 the way in a clcsed conduit of masonry, except in crossing the river 

 Harlem to reach the New York island, and in passing a deep valley 

 in the island itself. In these cases, as the principle of the syphon 

 was employed, cast-iron |>i])es were introduced. 



The general description of the conduit may be considered to be 

 as follows: — A bed of concrete is formed, consisting of three parts 

 of sand to one of hydraulic lime worked up into a mcu-tar, and 

 then mixed with three jiarts in bulk of sharp gravel or broken 

 stone to one of mortar; well ranmied in place, not shot in, as is our 

 very absurd English practice. V\>un this the side walls are executed 

 in rubble stone set in hydraulic mortar in the above jiropoi tions. 

 Tbe face of these walls is then rendered with a coat of hydraulic 



mortar, about g-inch in thickness, which is also laid on the concrete. 

 The proportions of sand to lime in this rendering coat are two of 

 sand to one of lime. 



A facing of sound, hard, well-burnt, and carefully selected bricks, 

 is then built u]i in hydraulic lime upon this coat of renderinT 

 mostly of half-a-brick in thickness for the sides and the invert; 

 the top is vaulted over in two half-brick rings; and, Mherever it 

 is possible, covered with four feet of earth, to remove the aque- 

 duct from the influence of the external atmosphere. The width 

 of the conduit at the bottom is usually 6 ft. 9 in.; at the springing 

 of the semicircular vault 7 ft. 3 in.; the versed sine of the invert 

 is 9 inches; the height from the chord line of the invert to that of 

 the vault is 4 feet. Occasionally the form of the conduit varies; 

 hut the above may be considered as the general description. Under 

 all circumstances, it is made so as to receive and to discharge 

 60,000,000 gallons in the twenty-four hours. 



In traversing valleys, the conduit is carried upon a wall of solid 

 masonry, executed in rubble stone, set in hydraulic mortar. The 

 whole is then covered over with earth, carefully rammed, and 

 the slopes pitched with dry stones. These precautions are neces- 

 sary to secure the water from the severe frosts of the North 

 American winters. The dimensions of the concrete floor of the 

 side walls, and of the spandril filling, are increased; and the 

 proportion of hydraulic lime to sand is augmented to one of lime 

 to two of sand, for all parts of the work. Great pains were taken 

 to secure the stability of the aqueduct when it was carried upon 

 the hill side, by forming culverts, or paved drains to carry any 

 torrential waters away from the foundations, which were cut into 

 the hills. 



W^iste weirs, with sluice gates, are provided for the discharge of 

 any surplus water, or for the purpose of leaving the aqueduct dry 

 in case repairs should be required. There are six of these weirs 

 in the length of the aqueduct. 



Ventilators, formed of hollow cylinders of stone, 14 feet above 

 the surface of the ground, are placed at distances of one mile apart ; 

 and every third one is made with a door to admit of inspection of 

 the conduit. The interior diameter of the common ventilators is 

 2 feet ; that of the ventilators with doors, 4 feet. The latter are 

 placed by the side of the conduit, to give room for a staircase 

 leading to the bottom; the cill of the door being made 12 feet 

 above the lowest point of the invert. The ordinary ventilators are 

 placed immediately upon the centre line of the aqueduct. All of 

 them are covered over with iron gratings. Besides these ventila- 

 tors there are man-holes, placed every quarter-of-a-mile asunder, 

 about 2 feet square. They are covered with a stone dam])er. 



The Gate-chamber at the fountain reservoir is established 

 nearly at the bottom of the artificial lake, and is situated at the 

 extremity of a tunnel about 200 feet long, which separates it from 

 the reservoir itself. The centre of the tunnel is 12 feet below the 

 surface of the water; so that floating bodies are not likely to be 

 carried into it, nor during the winter season can any intermission 

 take place in the supply from the reservoirs being frozen. In sum- 

 mer also the water « ill be drawn from a level where it is at a 

 lower degree of temperature than at the surface. At the Gate- 

 chamber are the regulating gates, and the guard gates, necessary to 

 controul the supply. 



The total distance between the fountain reservoir and the 

 receiving reservoir is 201,1 17't2 feet, or 38'09 miles. The total 

 fall is 43^^ feet. The least incline is 7J inches in a mile; the 

 greatest is about 13i inches per mile. The syphon upon the Har- 

 lem River Bridge is 1377^ feet long, with a difference of level 

 between the two extremities of 2'29 feet. The other syphon in the 

 Manhattan Valley is 4105 feet long, with a difference of level of 

 3'86 feet, to overcome the friction in the pipes. 



The depth of the water in the aqueduct at its entry into the 

 fountain reservoir is Ty'^ft. above the bottom of the invert. The 

 average sectional area of the aqueduct is made 53-34 square feet. 

 The curves used to change the direction of the line of the aqueduct 

 are never less than 500 feet; some ha\e a radius of 1000 feet; but 

 500 is the radius usually adopted in preference. The velocity of 

 the water has been ascertained to be I5 mile per hour, when there 

 is 2 feet depth of water in the aqueduct. 



During the construction of the dam at the fountain reservoir, 

 and very shortly before the completion of the works, a most ex- 

 traordinary Hood took place, which carried away the greater por- 

 tion of the dam, and spead ruin and desolation through the valley. 

 Dwelling-houses, mills, and everything the stream met with in its 

 first fury, were swept away, and three lives were lost. In repairing 

 the dam, the breach was filled-in with masonry instead of earth- 

 work, and it has since resisted very successfully. The masonry of 



