314 



ENGINEERING. 



dated Nov. 18, 1874, and Jan. 12, 1875. The 

 total length of the canal would be 172 miles, 

 of which 119 miles would be furnished by lakes 

 and rivers, in which there is already sufficient 

 depth of water, or in which such depth can be 

 obtained easily. This utilization of existing 

 water-ways is one of the great advantages of 

 the canal, and it has the additional advantage 

 of being about 800 miles farther north than 

 the Panama mute. Its disadvantages are, that 

 the passage would require at least three days, 

 and that there would be fifteen locks, the fail- 

 ure or injury of any one of which would ob- 

 struct the entire line. Another great disad- 

 vantage would be, that the harbor of Grey- 

 town, or San Juan del Norte, on the Atlantic 

 end, is irretrievably ruined. Major McFarland 

 believes that the only method by which an 

 artificial harbor can be formed at that point, 

 which may be expected to be permanently 

 valuable for canal purposes, is to carry the canal 

 boldly out through the harbor to the sea, into 

 thirty feet of water, and by constructing out- 

 side of it, at a convenient distance from its 

 extremity, a detached breakwater, so situated 

 as to form a deep-water harbor behind it. The 

 construction of an adequate harbor at the Pa- 

 cific terminus, at Brito, would also involve a 

 very large expenditure, because there is only 

 a slight indentation of the shore-line at that 

 point. From Grey town to San Carlos there 

 would be 42 miles of canal, followed by 63 

 miles of slack - water navigation, secured by 

 dams, on San Juan river, which would bring 

 the navigation to Lake Nicaragua. Then it is 

 proposed to cut channels from either shore to 

 the 28-foot curve, the cut in the soft material 

 to be .protected by a combination of ordinary 

 and sheet piling. The level of Lake Nicara- 

 gua, at its highest stage the summit level of 

 the canal is 107 feet above mean tide in either 

 ocean. Between the lake and the Pacific side, 

 two routes have been proposed. O. W. Chi'lds, 

 in his survey in 1857, chose the route by the 

 Rio Lajas, because the highest point of it is 

 only 49 feet above the level of Lake Nicara- 

 gua. Commander Lull, and Major McFarland 

 after him, pronounced in favor of the Rio del 

 Medio route, although the summit is 184 feet 

 above the level of the lake ; because, although 

 the cutting would be deeper, the line would 

 be straighter and shorter, because deep water 

 would be found nearer its lake terminus, and 

 because the crossing of many troublesome 

 streams would be avoided. While it is gener- 

 ally admitted by engineers that the route of 

 the Nicaragua Canal is practicable, a far more 

 searching investigation of details must be made 

 before any reasonably approximate estimate 

 of its cost can be made. 



The New Croton Aqueduct. The question of an 

 adequate increase in the water-supply for the 

 city of New York has attracted a good deal of 

 attention, and several plans have been pro- 

 posed. After a thorough study, it has been 

 decided that the Croton river water-shed af- 



fords more than enough for any demand likely 

 to be made upon it for a long time to come, 

 its area being 338 square miles, on which the 

 annual rainfall is over 46 inches. Making al- 

 lowance for evaporation, absorption, and leak- 

 age, this would supply daily about 425,000,000 

 gallons of water, while, with the present popu- 

 lation, the carrying capacity of the old aque- 

 duct is about 100,000,000 gallons a day. As 

 yet no decision has been reached as to the 

 best means of collecting and storing the possi- 

 ble supply of the future, but the weight of ex- 

 pert evidence is in favor of building an enor- 

 mous dam, 200 feet high at its highest point, at 

 Quaker Bridge. Such a dam, while it would 

 cost fully $4,000,000, would increase the area 

 of Croton Lake to 3.625 acres, and elevate its 

 surface about 34 feet above the present level. 

 At a rate of consumption of 200,000,000 gal- 

 lons of water, it would take 160 days to ex- 

 haust the quantity for which storage-room 

 would be thus provided. While the details of 

 the construction of this dam have not yet been 

 determined on, work has begun with the build- 

 ing of a new aqueduct from Croton Lake to 

 Harlem river. Substantially this aqueduct is 

 to be a tunnel, lined with masonry, 26 miles 

 long, with an average grade of 0'7 foot per 

 mile. Thirty-three shafts of an average depth 

 of 101 feet afford access to the working levels 

 and a means for the removal of debris. At 

 five points notably in crossing Pocantico riv- 

 er and Sawmill river the aqueduct emerges 

 from under ground and is carried along in open 

 cut. For the tunnel-work, two sections have 

 been adopted, dependent upon local circum- 

 stances. The first is a horseshoe arch, with in- 

 vert bottom, having a total height in the clear 

 of 13'53 feet and a width of 13'60 feet, lined 

 with 12 inches of masonry. The second form 

 is that of a true circle, ranging from 14 feet in 

 diameter in the clear, with 16 inches of ma- 

 sonry, to 10-5 feet, with 12 inches of masonry. 

 The reason for this variation is, that it is pro- 

 posed to divert a certain amount of water car- 

 ried by the aqueduct into storage-reservoirs in 

 the vicinity of Woodlawn Cemetery, to supply 

 the " annexed district. 1 ' For the smaller quan- 

 tity flowing beyond this point, a smaller con- 

 duit, .having a diameter of 12-25 feet, is suffi- 

 cient till Harlem river is reached, which is 

 crossed by an inverted siphon. Through the 

 sudden change in the grade, the water in the 

 tunnel would receive a dangerous accelera- 

 tion, and, to diminish the shocks, the friction of 

 the flow of the water is increased by de- 

 creasing the diameter to 10'5 feet. By these 

 variations in the diameter of the tunnel, the 

 passage of a uniform quantity of water at 

 a controllable speed is secured. In passing 

 through difficult ground, the greatest care is 

 taken to guard the tunnel against any collapse, 

 and to resist the percolation of water through 

 the brick-work with the aid of a water-proof 

 plaster. In order to prevent the entry into 

 the aqueduct of water that is under pressure, 



