SUBTEEEANEAlSr RIVEE WALKEE AND BOND. 715 



elevation of 355 feet above mean sea level, and will cover 2,218 acres. 

 It will contain, when full, about 40,000,000,000 gallons, of which 

 29,000,000,000 gallons, or 60 daj^s' continuous supply at 500,000,000 

 gallons daily, will be available. The main dam will be 1,813 feet 

 long; the total height will be 300 feet; it will be 230 feet thick at 

 the base, and 28 feet thick at the top. The average depth of the 

 reservoir will be 100 feet, and its maximum depth at the wall of 

 the dam will be 155 feet. An interesting feature of the construc- 

 tion is that the entire dam will be divided into sections by transverse 

 expansion joints, which will be placed about 80 feet apart longitudi- 

 nally. On one side they will be faced with concrete blocks, forming 

 a series of vertical tongues and grooves, against which the masonry 

 of the other side will be built. Near the up-stream face will be a 

 copper strip, which will cover the expansion joints and act as a water 

 stop, the strips continuing from the bottom to the top of the dam. 

 In order to catch any water that may seep through from the up- 

 stream side, diagonal wells will be built 15 feet apart, measured 

 longitudinally. They will be formed of porous concrete blocks. 

 They will reach from the top of the dam to a longitudinal inspec- 

 tion gallery at about the level of the reservoir bottom, which will in 

 its turn be connected with a transverse drainage gallery, which will 

 lead to the downstream base of the dam. This will entirely prevent 

 any seepage through the wall, and will avoid that discoloration 

 which is liable to mar the architectural beauty of structures of this 

 kind. 



AERATION AND FILTRATION. 



At both the Ashokan and Kensico reservoirs aerators will be 

 built, each of which will be capable of passing and treating all the 

 water which will flow in the aqueduct. The aerator is a large 

 rectangular basin, 500 feet by 250 feet, containing about 1,800 noz- 

 zles, through which jets of water will be thrown into the air. The 

 nozzles will be of such form that the water will be divided into a 

 fine spray, and this will permit of a thorough admixture with the 

 oxygen of the air and the removal of gases and matters which would 

 cause taste and odors. For the present no provision will be made for 

 filtrating the Catskill water, but provision has been made for a 

 filtration plant by the purchase of 350 acres of land near Tarrytown, 

 adjacent to the aqueduct. 



HILL, VIEW RESERVOIR. 



From Kensico the water will flow to the Hill View reservoir, which 

 will serve to equalize the difference between the amount of water 

 used in the city and the amount of water flowing in the aqueduct. 

 Also it will furnish a great quantity of water should there be an 



