THE NATIONAL GEOGRAPHIC MAGAZINE 



35 



A lofty masonry aqueduct was open to 

 danger of destruction ; pipe-lines were 

 both expensive and liable to leaks ; the 

 tunnel was decided upon. In some places 

 these tunnels go very deep, so deep that 

 the water exerts as much as three and a 

 half tons pressure per square foot. 



When the aqueduct builders came to 

 the Rondout Creek Valley they met with 

 a discouraging situation. They found a 

 very poor quality of rock under the valley, 

 with many faults. Their drills slipped 

 through into caverns of unknown depths, 

 and at one place they encountered a 

 spring deep in a rock fissure, which had 

 a flow of 2,000 gallons a minute. There 

 was sulphur present, also, and its fumes 

 seriously inconvenienced the workmen. 

 However, enough grout was put into the 

 spring to drive it out of their way ; with 

 channel rings and concrete the rock was 

 made strong where Nature had made it 

 weak ; and they steered clear of the caves. 

 This tunnel was only 727 feet below 

 grade, and little attention was paid to it 

 by the public. 



CARRYING WATER BENEATH THE HUDSON 



When the Hudson crossing was reached, 

 where the tunnel goes down so deep that 

 the Woolworth Building placed on top 

 of the United States Capitol and sur- 

 mounted by the Washington Monument 

 would leave only the capstone of the 

 latter showing above the water surface, 

 New York was gloomy and fearful. Fail- 

 ure of the undertaking was freely pre- 

 dicted. Nevertheless, the construction of 

 the spectacular Hudson tunnel was a far 

 easier task than the unnoticed one at 

 Rondout. The Hudson is tunneled 45 

 miles below Ashokan Reservoir. 



In the building of this under-the-river 

 tunnel, it was first necessary to ascertain 

 exactly the lay of the solid rock below the 

 river. First, an effort was made to drill 

 down to the surface of bed-rock with 

 drills mounted on scows. But that was a 

 failure. Drills were lost and all sorts of 

 hindrances encountered. Then it was de- 

 termined to dig a shaft at each side, about 

 300 feet deep, and from these to drill two 

 V's under the Hudson, one with a broad 

 and the other with a sharp angle. In this 

 way the engineers gained the necessary 

 data about the rock formation. 



Diamond drills were used. These drills 

 are circular tubes, the lower ends of which 

 are studded with seven black diamonds, 

 costing about $100 each. The drill cuts 

 through the rock like an apple corer 

 through an apple and brings the core to 

 the surface with each stratum in the posi- 

 tion in which it was found. 



Thus the position of the rock was re- 

 vealed and its density determined. The 

 engineers ascertained that they could put 

 their tunnel under the river nearly 1,400 

 feet beneath the surface of the water. 



AQUEDUCT BUILDING, ANCIENT AND 

 MODERN 



Engineering has progressed in great 

 strides since the days when the Romans 

 were building aqueducts. When the 

 Aqua Claudia was under construction a 

 tunnel under a mountain three miles long 

 was necessary, and the chief engineer 

 started work at both ends. He was cap- 

 tured by brigands, and when he was 

 finally liberated he found that his two 

 digging parties had missed one another 

 entirely and were excavating two tunnels 

 instead of one. When the Hudson tunnel 

 was bored the two parties met and were 

 not half an inch out of the way, although 

 the undertaking required the sinking of 

 two pits 1,114 feet deep, from the bottoms 

 of which the tunnel operations were 

 started. 



The Hudson crossing is about half way 

 between West Point and Newburgh, at 

 Storm King Mountain. Thirty miles 

 nearer the city, on the east side of the 

 river, is Kensico Reservoir, with a ca- 

 pacity of thirty-eight billion gallons — 22 

 gallons for every inhabitant of the earth. 



This reservoir is four miles long and 

 from one to three miles wide. The water 

 is impounded by a dam thrown across 

 the Bronx River, one of the finest struc- 

 tures of its kind in existence. A third of 

 a mile long, and 307 feet high, it is 235 

 feet thick at its base and 28 feet thick 

 at its crest. The exposed portion of the 

 down-stream side is made of huge granite 

 blocks. 



Above Kensico there is what is known 

 as a coagulation plant. Here provision 

 is made for treating muddy water with 

 a harmless coagulant. In flood periods 

 silt is brought down from the watersheds. 



