CHAPTER I 

 GENERAL POSITION OF AQUEDUCT LINE 



Surface topography constitutes the chief factor in determining 

 the general course of the aqueduct. It is planned to control the 

 water so that it will flow to New York city. There is therefore a 

 gradual descent of aqueduct grade from 510 feet A. T. at Ashokan 

 dam to 295 feet at Hill View reservoir. Wherever the surface of 

 the country is approximately the same as the aqueduct grade for 

 that district it permits of the so called *' cut and cover " type of 

 construction which is much cheaper than any other. Therefore, 

 other things being equal, the position that will permit the greatest 

 proportion of cut and cover work would have a decided advantage. 

 So it is possible from any series of good topographic maps to lay 

 out trial lines that are sure to be worthy of consideration. The 

 topographic sheets of the United States Geological Sur\'ey and the 

 maps of the New York Geological Survey are of great usefulness 

 in such preliminary work. 



But a little field examination shows that there are many other 

 features and conditions that materially modify even comparative 

 cost and are still more important factors in consideration of per- 

 manence and safety. Sometimes it is not apparent that a course 

 has any objectionable features till considerable exploratory work 

 has been done. Likewise a serious difficulty at one point may more 

 than counterbalance advantages at some other, so that considerable 

 portions of the line are finally shifted to a better average position. 

 In the course of these preliminary explorations much valuable data 

 have been secured that now relate to points a considerable distance 

 off the present line. The information has, however, been necessary 

 and useful. 



One of the cases of this kind where geologic conditions have 

 had an almost controlling influence is involved in the choice of 

 place of crossing of the Hudson river. It has involved a shift of 

 the whole line between the reservoir and the Highlands. Diffi- 

 culties encountered in finding a crossing of the Esopus also con- 

 tributed to the argument favoring a shift of the line {see map of 

 trial lines west of the Hudson] . One of the points where explora- 

 tory work had reached definite results before the more southerly 

 line was finally adopted is near West Hurley. Here wash borings 



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