64 



WATER SUPPLY 



FIG. 99. DEEP DRIVEN WELL 



Sometimes in a well driven in a valley, water comes 

 from the pipe with such force that it rises several feet 

 above the ground. This is spoken of as an Artesian 

 well. The cause of this phenomenon is a peculiar dip 

 in underlying rock layers. Water enters at high levels 

 and is confined between two rock layers and moves 

 toward the lowest point in the dip, as shown in Fig- 

 ure 100. When the top rock layer is penetrated near 

 the lowest point of the dip, water spouts up because 

 of the pressure of the water from the higher levels. 



FIG. 100. ARTESIAN WELL 



How are the inhabitants of large cities supplied 

 with pure water? The location of a city usually de- 

 termines how the water supply is secured. It is neces- 

 sary, therefore, for us to study the water supply of 

 several cities to obtain a clear idea of the various 

 methods in use. For this study the cities of New York, 

 St. Louis, Tucson, and Los Angeles have been select- 

 ed because of distinctive features in their method of 

 securing a water supply. 



New York now has a population well over six mil- 

 lion and is still increasing at a moderate rate. The 

 average daily consumption of water in the city is 

 more than 900,000,000 gallons. To insure the good 

 health, in so far as water is concerned, of so many 

 people, the city has been compelled to create one of 

 the greatest water supply systems in the world. 

 Water is collected from seven drainage areas which 

 total more than 1,400 square miles of surface and is 

 sent in some cases a distance of 125 miles to the city. 

 More than twenty reservoirs provide storage capacity 

 of 258,000 millions of gallons of water. 



The water supply system of New York City dates 

 back to 1842 when the Croton River was first used 



Courtesy Board of Water Supply, \cw York City 



FIG. 101. NEW CROTON DAM, NEW YORK WATER SUPl'LY SYSTEM 



as a source. Water was gathered in two reservoirs and 

 conducted a distance of fifty miles, through an aque- 

 duct, 1 to the city. Since that time the Croton water- 

 shed has been developed until it now covers 375 

 square miles, draining into twelve storage reservoirs 

 and six controlled lakes. Figure 101 shows a picture 

 of one of the great reservoirs in the Croton system. 

 Study the Croton watershed carefully, from the map, 

 Figure 102. 



More than thirty years ago it was observed that the 

 Croton area would not long supply the amount of 

 water demanded by the rapidly growing city. After 

 careful investigation of various sources a plan was 

 drawn to develop watersheds west of the Hudson 

 River in the Catskill Mountains about 120 miles from 

 the city. These areas are the present Esopus, Scho- 

 harie, and Catskill watersheds comprising about 600 

 square miles and capable of supplying 600,000,000 gal- 

 lons of water daily to the city. (See Figure 102.) 



The great Ashokan reservoir in the Esopus water- 

 shed has a capacity of nearly 130,000 millions of gal- 

 lons of water. This amount of water would cover all 



1 Aqueduct, an artificial channel for carrying a large quantity 

 of water which flows by gravitation. 



