GLACIERS AND LAKES 251 



Reservoirs may be constructed many miles away from the 

 city, and the water may be carried in open canals or in 

 closed pipes. The pipes may pass through a mountain or 



FIG. 133. SUPPLYING A CITY WITH WATER 



The dotted line is part of the boundary of the region which supplies 

 most of the water to the two streams flowing east. The shaded portion is 

 the area of a possible reservoir having natural hillside boundaries. If dams 

 or embankments are built at three places, d, the waters of the two streams 

 will be held back. 1. What is the elevation of the contour line bounding 

 the reservoir? 2. What must be the level of the top of the dams? 3. 

 The southern stream flows now at d, at an elevation of about 400 ft. If a 

 dam is built there, how high must it be? 



under a river, even up and down hill, always provided that 

 no part of the pipe is as high as the source of the water it 



