IRRIGATION AND DRAINAGE 147 



of large sums of money in constructing a temporary rock 

 dam that the flood was finally controlled and the valley saved. 

 Since that time, ownership of the irrigation system has 

 been gradually taken over by the settlers themselves, until 

 the actual users of the water are also the owners of the 

 system. 



240. Diversion of small streams. This same process of 

 diversion of stream flow is practiced on a small scale, also, 

 in many parts of the country. Concrete pipe is rapidly 

 taking the place of the old open ditch. It is a little more 

 expensive in the beginning, but saving in labor and water 

 soon makes up. 



241. Storage reservoirs serve a two-fold purpose. They 

 store up water for use when needed on farm and orchard; 

 and they regulate stream flow, thereby lessening the danger 

 from destructive floods. 



The Elephant Butte reservoir in Texas is one of the 

 largest, if not the largest, storage reservoirs in the world. 

 It impounds enough water to cover between two and three 

 million acres to a depth of one foot. Another large project 

 is the Roosevelt dam in Arizona, located on the Salt River 

 near its junction with Tonto Creek, about seventy-eight 

 miles northeast of Phoenix. It impounds 1,284,000 acre-feet 

 of water which is used in irrigating the farming lands of the 

 Salt River Valley in central Arizona. 



242. The underground water supply. As a rule, water 

 is obtained from this source by means of pumps. The power 

 employed depends on the amount of water desired and forms 

 of energy available. Those most frequently utilized are wind, 

 electricity, and the products of petroleum, such as gasoline, 

 kerosene, and similar substances. There is a definite limit 

 to the height to which water can be raised at a profit, depend- 

 ing on cost of installation and operation of pumping plant, 

 increased return secured by irrigation, and value of the 

 final product. 



