76 Our Surroundings 



Dams. A dam is a structure built to stop or check the flow 

 of water in a stream. In this way water is stored to provide 

 a supply for homes or for communities; to irrigate, or water, 

 tracts of land; to raise the level of streams in order to increase 

 their depth for navigation purposes; to hold flood water of 

 streams so as to reduce the danger of serious floods ; or to sup- 

 ply power to run machinery. In the latter case much of this 

 power is transformed into electricity in order that it may 

 be distributed over great distances to the points where it is 

 needed. 



The United States Reclamation Service has constructed won- 

 derful dams for the storage of water to be used in industrial 

 pursuits, especially in agriculture. Among these dams is the 

 Arrowrock dam in Idaho. This has a height of 349 feet, a 

 length of 1,100 feet and a capacity of 91,238,000,000 gallons. The 

 water from this dam will render productive about 234,000 acres 

 of desert land. 



The Roosevelt dam in Arizona is 280 feet high and 1,125 

 feet long. It is so placed that it backs up the water to form 

 an artificial lake having an area of over 25 square miles 

 and containing over 513,000,000,000 gallons. Such dams are 

 usually placed at points where advantage can be taken of the 

 general slopes of the ground to form reservoirs of considerable 

 area and of great depth. 



Although irrigation has been understood for many centuries, 

 it is only beginning to be developed on any extensive scale. It is 

 estimated that there are still ten million acres of land in our 

 western states which could be made of value for crop growing 

 purposes by irrigation. 



In a message to Congress, Theodore Roosevelt declared : "The 

 reclamation and settlement of the arid lands will enrich every 

 portion of our country, just as the settlement of the Ohio and 

 Mississippi valleys brought prosperity to the Atlantic states." Each 

 year the Reclamation Service of the United States undertakes new 

 projects calculated to conserve the water resources of the country. 

 No country that fails to do this can hope for continuous pros- 

 perity. 



