162 



Nature-Study Agriculture 



Artesian 

 wells 



Damming 

 streams 



FIG. 127. The main ditch of an irrigation system on a sugar plantation 

 in Hawaii. 



than do electric motors. The latter will run day and 

 night with no one near. 



In some favored localities there are artesian wells, 

 from which large streams flow continually. 



A large irrigation system intended to supply water to 

 many farms is made by damming a stream several miles 

 above the land to be irrigated. A lake forms back of the 

 dam, and an open ditch or sometimes a large pipe leads the 

 water out of it and down the valley (Fig. 127). But in- 

 stead of following the channel of the stream, this ditch 

 runs along one side of the valley. It is given enough fall to 

 make the water flow, but not so much fall as the stream 

 bed has. In this way the water in the ditch is soon many 

 feet above the natural stream bed and may be allowed 

 to flow out over the farms that are below it in the valley. 



