DRAINAGE AND IRRIGATION 33 



It is impossible to give here all the details about irrigation, 

 but the water is obtained either from streams, reservoirs, 

 or deep wells. In our western states there are many 

 streams which have their sources in the mountains and 

 are fed by the snow on the peaks. As these streams flow 

 out over the level country, ditches are dug leading out from 

 the rivers into the fields that are to be irrigated. Smaller 

 ditches run out from the larger ones to every part of the 

 fields. The banks of the ditches are made higher than the 

 rest of the land, so that when the water is dammed up in 

 the ditch bank-full, places called "gates" can be opened in 

 order to let the water flow over the field until enough is sup- 

 plied. The gate can then be closed and the ditch dammed up 

 further down and another gate opened and more of the field 

 watered, and so on until all the land is watered. Sometimes 

 the water is pumped out of the big ditches into the smaller 

 ones. Where water is obtained from wells, it is raised by large 

 pumps which can throw thousands of gallons in an hour. It 

 is pumped into ditches and allowed to run out over the land 

 as in the other cases. Irrigation from deep wells is especially 

 practised in the rice fields of Louisiana, Texas, and Arkansas. 

 Irrigation of rice is called "flooding." The water is turned 

 on several inches deep and allowed to stand for a few days, 

 then it is drained off. Rice lands are flooded two or three 

 times during a season of growth. For all crops other than 

 grain or grass crops it is necessary to stir the top soil as soon 

 as dry enough after irrigation in order to keep the water from 

 evaporating. 



