THE IRR1GA110N AGE. 



183 



the ditch bank and bottom. They are placed in the ditch at or near 

 the point where it is desired to turn out the water. These metal 

 dams are also used in the openings in the banks of ditches either to- 

 close them when checks are full, or to partly close them and still per- 

 mit part of the stream to enter the check to balance the soaking away. 

 They are made with sliding grates, as shown in Fig. 10, to be used 

 when part of the stream is to be allowed to pass through for any 

 purpose. 



Portable wooden dams are also used and 

 are of similar form to the metal dams. They 

 serve a good purpose, but are more cumber- 

 some, more likely to give out, and more difficult 

 to make water-tight except with some shovel- 

 ing. Wooden dams are, however, of much use 

 in quite small ditches and as gates for small 

 outflows into checks, etc. Figure 11 shows & 

 simple wooden contrivance which is widely 

 used. It is made of an inch board 6 or more 

 inches wide and 14 inches long. The lower end 

 is pointed so as to be readily driven into soft 

 ground. Above are two holes about an inch in 

 diameter, one or both to be used according to 

 the flow of water desired. The cut is made in 

 the ditch and the board driven well toward the 

 inside of the ditch to avoid a niche to catch 

 sediment. If a large flow is desired the board is pulled out and after- 

 wards replaced when it is desired to stop or reduce the flow. This 

 device works very well in small ditches. 



METHODS OP APPLYING WATER. 



When the distributing system has been secured methods of appli- 

 cation to the land must be determined upon in accordance with the 

 slope of the various irrigation faces and the crops to be grown upon 

 them. 



The methods in which application is made in field and garden 

 practice include the following: 



(1) Free flooding, or running water without restraint except that 

 afforded by the banks of the laterals conveying it. 



(2) Flooding in contour checks, or irregular- shaped inclosures 

 which are determined in size and shape by the inequalities of the sur- 

 face. 



(3) Flooding in rectangular checks, or inclosures which are ap- 

 proximately of equal size and with level bottoms. 



(4) Depressed beds, with raised ditches on the levees which hold 



Fig. 11. Small board dam 

 or gate. 



