346 Irrigation and Drainage 



and it is desired to place the upper edge of each 

 check under 2 inches of water, it would be neces- 

 sary to construct the levees, for checks 200 feet 

 square, about 10 or 12 inches high, because the water 

 would be 8 inches deep on the lower edge when the 

 surface was covered 2 inches at the higher side, and 

 a margin of 2 to 4 inches is needed for safety 

 against the water breaking across over slight depres- 

 sions or against wave action. 



If the fields are to be used continuously for mead- 

 ows, pastures, alfalfa, or either of these, in rotation 

 with small grains or similar crops which may be best 

 irrigated by flooding, it will usually be desirable to 

 make the check ridges broad and flat, so that mowers 

 and harvesters and even plows may readily move over 

 them. They thus become permanent features of the 

 field. If a 20-, 40- or 80-acre field is to be laid off 

 in regular checks, this would probably be most rapidly 

 and cheaply done by a system of plowing in repeated 

 back -furrows until the desired height of ridges is 

 reached. The sizes of the checks would first be deter- 

 mined, and then all the ridges extending in one 

 direction formed, first at the distance apart found 

 desirable, after which the field would be crossed in 

 the other direction, forming in the same manner the 

 other sides of the checks. 



In cases where a single plowing does not give 

 sufficient height to the ridges, and in countries 

 where the rainfall is sufficient to permit moderate 

 crops to be grown without irrigation, the labor of 

 fitting the ground in this way may be made a part 



