348 Irrigation and Drainage 



water from the first into the second and the second 

 into the third, over one or more breaks or weirs in 

 the dividing 1 check ridges. If, however, the checks 

 are large or very many, this plan will be unneces- 

 sarily wasteful of water, and a better plan is to take 

 the water down the crest between two lines of checks 

 in a secondary furrow. From this furrow the water 

 may be turned into the check on one side and then 

 on the other, flooding by pairs down the whole line. 



In the San Joaquin valley of California, in Kern 

 county, there is laid out one of the largest flooding 

 systems in the world. Here are more than 30,000 

 acres of alfalfa in a single solid block. The slope of 

 the country ranges from 5 feet to the mile to less 

 than 2. Large volumes of water are at the command 

 of the company, 30 cubic feet per second, and so 

 the checks-, laid out with their level ridges on contour 

 lines, have various sizes and many shapes. The 

 largest checks contain 200 acres, while the average is 

 about 40. The ridges are 12 to 20 inches high, with 

 a maximum width at the base of 12 to 18 feet, 

 broadly rounded, and all covered with the growing 

 alfalfa. 



Where the period of rotation is short, and where 

 crops not suited to flooding are used in the rotation, 

 then narrower and temporary check ridges would be 

 formed for the crops to be watered in this way. The 

 smallest ridges may be rapidly made on recently 

 plowed fields by using a V-shaped ridging scraper 

 drawn by horses, with the open side forward. The 

 spreading wings throw the loose earth into the angle, 



