EXAMPLE OF IRRIGATED FIELD. 191 



on those spots. It might be mentioned here that a very 

 smooth, fine- surf ace, is objectionable, as being very liable 

 to bake under the hot sun after watering. A soil that is 

 somewhat cloddy or lumpy, is not so apt to bake, and is 

 preferable to a very fine one. The ground is then leveled 

 with a scraper, the hollows filled with earth from the 

 ridges and swells, and as accurate a level as possible is 

 secured. 



When the level surface has been procured, or where it 

 is already sufficiencly level naturally, the course of the 

 furrows is to be laid out with due regard to the position 

 of the chief supply canal, and the foot drain by which 

 any surplus of water is to be carried off. It is under- 

 stood that the chief supply canal is made with as little 

 fall as possible ; in practice, this should not exceed 3 feet 

 per mile, and should not be less than one foot per mile. 

 From this canal the primary, or main distributing ditches 

 are made to diverge, and these should have a slope from 

 3 to 8 feet per mile ; the medium slope of 4 to 5 feet per 

 mile being preferable. From these primary ditches, 

 secondary ditches are laid out, having the same slope, 

 about 1,000 to 1,500 feet apart, when a large tract is to 

 be brought under irrigation ; a distance of one fourth of 

 a mile, or 1,320 feet, is a very convenient distance, as it is 

 equal to the size of a 40 acre lot, and divides an 80 or 160 

 acre tract into equal portions. A catch-water ditch should 

 be laid out parallel to the primary ditch, at about 2,000 

 to 3,000 feet distant from it ; a half mile, or 2,640 feet, 

 is a very suitable distance, as there would then be 160 

 acres, or two 80 acre farms in the enclosed quadrangle. 



As an illustration might be represented a plot of an ir- 

 rigation system, belonging to the San Joaquin and Kings 

 River Canal in California, as described in the report to 

 Congress of the Commission for the examination of the 

 valleys of California. This is shown in the diagram, fig. 

 81. The main supply canal has a fall of a foot in the 



