IRRIGATION AND DRAINAGE 137 



of 2\ inches to 100 feet for a ditch carrying 2 cubic feet per second 

 is not far out of the way. The amount of water to be carried varies 

 from \ cubic foot to 2 or more cubic feet per second. A ditch having 

 a bottom width of 24 inches, a depth of 6 inches, and sloping sides 

 ought to carry i| cubic feet per second on a grade of A inch to 

 the rod or 3 inches to 100 feet. Such a ditch may be built by first 

 plowing four furrows, and then removing the loose earth with shovels 

 or a narrow scraper or by throwing it up on the sides and top of the 

 ditch by means of a homemade implement resembling a snowplow. 

 Canvas dams, metal tappoons, or other similar devices are inserted 

 in the head ditch to raise the surface of the water opposite the 

 furrows. The chief difficulty in this method of irrigation is in 

 securing an even distribution of water among a large number of 

 furrows. A skilled irrigator may adjust the size and depth of the 

 ditch-bank openings so as to get a fairly uniform flow in the furrows, 

 but constant attention is required to maintain it. If the water is 

 permitted to flow for a short time unattended, the distribution is 

 likely to become unequal, with the result that parts of the ditch 

 bank become soft, and, as the water rushes through, the earth is 

 washed away, permitting larger discharges in some furrows but 

 lowering the general level of the water so that other openings may 

 have no discharge. Some orchardists of San Diego County, Cali- 

 fornia, insert in niches cut in the bank, pieces of old grain sacks 

 or tent cloth, over which the water flows without eroding the earth. 

 Another device is to place in the ground, at the head of each furrow, 

 boards pointed at the lower end and containing a narrow opening 

 or slot through which the water passes. Shingles are also sometimes 

 used to regulate the flow in the furrows. 



Short tubes in head ditches. In recent years short tubes or spouts 

 have been used in many of the head ditches of orchards to divert 

 small quantities of water to the furrows. These tubes are usually 

 made of wood, but pipes made of clay, black iron, galvanized iron, 

 and tin are occasionally used. 



For nurseries and young trees especially, but also for mature 

 trees, a cheap and serviceable tube may be made from pine lath — 

 the kind used for plastering. The 4-foot lengths are cut into two 

 equal parts, and four of these pieces are nailed together to form a 

 tube. One of these tubes, when placed with its center 2 inches below 



