Pipe Line Structures 147 



tomland. These sloping lands have grades of from one to three 

 feet per hundred feet, and the soil is gravelly loam or sandy loam. 

 The furrows are run straight down the steepest slope or nearly so. 

 Risers are placed on the main supply pipe line and on the laterals. 

 Each riser hood has four 2-inch side openings, and each opening 

 serves three furrows, not simultaneously but in rotation, beginning 

 always with the highest. Cultivation is in many cases continuous 

 across more than one plat. 



The quantity of water per furrow is regulated by means of the 

 valve and is measured by the height of the water level above the 

 center of the openings. The discharges per opening were meas- 

 ured and are given in Table XXI. 



TABLE XXI. discharge FROM 2-INCn SIDE OPENINGS IN HOODS 



In California small galvanized iron tubes with slip gates are 

 much used in place of the open holes. A correspondent, in reply 

 to a request for measuring the discharge from the galvanized tubes, 

 states that the discharges are as given in Table XXII. 



TABLE XXII. DISCHARGE FROM GALVANIZED GATES 2>^ INCHES LONG 



Head over top of gate 

 Diameter of gate 



Inches 



3% inches 7 inches 



Gallons per minute Gallons per minute 



1/2 17 24 



2 30 43 



3 62 88 



A system which is still found occasionally consists of risers with 

 the top sealed by a cement plug while the galvanized gates are on 

 the outside instead of inside. The gates leak and the system is 

 unsatisfactory. Another system that should be discontinued is one 

 in which the pipe line is only half buried in the ground and gal- 

 vanized gates are placed directly on the pipe line at intervals equal 

 to the furrow spacing. A light earth covering is placed on the pipe 

 line between the galvanized gates, but the line is not protected ade- 



