USE OF CONCRETE PIPE IX IRRIGATION. 



31 



open stands made of concrete pipe cemented together may be used 

 for this purpose. The water will rise in the pipe connected to the 

 inlet, and flow over a crest or notch into the other pipe, and thence 

 into the main (figs. 8 and 9). The lateral pipe leading from this 

 stand requires no gate, as the pressure will remain constant, allowing 

 no excessive pressures to accumulate in the lateral. If a lateral slopes 

 down grade from an overflow stand it is usual to provide a shut-off 

 gate where the lateral branches off from the stand. The gate may 

 be set in a low auxiliary stand that is cemented to the side of the 

 main relief stand. 

 Some relief stands 

 consist of one large 

 stand/pipe of suffi- 

 c i e n t diameter to 

 allow an overflow 

 pipe being placed in- 

 side of it (fig. 10). 

 Some orchard lat- 

 erals have a 12-inch 

 stand 6 to 18 feet 

 high fitted with a 6- 

 inch spillway pipe 

 inside, the 6-inch 

 pipe extending to a 

 foot or so of the top 

 of the 12-inch pipe. 

 In this case water is 

 diverted to the side 

 lateral from the 12- 

 inch pipe, the excess 

 of water spilling 

 down the 6-inch pipe 

 into the main. There 

 are a number of 

 modifications of this principle that will be taken up in detail under 

 the subject of diversion boxes and pipe structures. 



Nearly all measuring devices act as relief stands, especially weirs, 

 miner's-inch boxes, and ordinary recording irrigation meters, as such 

 devices are installed to allow the free flow of water over a crest in 

 an open box. 



MEASURING DEVICES FOR PIPE IRRIGATION SYSTEMS. 



A number of devices are in use to measure the flow of water 

 through pipes and laterals and from pumping plants and reservoirs. 

 Of these the following are briefly discussed — Venturi meters, weirs, 



Fig. 9. — Overflow pipe in rear and small diversion box in 

 front. 



