58 



IRRIGATION FARMING. 



gate, in order that the gate may be lifted. In construc- 

 tion the gate is most simple, any carpenter or farmer 

 being able to build one. A tight- 

 fitting slide over the end of the 

 box or pipe outlet is all that is 

 necessary to shut off the water. 

 The gate may be raised or low- 

 ered by a stick of 2x4 bolted to 

 the front of the gate and leading 

 up through slides or guide holes 

 in the end of the walk. Simple 

 means may be provided for fas- 

 tening the gate either up or down. 

 The pressure of the water against 

 the gate will keep it in position 

 and preserve a tight joint if the 

 sliding surfaces have been prop- 

 erly dressed or surfaced. Grooves 

 should be provided in the sliding 

 supports so as to make sure that 

 the gate will return to its seat 

 when it is desired to lower it. 

 Modifications of detail are many 

 and will suggest themselves to 

 any one as the conditions of the 

 work or the setting may require. 

 One of these is a cast-iron lift 

 gate working in an iron frame 

 with grooves, as seen in Fig- 

 ure 16. 



Evaporation and Seepage. 

 Evaporation is greatest during warm or windy 

 v.-c:ither, greater in shallow than in dei-p water ami 

 greater in running than in still water. The evaporation 

 of a canal dim MI: June, July and. August will rarely 

 exceed three to four inches a day. Durin/r theremain- 



FIO. 16. IRON* Ol'TLKT GATE. 



