DAM- MAKING. 219 



the veriest little dry bed for eleven months in the yenr 

 is a rushing torrent for the other month; and the capa- 

 city of the reservoir must be enormous if intended for 

 irrigation, unless it is fed by a constant stream or springs. 



But where the farmer has fully satisfied himself by 

 some years' local experience that a large reservoir for 

 irrigation is feasible, that the land he purposes to irri- 

 gate is worth it, that the river runs often enough to 

 ensure his always having water at the time required, and 

 knows by experience the extraordinary heiglit that these 

 apparently insignificant streams can rise, that the silt 

 and debris that come down are insignificant, and that 

 all the necessary conditions of success are there — he 

 should then have the site surveyed and full plans drawn 

 by an engineer before turnmg a sod — the cost of which 

 will be saved over and over again before the dam is 

 finished. If the engineer is a man of some years' colonial 

 experience, well and good ; if not, far greater provision 

 for carrying off the surplus water will be required than 

 he will be likely to provide. 



A dam for irrigation purposes that is dependent on 

 local surface drainage, no matter how large the drainage 

 area, will always prove a costly fiiilure, excepting for 

 irrigating an acre or so of garden-ground immediately 

 behind it : the amount of water required and the length 

 of the droughts are too great. 



