98 Fruitgrowing under Irrigation 



taken place, to do away with the accumulation of 

 salt already there. 



The first essential for a successful drainage 

 scheme is an assured get-away for the drainage 

 waters. If near a river or lagoon, drainage can take 

 place into these direct, or into a drainage system 

 leading into these. To cope with the drainage 

 problem on irrigation areas, shafts are often sunk 

 until a layer of drift sand is struck, and the water 

 led .into these. The drawback to this method of 

 drainage is that unless the layer of drift sand leads 

 directly into the river bed, into a lake, or into the 

 sea,, the "sand pocket" must in time fill up with 

 water, and consequently become useless for drain- 

 age purposes. 



After having secured a get-away for the drainage 

 waters by means of a well, dam, or drainage channel, 

 trenches, being given an even fall are dug through 

 the affected land leading into such drainage system, 

 and earthenware pipes laid in the bottom of them. 

 To ensure good drainage the pipes should be laid on 

 top of the layer of water-impervious subsoil that 

 prevents the water from passing downward, or as 

 nearly as possible to it. Local practice has proved 

 that pipes inserted at a depth from 4 ft. to 6 ft. 

 give good results in most instances. 



The trench is in the first place given an even 

 fall into the well or main drainage system, the pipes 

 are laid as evenly and as closely together as possible, 

 and the joints are then covered w r ith a small piece of 

 oiled or tarred paper, which, while preventing the 

 loose earth from getting into the pipes when the 

 trench is being filled in, yet does not prevent the 

 water from entering in at the joints. 



To remove the salts from alkali-impregnated 

 land, it is necessary, after the drainage pipes have 

 been put in, to give the land a heavy flooding of 



