116 



ARID AGRICULTURE. 



CULVERTS 



by setting boxes into the canal. They should be 

 so constructed that they will not wash out. Cut^ 

 ting around them is prevented by wing walls and 

 boards placed vertically to keep water from 

 starting through or around the box. A small 

 board dam or apron, placed at the lower edge, 

 prevents the eddies from undermining or carry- 

 ing away the structure. 



For carrying ditches across roads, railroads, 

 other ditches, and the like, culverts made of pipe, 

 are very suitable. Sometimes old boilers may 

 be used for this purpose, but usually clay or 

 cement sewer pipes are found preferable as they 

 do not corrode. They should be carefully placed 

 in line, the joints cemented and the earth tamped 

 around them until solid. Where there is much 

 alkali, unglazed clay pipe will only last a short 

 time. 



SMALL 

 FLUMES 



Often it is necessary to cross ditches or gul- 

 leys with flumes. These may be made either of 

 wood or metal. In wood flumes the frame work 

 should be made first, the trestles on which they 

 are held being made strong enough to hold 

 against all strains, and with a foundation made 

 secure against settling. The settling of a flume 

 in one or tw r o places may cause leakage of the 

 whole amount of water carried. The boards of 

 a flume usually should be laid lengthwise. Sev- 

 eral methods of closing the joints are practiced. 



