124 IRRIGATION FARMING. 



increasing or decreasing the mean velocity of the 

 current. The flume box may be made of two-inch 

 plank, seledled as free from loose knots or cracks as 

 possible. If a small box is needed for laterals a single 

 plank of fourteen to eighteen inches will do for the 

 bottom and similar ones for the sides. The supports 

 may in many cases be a single line of heavy fence 

 posts, which may be had in lengths as great as twelve 

 to fourteen feet. The butts set two or three feet into 

 the ground and well tamped give a good foundation. 

 When greater hights than ten to twelve feet are met, 

 a trestle of timber posts properly footed, braced and 

 anchored should be used. The planks before being 

 spiked together may be painted along the edges in con- 

 tact with a coat of very thick paint. This will not 

 only aid in making a water-tight joint, but will pre- 

 serve the wood at the joint. After the completion of 

 the flume go over all of the joints with a coat of thick 

 paint or tar, applied with an old stiff brush. A small 

 leak may often be stopped by filling the crack with 

 stiff clay or mud. 



Curves and Grades. — Where flumes are used and 

 pradlicable, they are set on a heavier grade than 

 canals — thirty to thirty-five feet to the mile is a good 

 rule — and are of proportionally smaller area than canals 

 with lesser grade. They should be construcfled in 

 straight lines if possible. Curves where required should 

 be carefully set out, so that the flume may discharge 

 its maximum quantity. In the ordinary style of con- 

 struc5lion, sills, posts, and ties support and strengthen 

 the work at every four feet. The posts are mortised 

 into the ties and sills. The sills extend at least twenty 



