94 IRRIGATION FARMIXG. 



erals 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 preserve 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 stiif 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 

 practicable, 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 constructed in straight 

 lines if possible. Curves where required should T>e care- 

 fully set out, so that the flume may discharge its maxi- 

 mum quantity. In the ordinary style of construction, 

 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 inches beyond 

 tjie posts, to which side braces are nailed to strengthen 

 the structure. Where flumes are not supported on tres- 

 tles, but rest on an excavated ledge, it is desirable still 

 to use the stringers, which should be placed just outside 

 the posts, so that water leaking from the sides will drop 

 clear of them. Main supports, such as trestles, are placed 

 eight or more feet apart. Planking should be of pine. 

 redwood or hemlock. The cross section of a flume should 

 be no narrower than the bottom of the ditch, for if not 



