CHAPTER IX. 



FLUMES AND THEIR STRUCTURE. 



Flumes arc boxes or troughs used to convey water 

 where ditches are impracticable, or needlessly expensive 

 either to construct or to maintain. Where a ravine, 

 valley, or any considerable depression crosses the line of 

 a ditch the water may be turned into a flume, carried 

 over the depression, and then discharged into another 

 ditch on the further side. It may be advisable to carry 

 the water in a flume over loose sandy soil, where the loss 

 by percolation would be so excessive as to render a suffi- 

 cient delivery from an open ditch either difficult or 

 impossible. Special forms of sheet-iron or other sheet- 

 metal flumes are much used in mountainous sections 

 because of their lightness, tightness and economy, and 

 the facility of erecting them in difficult places. As 

 usually constructed flumes are merely wooden boxes open 

 at the top and of such size and strength as is necessary 

 to carry, and support the water supplied. Many in the 

 West are of great size and strength, and traverse great 

 distances and at great hights. The grades may, if neces- 

 sary, be somewhat lighter and the size smaller than those 

 of the ditches supplying them, because of the lesser fric- 

 tion and the greater facility of flow. The volume of 

 water to be carried will regulate the size the same as in 

 the ditches, and the grade will in the same way regulate 

 the carrying capacity by increasing or decreasing the 

 mean velocity of the current. The flume box may be 

 made of two-inch plank, selected as free from loose knots 

 or cracks as possible. If a small box is needed for lat- 



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