WATER GATES 



247 



or liiglit of the water above the opening, as upon this 

 depends the velocity of the stream escaping. The exact 

 velocity of the stream issuing under a certain head is not 

 ascertained by any arbitrary rule, but is estimated and 

 agreed upon by irrigators as a matter of custom and con- 

 venience. 



The method of measurement common in this country, 

 is by an opening of so many square inches with a head of 

 three inches of water in the flume. The actual quantity 

 of water which may flow through this opening depends 

 upon many varying circumstances, such as the size of the 

 canal, the substance of which the flume is made, the 

 shape of the flume, its position with regard to the course 

 of the main current, with other modifying influences, all . 

 of which may cause differences in the quantities delivered 

 through openings of the same size. By and by, when 

 our circumstances require it, however, some more precise 

 method to arrive at the exact quantity of water escaping 

 through the orifice will undoubtedly be discovered. 



The gates for the passage of water into the smaller 

 canals should be care- 

 fully made. Wooden 

 sluices are destructible, 

 and can scarcely be made 

 close. If timber sills, 

 sideposts, and plank are 

 used, they should be 

 made of the best of oak. 

 A cast-iron plate should 

 be laid in the sill for the 

 gate to close upon, and 

 the gats should be shod 

 with a cast-iron shoe, 

 beveled and planed to fit Fi S- ISO.-SECTION OF GATE. 



the planed surface of the plate. There will then be no leak- 

 age. A well constructed sluice-way should have a cast- 





