198 THE IMPROVEMl.M' OF RIVERS. 



Discharge Areas. To determine the total area of discharge required (which is 

 usually made the same for the filling as for the emptying valves) the following rule 

 may be used: 



Let s be the horizontal area of the chamber; 

 A, the total net area of the valves; 

 h, the lift between pools; 

 g, 32.2 feet, the acceleration of gravity; 

 t, the time of filling or emptying in seconds, all valves being opened fully and 



simultaneously ; 

 ttt, the coefficient of contraction, equal to about 0.62. 



Then *--! J5. .*2L 



> \ g t X 0.62 4.01 



In a comparison of a number of locks in America we found that the proportion 

 of net opening for filling or emptying the chambers varied from one square foot in 1800 

 cubic feet to one square foot in 4000 cubic feet, the first ratio applying to locks of low 

 or moderate lift (up to 9 or 10 feet), and the second to locks of high lift (up to 18 feet). 

 The cubic feet referred to are based on the number of cubic feet of water required for 

 a lockage when both pools are at the crests of their respective dams, and the ratio is 

 therefore independent of the size of the chamber. In certain of the large locks of the 

 lower Seine the proportion is i in 4300, and in examples on the Moldau i in 3400. 



