Appendix. 163 



due to the head is not acquired until the lowest level is reached. In 

 a tidal sluice, both the depth of water and velocity will vary from the 

 time when the doors are first opened till they are closed again by the 

 rising tide. The calculation must therefore be made on the mean 

 velocity of the water. 



Example. — A sluice with pointed piers, and doors fully open, 

 allowing a free discharge of the water, having 16 feet opening, with 

 depth of water 9 feet, and the head, or difference in the level of the 

 surface above and below the sluice, of 2 inches, or say o* 16 foot, and 

 allowing a deduction of 4 pet cent, for friction, would discharge 

 442 • 36 cubic feet per second. 



Area = 16' o" x 9' o" = 144' o". 



Velocity = 8^-i6x'96 = 3*o72 feet per second. 



Discharge = 144 x 3*072 = 442*36 cubic feet per second. 



If the water approached the sluice with a velocity of i * 50 feet per 

 second, allowance would require to be made for the head due to this, 

 then : — 



Head due to this = /z = ( — -A — - ) = o • 038, 



\*96 X 8/ "^ 



Adding this to the head through the sluice, the head = • 16 + '038 

 = -198, which gives a velocity of 3*4176 feet per second, and dis- 

 charge of 144 X 3*4176 = 49 2*134 cubic feet per second. 



TABLE VII. 

 Tidal Sluices. 



To find the quantity of water due to 24 /tours' rainfall if discharged 

 in a limited time, owing to the sluice being closed by the tide. 



Multiply the given discharge per hour, minute, or second, by the 

 multiplier opposite the number representing the hours the sluice 

 doors are open each tide. 



Example. — The discharge from the rainfall of 24 hours over a 

 given area is equal to 500 cubic feet per minute. This has to pass 

 through a sluice, the doors of which are closed 5 hours each tide, or 

 10 hours out of the 24, consequently the discharge will have to be 

 effected in 14 hours, or 7 hours each tide, and the quantity per 

 minute will be 855 cubic feet :— 



500 X i'7i = ^5S' 



M 2 



