144 



HYDEAULICS AND ITS APPLICATIONS 



Fteley and Stearns, 1 from experiments on suppressed weirs 5 and 

 19 feet long, and with beads ranging from '07 to 1*60 feet, and also 

 from a discussion of Francis's results, obtained the formula for a sup- 

 pressed weir 



Q = 3-31 b H* -f -007 b cub. ft. per sec. 



For a weir with end .contractions, b is to be replaced by (b '1 n H). 

 The velocity of approach is to be allowed for by putting the effective head 

 = H -f a h, where 



a = 1*5 for. a suppressed weir, 

 a = 2'05 for a weir having two end contractions. 

 These are mean values. Actually the experiments showed that a varies 

 with H, as shown approximately in the following table : 



Hamilton Smith, 2 from experiments by Fteley and Stearns, Francis, 

 and self, with weir lengths from "66 up to 19 feet, heads up to 2 feet, 

 altered Francis's formula so as to take a correction H -\- a h = D, for 

 the velocity of approach, giving a the values 1*4 for a contracted, and 

 1*33 for a suppressed weir. 



Then Q = 3'29 j b + 



D } & 



-= \ D 2 for a suppressed weir. 



^ ~ - ~ ~ for one end contraction. 



f D} 3. 

 Q = 3*29 -I b r^, ! D 2 for two end contractions. 



-s 



Smith also suggests determining v, and therefore h, by measuring the 

 surface velocity in the approach channel, the ratio of surface velocity to 

 mean velocity being usually approximately equal to a. 



Bazin, 3 from his own experiments on suppressed weirs from 1/65 to 



1 "Trans. Am. Soc. C.E.," 1883, pp. 1118. 



2 Hamilton Smith, "Hydraulics," pp. 99 and 137. 



8 " Annales des Fonts et Chaussees," 1898, 2tne (rimestre. 



