XLVIII. J. I. HAYCROFT. 



If O = area of opening in square feet, it 



Q - 2 - 1147 CRA 



Velocity 6 6 



= 0-32 OR A 1 



= 0-32 CR (640 M) 1 



= 40 M 1 



= Professor Kernot's formula when 



C = -5 and R = 2" 

 If C = 0-625 & R = 2 " 



O = 50 M f 



And if C = 1 k R = 2 " 



O = 80 M 1 



The question now arises, after having by some means deter- 

 mined the amount of water to be provided for, what shall the 

 nature of the provision be? This is a point about which 

 engineers differ, though the scope for difference is much more 

 limited than in choosing a formula for run off. 



Let a typical case be taken. Say, for instance, where a catch- 

 ment discharges 60 cubic feet of water per second, this quantity 

 of water has to be passed under a railway or road bank, with 

 safety to the bank and the structure itself. 



A low velocity of discharge, except in special cases, is prefer- 

 able for several reasons. For example, when a culvert is to be 

 constructed, the facility for getting sufficient grade to attain a 

 high velocity is very limited, for the outlet should be designed 

 to provide a rapid get away. Surcharged culverts are not here 

 considered. Another and more important reason is as follows; 

 Suppose engineer M in adopting a velocity of six feet per second 

 through his structure, requires ten square feet of section, and an 

 engineer N adopting 18 feet per second, and, therefore 3 J square 

 feet of opening ; then the latter will require less material, and 

 design, therefore, a cheaper structure so far as first cost is con- 

 cerned. Other effects, however, result, which may more than 

 counterbalance the supposed advantage ; as, for instance, if the 

 velocity as designed, for some reason cannot be realized, the 



