L. J. I. HAYCROFT. 



not because injury would be likely to accrue to the structure, 

 through the occasional occurrence of such a high velocity, but 

 from the fact that the velocity of water approaching a culvert 

 never reaches such a rate, and whilst decrying any attempt to 

 reduce the natural velocity of approach, there does not appear to 

 be any utility in increasing it for such a short length, as ordinary 

 culverts reach. 



Now, what is the natural velocity of approach of a stream. 

 Is it not determined by one of two things, or, perhaps, by both — 

 viz., the inclination of the bed, and the material through which 

 it passes ? 



On page 164 of "The Australian Municipal Pocket Book of 

 Engineering," compiled by J. H. Cardew, Assoc. M. Inst. C.E., 

 will be found the following information as regards limits of 

 velocity : — " To prevent injury to the bed and banks, the velocity 

 of water, in feet per minute, in a channel should be proportioned 

 to the tenacity of the soil." The minimum velocity is given for 

 soft alluvial deposits as 25 feet per minute, rising to from 300 to 

 400 feet per minute for shingly and rocky beds. On the next 

 page the velocities in feet per second are given at which various 

 substances are carried off, that at which hard rock will be affected 

 being 10 feet per second. 



400 feet per minute, it is hardly necessary to remark, means 

 6§ feet per second. Now, if this is correct, as undoubtedly the 

 author of such a book would be, the maximum velocity in nature 

 is 10 feet per second, and hence, except it is desired to shift 

 creation, there can be no necessity for increasing this velocity of 

 nature, especially when by doing so the only tangible result is to 

 make the are theculvert so small as to render it liable to be 



obstructed. 



Jackson, in his " Hydraulic Manual," states that the velocity 

 of slow rivers is 0*33 feet per second, of ordinary rivers is 2J 

 feet per second, and of rapid rivers is 10J feet per second, and 

 also that the safe bottom velocities for the softer rocks, brick and 

 earthenware, is 4J feet per second, and for hard rock from 6 to 

 10 feet per second. 



