LVIII. DISCUSSION. 



ment. To this he could not agree. Assuming that some 

 of the catchments to be provided for were small, then it 

 might, perhaps, be safe to base the calculation upon 6" of 

 rainfall. This large provision, however, in his judgment, 

 and in that of the authors of the formulae given, was quite 

 unnecessary. With regard to the author's assumption of 

 a co-efficient of run-off equal to unity when designing storm- 

 water channels in towns, experience proved that this assumption 

 was wide of the fact, in proof of which the cases illustrated in 

 the foregoing table were produced. Such channels had been 

 built in every part of the city, and had proved ample in capacity 

 to carry off the most severe rains. 



Mr. C. J. Ross thought the author was to be commended 

 for introducing a subject upon which such a diversity of opinion 

 exists, and one which deserves more, and receives so little 

 professional attention. Especially was this the case in 

 Municipal Engineering, as his experience went to show that the 

 matter was usually treated by the old " rule of thumb " method 

 of personal judgment. He would mention one or two points that 

 had occurred to him in dealing with the question. First, with 

 regard to flood marks He had found that one might very easily 

 be misled by accepting even apparently well-authenticated flood 

 marks. Again, with regard to the basis of rainfall necessary to 

 adopt for local municipal requirements, he agreed with the 

 author in placing it at the six-inch rate, since this was not 

 phenomenal, and (more especially as regards the immediate 

 northern suburbs) the topographical features were very rugged, 

 and, consequently, the gradients were, as a rule, steep, while the 

 catchment areas were small. Again, the natural provisions for 

 drainage were supplanted by artificial ones, and concentration 

 was, therefore, made at every hand. 



Mr. Cardew thought that the table of discharges in the 

 paper compiled from the formulae of Biirkli-Ziegler, Dickens, 

 Fanning, and others, was, to a large extent, useless, either as a 

 table of comparison or reference, since the author did not quote 

 the factors employed in each — such as the rainfall, slope, length 



