ENGINEERING CONSTRUCTION AND RAINFALL. XLVII. 



enumerating various formulae " all these features, therefore, 

 emphasize the difficulties of the task and the necessity of 

 employing specially trained engineers, or expert hydraulicians, 

 for all important work of this kind, as the true value of the 

 application of theory to this problem is directly proportional to 

 the correctness of the assumptions borrowed from practice ; in 

 the hands of a practical and experienced adept the data bearing 

 on the case, consisting of part theory, part assumptions and 

 observed facts, will be moulded into fairly good shape, and some 

 tangible and valuable results obtained." The formula known as 

 Biirkli-Ziegler's, when intelligently used, is (judged by the 

 experience of the writer) as reliable as a formula of such a nature 

 can be, and is preferable for general use to any other of the 

 indicated formulae. 



During a recent investigation of the applicability of these 

 several formulae to local conditions, it was found that the only 

 formula devised for general Australian use, and proved to be reli- 

 able in comparison with existing waterways, was that of Professor 

 Kernot, of Melbourne University. Under certain conditions it is 

 identical with that of Biirkli-Ziegler, the proof of which is as 

 follows : 



Biirkli-Ziegler's formula is — 



Q' = OR V _ where Q' == cubic feet per sec. per acre. 

 A 



reaching the outlet. 



C is the co-efficient of run off. 



R, is the rate of rainfall in inches per hour. 



S is the average slope of the catchment, in feet per thousand, 

 and A is the area of the catchment in acres. 



Is ow let Q = total run off, in cubic feet per second, from the 



catchment, then Q = Q'A = CK ^ S A f 



Let S = 20 feet per thousand 



Then Q = 2-1147 CR A 1 



Now let the velocity of flow, through the proposed opening, be 

 4 J miles per hour =6*6 feet per second. 



