WATERWAYS OP BRIDGES AND CULVERTS. 561 



1. As far as I can learn no structure approximating to the size 

 called for by the rule has failed to do its duty. 



2. Tliat those most deficient when compared with the rule, 

 namely, Bridge water in Tasmania (13 square feet to 2}^ square 

 miles), Sandhurst in Victoria (190 square feet for 16 S(iuare miles), 

 Cootamundra in New Soutli Wales (.5.3 square feet for 20 square 

 miles). Plenty River in Victoria (440 square feet for 60 square 

 miles), and Barwon River in Victoria (4,000 square feet for 1,700 

 square miles), have all been the scene of disastrous failure and 

 costly reconstruction with greatly increased waterway. All these 

 are shown by the rainfall maps to have nearly the same amount of 

 annual rainfall, a statement which is roughly true of all the ex- 

 amples shown, no cases having been chosen from those zones of 

 intense rainfall on the coast of New South Wales and in central 

 Gippsland. 



I, therefore, put forward this purely empirical rule as applicable 

 in average cases, subject of course to reasonable modification at 

 the discretion of the engineer in instances which are specially 

 favourable or unfavourable as to rainfall, shape of basin, character 

 of surface, or amount of damage like to ensue in event of failure. 

 Of one thing I feel confident that the general recognition of such 

 a rule would' have prevented in the past such disasters as those at 

 Bridgewater, Cootamundra, Sandhurst, or on the Plenty and 

 Barwon Rivers, and further that it would have checked the 

 expenditure of very large sums of money on structures that I 

 could name did time permit, which can be shown by entirely 

 independent lines of reasoning to be from twice to twenty times 

 as large as is necessary to discharge the maximum flood of the 

 stream passing through them. 



In conclusion I would say, that I have been greatly indebted as 

 to data for the present paper to Mr. Steane, whose labours to 

 improve practice in these matters are beyond all praise, to Mr. 

 Gordon, whose valuable pajjer has already been cited : to Jackson's 

 "Hydraulic Manual," to the "Proceedings of the Institution of Civil 

 Engineers," and tlie "Report of the Royal Commission on Railways 

 and Public Works of Tasmania," to surveys and sections taken by 

 Mr. T. B. Muntz, C E., in connection with the great flood on the 

 River Barwon in 1880, and the litigation arising thereupon ; and 

 to my brother Mr. M. E. Kernot, of the Victorian Railway 

 Department. 



I should feel greatly obliged to any member who would supply 

 me with reliable particulars as to other cases, either failures or 

 structures, that long experience has proved sufficient, but not 

 excessive, which I can add to the diagrams, and so confirm or 

 modify the conclusions already stated. 



Kl 



