WATERWAYS OP BRIDGES AND CULVERTS. 555 



Thursday, August 30, 

 The President delivered the following Address : — 



WATERWAYS OF BRIDGES AND CULVERTS. 



The deterniination of the requisite waterway to be provided in 

 bridges and culverts draining given areas is one of the initial 

 problems that meets the engineer engaged in the construction of 

 I'ailways, roads, canals, or any other works that stretch in long 

 lines across considerable tracts of country, and generally con- 

 stitutes tlie very tirst question of real complexity that he has to 

 face — unless indeed he should be so fortunately circumstanced as 

 to be able to locate his works entirely along a watershed line, a 

 state of things met with but rarely. 



The correct solution of this question is a matter of the highest 

 importance, for on the one hand bridges and culverts involve, in 

 their construction, a very large proportion of the total cost of 

 many of our roads and railways, and a comparatively small excess 

 beyond actual requirements will represent a most serious waste of 

 money. While on the other hand, an insufficient provision may 

 involve costly reconstruction sooner or later, beside jeopardizing 

 the lives of travellers and others, and damaging property in the 

 vicinity. 



Beside being vitally important, this question is one of decided 

 difficulty, and upon which the experience of a considerable number 

 of years is needed before one can pronounce a given waterway 

 certainly sufficient. The flow of streams in Australia is so variable, 

 and the maxinmm discharge is reached so seldom, that it is quite 

 possible for the designer to be greatly misled, and to go on for 

 years providing waterways so small as eventually bring about 

 serious disasters. Several years will frequently elapse during 

 which the average flow of a stream will never equal one-fourth of 

 its maximum, and during which, therefore, culverts and bridges 

 of less than one-fourth of the proper size will suffice. The largest 

 Victorian stream that I have had the opportunity of thoroughly 

 investigating — the Barwon at Geelong — was in full flood in 1852, 

 and then was comparatively harmless until 1 880, when a flood, 

 nearly equalling that of 1852 occuri-ed. Suppose then the 

 acquaintance of an engineer with this stream had connnenced in 

 1853, he might have gone on for twenty-seven years building 

 bridges of half the proper size and never found out his mistake 

 until the 1880 deluge swept his works away wholesale. 



