Floods on the River Bamvon. 9& 



disastrous than that was. The water would rise to within 

 a very little of the level it then attained ; for it must be 

 remembered that it only rose to the levels shown by most 

 of the flood-marks after the bank had cut away to nearly 

 the extent of the existing waterway. The mean velocity 

 of the water flowing through the JBarwon bridge (obstructed 

 by struts, &c.) would, in another similar flood, be about 

 5 J feet per second ; while, through the Waurn Ponds bridge 

 it would be more than 7 feet per second. Under these 

 circumstances, can it be expected that the banks, in their 

 present unprotected state, would not again cut away ? It 

 may well be questioned whether anything short of masonry 

 abutments would be perfectly safe in case of another flood 

 similar to that of 1880 ; certainly nothing less could with- 

 stand another flood similar to that of 1852. Supposing, 

 however, the banks to be adequately protected, there would 

 still remain the risk of a serious scour under both bridges. 

 In the author's opinion, it is necessary considerably to 

 lengthen the waterway at the same time that the headway 

 under the bridges is increased, before the line across the 

 Bar won can be considered safe. 



23. This is a subject, it may be remarked, which does not 

 require an engineer experienced in railway construction to 

 decide ; it is especially one for a hydraulic engineer. Con- 

 siderations of the waterway apply as well to a bridge for 

 a common road as to one for a railway. Flood waters and 

 large volumes of water in motion generally are not to be 

 controlled, except by proper methods, based on sound 

 hydraulic principles. General rules, the result of long 

 experience in all parts of the world, are laid down in standard 

 works on this branch of engineering; and when such, accepted 

 and constantly used by the heads of the profession, are set 

 on one side, good reasons for so doing should be forthcoming. 

 Practice is a most valuable guide ; but in order that it may 

 be turned to the best account, it requires to be supplemented 

 by theory, or a thorough knowledge of the principles of 

 construction and of the sciences on which engineering 

 depends. In hydraulic works, an engineer requires to know, 

 as nearly as possible, the volume of water he has to deal 

 with, its velocity when in motion, and such other information 

 as, under the special conditions of the case, he is able to 

 obtain. If exact results are unattainable, an approximation 

 is better than total ignorance on these points ; though the 

 more uncertain the results, the greater the margin for safety 



