114 Floods on the River Barwon. 



from the Collins' Mill flood mark and the 16.53 level at the 

 railway, the result is found to be no less than 180,000 cubic 

 feet per second. But the openings provided at the railway- 

 have an effective area up to a level of 16.53 of less than 

 5000 square feet. Dividing 180,000 by 5000 we And that 

 to discharge the flood the water must pass through the 

 openings at the incredible velocity of 36 feet per second, 

 or more than 20 miles per hour. To produce this velocity 

 a heading up of W feet in height would be needed. Had 

 the railway engineers made this simple calculation when 

 designing the bridge, one of two results must have happened — 

 either they would have enlarged the waterway at least four- 

 fold, or they would have rejected the data upon which the 

 computation was based, and sought further information. 



If we abandon the Collins' Mill flood mark, and take the 

 16.53 flood level at the railway as the only datum, it is not 

 possible to make any calculation at all, as no velocity can be 

 ascertained. However, an experiment upon the model 

 before-mentioned showed that when the water stood at 16.53, 

 at the Breakwater it was about level with the flow of the 

 Victoria Mill, 17.30, and that if the railway bank were then 

 inserted the water rose to 20 at the mill, flooding it to a 

 depth of 2.70 feet. In view of this experiment and the 

 preceding calculation, I must dissent most emphatically from 

 the statement of the railway engineers, that the bridge was 

 correctly designed in view of the data supplied by the field 

 officer. 



In the evidence given on the side of the department, it 

 was repeatedly asserted that the railway works gave about 

 double the waterway of the large road bridge in the vicinity, 

 and the waterway was stated to be 735 and 390 lineal feet 

 in the two cases respectively. Upon this comparison the 

 opinion of the railway engineers as to the sufficiency of their 

 works appears to have been based. But the comparison is 

 altogether erroneous. In the first place it is tacitly assumed 

 that the road bridge was large enough, whereas experience 

 proves that it is not, a portion of the flood escaping over a 

 low part of the approaches. Next the 735 feet includes 

 the Waurn Ponds Creek Bridge 135 feet long, and as this 

 creek is a totally distinct stream from the Barwon, it is 

 manifestly quite unfair to include it. Thirdly, the bridge over 

 the main stream, though really 600 feet long, is placed in so 

 peculiar a position as to leave only 290 feet between its 

 south end and Haworth's Tannery, through which the whole 



