86 Floods on the River Barwon. 



taken at 40 square miles, the flood discharge would probably 

 be 4000 cubic feet per second ; but the catchment area being 

 so much smaller thau that of the Barwon, the flood from the 

 creek would have begun to subside long before that from the 

 Barwon was at its height. The author considers that 2000 

 cubic feet should be added for the discharge of the Waurn 

 Ponds Creek when the flood coming down the Barwon was at 

 its height (at eleven p.m.). This would make the quantity 

 passing at that time through the gorge (C.S. No. 1) 73,000 

 cubic feet per second. 



10. The water impounded by the railway embankment, 

 when it began to flow off, would also pass through this 

 gorge ; but, except for the cutting away of the banks, the 

 impounded water would not, under the conditions of the 

 case, flow off till the water level below the embankment had 

 begun to fall. As regards the effect of the cutting away of 

 the bank in this case, it is allowed for in the calculation of the 

 additional water (2000 cubic feet) coming down at eleven 

 p.m. In any case, the increase due to the impounded water 

 flowing off could have been but very small. Taking the 

 area at 36,000,000 square feet,andthe fall in the water level at 

 nine inches by the next morning (say, in twelve hours), the 

 mean quantity would be only 625 cubic feet per second ; but 

 as up till eleven p.m. the fall is estimated by the author at 

 only xVfoot, or a little more, the increase was, in the first 

 six hours, less than 200 cubic feet per second. After eleven 

 p.m., as the flood was decreasing, the additional quantity of 

 the impounded water flowing off (a little over 1000 cubic feet 

 per second on the average of the six hours, less at first and 

 more afterwards) did not affect the maximum discharge at 

 the gorge (C.S. No. 1). Evidently, when the flood level 

 was falling, less water must have been flowing past this 

 point, unless some sjDecial cause were at work to produce 

 any other result. 



11. Having ascertained the volume of the flood, it is possi- 

 ble to inquire into its action at various important points. 

 The water was flowing with a velocity of nearly 9 feet 

 per second through the two openings of the iron bridge, 

 aggregating about 400 feet in length, into a basin of compa- 

 ratively still water at least 1600 feet wide; the stream was, 

 in fact, confined at first to a width of 400 feet only out of 

 the 1600 feet width of the river; but its width rapidly 

 increased as it advanced, and its velocity was retarded. 

 In consequence of the contracted waterway, the set of the 



