WATERWAYS OF BRIDGES AND CULVERTS. 563 



REFERENCE TO PLATE XXXVIII. 



Figs 1, 2, and 3 are intended to exhibit graphically the relation existing 

 between area of catchment and area of waterway in a number of well- 

 known average cases. The horizontal measurements give area of catchment 

 in square miles, the vertical ones area of waterway in square feet. Sufficient 

 waterways are shown by round dots, insufficient ones by crosses. The 

 curves and dotted lines are plotted by means of the various rules or formula 

 given by different authorities. For small areas of less than one square mile 

 the results are somewhat various and inconsistent, owing probably to 

 variations in absorptive power of the surface drained. The larger areas 

 being all country land grassed and timbered, are fairly consistent with the 

 proposed rule. 



In Fig. 1, all except No. 5 are in the City of Sandhurst, and are obtained 

 from Mr. Steane's paper on "Rainfall and Flood Discharge" (Proc. Roy. 

 Soc. Victoria, Vol. XXIV., p. 157) ; No. 5 drains Royal Park, near Mel- 

 bourne ; Nos. 2 and 9 are stated to be nearly sufficient, but not quite. 



In Fig. 2, No. I is at Essendon, near Melbourne ; No. 3 at Bridgewater, 

 Tasmania; No. 11 Cootamundra, New South Wales ; Nos. 13 and 14 on the 

 Moonee Ponds Creek, near Melbourne ; No. 15 on the Plenty River, near 

 Melbourne. The remainder are in the vicinity of Sandhurst, and are from 

 Mr. Steane's paper above mentioned. 



In Fig. 3, Nos. 1, 2, and 3 correspond with 13, 14, and 15 in Fig. 2; 4 

 and 5 are on the Merri Creek, near Melbourne ; 6 is a railway bridge over 

 the Macdonald River in New South Wales ; 7 one over the Saltwater River, 

 near Melbourne ; 8 and 9 are over the Macquarie River at Bathurst ; 10 is at 

 Collingwood, near Melbourne, over the Yarra River, while 11 and 12 are the 

 road and railway bridges over the Barwon River at Geelong. The former of 

 these proved not quite sufficient to discharge the last great flood, a small 

 portion of the water flowing over the embankment, impeding traffic, but 

 doing no further damage, while at the latter several hundreds of feet 

 in length of embankment were swept away, and the waterway enlarged by 

 the action of the river itself to nearly twice its original size. 



