170 



Proceedings, &c. t for 1885. 



Hence Mr, Steane deduces the formula 



Area in sq. chains x 181 



D = 



1-23 



(length in chains) +1800 

 This has given good results in nearly all cases by which it was 

 tested after construction, as is shown by the following table : — 



Locality. 



Discharge. 



Remarks. 





Actual. 



By Formula. 







Cubic feet per 



Cubic feet per 







sec. 



sec. 





Flinders Street Drain 



410 



430 





Reilly Street Drain . . . 



1,118 



1,342 





Axe Creek,at Harrow 



4,970 



4,540 



Doubtful 



„ „ Axedale 



13,827 



11,820 



J» 



Campaspe ... 



54,000 



34,600 



Approx. 

 dimension only 



Yarra (flood of 1863) 



35,000 



36,700 





It may be worth while to notice what rainfalls have given rise 

 to large floods. 



The largest-known flood at Sandhurst occurred in April, 1878. 

 The rainfall in Sandhurst was "63 inches, and at Crusoe Reservoir 

 1'91 inches in one hour. 



The drainage area is 10,000 acres. If 1*91 inches had fallen 

 over the whole area at the same time, the flood would have been 

 three times as great as the largest known. 



The next largest was during the heaviest twenty-fours' rain, 

 during which time 3*67 inches was recorded at the Survey Office, 

 and 4*72 inches at the Crusoe Reservoir, so that this rain was 

 evenly distributed over the district. The maximum fall in one 

 hour during this rain was "46 inches, and during two hours '76 

 inches, and the discharge was only three-quarters of that on the 

 former occasion. 



The following forrnulse are given by some writers for the 

 discharge of channel pipes in cities : — 



D // = 4-786A l3j L lV 

 or else, which is more recent, 



T>=rcJ± 



a 



in which c—'lb for dense cities 



= *31 for suburbs, with gardens, &c. 

 r = average rainfall 

 i = slope 



