in the City of Melbourne. 7 



caused the change is still at work, and will for many years 

 to come still further increase both the suddenness of the 

 street floods, and the volume of water discharged in a 

 given time. 



Nor can we reason with any safety that the rainfall itself 

 will not increase, for it is on record that no less than 

 10J inches fell at Newcastle, N.S.W., in 2| hours. If half 

 that quantity were to fall here in the same time, it is 

 impossible to foretell the damage that might be done. 



Besides the damage that has been, and may be, occasioned 

 with a given amount of rain, the loss may be much 

 increased by the partial stoppage of the street-channels. 

 At the last heavy street-flood, no less than five of the 

 bridges were carried away, some of them being left in such 

 a position as to partially dam the street-channels ; and 

 should the barrier be increased by planks, packing-cases, 

 vehicles, or portions of the boarding round places where 

 new buildings are being erected, the same amount of rainfall 

 that we have had might be much more disastrous in its 

 consequences. 



To guard then, as far as possible against these evils, I 

 advocate the construction of a tunnel or underground drain 

 from the northern part of the city westward into the 

 swamp, through which the intercepted waters of no less 

 than 547 acres might be discharged, and so reduce the 

 volume of water passing along Swanston, Elizabeth, and 

 Flinders-streets, to the extent previously named. One 

 objection urged against this plan is that " it is impossible 

 to make a tunnel large enough." To this I answer that the 

 distance from the commencement of the large tunnel in 

 Elizabeth-street to its outlet on the swamp is under a mile 

 in length, and the fall is sufficient to enable a tunoel of only 

 five feet in diameter to discharge 100 millions of gallons per 

 day. I have already mentioned that the heaviest rainfall 

 recorded in the colony for one day amounted to 74 millions 

 of gallons upon an area of 956 acres; and as the tunnel 

 would intercept the drainage of 547 acres of this area, it 

 might be supposed to be large enough ; still, to guard 

 against the most exceptional rain-falls, it would be prudent 

 to err on the safe side ; and I would therefore recommend a 

 tunnel eight feet in diameter. This tunnel, with the same 

 rate of inclination, would discharge four times more water 

 than a five-feet tunnel, notwithstanding their sectional 

 areas are as 25 to 64. 



