120 Surface and Underground 



be intercepted by the tunnel, and that, consequently, the 

 open channels in Swanston-streets would he relieved to the 

 extent of nearly 59 per cent, of the waters that are now 

 discharged by these channels during a storm. 



The source of their supply would he "bounded by Latrobe- 

 street on the north, and the remaining 41 per cent, of the 

 water would gradually accumulate on its way to the outlet, 

 At Bourke-street, for instance, only 15 per cent, of the 

 present quantity would be discharged during a storm, effec- 

 tually preventing any overflow to increase the flood in 

 Elizabeth-street. 



Again, by referring to the area drained by the outlet at 

 A, we find that the total acreage is 5. 3 0*3 5, out of which we 

 must subtract the area 33 35, drained by the same outlet, 

 but unconnected with Elizabeth-street. Of this, the drainage 

 of 371 '65 acres would be intercepted by the proposed tunnel, 

 and, consequently, the outlet would be relieved of nearly 75 

 per cent, or three-fourths of the storm-water and sewage, 

 that is now discharged through its channel, or even during 

 such a heavy rainfall as occurred on the 23rd September, 

 1856. 



The result of this relief would be that at Lonsdale-stree^ 

 instead of 83 per cent, of the total quantity of water dis- 

 charged at the outlet being received into the open channel, 

 there would be only about 8 per cent. At the Post Office, 

 14 J per cent, instead of 89 J per cent. At the Clarence 

 Hotel, Collins-street, 20 per cent, in place of 95 per cent, 

 and at the outlet itself, 25 per cent. 



Irrespective of these great benefits that would accrue from 

 this plan being carried into practice, there are others that 

 are worthy of consideration, inasmuch as at the present time 

 the city surveyor has to contend with these large bodies of 

 water in the construction of the numerous crossings in the 

 city. 



If he makes these crossings too acute, or deep in their 

 angles, they greatly interfere both with the comfort and 

 safety of the passengers in vehicles crossing over them. If, 

 on the other hand, they are made too obtuse or shallow, the 

 crossings are subject to a deposit of the stones and sand, 

 washed by the force of the current from the street, and the 

 consequence is that he has no alternative left but to adopt a 

 medium course, in which both evils are fully represented. 



This, to a great extent, would be remedied by the plan 

 now submitted, more particularly as the storm-water would 



