Drainage of Melbourne. 119 



improve the value of property in the immediate neighbour- 

 hood by converting what is at present an unsightly and 

 unhealthy swamp, into ground capable of beifig drained and 

 built upon. 



The first 43 chains of the underground sewer would not 

 require to be more than 12 feet in sectional area, and the 

 remaining portion, namely, from Elizabeth-street to Batman' s- 

 swamp, from 36 to 44 feet in sectional area, according to the 

 inclination it might be found desirable to give it. 



These tunnels should be elliptical, or, as it is commonly 

 called, egg-shaped, and should be constructed of hard burned 

 bricks, moulded to suit the several curves, and set in Port- 

 land cement. 



With respect to cost. This would depend upon the nature 

 of the material to be excavated, but under any circumstances 

 it would not cost the Government one-half the sum that is 

 now, and has been for nine years, lying idle in the shape of 

 cast-iron sewer covers on Batman's-swamp. Probably the 

 best thing the Government could do with the said sewer 

 covers would be to sell them to the ironfounders, and with 

 the money thus obtained, execute the work now suggested, 

 more especially as they will never be used for the purpose 

 for which they were intended. 



With respect to the extent that this plan would relieve 

 Swanston, Elizabeth, and Flinders-streets ; this may be 

 accurately determined by reference to the foregoing tables, 

 and the comparative areas that such tunnel would drain out 

 of the areas at present drained by the open channels in 

 Swanston, Elizabeth, and Flinders-streets. 



Referring to the map you will perceive that the area tinted 

 blue amounts to 530*35 acres, and that the area tinted red 

 drains 248 2 acres. As the line of the proposed tunnels 

 intersects those areas, as shown upon the plan, I have 

 measured then collective area to the north of the tunnel, 

 and find it to be 5172 acres, being 11 5 J acres, or 28 J per 

 cent., more than the entire area of the city proper (that is, 

 between Spencer and Spring-streets, Latrobe and Flinders- 

 streets). But, inasmuch as the whole of the water from the 

 517'2 acres passes through Swanston and Elizabeth-streets 

 to the outlets A and B, the ratio of the difference between 

 the quantities intercepted and the quantities discharged at 

 the outlets A and B, will be considerably increased. 



By referring to the area drained by the outlet B, namely, 

 248 - 2 acres, we find that the drainage of 145 6 acres would 



