68 The Drainage of Melbourne. 



20. The importance of frequent flushing not being recog- 

 nised, the absence of the allusion to the gradients of the 

 sewers leads one to doubt whether this point has received 

 full consideration, especially as it is remarked in one place — ■ 

 " Melbourne has for the most part favourable gradients for 

 the employment of small sewers," and again, " the sewage 

 will flow away wherever the ground is sufficiently inclined. 

 In general, there is ample 'fall to secure this."* The only 

 misgivings as to the slope obtainable generally, are expressed 

 in the remarks made regarding the special treatment proposed 

 for certain flat areas ; this treatment will be examined in the 

 next two paragraphs. To explain what the sewers are 

 capable of doing, the gradients to be given to them are 

 necessary to be known, as well as their sizes ; the essay 

 gives the sizes only. The efficient and economical working 

 of the system, as well as much of the comfort of the inhabi- 

 tants, will depend largely on sufficient gradients being- 

 given to the sewers, particularly to the smaller ones. 



21. Where the slope of the ground is very slight — Rich- 

 mond Flat, Collingwood, head of Wellington-street, and part 

 of Sandridge are specially named in the essay — it is pro- 

 posed to use cast-iron pipes, the contents of which might be 

 forced " into the main sewer once or twice a day by hydraulic 

 pressure from the water main, the house sewers being fitted 

 with reflex valves."")* It would be interesting to know the 

 details of the proposed arrangement, where it has been tried, 

 and how it has been found to answer. If it is intended to 

 connect the water main with the sewer in order to obtain 

 the hydraulic pressure mentioned, this arrangement is open 

 to the very serious objection, that the water in the main 

 would be thereby liable to contamination occasionally by 

 sewer gas. In any case, Yan Yean water would be required, 

 and, apparently, a considerable quantity of it, to work this 

 system. 



22. These cast-iron sewers are not, however, to be intro- 

 duced till the localities named become more populous ; for 

 the present, it is proposed that the house drainage should 

 continue to flow into the gutters, and be swept into the main 

 sewer by manual labour. This would not be much of an 

 improvement, if any, on the existing state of things; and it 

 is not likely to be satisfactory to the ratepayers of the 



* See paragraphs 6 and 14 of the essay. 

 f See paragraph 44 of the essay. 



