The Drainage of Melbourne. 65 



should be encouraged ; but the sewage farm mentioned in 

 the essay is apparently considered a matter of secondary 

 importance, being chiefly intended for the disposal of the 

 sludge collected by the strainers. Only a very small portion 

 of the sewage could be used for irrigation at this farm, and 

 that in dry weather merely. Since, therefore, no special 

 provision is made for irrigation on a scale sufficient to affect 

 the result, the 120 acres of filtering beds must be capable 

 of purifying the whole of the sewage. 



14. The case of Merthyr Tydvil is referred to in support 

 of the recommendations made in the essay. But Mr. Bailey 

 Denton, by whom the arrangements there were designed in 

 1871, wrote six years afterwards, that, for a time, 20 

 acres of land sufficed at Merthyr for the purification of the 

 sewage from a population of 30,000 persons,* or 1500 per acre; 

 and he believed purification by the same process " could 

 have been assured for a permanency by the use of 75 acres,""f* 

 which would give 400 persons to the acre. The population 

 of Melbourne being taken at 200,000, and an area of 120 

 acres being provided for the permanent purification of its 

 sewage, the average is 1667 persons per acre, instead of only 

 400, as at Merthyr; while for the four months that the sewage 

 would be flowing on to 40 acres only, each acre would have 

 to purif}^ the sewage of 5000 persons, instead of only 1500, 

 as at Merthyr. 



15. Again, if the quantity of sewage to be dealt with is 

 considered, the filtering area still appears to be inadequate. 

 The quantity of sewage is nowhere definitely stated in the 

 essay ; the only information on the point is furnished in the 

 statement of the work the pumps are required to do. Sup- 

 posing two of the three pumps (leaving one as a reserve), each 

 raising 6100 gallons a minute, to be working, the quantity of 

 sewage to be disposed of would be 17,568,000 gallons — equal 

 to 2,810,880 cubic feet — in 24 hours. This poured over 40 

 acres, or 1,742,400 superficial feet, would give a depth of 

 over 19 inches to be absorbed daily. This certainly w^ould 

 be in wet weather only ; the dry weather discharge might 

 be half this, or a depth of nearly 10 inches. The average 

 of the year may be taken at one pump working every day, 

 and a second pump every third day only ; this w^ould give a 

 little over one foot daily to be absorbed. My own experi- 



* Bailey Denton's Sanitary Engineering (1877), p. 327. 

 f Ibid, p. 329. 



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