978
THE HONGKONG GOVERNMENT GAZETTE, 27TH SEPTEMBER, 1890.
36. To form a judgment as to the desirability of undertaking these intercepting works, an estimate of the probable annual cost of working must be made: as follows:-
1 Driver at $1.00, per day,
2 Firemen at $0.40,
"
.$ 365.00
292.00
2 Coolies at $0.20,
146.00
**
An average Engine power 7 H.P. at 6 fbs. of coal per H.P. per hour=164 tons at $12.00,.. Oil, tallow, waste, &c.,.
1,968.00
200.00
Total,..
.$2,971.00
37. If the Eastern District were extended by reclamation, the sewers of the new area would drain backwards from the new Praya to the receiving-wells in the old Praya. These sewers would also serve as storm-overflows. The syphon system offers great facilities for future extension. If, at any time, the proposed syphon were found to be too small for its work, it will only be necessary to lay a new pipe, a much easier operation than the construction of a low-level sewer.
38. The direct out-falls, though by no means a perfect method of disposing of the sewage of this district, will undoubtedly be a great improvement on the present state of affairs, in which the sewage is discharged, directly through the Praya wall, on to the foreshore at low-water, and into the slack water, in front of the wall, at high tide. But, even if the sewage were carried out to beyond low-water mark, some portion thereof would work inwards on to the foreshore, on the flood tide; and during northerly winds; and from deposit in the shallow water. This would create a nuisance, though a lesser one than that which exists at present, and it would scarcely constitute a danger to health. This nuisance can be completely removed by interception in manner described, for a capital expenditure of $70,000 added to an annual expenditure of about $3,000 representing, at 5%, a capital of $60,000. I leave it to Government to decide whether the benefit to be derived, justifies this expenditure. The intercepting syphon can be constructed at any time, without material alteration of the direct out-fall system; but it will be somewhat more economical to carry out the whole at the same time.
39. Having now completed the discussion the sewerage system of Victoria, I will now briefly recapitulate the recommendations made; and the arrangements proposed, for carrying them into effect.
40. The whole of the city should be sewered with pipe sewers of small diameter.
41. The dry-weather flow of the sewers, or sewage proper, should be wholly intercepted from the storm-water channels, which are not, and cannot be made fit for its reception and conveyance. The sewage should only gain access to the storm- water channels, when so freely diluted with rain, as to loose the character of sewage.
42. Rain-water should be excluded from the sewerage system, as far as possible. Rain from back-yards and from some portions of the roofs, must be admitted to the house-drains, and carried by them to the street sewers. These, however, should not be specially enlarged to provide for the rain-fall, but they should be freely furnished with storm over-flows; whereby any excess of flow, over and above their carrying capacity, will escape to the storm-water channels, and thus prevent all danger of flooding private property.
43. The sewers, both great and small, must have self-cleansing gradients: that is to say the normal flow of sewage must sweep them clear of deposit.
44. In the Western and Central District, unless the whole sewage is removed entirely from the harbour frontage of the city, nothing will be gained by its concentration at any one out-fall. When the Praya Reclamation is finished, the whole frontage will be equally good, as a position for out-falls, and the increased depth of water and improved tidal current, will prevent any nuisauce from them. This being the case, it is only necessary to place the out-falls sufficiently near together to allow of self-cleansing gradients: but each out-fall must drain an area sufficiently large to supply the quantity of sewage which will fill it to the depth that will establish a self-cleansing velocity.
45. The level of the sewers at the out-fall should be little below mean-sea-level: so that, for half of each day, the sewage may sweep freely through them.
46. The Eastern District offers no really favourable sites for out-falls. The nuisance which now arises from the out-falls may be abated, very considerably; by carrying out cast-iron pipes below low-water mark; so much so that the improved out-falls will no longer be sources of danger to health.
47. The sewago can easily be intercepted from the foreshore of the Eastern District, but to do so pumping will be required. The best out-fall in this case will be North Point.
48. The sewage of the Western and Central District, as well of that of the Upper District could be conveyed to an out-fall at Sulphur Channel. But to do so, at least one-third of the sewage would have to be pumped. The works for this purpose would be costly, and it is more than doubtful whether the advantages derived, would justify the expenditure.
49. The sewerage system of the Upper District, mainly inhabited by Europeans, should be wholly independent of the Lower Districts.