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The area of this district is 233 acres and it is almost entirely built over. The sizes of the sewers have therefore been calculated to discharge 2.40 inches of rain-fall per 24 hours, or of an inch per hour, over the whole area.
Main No. 3 providing for the sewerage of District No. 3 (coloured yellow on plan sheets I and II,) will commence in Queen's Road Central, at the Corner of Murray Barracks, where it will receive the sewerage from Garden Road, and will pass down Murray Road to the Praya where it will turn along the Praya in a westerly direction as far as Winglok Street, which it will traverse and thence discharge into the harbour at Possession Point. This main is designed to pro- vide for the portion of the city situated between Queen's Road Central and the Praya the area of which is 190 acres.
The circumstances prevailing in two portions of this District are so different that in calculating the sizes of the sewers I have sub-divided it into the area draining above Ice House Lane, which may be called Sub-district 3A comprising 120 acres extent and the arca draining below Ice House Lane to the west which I will call Sub-district 3B, 70 acres in extent.
In sub-district 3A, are situated Government House, and the Botanical Gardens occupying extensive grounds and not likely ever to be closely built over, moreover, the elevation and position of the Albany Nullah, admit of a free outlet being always obtained for storm waters in this neighbourhood. The size of the main sewer along the Praya has therefore been calculated to convey inch of rain- fall per 24 hours over this sub-district. The other sub-district 3B being closely built over, the sizes of the sewers have been calculated to discharge 2.4 inches of rain per 24 hours falling over the whole sub-district in addition to the inch con- tributed by sub-district 3a.
Main No. 4 providing for the sewerage of district No. 4 (coloured brown on plan sheet II,) will commence in Queen's Road Central opposite the Royal Naval Yard and will traverse Queen's Road in an easterly direction as far as the Eastern Guard House, where it turns down Arsenal Road to the Praya, and continues along the Praya as far the Bowrington Canal and there discharges into the harbour. At this point also it receives the sewage of the Bowrington District.
Though the best available without pumping I cannot recommend the pro- posed position of this out-fall as a permanent measure and would strongly advise in preference, that the main be extended to the alternative point of out-fall at North Point.
The area of the eastern District is 247 acres. In it are situated the Barracks and Military and Naval Establishments but the higher levels are at present but little built over.
The sizes of the sewers have been calculated to discharge 1 inches of the rain-falling over the whole District. As just stated, I am only able to recom- mend the construction of the out-fall at Bowrington as a temporary expedient and I therefore deem it desirable to submit herewith a plan (sheet No. III,) and also a section showing the necessary works that would have to be undertaken in order to extend the out-fall to North Point. Such an extension, if carried out, would provide also for the sewerage of the Causeway Bay Reclamation and of Tung-lo-wan, giving a total area draining to North Point of 270 acres.
The size of the out-fall has been calculated to discharge per 24 hours 1 inches of the rain which falls over the whole area. The invert of the sewer being 5-37 feet below Ordnance Datum it will be necessary to adopt Pumping Machinery in order to discharge the sewage into the harbour.
Taking 1 inches of rain-fall per 24 hours over the whole surface, we get a flow of 1,470,150 cubic feet per 24 hours.
The present dry weather flow of sewage I estimate does not exceed 100,000 cubic feet per 24 hours and notwithstanding any future increase in houses and population probably will never exceed 300,000 cubic feet. I recommend there- fore that high class machinery in duplicate be installed capable of lifting 300,000 cubic feet per 24 hours and that pumps of a less costly character though not so economical in working be installed for the purpose of dealing with the larger volume ie. 1,470,150 cubic feet occasionally brought down during heavy rains."