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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 calculate:l to disebarge 2.40 inches of rain-full 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 area draining below Ice House Lane to the west which 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 insure 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 calenlated to discharge 14 inches of the rain-falling over the whole District. As just stated, I am only able to recom- mend the construction of the out-fail 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 14 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 14 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 thongh not so economical in working be installed for the purpose of dealing with the larger volume že. 1,479,150 cubic feet occasionally brought down during heavy rains.
( 17 )
The sizes and gradients proposed for the new sewers have been the subject of careful calculation the aim and intention being to maintain a self cleansing velocity throughout the whole system. Considering the existence of large drains through- out the city and the facilities offered for getting rid over the surface of the storm- water in back yards during heavy rain-falls I am of opinion the sizes proposed for the new sewers will be found ample to meet the requirements of the increasing population.
The Separate System as designed contemplates the provision of overflows along the lines of the proposed intercepting sewers in order to relieve them in case it should be found impracticable for the present to exclude from them as much of the storm-water as I have specified. In many instances the rain from the back yards of private houses will be admitted into the proposed new sewers but. where back yards are continuous from one street to another such storm water can easily be diverted from the sewer by a continuous surface gutter from yard to yard, iron gratings being fixed in the communication holes at each partition wall. Some rain- fall from the backs of houses nust, under any circumstances, be admitted into the proposed new pipe sewers but the special method of providing for the carrying off of storm-waters from private premises is a detail that must be considered indivi- dually in each case.
The proposed sewers are intended to be laid out in straight lines and man- holes are provided at every change of direction in order to facililate inspection or As a rule every the removal of obstructions should the latter at any time occur. manhole will be furnished with a ventilating grating to be placed as near as Additional ventilators will also be provided possible in the middle of the street.
Flushing wherever the interval between two manholes is longer than 350 feet. doors will also be provided in some of the manholes on the mains where the full or inclination is stall, and for the purpose of obtaining a rapid change of air in the sewer and of preventing a decided set of air therein to one point, traps and The out-falls will be protected by valves will be fixed in some of the manholes. tidal valves.
I have not considered it necessary to design any systein of sewers for Kennedy- town situated at the extreme west of the city, as that suburb is at present very sparsely built over, and because sewers can at any time without difficulty be cou- structed leading into the Sulphur Channel, the scour through the Sulphur Channel being sufficient to prevent any nuisance therefrom.
HOUSE-DRAINS.
As I am here dealing with the subject of main-drainage and not of house- drainage I need not enter very fully into the question of house-drains though I need scarcely add I have considered this matter very carefully before laying the scheme I would however state for the proposed main sewerage of the city before you. that in my opinion, Ordinance No. 24 of 1887 together with the Bye-Laws now before the Sanitary Board clearly define what a house-drain ought to be and only place such restrictions on house owners as are placed on them in England and as I have found necessary in my experience as a Sanitary Engineer.
Unless house-drains are properly constructed under such sanitary provisions as those contained in the Bye-Laws above referred to they will be practically worse than no drains at all, and considering their close proximity to buildings, house- drains obviously require even more careful supervision than main sewers.
I consider that it cannot be too strongly impressed upon the public mind that it is to the connexion with the Government inain sewers, of badly laid out and badly built house-drains in private premises, wherein the house-sewage, is imprisoned for long periods, and therefore entirely decomposed before it leaves such private premises to pass into the Government mains, that is to be attributed the chief cause of foul emanations from the main sewer-openings in the streets and elsewhere, and that therefore the first or initial step towards sanitary reform is obviously the reconstruction of honse-drains. It is therefore of the utmost importance that defective bouse-drains should be dealt with as soon as possible and I see no reason why this should not be done at once under the powers conferred by the Public
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