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EXISTING SEWERS.
In the early days of the Colony the drainage of the city of Victoria was naturally provided for by the streams traversing the numerous valleys running south to north. As the city increased lateral drains were constructed of brick and stone of a very imperfect character and some of these may still exist. Within more recent times, especially after the Reclamations between Queen's Road and the Praya had been made it became necessary, in order to maintain cleanliness and also for the convenience of the public to cover in most of these streams, large drains built of granite were therefore constructed along the valleys as shown by red lines on the plan which accompanies this Report. There are altogether without counting small branches 33 main outlets into the harbour along the Praya, their sizes vary from one foot and a half to six feet. Most of these sewers have vertical sides with V shaped or flat segmental inverts and are covered over with granite slabs. A full description of the various sections together with diagrams is to be found in Mr. CHADWICK'S Report Part 1, Sections 2 to 4. The duty of these drains as sewers is small compared with their duty as sub-soil and surface drains as the whole of the sub-soil and surface-waters from the northern slopes of the hills above the city have to find their way into the sea by passing through then.
The drainage-areas are comparatively small but the heavy tropical rains that this island is subject to, render it necessary to provide for the discharge of unduly large volumes of water in the lower portion of the city.
After studying the rain-fall and the character of the hills, I am of opinion that during heavy storms the built area may contribute 3 inchies and the hill sides above the city 2 inches of rain-fall per hour, over their respective areas. It is clear therefore that no half measures can be entertained for getting rid of the surface waters, and considering the surface levels we have to deal witli, any scheme for obtaining their ultimate discharge at points outside the city is practically out of the question.
Experience has proved that the existing drains of the town are of ample size and that they efficiently fulfil their purpose as surface water drains. It may also be mentioned that the most advantageous courses in respect of efficiency and economy č.e. the natural valley lines have in most cases been selected, and that the drains are constructed in a substantial manner. As surface-water drains therefore their construction leaves little to be desired, though they may no longer be suitable as sewers.
In the earlier days of the city the Combined System of drainage was undoubtedly by far the more economical system, and perhaps with the small population and limited public revenue at its disposal the Colony would have shrunk from the expense of a dual system, but when one considers the present position of the city, the limited area of land available for building purposes and consequently the excessive crowding that exists in many portions especially in the Western and Central Districts where the population reaches to as many as 1,600 persons to the acre, the time has, in my opinion, arrived when every endeavour should be made that modern sanitary science places within our reach, to improve the sewerage of Victoria.
The principal objections to the continued use of the existing system of drains for the conveyance of sewage are :--
(1.) that the numerous outlets along the Praya render the condition of
the foreshore objectionable,
(2.) that the large sizes of the sewers cause considerable deposit in the
lower levels during the dry season,
(3.) that no efficient means of ventilation exist.
The first two evils, from what I have said, cannot be remedied, and the third also presents considerable difficulty. In drains of such necessarily large size as to be able to discharge at times large volumes of storm water any such interruption as would be caused by large flaps or traps would probably lead to the bursting of the sewer, and further, during the dry season an extensive accumulation of sewer gas must take place, for the natural forces at work in the sewers are insufficient to effect a complete change of air in a short period. From what I have seen of soine of the branch drains I believe there still exist old drains in the city which should either be used for surface and sub-soil water only, or else replaced by pipe sewers.
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There are few water closets in the city their construction being prohibited by law. The system generally adopted for removing the excreta being the pail system as described in Mr. CHADWICK'S Report. I certainly agree with Mr. CHADWICK that if a sufficient water supply can be obtained the more general adoption especially iu Hotels, Clubs and large mercantile and other offices, of water closets would be advisable on sanitary grounds.
There is practically no sub-soil drainage in the city except in the Wonguei- chung Valley where such drainage has been carried out during the last six months.
PROPOSED WORKS.
After careful consideration of the whole of the foregoing facts and a close study of the locality I am of opinion that the ends of efficiency and economy will be best met by:~~~
(1.) the construction of a new system of pipe sewers admitting only a limited quantity of surface-water and by adopting out-falls for such a system at suitable points east and west of the city. (2.) the utilization of the existing drains for conveying the natural streams through the city and for carrying off surface and sub-soil
waters.
Though the sub-soil drainage of malarial soils is a matter of great importance to the Public Health, this will be impracticable in the lower parts of the city at present unless such sub-soil drains are connected with the sewers, an expedient that would be attended with serious risk for it would convert such sub-soil drains into channels for the escape of sewer air through the sub-soil into the houses them- selves. Owing to the long periods of drought or of limited rain-fall and to the steep declivity of the greater part of the drainage areas, the flow of water in sub-soil drains
In the latter case " will always be very variable and will no doubt very often be nil. drain traps attached to sub-soil drains will prove ineffective and sewer air will freely course through such drains and issue through the interstices provided for the escape of sub-soil water.
Further, in the case of any stoppage occurring in a foul water sewer with which sub-soil drains happened to be in communication, sewage might back into the sub-soil drains and escape through the joints as just described. These objections will be got rid of if all foul waters are diverted from the existing drains of the town into special channels of their own sub-soil drainage then becomes possible and may be led without risk into the present existing drains.
I will now briefly describe the new Separate System of sewers proposed. On looking at the plans it will be seen the city is naturally divided into four drainage districts. Three of these districts are situated to the west of the Albany Nullah, and one to the east. There are thus, four proposed main intercepting sewers which for the convenience of reference I will allude to as numbers 1, 2, 3 and 4, draining districts Nos. 1, 2, 3 and 4 respectively as marked on the accompanying plan.
Main No. 1 providing for the drainage of district No. 1 (coloured red on plan sheet No. 1,) will commence in Caine Road opposite Castle Road where it receives the sewage from Seymour Road, Castle Steps and Castle Road, it then takes a westerly course along the Caine Road, Bonham Road, Hill Road and Queen's Road West receiving the sewerage from Robinson and Richmond Roads, and ulti- mately discharging into the harbour at Belcher's Point.
The area of this district is 160 acres, and it is only thinly built over, but in order to allow for future extensions the sizes of the sewers have been calculated to discharge per 24 hours as much as 14 inches of rain-fall over the whole area.
Main No. 2 providing for the sewerage of District No. 2 (coloured brown on plan sheet No. 1,) will commence in Queen's Road Central opposite Pottinger Street and takes a westerly course along Queen's Road receiving the sewerage from those portions of the Chung-wan, Tai-ping-shan and Sai-ying-pun districts which are situated south of the Queen's Road. On reaching Centre Street this main will take a northerly course down Centre Street, and arriving at the Praya will turn again to the west and follow the line of the Praya where it will receive the sewage of a portion of the Shek-tong-tsui District and ultimately discharge into the harbour at the proposed ont-fall at Belcher's Point.
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