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ALTERATIONS & ADDITIONS TO EXISTING SEWERS.
11. If the salt water flush system were made general throughout the City and the existing outfalls were used for the discharge of sewage direct into the harbour, only very small alterations and additions to sewers would be necessary so far as can be foreseen and these are too numerous to show on plan-they would consist chiefly of alterations and additions necessitated by the laying of salt water mains, short lengths of new sca- venging lane sewers on Crown Land and new connections to sewers. It might, under a general flushing scheme be found that some of the old sewers, on reclaimed areas of the lower levels of the Western district, at present dealing satisfactorily with sullage, would require relaying.
I
12. If the system were made general through-out the City and it was considered that the existing sewer outfalls could not be used owing to harbour pollution, then the Colony must face a fairly costly scheme of drainage with modern Sewage Purification Works. have shown on plan two suitable sites for the latter-one at Causeway Bay where a small reclamation would be required and the other adjoining the Destructor and Engine House at Kennedy Town; the treatment would be the activated sludge process, being highly efficient, requiring small land area, comparatively low cost of installation and low main- tenance charges. The sewage now passing through the water front would be intercepted lifted and diverted through two intercepting sewers running east and west, by air lift pumps or ejectors fixed in required positions which would be operated by Air Compres- sors through low pressure air mains from the Engine House at Kennedy Town. The power required for operating the activated sludge plant would also come from the same source though it might be found desirable in the case of the plant at Causeway Bay to provide independent power. With regard to existing drainage, a complete survey of ex- isting conditions will be necessary to ascertain what volume of storm-water, at present entering the sewers, must be eliminated. This I regret, is a matter which, on account of pressure of other work in making good storm damage, I have been unable to under- take up to the time of my departure on leave.
FRESH WATER SCHEME FOR MIDDLE LEVEL ZONE.
1. Population:-The population in this zone is estimated as follows:
200 houses East of Garden Road at 20 persons per house 500 houses West of Garden Road at 20 persons per house University, Schools, Hospitals &c.
Total
4.000
10,000
2,000
16,000
All areas south of Pokfulam Road, Caine and Kennedy Roads referred to in the latter part of 5 could, if it were thought desirable, be dealt with entirely separate from the low level zone described in 1 to 10 and in order to obtain the necessary data on which to base the scheme, gaugings to ascertain the minimum dry weather flow of all streams on the north face of the Island have been carefully taken at the required elevations during December and January and will be continued throughout the dry season to ascertain any diminution of flow.
The rainfall for the four months October, November, December 1926 and January 1927 was 3.275, 4.965, .455, .310 inches, a total of 9.005 inches compared with an average of 8.96 inches for the last 15 years, from which it may be said that the minimum gaugings which have been taken, represent an average dry weather flow that can be relied upon for a fresh water flushing supply.
The present population in the district which it is proposed to serve is estimated to be 16,000 and the estimated increase during the next 30 years say 20% which at an average of three 2 gallon flushes per day per person or 6 gallons a day will require (19,200 × 6) say 115,000 gallons per day.