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(2.) The scheme would not deal with one of the most important points, .e., the elimination of sewage, which at present enters the Harbour of Refuge by existing drainage.
(3.) It involves the laying of considerable lengths of C.I. sewer through sea water logged ground at depths varying from 0-15 feet approximately below Ordnance Datum.
(4.) The laying of the sewer at such a low level might endanger the stability of
old Chinese property which has been built on reclaimed areas.
(5) The cost of construction due to item (3) would be very heavy and the possi-
bilities of damage due to (4) could not be ignored.
(6) The maintenance supervision would absorb most of the time of an additional
overseer and would require a permanent Chinese Staff.
(7.) The annual cost of pumping would be fairly considerable.
A pumping scheme therefore is not to be recommended if a solution of the problem can be found on other lines, broader in scope, more flexible in character and less costly in construction and maintenance.
What I have in mind is a scheme the operation of which is based on utilizing flood tides as a motive power for flushing and operating the system. It is a
It is a problem of providing, if possible, a self-cleansing sea water conduit and the main principle hinges upon tidal range at its worst phase, which governs the efficiency of any such scheme at that period.
I am now working on these lines, but owing to pressure of other work, the result of storm damage, I have been unable to obtain all the required information, but will report as early as possible.
In addition to preparing the necessary sections to ascertain how such a scheme would fit in with the existing storm water drainage system of Kowloon, a considerable amount of work is also involved in obtaining the necessary data from tide graphs, as to yearly tides and the periods of time which can be safely reckoned upon for charging and discharging, consistent with obtaining the necessary self-cleausing velocity.
13th May, 1921.
Annexe 9.
E. NEWHOUSE.
Hon. DIRECTOR OF PUBLIC WORKS,
(a.) I now beg to forward plan of a scheme of drainage of the Western portion of Kowloon Peninsula on the lines suggested in my minute of 13th May, 1921. The proposal consists of two 42" low pressure intercepting tank sewers charged at flood tides from suitable existing storm-water culverts and nullahs along their lines of route and flushed on the ebb tide by sea water impounded in the Waterloo Road Nullah.
(b.) The attached table (1) of tidal ranges (high tide followed by the next succeeding low tide) for 1921, which vary only very slightly from those of other years, shows in italics the tides below 35 feet range when a velocity of less than 24 feet per second is obtained.
(c.) Accepting 24 feet per second as a safe cleansing velocity for sewers of this size it will be seen that only on 76 days in the year does the velocity fall short of the standard, and, as such days are well distributed with alternate periods of very high tides and consequent high velocity of discharge, I consider that no fear need be enter- tained as to the system being self cleansing. It might be argued that tides, affected by wind are unreliable, but it would appear, that wind adversely affecting a flood tide would generally act beneficially on the ebb.