26
(Enclosures.)
PUBLIC WORKS DEPARTMENT,
HONGKONG, 17th October, 1903.
SIR,-I now have the honour to submit a plan and estimate of the works which I propose should be undertaken at once in connection with the Tytam Tuk Scheme for augmenting the City and Hill District Water Supply.
2. The trial works which have hitherto been carried out show that it is ques- tionable whether the site which appeared so admirably adapted for the construction of a dam of moderate dimensions and having a large impounding capacity will be the most favourable, and, with a view to proving this, it is advisable that works of a similar nature should be carried out on other sites. Such works have already been put in hand on two alternative sites somewhat further inland, at either of which, in order to obtain an equivalent capacity, a dam of greater length and of greater height above ground level than at the site originally selected will require to be constructed. In consequence, however, of the great depth to which the founda- tions would extend in the case of the latter and the difficulties which would be created by having to go to such a depth, it is probable that one of the alternative sites may be found more economical and may admit of the work being executed more expeditiously.
3. The carrying out of such an important undertaking, which is designed largely to meet future requirements, will evidently occupy a somewhat prolonged period, and it is desirable that some works to meet present requirements should be undertaken at once.
4. Meanwhile, as the gauges recommended by Mr. CHADWICK have been con- structed at suitable points in the valley, information will be obtained which will be of much value in more accurately estimating the yield of the drainage area than is possible with any information hitherto available.
5. The supply rendered available by the existing works for tiding over the dry season is as follows:
Maximum contents of Tytam Reservoir,
Pokfulam Reservoir,
Gallons. .407,000,000
70,400,000
Tytam Bye-wash Reservoir,. 30,000,000 Wongneichung Reservoir,... 33,900,000
Do. Do.
Do.
Yield of streams intercepted by reservoirs, conduits,
&c., say,
100,000,000
Yield of streams rendered available by pumping from
Tytam Tuk streams, say,
.100,000,000
Total,......
741,800,000
6. The Bye-wash Reservoir and the Pumping Plant for rendering available the dry-weather flow of the Tytam Tuk streams are practically completed and are therefore referred to as existing works.
7. Assuming the daily consumption at 4 million gallons, the existing works may be said to afford 185 days' supply. Under ordinary circumstances, the daily consumption would require to be estimated at a higher figure, but. with the in- troduction of rider mains, it should be possible to keep it well within the quantity stated during the next few years notwithstanding the constant increase in the population. As some time must clapse before the rider-mains can be introduced, however, it is advisable not to assume too low a figure.
8. After full investigation, I now propose to undertake the construction of a dam on the site (No. 4) referred to in Mr. COOPER's report of the 9th May, 1896, (vide plan). By increasing the height of the dam to the extent of 20 feet beyond what he proposed, its impounding capacity will be raised from 100 million gallons to 194 millions, a quantity which the pumping engines now on order will be capable