Sessional_Paper_1901 — Page 133

Conclusion.

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11.-In conclusion, I would state that, in my opinion, the project is one that should be carried out at an early date. Some of the details of the design require re-consideration. The principal point to be decided is the feasibility of substituting a masonry for an earthen dam. To determine this some trial pits might be sunk, both on the site of the proposed reservoir and in the body of the reservoir.

17th August, 1900.

Public Works Department.

PUBLIC WORKS OFFICE, HONGKONG, 12th December, 1900.

KOWLOON WATER SUPPLY.

SIR-Referring to C.O.D. 29, I have the honour to report further on the proposed New Water Supply for Kowloon with special reference to Mr. O. CHADWICK's report.

2. Care will be taken to prevent the opening for cultivation of any more land in the gathering grounds, and early next year the area under cultivation will be surveyed and purchased from the natives. There are no buildings in the drainage areas, and none will be permitted. The uncultivated land will probably turn out to be Crown property, so far I am not aware that any claim to it has been put forward.

3. There is every reason to believe that the rainfall in this valley is quite as much as in British Kowloon. Being nearer the Tai-Mo-Shan range, which is the highest land in the New Territory and has peaks over 3,000 feet high, it is probably greater. As soon as a bungalow is built for the officer who will have charge of the work, a rain gauge will be established and steps will be taken to gauge the streams in the driest weather next year.

4. I entirely concur with Mr. CHADWICK as to the advantages a masonry or concrete dam possesses over an earthen one, and after a further careful examination of the ground, have found an excellent site for a masonry dam 600 feet lower down the stream than the site proposed by Mr. GIBBS for the earthen dam and 30 feet below it in level. At the site I now recommend adopting, two other considerable streams have joined that intercepted by Mr. GIBBS' dam, the combined waters passing through a narrow cleft over solid hard rock. It is evident that sufficient good stone for the dam can be obtained in the vicinity. The geological formation is similar to Hongkong and granite boulders in decomposed granite are plentiful.

5. By placing the dam at this lower site, the necessity for a catch water is done away with for some years to come, as the drainage area is increased from 333 acres to 417 acres. With a minimum rainfall of 30 inches on this area, we may expect to obtain a supply of 775,620 gallons daily. I pro- pose at first to construct at this site a dam 80 feet high with a top water level of 73 feet; this will impound 152,000,000 gallons. As the demand increases the dam can be raised 20 feet, thereby increasing the storage to 310,000,000 gallons, while 100 acres can be, when necessary, brought into the drainage area by a catchwater from No. 2 Reservoir site, increasing the collecting ground to 517 acres and the supply to 961,620 gallons daily. There is reason to expect from the rapid growth of British Kowloon that in ten years' time all this will be required.

6. A very great advantage connected with this lower site is the fact that a natural spill or bye- wash exists at the point marked on plan "overflow" which is 437 feet O.D. or 82 above the B.M. in the bed of stream at the new site for the darn. In this narrow saddle there is abundance of rock visible on the surface, and a rapid fall to the valley on the west, a better position in every way for a spill water could not be found.

7. By raising the masonry dam to the same level as the originally proposed earthen dam, I esti- mate that the reservoir would contain 310,000,000 gallons, but while designing the dam with a view to its ultimately being raised to that level, I would at first only provide for a height of 80 feet, or to O.D. 432. At the same time the site of the bye-wash would be cleared and levelled and the founda- tions laid of the waste weir, to be hereafter raised.

8. The level of the bottom of the stream at the point selected for the centre of the dam is 355 feet above O.D., but owing to the rapidness of the fall for a short distance above, very little storage will be lost by making the solid concrete foundations for the dam up to 10 feet above this B.M. I would propose cutting out all fissured, soft, or doubtful looking material, from the bottom of the stream, and doing a certain amount of benching in the bottom and sides, so as to form a good key for the concrete, and then filling up to 365 O.D., with good cement concrete in mass for the full width