Sessional_Paper_1901 — Page 131

REPORT ON WATER SUPPLY OF KOWLOON.

BY

OSBERT CHADWICK.

127

Existing Works.

1. The existing works were projected by myself whilst in Hongkong in 1889-90. The main feature of their design was to obtain a supply, from sources within the then limits of British territory. Now that the hills, inland, have been annexed, it is but reasonable that an augmented supply should be obtained from them by gravitation.

Feasibility of Proposed Works.

2.-The proposed works are quite feasible, and may safely be sanctioned, as regards the first instalment, providing 590,000 gallons a day. The gathering grounds of sources 1 and 2 should be forthwith expropriated, and no buildings should be permitted upon them, so No. 2 will be available for future extensions.

As regards the other sources, the Government should acquire a lien upon them, so that they may be acquired on reasonable terms if required in future.

Probable Supply.

3.--The probable supply is correctly estimated, according to the data obtained by actual experience in Hongkong, on the assumption that the rainfall is the same in amount and distribution on the main- land, as it is in Hongkong. It is probable that such is the case, but not absolutely certain. Short of actual measurements, made over a number of years, there is no means of predicting, with certainty, the actual quantity of water which will flow off from a given gathering ground. To make such prolonged measurements would unduly postpone the construction of the works. The only plan is to base the calculation upon the Hongkong data. In my report of 17th September, 1896, I analysed these data using a train of reasoning somewhat different to that adopted by Mr. COOPER, in his report of 1896, and arrived at the following conclusions. They agree closely with Mr. COOPER's conclusions.

(a.) That the minimum annual available rainfall amounts to 30 inches.

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(b.) Therefore a gathering ground of 1,000 acres will afford 1,860,000 gallons per diem in

the year of minimum rainfall.

(c.) That to provide this quantity 200 days' storage will be required.

The gathering ground of proposed source No. 1 is 333 acres, or one-third of 1,000. A supply of 1.800.000 620,000 gallons a day may, therefore, be expected, and to secure it, a reservoir capacity of 124 millions of gallons will be required. The desired immediate supply is only 413,000 gallons, and the proposed reservoir contains 120,000,000 gallons. According therefore to Hongkong data there is a liberal margin; and there can be little doubt that a bountiful supply will be obtained. The actual amount must remain in uncertainty until the works are completed. It is desirable that rain gauges should be forthwith erected on each of the proposed sites. Observations should be commenced Comparison of the first year's observations with present and past observations at the Observatory, will afford a means of correcting the estimate of probable yield.

at once.

Material of Reservoir Dam.

4. It is proposed to make an earthen dam with a puddle wall in the centre in the ordinary manner, at sources Nos. 1 and 2, on account of apparent scarcity of good building stone.

} must, however, record my opinion that a masonry or concrete dani, like that at Tytam, will be far preferable, even if it cost somewhat more. With a masonry dam, a leakage merely amounts to a loss of water. With an earthen dam, it may result in destruction. I therefore recommend that careful examination be made for building stone, before earth is decided upon as a material. I have never visited the mainland, beyond the former frontier; but I presume that the geological formation is similar to that of Hongkong, where solid masses of granite are found imbedded in decomposed granite; but not visible at the surface. If I remember rightly, in the Tytam Valley, in its original condition, very little rock appeared at the surface; yet plenty of stone was obtained. It must be clearly understood that, with care, a thoroughly efficient and safe reservoir can be constructed. I merely assert that, if stone can be obtained, masonry or concrete is a preferable material.