CO129-459 - Individuals - 1919 — Page 268

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JAFFÉ ON HONG KONG WATERWORKS,

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in 15-inch courses. The piers supporting the arches of the road- way over the overflow-crest are of rough-punched ashlar in 18-inch courses, composed of stones weighing up to 2 tons each. These stones were bonded together from top to bottom of the piers with steel bars (11⁄2 inch in diameter), 3-inch holes being drilled right through them for this purpose and filled with cement grout after the bar had been inserted. The arches between the piers are of reinforced cement concrete, faced on both sides with ashlar.

All the granite for the facing, displacers and broken stone was obtained from three quarries in Taitam Bay. The stone was rough-dressed at the quarries and then transported by junk to a landing-stage near the site of the works, the distribution was by a light railway, and the elevation of the stone to the dam was effected by hand-hauling the trollies up a series of inclined-plane scaffoldings formed of China fir and bamboo poles tied together with bamboo lashings. The Chinese excel at this kind of scaffold- ing and can be relied upon to erect it sufficiently strong for the purpose for which it may be required. The facing of the dam required 164,858 cubic feet of ashlar and 59,400 cubic feet of rubble.

GENERAL.

The arrangements in the valve-tower (Fig. 5, Plate 1) for drawing the water from the reservoir comprise two 18-inch diameter stand- pipes, one in each valve-well, from which 15-inch draw-off pipes at intervals of 10 feet connect with the reservoir. Valves for con- trolling the draw-off pipes are placed within the valve-wells, external pen-stocks being also provided for cutting off the water in the event of damage to valve or pipe. The valves are operated by head- stocks and the penstocks by bevel gearing placed in the valve-house, which also contains a water-level indicator.

The roadway over the dam forms part of a road which encircles the greater part of the Island of Hong Kong, and as this road is now being widened and improved for motor-traffic, it was decided to construct the portion over the dam with a clear width of 16 feet between the parapets, so as to admit of two cars passing each other to get this width two corbel courses and one string course were required on each face of the dam. The road surface is of "granolithic," 2 inches thick, composed of 1 cement to 3 granite siftings (inch to dust).

The culverts through the dam were permanently closed in May, 1915 (2 years and 7 months after the signing of the contract), and

Papers.] LOW-LEVEL RESERVOIRS AND WORKS FOR PUMPING. 15

water was allowed to rise in the reservoir to 10 feet above the lowest draw-off, which enabled 86 million gallons to be pumped from it in that year. In 1916 the water in the reservoir was allowed to rise to 50 feet above the lowest draw-off, at which level the effective impound is 211 million gallons. In 1917 the dam was completed, and water was allowed to accumulate in the reser- voir throughout the year. The distribution of the rainfall during 1916 was

an unfortunate one, as out of a total of 79-8 inches 45 inches fell in May and June and only 24.7 inches during the latter 6 months of the year. The result of this was that the dry season, which proved to be a very severe one, opened with only 740 million gallons in store, and it became necessary to resort to drastic measures for the restriction of the supply. The reservoirs reached their lowest levels on the 15th May, 1917, when the aggregate storage only amounted to 69 million gallons (Fig. 7).

The prospect of filling the Taitam Tuk reservoir in 1917 was therefore a poor one, especially as none of the catchwaters for augmenting the drainage-area had been constructed. Nevertheless, though the rainfall for the year only amounted to 81 49 inches at the Observatory (80-37 Taitam gauge), 970 million gallons were collected by the 13th October, when the reservoir attained its greatest height of 80 feet above the lowest draw-off, or 20 feet below overflow level. The Intermediate reservoir was then at sill level and contained 196 million gallons, so that the total storage in the pumping-supply reservoirs amounted to 1,166 million gallons on that date. This quantity, in conjunction with the contents of the gravitation reservoirs (346 million gallons on the 13th October) assured full supply for the ensuing dry season.

PUMPING-STATION (Figs. 8, Plate 1).

The pumping station was constructed in 1904 to 1905, to accommodate the pumping-machinery installed in connection with the Intermediate reservoir, but the site was prepared with a view to enlargement for the additional pumping-plant required later for the Taitam Tuk reservoir. The engine-room was made of sufficient width for the bigger engines which would then be installed. The site is on the shore of Taitam Bay, and was prepared by cutting a plateau in the hillside at the level of 23 feet above L.W.O.S.T. The earth and stone removed in the course of the excavation was dumped into the sea to form a reclamation adjoining the plateau at a level of 12 feet above low water (4 feet above high water). This reclamation proved useful during the construction of the first

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