Q 77
P.W.E. Hongkong.
133. Tytam Tuk Scheme, Second Section.-Very good progress was made with the construction of the dam. To enable the extent of such progress to be realized, the fact may be recalled that, at the end of 1914, the total length over which excavations had been completed and concreting had been undertaken was 470 feet, whilst the height to which the concrete and masonry of the dam had been constructed varied from 32 feet below to 40 feet above Ordnance Datum.
By the end of 1915, the total length over which excavations had been completed was 630 feet, whilst the height to which the concrete and masonry had been carried varied from 35 to 59 feet above Ordnance Datum. The height to which construction had been carried above the deepest part of the foundations, namely, where the dam crosses the old streambed, was 77 feet.
In all, 9,534 cubic yards of soft material and 2,556 cubic yards of rock were excavated during the year. The quantities of cement concrete deposited and of granite ashlar set were as follows:-
Fine cement concrete, 8,722 cub. yds. Hearting concrete, containing granite displacers, 39,968 Granite ashlar, 49,074 ft. 31In order to provide for impounding water during the dry season, the culverts were permanently closed with masonry and concrete at the end of May and, in September, the valves on the wash-out pipes were closed to enable impounding to be begun, but, as the rainfall during September proved to be considerably below the average (5.71 inches compared with an average of 9.67 inches), it appeared as if little advantage would be gained from the new reservoir. The deficiency of rainfall during September was however made good in October, when 11.71 inches fell, resulting in filling the new reservoir to more than half its capacity at that period. The water attained its maximum height on the 10th November, when it stood at 10 ft. above the lowest draw-off, at which level the effective impound is 57 million gallons.
Pumping from the new reservoir was begun on the 22nd October and continued throughout the remainder of the year. In all, 853 million gallons were pumped from this reservoir up to the 31st December. During the period mentioned, (22nd October to 31st December), the accretions from streams flowing into the reservoir amounted to 803 million gallons, or 110 million gallons per day.
The laying of the two additional 18" cast iron rising mains from the pumping station to the gauge-basin at the inlet of the Tytam tunnel was completed. The laying of the two 18″ suction mains from the draw-off tower of the low-level reservoir to the pumping station was also completed.
As the 18" cast iron suction main laid in 1905-06 from the intermediate reservoir to the pumping station would have been submerged by the waters of the new low-level reservoir for practically