Sessional_Paper_1896 — Page 263

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In the consideration of this matter it must not be lost sight of that the Taitam project of 1873 was for the supply of water to 92,000 persons, at the rate of 13.57 gallons per head giving a total daily supply of 1,248,000 gallons, a result which was more than realised during the unprecedented dry year of 1895. Unfortunately, the works were not completed till 1889 by which time the popula- tion had increased to upwards of 170,000.

FUTURE REQUIREMENTS.

140. It is estimated that the population of the City and Hill Districts is increasing at the rate of 5,000 per annum.

If this rate be maintained, the rate of consumption of water being taken at 15 gallons per head per diem (see paragraph No. 125), the annual increase of water required for distribution will be 27,375,000 gallons or at the rate of 75,000 gallons per diem.

141. The existing works with the proposed extensions are estimated to yield a minimum of 3,200,000 gallons per diem or sufficient for a population of 213,000, so that by the end of 1899 it is probable that the requirements of the City and Hill Districts will have outgrown the supply obtain- able from these works during years of comparatively small rainfall.

142. As the construction of works of the nature required to meet this increased demand for water will occupy some time, I have considered projects for still further increasing the present water sup- ply, and now propose to briefly describe what appears to be the best practical solution of this question. 143. It must be remembered that the sites available for reservoirs are very few and owing to the steepness and narrowness of the valleys, do not admit of the construction of extensive impounding reservoirs.

144. With a view to ascertaining the most suitable sites for the construction of reservoirs, detail surveys have been made in the Pokfoolum and Taitam valleys, and the following projects are submitted.

PARTICULARS OF PROPOSED WORKS TO MEET FUTURE REQUIREMENTS.

POKFOOLUM VALLEY.

145. Proposed Reservoir.-In the Pokfoolum Valley a suitable site exists below the present reservoir as shown on Drawing No. 2 for the construction of a reservoir having a capacity of 78,000,000 gallons and catchment area including that of the present reservoir of 500 acres.

This reservoir would be formed by the erection of a concrete and masonry dam across the ravine

a little above the existing bridge on the Aberdeen Road as shown on Drawing No. 3.

The top water level would be 480 feet above Ordnance Datum, and the maximum depth of water below overflow level 40 feet.

The Valve Tower and outlet works are situated in the north-west corner, the level of the lowest draw-off being 450 feet above Ordnance Datum. A wash-out pipe only is provided through the dam,

The waste weir is located on solid ground at the south-eastern extremity of the dam and has a total length of 110 feet which is ample with an overflow of 4 feet 6 inches to discharge the water flowing from the catchment area during such extraordinary rainfalls as the one occurring in 1889.

The Overflow Weir and Bye-wash Channel to be constructed of masonry and cement concrete throughout.

The construction of this reservoir will necessitate the raising of the Aberdeen Road skirting its western bank and the diversion of the southern portion as shown on Drawings Nos. 2, 3 and 4. The material for raising the road and portions of Farm Lots 18 and 19 to be obtained from the area of the reservoir, the banks of which are to be formed as shown on Drawing No. 4, the western bank being composed of filled in material it is proposed to pitch with stone.

The construction of this reservoir will further to some extent encroach on Rural Building Lot No. 51 and Farm Lots Nos. 18 and 19 and involve the destruction of the small village of Pokfoolum. 146. Proposed Main. The elevation of the site does not admit of the discharge of the water from the proposed reservoir into the existing Pokfoolum conduit. It is therefore proposed to provide for the water being conveyed in a cast iron main 12 inches in diameter contouring the hillside on the west of the Pokfoolum Road till it reaches the northern boundary of the Chinese Christian Cemetery. From this point the main to be reduced to 10 inches in diameter and follow the line of the Pokfoolum Road as far as Shektongtsui Nullah where it enters Crown land and terminates in the proposed filter beds situated near the Bonham Road pumping station.

This main will be capable of discharging 1,500,000 gallons per 24 hours.

It is also proposed to connect the existing outlet pipe from the Pokfoolum reservoir to this main and extend the latter to join the conduit near the present filter beds. In case of necessity this main will be available for the purpose of conveying water from the existing reservoir to the present filter beds at the rate of from 600,000 to 1,000,000 gallons per 24 hours according to the level of the water in the reservoir.

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