October_1970 — Page 35

5,150 million gallon

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boost for Singapore reservoir

SIMPLY by further exploiting the na- tural catchment area of an existing reservoir, Singapore's Public Utilities Board has added an extra 30 million gallons a day to the republic's total water supply, and in doing so has creat- ed its largest reservoir capacity 5,300 million gallons.

Seletar reservoir has been enlarged 35 times from the original capacity of 150 million gallons. It now has a sur- face area at top water level of 800 acres and maximum depth of 56 ft.

The extension of the reservoir was first conceived in the 1950's when it was realised that full use was not being made of the catchment area. But with priority being given to other projects it was not until 1960/61 that surveys and ground investigations began. Con- struction work eventually started in 1967.

Binnie & Partners (Malaysia) were appointed as consultants for the design and construction of the main dam, saddle dam and ancillary works of the reservoir, while the Board's own staff in the Water and Architectural Depart-

BINNIE & PARTNERS (MALAYSIA)

ments engineered the necessary exten- sions to the associated Woodleigh Treat- ment Works.

Impounding of water commenced as scheduled at the end of August 1968 and the dam was brought up to crest level in mid-November 1968.

There is a feature about Seletar which has confirmed the direction of the Board's planning for the future. Unlike Singapore's two impounding reservoirs, MacRitchie and Pierce, Sele- tar does not depend entirely on the rain that falls within its catchment to fill the reservoir. Seletar has an addi- tional source of supply from eight streams to the north and west of Sele- tar. The water from these streams is

collected and pumped into the Seletar Valley to increase the natural flow from its catchment.

This involved the construction of an intake structure at each stream and a small concrete-lined basin on high

consulting engineers

ground near the stream. Water is pump- ed into this basin from the intake pump- ing station which is by the side of stream.

A relift pumping station pumps the water into Seletar reservoir through steel delivery pipelines which cross the watershed at three points and release the water down concrete-stepped cas- cades for maximum exposure to air and sunlight.

To permit water from Seletar to be transferred to Pierce reservoir and thence to the Woodleigh waterworks, a new pumping station was constructed adjacent to the existing pumping sta- tion at Seletar.

Clay core

The Seletar reservoir consists of the principal dam, 100 ft. in height from its foundation to the top, but 65 ft. from the original ground level - a quarter of a mile upstream from the

Far East BUILDER, October 1970

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