No_3_March_1969 — Page 37

PROP PHASE

DIVERSION

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मिलक

macritchie

PROP. PHASE | DIVERSION

Civil engineering and public works

Proposed phase I diversion to Ulu Pandan Proposed phase li diversion to Sg. Kailang Balance to Bukit Timah/Rochor canal

Existing Bukit Timah canal catchment

2600 Ac

3000 Ac

1700 Ac

7300 Ac

roa

PANDAN

OUTLET

Imfora canal

BUKIT TIMAH FLOOD ALLEVIATION SCHEME

PHASE 1 DIVERSION TO SUNGEI ULU PANDAN

PHASE II DIVERSION TO SUNGEI KALLANG

-N-

KEY PLAN

2 mi.

Two-stage scheme will end Bukit Timah floods

THOUGH not of the type associated with devastating destruction, floods in Singapore occur regularly in many parts of the island.

The drainage catchments are very small, the largest having an area of only 17,800 acres (27.8 square miles). Excluding swamp land, the total area subject to floodings is not less than 9,300 acres, which is 6.5 per cent of the country.

The island has a characteristic equatorial climate with plenty of sun- shine and an abundant rainfall all through the year. Temperatures range between 67 and 95 degrees F. Long- term averages depict a similarly even distribution of rainfall of 6 to 8 in. of monthly precipitation, except in the three months period from November to January when the north-east mon- soon brings in more frequent rains averaging around 10 in. a month thereby iifting the monthly total to about 95 in.

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Floodings in Singapore generally occur in the form of flood water cover- ing the roads or used land to a depth of about 1 ft. to 5 ft. for a duration of half an hour to about 24 hours.

The cause of this flooding is three- fold: the low-lying nature of the land, the rapid development of the land, and an inadequate drainage system.

A typical inundation, which has become a commonly known fact in Singapore, is the flooding of the Bukit Timah canal. The 50,000 ft. long canal serves the drainage of a catchment area of 7,300 acres (111⁄2 sq. miles). It runs along the trunk road which connects the city to Johore Town of Malaysia. Its summit is at 81⁄2 m.s. Bukit Timah Road and it flows along the main road through the city to the sea. The last stretch of 10,000 ft. is right in the mid- dle of a densely populated town.

The canal floods regularly during the north-east monsoon season for three or four times a year, covering

an area of about 920 acres. During the flood certain parts of the main road would be under a depth of up to 4 ft. of water for up to 24 hours. Traffic would be disrupted, damages sustained and fairly chaotic conditions would result in some areas.

It is interesting to note that at- tempts were made as early as 1935 to alleviate the Bukit Timah floodings, but no substantive effort was made until quite recently.

The present-day effort is more ur- gent for two reasons: first the frequency and severity of the floods has increased with the rapid development within the catchment, and second, losses caused by flooding have become more serious because of the more intensive develop- ment of the area.

Choice of scheme

In a country like Singapore where rainfall is heavy and concentrated and where flood reservoirs are not available

Far East BUILDER, March 1969

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