June_1971 — Page 46

N

TAI

FROM PLOVER COVE RESERVOIR

LOWER SHING MUN

RESERVOIR

SHA TIN

TREATMENT WORKS

SHA TW

TOLO HARBOUR

LEGEND

PLOVER COVE RESERVOIR

DAMS TUNNELS CATCHWATERS

PIPELINES

PUMPING STATIONS

CATCHMENT AREA

FEEDER ROADS

ACCESS ROADS

VILLAGES TO BE REHOUSED REHOUSING AREA

MA ON SHAN

SPILLWAY

SAI KUNG

LONG HARBOUR

WEST DAM

HIGH ISLAND RESERVOIRU

HIGH ISLAND

DO)

TO DISTRIBUTION SYSTEM THROUGH LION ROCK TUNNEL

PORT SHELTER

HIGH ISLAND WATER SCHEME

Work has already begun on the construction of access roads to the dams and tunnel portals, estimated to cost some HK$40 million. It is expect ed that the tunnels will be ready for service in 1975.

International tenders for the con- struction of the main dams will be in- vited at the end of this year. Com- panies from Britain, France, Italy, America and Japan have already ex- pressed an interest in the contracts. The reservoir will start to impound water in the wet season of 1976 and will contribute to the colony's water needs in the 1976/77 winter.

Mr. Robson explained that pro- posals for the High Island scheme were first put forward in a report on the overall development of the colony's water resources which was received in 1967. Government then commissioned the consulting engineers, Binnie & Partners, to report on the practicabili- ty and economics of such a scheme in relation to modern methods of ex- tracting fresh water from the sea.

He said: "Whilst the consulting en- gineers have reported that this scheme is both practical and economical when compared with the cost of converting

36

sea water into fresh water, because of the shortage of further watersheds it will be the last conventional water scheme of this size to be undertaken in Hong Kong'.

Huge rock dams

The High Island reservoir will be formed by the construction of two huge rock dams rising 210ft. above sea level and 340ft. above the lowest foun- dation level. One will be 2,500ft. long and the other 1,500ft.

At top water level the reservoir will be 31⁄2 miles long and 2 miles wide, and will cover an area of about 1,700 acres.

In addition to the two main dams, three smaller rock dams will be built to seal the neighbouring valleys against overflow when the reservoir water level rises above 170ft. These three dams, one on High Island and two on the mainland, will be 550ft., 125ft. and 63ft. in length.

A concrete siphon bellmouth spill- way some 60ft. in diameter will be constructed to the north of the west- ern main dam and will discharge sur plus water through a tunnel into the plus water through a tunnel into the sea at Yuen Ng Fan. The reservoir, at

EAST DAM

its eastern end, will be 200 ft. deep three times deeper than any point in Plover Cove.

It will be necessary to dredge 81⁄2 million cu.yd. of material from the seabed in order to establish suitable foundations and 16 million cu.yd. of rock and earth will be required to form the dams.

Water will be led into the reservoir via a network of subsidiary tunnels leading to a main tunnel joining High Island reservoir, the Sha Tin treatment works and the lower Shing Mun reser- voir.

Normally, water will be led into the tunnel system through stream in- takes built into the hills, about 350 ft. above sea level, but in cases where large watersheds lie below villages, low-level pumping stations will be built to deliver water up to the tunnel system.

Depending on the level in the High Island reservoir, water from it will either gravitate or be pumped to the treatment works at Sha Tin. A pump- ing station for this purpose, with a capacity of 120 million gallons a day, will be built at Pak Tam Chung, near the western dam.

Far East BUILDER, June 1971