【明報專訊】High Island Reservoir (萬宜水庫), the largest water storage facility of Hong Kong, came into operation 35 years ago today.

1. Background

The Hong Kong British government first came up with plans of building High Island Reservoir in 1969. At that time, a number of new reservoirs had just been completed, including Plover Cove Reservoir (船灣淡水湖), the world's first "reservoir in the ocean". But they had proved insufficient to tackle Hong Kong's water shortage problem. For some time in the 1960s, water was supplied only once every four days.

The government designated the part of sea between the southern coast of Sai Kung Peninsula (西貢半島) and High Island (糧船灣洲) as the site of the new reservoir. Construction involved building two huge dams east and west of the site, pumping out sea water and building pipework (管道). The project was handled by the UK engineering consultancy Binnie & Partners.

2. Construction of High Island Reservoir

Construction of the new reservoir began in 1971. It was an extremely complicated project. Workers first enclosed the site with cofferdams (圍堰), separating it from the sea. Sea water was pumped out before the seabed was cleaned of clay and sand. Then the construction of the two dams began. The eastern dam, which faces the South China Sea (南海), measures 1,593 feet in length and 348 feet in height, while the western one is 2,470 feet long and 333 feet tall. The eastern dam is accompanied by a large concrete (混凝土) groyne (防波堤) to prevent erosion (侵蝕) by the sea. Three smaller dams were also erected.

High Island Reservoir is supplemented by pipework. It includes a 74,000-feet-long tunnel that leads water to a water treatment plant in Sha Tin, smaller tunnels that collect water from rivers and streams and a waterway that connects High Island Reservoir to Plover Cove Reservoir.

It is estimated that as many as 13,000 workers took part in the construction of High Island Reservoir. It was tough work for them. Some recall 12-hour workdays and frequent accidents. Official figures state that two foreign architects and three local workers lost their lives building the reservoir. Some believe that the toll was heavier.

The project was completed in November 1978 and came into operation on 9 February 1980. It has a capacity of 280 million cubic metres.

3. Geological Value

High Island Reservoir is part of Hong Kong Global Geopark (香港世界地質公園), which is listed by UNESCO (聯合國教科文組織) as part of its Global Geoparks Network (世界地質公園). The High Island Geo Trail (萬宜地質步道) is surrounded by geological delights such as hexagonal rock columns (六角形岩柱), faults (斷層), distorted rock columns and an intrusive dyke (侵入岩牆). The eastern dam of the reservoir commands a magnificent view of the sea stacks (海蝕柱) of Po Pin Chau (破邊洲), a geological feature formed by the erosion of rocks by the sea.

4. Water supply in Hong Kong

Hong Kong's two main sources of water are rainfall from natural catchment and supply from Dongjiang (東江) in Guangdong. The latter is now the major single source of raw water supply for Hong Kong.

There are 17 reservoirs and 9 irrigation reservoirs (灌溉水塘) in Hong Kong. They are open to the public for fishing off the breeding season.

The Water Supplies Department (水務署) also supplies sea water for flushing purposes to nearly 80% of the population.