ENG-1960 — Page 37

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REVIEW

included compensation to villagers and anti-malarial and medical staff, and made no provision for service reservoirs and trunk mains to distribute the water into Hong Kong and Kowloon, nor for the catchwaters. The revised scheme provides for a higher dam, and for storage of some 5,400 million gallons instead of only 4,125. The reservoir will thus be larger than Tai Lam Chung (4,500 million gallons) and will increase the total storage capacity of the Colony's reservoirs by 50%. The project will be capable of delivering a peak supply of 35 million gallons a day and the average yield is expected to be about 26 million gallons. The dam itself will be 2,300 feet long at the crest and will rise to a height of 180 feet above the original ground level. The maximum width at the foot of the dam will be 1,200 feet, tapering to 20 feet at the top. An earth dam of these dimensions requires vast quantities of materials, estimated at 5.3 million cubic yards, all of which will be found on the site. The direct catchment area draining into the reservoir measures three square miles; this will be supplemented by 9.6 square miles of indirect catchments, the water being led round or through the intervening hills by 15.3 miles of concrete catchwaters and 3 miles of tunnel.

A reservoir of this type, constructed largely of earth, cannot be allowed to overflow, for the water would quickly erode the top and downstream side of the dam. A bellmouth at the maximum permitted level of the reservoir will allow for over topping, and the surplus water will escape to a tunnel blasted through the hillside at one end of the dam, and so out to sea. This tunnel has been designed to cope with a catastrophic intensity of rainfall, being 17 feet in diameter and lined with concrete. Special measures will prevent silting inside the tunnel. A supply tunnel will draw off water from the reservoir to a pumping station, and from there the water will go to a filtration plant on high ground overlooking Silver Mine Bay. The filters will be of the latest rapid gravity type and the water will also be chlorinated and fluoridated. The filtered and treated water will gravitate from a small service reservoir to Hong Kong Island through two 30- inch diameter steel pipes laid in a trench on the sea bed and protected from corrosion by the most up-to-date methods. The sea crossing is about eight miles long and the laying of the pipeline will be one of the most difficult operations in the whole project.