HKU Bulletin May 2004 (Vol. 5 No. 3)

9 8 THE ENVIRONMENT Reducing the Environmental Impacts of Reclamation T he Department of Civi l Engineering is developing a new reclamation technique, which has the promise of being cheaper, faster and more environmentally friendly than current methods. Researchers aim to make land suitable for reclamation by sucking out air and water from soft marine clay below the seabed, to make it firmer and more suitable as foundation for buildings. Currently, the clay is either dredged and dumped elsewhere, which creates numerous environmental problems, or the water is squeezed out under the weight of several metres of rock and sand. The latter can take two years to make reclaimed land suitable for building on. The suction method to be tested by the Department is expected to make land suitable within only three to four months. It has already been tried in shallow waters in Japan and China, but the Department’s researchers want to develop it for use in deep marine waters. Vertical piles will be driven into the marine clay. A filter will be laid on top of the sea bot tom and covered with rocks and sand to prevent clay escaping. All of this will be enclosed in a vacuum system, in which a pump at ground level will suck the water and air up from below the seabed. The main cost will be the electricity to keep the pumps going. The project is led by Professor Lee Chack Fan, Professor: Chair of Geotechnical Engineering and has recei ved $3 mi l l ion f rom the Research Grants Council’s Central Allocation Vote. The Department will be working in collaboration with the Hong Kong Uni versi ty of Science and Technology. Negotiations are underway to conduct field tests at the Shenzhen Western Crossing and Professor Lee said the project could have application outside of Hong Kong. “In many parts of the world they don’t really need to reclaim land, but in Hong Kong and many coastal areas of China they do and they have to deal with this soft sediment,” he said. “The innovative part of this project comes from the potential for off-shore application.” Fish Stocks in Crisis F ish stocks have plummeted to some of the lowest in the world at the Hoi Ha Wan Marine Park, in Sai Kung, since its establishment in 1996. Over-fishing has reduced stocks on the coral reef by half, according to Dr Andy Cornish of the Swire Institute of Marine Science, who has just completed a six-year study. Although trawling, spearfishing and recreational fishing have been banned, commercial fishermen with a permit from the Agriculture, Fisheries and Conservation Department, continue to fish by hook and line, or with fish traps and gill nets. The result is that large coral fish are on the verge of extinction in Hong Kong waters. A survey of two other coral areas reveals a similar story of over-fishing. “We know from interviews with people who have been diving in Hong Kong for decades that large reef fish used to be found among these shallow coral communities. “In fact, a decrease in the size of fish is one of the main indicat ions of over-f ishing. Even though the number of fishermen with permits has declined in the last eight years there are still 280 working in the Hoi Ha Wan area. Each can do unlimited amounts of fishing.” Even in the coral community of Tung Ping Chau Marine Park, where fishing has been banned since 2000, the fish stock has not recovered. Cornish thinks this is because the area is too small to support roaming fish like parrot-fish. At Sharp Island, where there is no restriction on fishing, stocks have dropped by 80 per cent. “Fish are probably the most over-exploited marine source in Hong Kong and much more needs to be done to conserve them,” he said “ . I would l ike to see coral communities within the Marine Parks, and possibly some outside, made off- l imi ts to f ishing al together, to protect the biodiversity and to allow juvenile f ish to mature and reproduce before they are caught.” Cornish’s proposals would benefit local fishermen in the long- term. “They have little to gain by continuing to fish among corals as there are so few large f ish remaining,” he said. Project leader Professor Lee Chack Fan. Juvenile snapper. Photography: A. Cornish Fish trap.