Working underneath the seabed does not constitute reclamation, the Airport Authority said yesterday in defence of its decision to carry out a trial project for the proposed third runway without first informing the public.
The 'deep cement mixing' project took place in January and February and drew criticism from environmentalists because it was not gazetted. It involves injecting cement into soft mud pits to form pillars, which then become the base for reclamation work.
WWF Hong Kong said the work created a bad precedent for the government to reclaim seabed wherever it liked.
But Tommy Leung, the Airport Authority's general manager of projects, said it sought advice from the Department of Justice before starting the project and was told it did not contravene any laws.
'The project didn't leave any temporary or permanent structures on top of the seabed ... Sand and geotextile [a permeable fabric] were laid, so that the seabed was protected and could return to its previous state after the trial,' Leung said.
According to the Foreshore and Sea-bed (Reclamations) Ordinance, reclamation means any work over and upon any foreshore and seabed. Thus, work underneath the seabed does not necessarily constitute 'reclamation'.
The trial involved drilling 20 metres under the seabed, injecting the cement and allowing it to solidify into pillars. Ten such pillars were made, Leung said.
Water sampling showed no harmful materials were released from the mud during the cement-mixing process, he added.
A total of 650 hectares of land will need to be reclaimed for the proposed third runway, and there are mud pits covering 40 per cent of the area. The new technology, which costs up to four times that of traditional reclamation methods, ensured reclamation was more environmentally acceptable, Leung said.
However, Leung's explanation failed to convince the green groups, which said the trial altered the natural habitat for marine creatures, irrespective of whether it amounted to 'reclamation'.
'A cement surface is totally different from sand,' WWF HK senior conservation officer Samantha Lee Mei-wah said.
Lee said invertebrates lived in the seabed, and formed part of the marine food chain. They could be destroyed by construction work underneath the seabed, she argued.
Samuel Hung Ka-yiu, chairman of the Hong Kong Dolphin Conservation Society, said dolphins were displaced even when no structures were erected on the seabed.
'Dolphins usually dive to the seabed to find food. The placement of geotextile on it means they can no longer find food there,' he said.
Former president of the Hong Kong Institute of Engineers Gregory Wong Chak-yan said the use of the geotextile layer raised questions about whether the project should be governed by reclamation laws.
Although the geotextile would not stay on the seabed for ever, local regulations governing seabed works did not differentiate between temporary and permanent projects, he said.Topics: Environment Environment Land Reclamation Central, Hong Kong Environmental Soil Science Hong Kong Dolphin Conservation Society Environment