Seabed blasts trigger wave of concern for marine life

PUBLISHED : Friday, 11 January, 2002, 12:00am
UPDATED : Friday, 11 January, 2002, 12:00am

Sixteen tonnes of high explosives are to be detonated underwater off Sham Tseng during the construction of a sewage treatment plant, bringing fears for marine life.

A researcher said the blasts, to be carried out over a two-month period, could injure rare white dolphins, while Ma Wan fish farmers said their stocks could be killed by the shockwaves.

A trial blast has been scheduled for next month to try to allay fears over their potential impact. The contractor, China State-ATAL Joint Venture, has pledged to compensate fishermen for any fish deaths during the trial.

The blast on the 20-metre-deep seabed will be just a few hundred metres from waterfront homes. The project will begin immediately if the trial is successful.

The aim of the blasts is to construct a trench in the rocky seabed to accommodate a 160- metre sewage outfall pipe for the $438 million treatment plant.

For each blast, about one tonne of explosives will be used.

Lai Tak-chuen, chairman of Ma Wan Fisherman's Rights Association, said he feared the pressure generated from the blasts could kill fish in their farms 1.5km away. 'It will cause waves and noise underwater that might kill the fish or damage their internal organs,' he said.

Samuel Hung Ka-ya, a white dolphin researcher at the University of Hong Kong, feared the blasts might affect the mammals. 'Dolphins rely on sound and echoes to hunt and position themselves. They might lose their hearing because of the blast,' he said.

However, the contractor plans to emit sonic pulses from an electronic device to repel dolphins that try to enter the blast zone 30 minutes before each explosion.

A 500-metre exclusion zone will be in force for sea traffic for 30 minutes before and after each blast and a seismograph will be set up nearby to gauge the blast's impact.

Legislator Wong Yung-kan accused the Drainage Services Department of hiding the ecological impact of the blasting from the legislature when it sought approval in March 2000.

'They never explained why explosions were needed and how the blasts would be carried out when they sought funding from us,' he said.

Tsuen Wan District Council was also consulted about the project in 1998 but was not told about the blasting.

Drainage department chief engineer David Cheung Yee-tin dismissed the worries.

'There would be no impact to the fish farms at all as the pressure wave would be blocked by Ma Wan Island itself,' he said.

'The pressure wave would completely dissipate beyond 1,500 metres and its impact would be even less than the pressure from slamming a door.'

Mr Cheung said the explosives would be handled in accordance with safety guidelines and that the chances of an accidental explosion were minimal.

Charles Ng Wang-wai, Assistant Professor of the Department of Civil and Structural Engineering at the University of Science and Technology, said underwater blasting was common and could be done in a controlled manner.

Graphic: MAP11GET