Hong Kong-Zhuhai-Macau bridge

Mass dredging works raise fears for harbour

PUBLISHED : Sunday, 05 September, 2010, 12:00am
UPDATED : Sunday, 05 September, 2010, 12:00am

A host of big engineering projects due to start beneath the waters of Victoria Harbour this year and next have raised fears over what effects the collective dredging operation might have on marine life and water quality.

The seabed, from east to west, will undergo a massive transformation as various projects involving dredging start almost simultaneously. It is likely to be the biggest collection of such jobs since the early 1990s, when the so-called rose garden projects - the new airport and related road and rail links - saw vast land areas reclaimed from the sea.

While all the latest projects have been approved by the environmental watchdog, questions are being raised about why they are being allowed to start at about the same time and whether the effects on marine ecology and water quality have been properly assessed.

At least a dozen marine projects - including roads, ports, tunnels and submarine pipes - are due to start this year or next, and they will continue into 2012 and beyond. Together they will produce an estimated 40 million cubic metres of sediment - enough to fill 16,000 Olympic-sized swimming pools - that will have to be disposed of somewhere.

At least seven million cubic metres of this material is contaminated with heavy metals like silver, mercury, arsenic, copper and zinc released into the water and dropped to the seabed since the unregulated industrial boom of the 1960s and '70s. Individual sediment samples at the site of one project - a cross-harbour gas pipeline - was found to contain heavy metal levels up to eight times the maximum used by the Environmental Protection Department to decide if such sediment must be dumped in an isolated area.

A pollution scientist at City University, Dr Michael Lam Hon-wah, said toxins previously locked in the sediment might become active again during the dredging. 'They might become biologically available again and enter the food chain, such as marine life eventually consumed by humans,' he said, warning that it would be unwise to fish in the harbour during the work period.

Lam said the dredging activities, especially within the harbour, would undermine the recent success of the harbour sewage treatment scheme in cleaning up the water.

'Marine life has been returning to the harbour in recent years after efforts to divert raw sewage to the treatment plant. But all this dredging may turn the clock back.'

The most recent job to seek a permit from the department proposes dredging the Kwai Chung container port basin two more metres to a depth of 17 metres to allow safe navigation of ultra-large container ships.

That project - covering a seabed area of 446 hectares and lasting for two years from the third quarter of next year - will generate up to 4.4 million cubic metres of spoil, including 2.6 million cubic metres contaminated with heavy metals such as copper and silver. The toxic mud will be dumped at confined undersea mud pits at East Sha Chau, off North Lantau or at the planned South Brothers Island facility.

The less toxic mud will be abandoned south of Cheung Chau and the Ninepins Islands.

A consultancy study commissioned by the Civil Engineering and Development Department concluded the impact on water quality and marine ecology was acceptable.

It also listed nine concurrent projects - all confirmed with tentative construction programmes overlapping with the port dredging - and said computer modelling concluded that the cumulative impact of these was also limited.

These parallel projects take place in different parts of Hong Kong's waters and some of them involve even larger dredging operations. Most of them already had their environmental impact assessment reports approved by the government.

About 16 kilometres away from the port, the boundary crossing of the Hong Kong-Zhuhai-Macau Bridge east of the airport will be four times larger than the Kwai Chung project in terms of dredging volume. The work will start in the third quarter this year.

It alone will produce 18 million cubic metres of unwanted sediment, on top of the combined 10 million cubic metres from the connecting road link of the bridge and the related Tuen Mun-Chek Lap Kok Link.

The Wan Chai Development Phase II will start in 2011 and produce 1.15 million cubic metres of sediment. In 2011, dredging for the cruise terminal in Kai Tak will also start, generating 1.38 million cubic metres of sediment. Other works within the harbour requiring dredging include a submarine gas pipeline to be laid by Towngas from To Kwa Wan to North Point, which will require removal of 260,000 cubic metres of sediment.

Alan Leung Sze-lun, conservation manager of WWF Hong Kong, said he wanted each of these marine projects properly monitored to ensure they met the environmental outcomes forecast in the respective environmental impact assessment reports.

'There also needs to be a clear contingency plan for each project for what should be done if there are breaches in water quality objectives and there has to be some kind of co-ordination when something unpredictable and bad for the environment happens,' he said.

Leung said there should have been a strategic impact assessment of the cumulative impact of all the projects and an acceptable work schedule should have been worked out before construction started.

Under the current Environmental Impact Assessment Ordinance, the cumulative impact of concurrent works - which might have a bearing on the environmental acceptability of a particular project - will have to be gauged. But there seem to be no clear guidelines on how to identify those concurrent projects, such as whether it is by distance or scale.

For instance, the Kwai Chung port project takes into account concurrent projects as far as the cross-Pearl River Estuary bridge, but does not explain why it did not include the closer cruise terminal dredging at Kai Tak.

Sometimes, the dredging of a project considered in an impact study of another project might not happen as planned, making it even harder to predict the outcomes.

The dredging work for an undersea water mains between West Kowloon and Sai Ying Pun that involves disposing of over 500,000 cubic metres of mud started this year, instead of early last year as planned.

The massive dredging works are also expected to overload local marine dumping grounds for toxic mud. The undersea mud pits at East Sha Chau are likely to be filled by 2012, three years earlier than scheduled. Given the vast quantity of less toxic mud suitable for open-sea disposal, some of it might also have to be dumped in mainland waters.

Leung Mei-yee, an assistant professor from the ecology and biodiversity department at the University of Hong Kong, said there was no need to panic about the marine works, which were not the worst the city had seen.

'This isn't the worse scenario. The harbour area used to be in a much worse shape during the construction of the airport and its related works in the mid and late '90s, when dredgers could be seen all around working,' he said. The new airport project involved at least 184 million cubic metres of mud dredged from the seabed.

Leung said there had been great advances in dredging technology, such as the use of silt curtains, and improvement in works management, such as controlling the dredging rate, that could significantly reduce the impact on the sea.

He said controlling the number of concurrent projects was unrealistic as it might increase the building cost and duration of such works that could not be avoided anyway.

While he admitted that it was inevitable that some pollutants might be stirred up from the sea and spread out in the waters, he said an environmental cost sometimes had to be paid for development. 'There is a sacrifice one has to make unless we don't want any development at all.'

An environment department spokesman said the environmental impact assessment and monitoring system was in place to ensure the cumulative impact was within an acceptable range. 'Only when the assessed cumulative water quality levels are in compliance with relevant water quality objectives ... will the environmental impact assessment reports for dredging works be approved,' he said.