Noisy piling works from the construction of a planned offshore gas receiving facility off Hong Kong’s southern Lantau Island could cause hearing loss in finless porpoises, according to a conservation group.
An environmental impact assessment (EIA) submitted by CLP Power failed to show how work would really affect marine mammals in the area and needed to be redrafted, WWF-Hong Kong claimed.
“We are disappointed by CLP’s EIA report,” said Samantha Lee Mei-wah, assistant director for oceans conservation. “It hasn’t demonstrated clearly how noise from pilling works will affect Chinese white dolphins and finless porpoises that use these waters.”
The power firm is seeking an environmental permit to build a 2.5-hectare offshore liquefied natural gas (LNG) receiving terminal off the Soko Islands.
A regasification vessel – which converts LNG offloaded by tankers back into gas and sends it to the city’s power plants via undersea pipes – will also be berthed permanently at a new jetty.
The jetty will sit on 80 piles, driven into the seabed.
To get the green light, CLP must conduct and meet all criteria of an EIA.
CLP proposed mitigation measures such as erecting noise insulating curtains and a 500-metre exclusion zone, but concluded that there was “no unacceptable noise impact associated with the construction of the project particularly”.
But Lee said the EIA lacked details on noise propagation modelling, which quantified how sound travelled underwater and measured its cumulative effects. So WWF commissioned an independent consultant to do such modelling.
Its study found that noise from a pile being hammered once into the seabed could travel 4km. This would affect finless porpoises, which are known to forage in the area from December to May.
According to the model – which factored in data such as sea depth, temperature and density – any porpoise in the area could suffer reduced hearing distance of 50 to 100 per cent.
Near endangered, finless porpoises – like many cetaceans – emit “clicks” of different frequencies to communicate and navigate. They are extremely sensitive to noise.
Studies have shown that noise over 160 decibels can directly affect cetacean behaviour.
According to WWF’s study, noise from a single hammer strike would reach at least 200 decibels within the “zone of influence” from CLP’s work site. Repeated hammering increased the noise exponentially, Lee added. “It may affect their ability to find food or a mate.”
She urged the government and members of the Advisory Council on the Environment to defer approval of the EIA until the power firm provided more information.
A CLP spokesman said its EIA results indicated that underwater sound propagation decreased as sound waves travelled over long distances.
“Thus, sound would not cause harm to marine mammals at locations several hundred metres away from the sound source,” he said.
“Underwater construction mainly generates low sound frequency, whereas marine mammals are generally more sensitive to high sound frequency.”
Dr Samuel Hung Ka-yiu of the Cetacean Research Project said finless porpoises were easily frightened and would avoid any noise, whatever the level. “Many would probably be displaced by all the boats there, even before the piling began,” he said.
But Hung said the issue could be easily resolved if CLP agreed to keep piling works limited to the low season – June to November – when the porpoises were elsewhere.
CLP said it had already adopted the suggestion.
The Environmental Protection Department said it would consider all legal requirements, public comments and the council’s views before September 14, in deciding whether to issue the permit.
Few reports submitted to the government are ever rejected.