Imagine a 50-storey high tower of gravel and mud with a base the size of Victoria Park. That's roughly the initial estimate for the landfill needed to build the sea wall for the proposed road linking Tuen Mun and Chek Lap Kok airport.

The dredging alone would require 170 daily vessel trips - and while this may have been acceptable decades ago, concern over marine habitats and the welfare of Chinese white dolphins in the vicinity meant another solution was needed.

The road will form part of the high-speed transport network girding the Pearl River Delta, a major infrastructure project that includes the Hong Kong-Zhuhai-Macao Bridge and new Boundary Crossing Facility (BCF) in Hong Kong.

While some might argue the construction of the high-speed road network is not itself environmentally friendly, the engineers and contractors behind the project have made significant strides in mitigating the impact that the works will have on the marine life around Lantau and northwest New Territories.

For instance, one innovative solution has been found for the building of the seawall to support the reclamation required for the road and the BCF.

"The conventional method would be a dredged sea wall," says Albert Liu, chief engineer at the bridge's project management office.

For the first time in Hong Kong, a bank of tubes, or 'steel cells', each measuring 30 metres in diameter will be used, eliminating the need for dredging. "We cut dredging by 95 per cent, and the creation of suspended particles by 70 per cent," says Liu.

Furthermore, the new technique requires around half the number of boat trips for construction.

The project is a pioneering example of how engineers and contractors can work with the community. For instance, working with dolphin-protection groups, the contractors have set up a "dolphin exclusion zone" around the silt curtains. "If we see any dolphin within 250 metres of our site area, we will have to stop work and wait until the dolphins go away," says Liu.

But perhaps the most sustainable feature of the project is not just the construction technology used, but also the consultation and consideration that took place before the plans were cemented.

For engineering reasons, the whole planned site for the BCF was initially placed northwest of the airport. After a round of consultations, it was found that this could affect tidal flows and dolphin habitats, and would also increase transit time for people driving to and from the airport. As a result, the site was moved to the east of the airport reclamation, a victory for sustainable engineering.