How Hong Kong’s third runway was built to protect and boost nearby marine life

Instead of dredging, the Airport Authority used deep cement mixing at an unprecedented scale for this type of project. Specialized rigs injected cement slurry into the soft seabed mud, which hardened into more than 360,000 columns. The columns served two purposes: they provided foundation support for the new reclaimed land and they locked contaminants in place so they would not spread into the marine environment.

Tommy Leung King‑yin, executive director of engineering and technical services who oversaw most of the project, said deep cement mixing allowed containment of contaminants while solidifying soft material. The approach was costlier up front but saved about a year in settlement time and reduced fill material needs by around 10 percent.

To avoid trench dredging for fuel lines, engineers used horizontal directional drilling (HDD) to install two aviation fuel pipelines. Each pipeline is 5.2 km long and was routed about 100 m below the seabed. At the time, this was the world's longest installation of pipelines using HDD for such a purpose. HDD limited seabed disturbance and reduced risk to marine sediments.

Environmental mitigation and enhancements

The project implemented more than 250 mitigation and management measures addressing construction and operational impacts. Beyond mitigation, the Airport Authority added voluntary enhancement features designed to improve local marine habitat:

• A 13 km sea wall incorporates over 500 eco‑enhanced blocks with grooved surfaces and water‑retaining cavities. The design mimics rock pools that hold water at low tide and provide shading and shelter for marine organisms. Marine ecologist Professor Kenneth Leung Mei‑yee said such designs can double biodiversity compared with conventional sea walls.

• Installation of 600 artificial reefs along the adjacent waters.

• Release of almost 90,000 fish fry and additional shrimp fry into waters near the airport.

• Support for the designation of the 2,400‑hectare North Lantau Marine Park, the largest and newest marine park in Hong Kong, as part of a network of protected areas.

The combination of containment, low‑disturbance construction, and active habitat measures aimed to limit pollutant release during reclamation and to create opportunities for marine life to recover or increase in abundance around the new infrastructure. The project's engineering choices also delivered program advantages by reducing settlement time and fill requirements.

What this means for future coastal projects

The approach shows a higher upfront cost can be traded for faster programme delivery and reduced material demand, while achieving environmental safeguards. Techniques such as large‑scale deep cement mixing and long‑reach horizontal directional drilling are practical options when reclaiming land over contaminated seabeds or sensitive habitats.

By pairing containment engineering with deliberate habitat enhancements and protected area designation, the airport expansion attempts to keep development and marine conservation working together at the project scale.