How Hong Kong is extending a town the eco-friendly way

The Tung Chung New Town Extension (TCNTE) is the first project since 2003 to expand one of Hong Kong’s new towns on to land reclaimed from the sea.

It’s a major initiative under the government’s multi-pronged plan to increase the supply of land.

The TCNTE will provide about 62,100 residential flats for Tung Chung’s population of 184,000.

It will also provide about 500,000m2 of gross floor area for office use, 327,000m2 for retail use and 50,000m2 for hotel use.

Land has been reserved in the extension area for recreational, educational and community uses.

The challenge of reclamation

The seabed surrounding Hong Kong is generally covered by a layer of very soft marine sediment – in other words, mud.

This is highly compressible and will settle significantly over time under the weight of the reclamation material.

In the past, dredging (excavation) was used to remove marine mud during reclamation works, but the process would affect the environment and increase greenhouse gas emissions.

Deep cement mixing

To speed up the reclamation process, the deep cement mixing (DCM) method was applied for the first time by a public works project.

This involves injecting cement slurry from works vessels into the mud and ‘mixing’ the two materials.

Importantly, DCM doesn’t require marine mud to be removed.

This reduces the generation of suspended particles in water, which minimises the impact on the quality of the surrounding water and marine ecology.

Reducing emissions from transport

In addition, since no transport is needed for shipping the mud, it reduces carbon dioxide emissions.

It’s estimated that the TCNTE project has avoided dumping 4.4million m3 of marine mud, which would have required 17,600 vessel trips.

Reusing materials

To further enhance sustainability, the project re-uses inert (chemically inactive) construction waste (public fill), which is made up of rocks, concrete, asphalt, rubble, bricks, stones and soil, as reclamation material.

Smart management

Since 2019, the project has introduced the concept of smart management by way of a digital platform, InnoTCE.

This has enabled managers to keep track of work as it happens on the site and make faster and more accurate decisions.

Mangrove eco-shoreline

The TCNTE reclamation is the first public works project to introduce eco-shorelines.

The aim is to mimic the natural intertidal zone, or the area where the ocean meets land between low and high tides, as far as is practical.

This is to provide a suitable habitat for the growth of marine organisms and thereby form a tidal ecosystem.

The eco-shorelines were established in the intertidal zone, where waves have less impact, and near the outlets of rainwater channels.

Mangroves are greening these areas and reducing coastal erosion.

A home for biodiversity

A mangrove eco-shoreline offers an attractive home for a range of marine organisms. Many fish and invertebrates can feed on fallen mangrove leaves, for example.

Holes are being drilled into seawalls and containers resembling flowerpots are being installed on them to provide shelter and habitat for marine species.

The walls are also covered with eco-tiles with uneven surfaces to which small organisms can easily attach themselves.

Placed at sites that are more exposed to wave action, bio-blocks are structures that are completely submerged at high tide and store enough seawater to form viable pools at low tide.

These too provide a suitable habitat for a range of marine species, again boosting biodiversity.

New neighbours in Tung Chung

In 2019, the project set up a trial site for an eco-shoreline at Siu Ho Wan, east of Tung Chung.

The trial includes monitoring the conditions of ecological facilities, such as mangroves and bio-blocks, and collecting data to inform design improvements.

From the trial stage to completion in the TCNTE earlier this year, more than 30 species were identified living on the eco-shoreline, including fiddler crabs, mudskippers and gastropods.

Using the sustainable DCM method, the first parcel of land (7ha) was completed in 27 months in March 2020 and handed over for public housing development.

Despite the pandemic, the project team made the utmost effort to complete the reclamation by January 2023, more than six months ahead of the original schedule.

The project was Highly Commended in the Edmund Hambly Medal (Creative design for sustainable development) category at the ICE Awards 2023.