Red zone a living lab for adapting to sea level rise

Saturday, 15 November 2025

The red zone is an example of what managed retreat could look like elsewhere around the world.

Why is the European Union investing almost $3 million into the Christchurch red zone? Because it sees those 600 hectares as a proving ground for managing retreat from sea level rise. WILL HARVIE reports.

The 600-hectare red zone in east Christchurch is globally unique.

No other country has bought thousands of homes, demolished them and prepared the land for a return to nature.

With about 600 hectares, the red zone has room for volunteer plantings and international research.

But in the decades ahead, every country with a coastline may have to move thousands of residents and demolish all of their buildings.

The red zone is what managed retreat might just look like – the local context aside.

The red zone is thus a “frontrunner”, said David Little, Christchurch City Council’s red zone manager, and that we are decades ahead of everywhere else.

The red zone – officially the Ōtākaro-Avon River Corridor – has become a “living laboratory” for figuring out what do to with land after retreat, Little said.

This situation is now attracting considerable overseas money – €1.4 million (NZ$2.9m) from the taxpayers of the European Union through its Rise-In and Horizon Europe programmes.

The EU wants to know how to treat soils contaminated with heavy metals and organic residues like coal tar, which is hazardous to health but was used to build many of the roads in the red zone.

The red zone is a great place for recreation. Now it is likely to be used for science as well.

Officials want to know if crops can be grown on those lands, and how to make carbon credits and money from abandoned lands, so they are not a constant drag on the taxpayer. They want to know how technology, like remote sensing, can improve monitoring.

The EU does not care the research is happening on the other side of the world, and did not ask for matching funding from New Zealand.

Two broad research areas will be investigated over five years by scientists from the University of Canterbury and Crown Research Institute Landcare, now part of the new Bioeconomy Science Institute, with support from the council’s parks and Smart Christchurch teams and ChristchurchNZ.

Under the plan, the Christchurch research will be picked up by “replicator” cities in Turkey, Belgium and Ukraine, which will adapt it to their conditions.

Biochar treatment

Biochar is an especially stable form of carbon that is manufactured from waste organics, like forestry slash.

It looks like charcoal and will be ploughed up to 30cm deep in red zone sites identified by Landcare. Because of its stability, it may last a thousand years – although nobody knows exactly how long.

Biochar is thick with benefits. It acts as a sort of super-compost, enriching the soil, boosting microbial activity, improving soil structure and amplifying plant growth, said Brett Robinson, a professor of environmental chemistry at the University of Canterbury, who is contributing to the research.

Brett Robinson is a professor of environmental chemistry at the University of Canterbury who is contributing to research in the red zone funded by the European Union.

Biochar also binds heavy metals and makes them less likely to leech into waterways, for example. The red zone is well contaminated with heavy metals after decades as an urban area.

It’s also contaminated with organic compounds, such as coal tar. Biology colleagues of Robinson will supplement the biochar with microbes that consume these sorts of petrochemicals.

Perhaps the biggest promise of biochar treatment is carbon sequestration. The biochar is itself carbon, from forest slash, say, that would otherwise enter the atmosphere. Robustly growing plants “pump” carbon underground – another benefit, Robinson said.

Biochar also improves the ability of soil to absorb carbon. And the poorer the soils, the more carbon they can absorb.

Red zones soils are notoriously poor after decades of compaction and isolation under houses, driveways and roads, Little said.

The Bioeconomy Science Institute is currently identifying the red zone areas with the poorest soils, which are likely to be out New Brighton way, Robinson said.

Another goal here is bringing soils into carbon credit schemes, a hot topic globally.

Advocates argue soil carbon credits will nudge the world closer to net-zero carbon emissions. Critics argue the science and economics are not yet advanced enough to allow them.

Australians can earn and trade soil carbon credits and other nations, including New Zealand, are studying the issues.

Among the problems is measuring the amount of carbon in the soil and how much is added (or lost) over time.

NZ flax or harakeke is a promising biomaterial.

In the red zone biochar plots, the amount of carbon in the soil will be known.

Change will be measured using traditional methods like digging for samples and testing them in University of Canterbury labs.

The EU money will also pay for “flux boxes” – remote sensing devices that use infrared sensors to measure carbon.

If the flux boxes are proven to work in the red zone, they may be deployed elsewhere.

As indicated, the EU wants abandoned land to turn a surplus, and well-measured carbon credits might be the way forward.

Harvestable crops

The council currently mows grass on large parts of the red zone, which costs money and enforces a monoculture of mostly exotic plants.

It would be better if that land was productive, and there is a native plant – harakeke or New Zealand flax – that shows great promise as a hi-tech material.

Researchers and entrepreneurs are showing its fibres can replace fibreglass and carbon fibres in snowboards, racing cars, weed mats and the like. The carbon fibre market is worth billions of dollars annually and flax could be a cleaner, greener competitor.

The idea is to plant flax in appropriate places in the red zone and start harvesting in a few years.

The Europeans are not interested in planting harakeke in Belgium, of course. But it is agreed there are European natives that could be suitable cash crops over there.

There are important tikanga – Māori customs and values – associated with harakeke and work is under way by suitable experts to meet those expectations and standards, Little said.

It is possible other native species like kānuka could be planted.

Little said he takes New Zealand and international visitors to the red zone about once a month. In a few years time, he can expect even more visitors – among them Europeans inspecting how their money is being spent, surely.

He will also have more to show them.