Floating houses on the Avon River could revitalise red zone

Design concept for a demonstration floating house on the Avon River in Christchurch's red zone.
BUCK ARCHITECTS/SUPPLIED

Design concept for a demonstration floating house on the Avon River in Christchurch's red zone.

OPINION: What to do with abandoned red zone land in Christchurch is still unresolved. Conventional housing has been ruled out, while improving the land to reinstate it for housing would be inordinately expensive.

Gary Teear, a director of Offshore and Coastal Engineering Ltd, has come up with a plan for a practical alternative: floating houses. Teear believes floating houses would appeal to locals, investors, and tourists alike, and also that they would mitigate concerns over rising sea levels – an issue certain to intensify.

So how would the plan work? Red zone areas are mostly centred on the Avon River and along the Estuary shoreline on the South Brighton/South Shore side. 

The Christchurch estuary could be the site for floating houses, accessed from the red zone.
IAIN MCGREGOR/STUFF

The Christchurch estuary could be the site for floating houses, accessed from the red zone.

"The land has been subject to liquefaction and has sunk and spread laterally," says Teear. "It is much closer to river/sea level in most cases.  In a future seismic event the land could be expected to liquefy again – hence the decision to red zone it."

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Access to floating houses would be via a gangway from shore. Each house would have its own berth with road access to the ...
BUCK ARCHITECTS/SUPPLIED

Access to floating houses would be via a gangway from shore. Each house would have its own berth with road access to the shore end of the gangway.

New developments must be above the flood plain level, which the Christchurch City Council has set at 19.3m. Properties further than two blocks back from New Brighton beach toward the Avon are all under 19.3m. If owners want to do new builds or modify the properties they have to raise them at their own expense, and it is not clear what protection – if any ­– the council will provide. It may raise the level.

"This makes it very hard to kickstart New Brighton," says Teear. He says floating houses would neatly bypass the flood plain problem. They are resilient and adaptable to climate change.

"Each house, supported on its own independent floating foundation and held in position off the bank either by piles or radius arms, would be unaffected by seismic action and rising water levels. The houses simply float up.  The water acts as a base isolator, effectively decoupling the house from strong ground movements in a seismic event.

Floating communities would be novel for Christchurch, however they are developing overseas as one solution to the ...
BUCK ARCHITECTS/SUPPLIED

Floating communities would be novel for Christchurch, however they are developing overseas as one solution to the prohibitive cost of land in big cities.

"Access would be via a gangway from shore. Each house would have its own berth with road access to the shore end of the gangway."

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Infrastructure in the form of roads, sewerage, water and power supply already exists in the red zone areas, but is damaged.  Along South Shore the infrastructure is in place and fully functional; the services have been cut off at the boundary of the red zoned sections and the houses previously on those sections removed.

It is likely to be cheaper to repair existing infrastructure rather than install completely new infrastructure at new 'greenfield' housing sites, says Teear. Housing could coexist with wetland restoration, and increase the number of people living close to the central city: a "win-win" all-round.

Locations or berths close to the Avon River such as in Bexley or New Brighton could be linked to the river or set into the side of the river to keep the houses out of the main flow. The excavated material would be used to build up the land level. 

In an area such as the Avon Loop close to the city centre a pond could be developed in the sunken land area inside the ring road running along the river bank, connected to the river by a short canal, and used to accommodate a community of floating units. 

Residents' kayaks could be moored alongside or held on davits onboard the floating units. 

Floating housing areas could be integrated with the proposed flat water sports lake and wetland areas.  Being surrounded by restored wetland areas with birdlife would be an attractive feature of a floating house community, says Teear.

Polyethylene pipes are a cost-effective and maintenance-free option for the flotation required to form a pontoon base for each house.  Foundation costs would likely be less than for a conventional house. Services would be via flexible lines running under the access gangway.

Floating communities would be novel for Christchurch, however they are developing overseas as one solution to the prohibitive cost of land in big cities.  People have always lived in barges on canals that were first used to transport heavy goods in Europe and fell into disuse when first rail, then heavy truck transport supplanted them. Now floating communities are emerging in the heart of big cities, such as Waterbuurt in Amsterdam.  Waterbuurt is a community of 1000 people that features modern apartments. Teear says another floating community in the harbour in the centre of Victoria on Vancouver Island is a tourist attraction in its own right. 

Floating houses in Christchurch would be an effective, unique and attractive way of utilising red zone land.  Teear suggests berth spaces could also be leased rather than sold, which would address the issue of high land prices. Architects would be free to design an attractive range of distinctive floating homes.

Teear is prepare to invest in floating houses himself. "The most effective way in our view to kick start the floating house concept in Christchurch is to build a demonstration house in a prominent attractive location. We are prepared to do that ourselves by buying land off Regenerate Christchurch – the purchase being contingent on obtaining a permit to build the demonstration house – with the potential to buy additional land as demand increased."

* Freelance journalist David Killick wrote this on behalf of Offshore and Coastal Engineering Ltd.

 - Stuff

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