20 Jul 2017

Future proofing Christchurch

From Nine To Noon, 9:37 am on 20 July 2017

Despite facing the twin challenges of rising water tables and being in an active seismic zone, Christchurch has some natural advantages a US landscape architect says.

Dr Kristina Hill is in Christchurch to speak about her recent work in the San Francisco bay area, a region with similar problems to Christchurch.

Dr Hill, a professor of landscape architecture and urban planning at Berkeley, specialises in resilience, in particular coping with sea level rise and helping cities recover from disasters.

There are 13,500 properties which are vulnerable to flooding and liquefaction following the Christchurch earthquakes.

There are 13,500 properties which are vulnerable to flooding and liquefaction following the Christchurch earthquakes. Photo: RNZ / Nicola Grigg

She says one of the smartest things New Zealand did was taking red-zoned Christchurch land into public ownership.

“That gives the city enormous flexibility in thinking about ways to support bio-diversity and water quality and I haven’t seen that happen in many places.”

She says the red zone land offers an opportunity to experiment with manipulating the landscape to help mitigate floods.

“Christchurch has been very smart to acquire the red zone as public land because that gives it a chance to run pilot projects, to manipulate the landscape in that zone adding marshes or working with levees, dykes canals and ponds.”

She says the landscape can be a “very muscular” ally to help cities adapt. The Avon River for example is taking sediment to the coast and is building up dunes there, she says the Dutch paying a lot of money to do this.

Avon River - Red Zone

Avon River Photo: Frank Film

Rising water tables create problems for many cities because as sea levels rise, denser salt water pushes up fresh water tables.

Governor of California Jerry Brown - a “science guy” Dr Hill says - has commissioned a study to help shape development policy in the state.

It has advised policymakers to expect sea level rises of between 1 metre and 1.5 metres by 2100 and possibly 3 meters at the more extreme end of predictions. So major investments in the state are expected to factor in a 3 metre rise and private developers the lower estimate.

San Francisco is exploring a range of innovations to help it adapt – some technological, some to do with restoring environments.  A tax has been levied on waterside homes in the city which is being used to build new marshes in the bay.

“These marshes reduce wave energy, which helps us buy time for adaptation”, she says.

The city is looking at techniques such as floating foundations, she even envisages entire city blocks on such foundations.

“It’s not like a water bed, it’s a very stable experience and the more pieces are connected to each other, the more stable it is. We’re imagining urban blocks that float.”

Some cities, however, will find it nigh on impossible to adapt.

“There are some very tough locations, the toughest one in the US is Miami. Even though it’s getting a lot of press now for putting in pumps, because they struggle with hurricanes that can produce storm surges of 10 metres and waves on top of that it’s very difficult to imagine how that city maintain itself over the next 100 years.”

She says the low-lying Dutch, who know a thing or two about flood management, have been borrowing and investing in infrastructure now to adapt to rising seas in the future.   

“The Netherlands invested in a really smart way when interest rates were low. In the UK the strategy is more just in time. They’re going to build things as they see sea level rising.

“The weakness in that strategy is the entire world will be borrowing money at that point and the price of steel is going to go through the roof.”