Matthew Bradbury: Let's build green defences against rising sea

Rising oceans will make a merciless attack on man-made structures. Photo / AP

Opinion

Waterfront cities such as Auckland need buffers to combat likely flooding, writes Matthew Bradbury.

When Hurricane Sandy hit New York, the city was buffeted by immense tidal surges and inundated by flood waters. It was both a reminder of the might of nature and a warning to all waterfront cities.

It illustrated that the construction of dense, heavily built up cities exacerbates the effects of storms. Roads and pavements increase the chances of flooding by preventing rain from soaking into the soil.

Heavy seawall defences can actually aggravate flooding.

An answer could be found in the building of a soft green infrastructure that imitates natural systems.

This is one of the conclusions of a draft report by the NYC2100 commission. The report makes a number of recommendations. Green roofs, pavement swales and urban wetlands that will reduce stormwater build-up. The restoration of a natural littoral by rebuilding native marshes and wetlands to help mitigate storm surges.

If this sounds far-fetched we should look at the new waterfronts being constructed in China.

With so many Chinese cities either on the coast or along rivers, the environmental issues of flooding, stormwater control and pollution have concerned the Chinese authorities for a number of years.

However, Chinese designers have also seen these environmental problems as an opportunity to create sorely needed public space.

Houtan Park, designed by Turenscape and built for the Shanghai Expo in 2010, is a great example. The 17ha park is located along the heavily polluted Huangpu River.

The park features a 1.7km-long wetland (roughly the distance from the Wynyard Quarter to the Bledisloe container terminal in Auckland). The wetland acts as a soft waterfront flood barrier replacing the stark concrete levee and is also a green retreat from the hectic city life of Shanghai. In addition it treats the heavily contaminated water from the Huangpu River through a series of ponds and reed beds, improving the quality of the water before returning it to the river. The Auckland CBD is a highly urbanised district with large areas of impervious surfaces. During storms there are large discharges of stormwater into the harbour. A rise in sea level through climate change with increased storm events can be expected to lead to widespread urban flooding.

To prevent this we should consider a waterfront that is radically different to the promenade of bars and restaurants of the Viaduct.

It will be more like a park, a watery littoral with native wetlands and coastal planting. Paths and boardwalks would weave in and out of an ever-changing landscape as the tide rises and falls, the growth of native flora would encourage the return of native fauna, the waterfront could become a valuable ecological link between the Waitakeres and the archipelago.

A good example of how this new waterfront might look is a proposed park for the Wynyard Quarter designed by Bryce Hinton. He suggests turning the end of the Wynyard quarter into a park with reserves, public spaces and fields. The edge would be protected with buffer zones of mangroves. The green infrastructure would also treat the millions of litres of contaminated stormwater from the Freemans Bay catchment. The result would be a new kind of public park for Auckland.

The implications of Hurricane Sandy are profound. This is an opportunity for Auckland to develop the techniques needed to ameliorate the effects of climate change.

The green waterfront could become New Zealand's calling card to the world.

Matthew Bradbury is senior lecturer in the department of landscape architecture at Unitec, Auckland.

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