Cyclone Gabrielle highlights landslide at Shelly Bay – Stuff

Rewi Newnham is Professor of Physical Geography, and director of the Centre for Science in Society, at Te Herenga Waka-Victoria University of Wellington.

OPINION: Having recently written on the coastal flooding threat to the Shelly Bay development now under construction, I am moved to point out an additional hazard that has been highlighted so dramatically and tragically in other regions by Cyclone Gabrielle.

Although Wellington experienced only the tail end of the storm and suffered little damage, there is no room for complacency.

A compelling warning comes from the small coastal settlements of Muriwai, Piha and Karekare, west of Auckland, where local communities are still coming to terms with the terrible costs of the cyclone in lives, livelihoods, infrastructure and dwellings.

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Shelly Bay shares many geographical similarities with these impacted settlements.

It sits at the foot of steep, partly vegetated slopes that will likely be even more susceptible to landslides than the more densely clothed slopes of the Waitakere Ranges of west Auckland.

Despite the comparatively established native forest cover, for example, several houses at Karekare were destroyed by devastating landslides.

These landslides were triggered by a combination of high-intensity rainfall and high winds, and although these were unprecedented for Auckland (in living memory), Wellingtonians are well aware of our city’s susceptibility to landslides from much less extreme weather. Not to mention the additional threat from earthquake-triggered landslides.

There is a mosaic of pine plantations at various stages of the life cycle: some tall top-heavy trees, susceptible to windthrow with signs of previous damage; some recently harvested areas, now presenting exposed soil surfaces complete with forestry slash.

This is precisely the scenario that proved devastating in Tairāwhiti once Gabrielle came to call. To add to the volatile mix, there are pockets of wind-blown sand deposits originating from the recent ice ages that provide another source of loose, unconsolidated material that adds both to the instability of these slopes and to the downstram consequences when they do fail.

As with coastal flooding, it is not a matter of if but when the Shelly Bay dwellings under construction meet the same fate as Karekare and Tairāwhiti.

Fire and Emergency NZ has been running a public awareness campaign with the message: the best way to put out a fire is not to start it in the first place.

Cyclone Gabrielle has issued a similar message with regard to climate-relate hazards.

My heart goes out to people in west Auckland and the eastern North Island who have lost homes and livelihoods and now face a perilous dilemma – whether to return and rebuild, with insurance premiums and prospects for future devatstation stacking up against them; or start anew in a location and situation where there is lower vulnerability to climate-related hazards.