Some coastal suburbs in doubt

Concerns have been raised about the future of two coastal suburbs in Christchurch. Southshore and South New Brighton suffered heavily in the earthquakes of 2010 and 2011. But their recovery is being hampered by the sunken land that both sit on and its increased vulnerability to storms.

Perhaps the primary source of concern is how these communities will cope with rising sea levels, and increasingly volatile weather systems. New Brighton and South Shore have never been very high above sea level and occupy a narrow spit less than a kilometre wide, which has sand dunes on the coastal side and an estuarine environment on the other. And in recent years their vulnerability to the effects of flooding from storm surge have been shown.

Earthquakes are a second cause of concern. As a result of ground motion particularly on 04 September 2010 and 22 February 2011, land around the Avon-Heathcote estuary, the lower reaches of both rivers and the Brighton Spit slumped in some cases by up to 50 centimetres. Since then flooding can happen with brief rain or a large tide.

But there is a wider problem. Christchurch is not the only part of New Zealand with low lying housing. Coastal bays in Wellington, estuarine parts of Auckland and low lying land that might be protected by sea walls or sand dunes, but be at or close to sea level is also at risk. Good examples of the potential damage can be found in the winter storms of June 2013, and more recently Cyclones Fehi and Gita, which caused widespread storm damage along the West Coast and around Nelson

Whilst there are provisions in the Resource Management Act and statutory planning tools such as the Regional Coastal Policy Statements, councils have to trade off between environmental pressures and developmental pressures.

The last two years in New Zealand have been particularly stormy. During the summer of 2016-17, the Southern Oscillation Index was neutral, meaning weather came from all corners of the compass. For example a weather bomb – a rapidly deepening system of short duration, but quite intense in terms of rain and wind – passed over in January, dropping 300mm of rain in Arthurs Pass in a day in mid-January 2017. In June and July 2017 big southerly storms lashed Canterbury and large parts of the South Island’s east coast causing widespread flooding, and extensive coastal erosion. In February 2018, as mentioned earlier, two tropical cyclones passed over New Zealand just three weeks apart.

All of these storms caused millions of dollars in damage. In the case of Cyclones Fehi and Gita, they raised concerns about how coastal communities in less densely populated regions might fare in the long term. A low population region such as the West Coast does not have the financial resources to draw on from its ratepayer base that a region such as Canterbury or Auckland have. This makes coastal measures expensive, but have to be weighed up against moving and disrupting communities.

Even if the world went carbon neutral today, so much has been ejected that it would take several years or even decades for the effects of going carbon neutral to begin to be recognized. Even the 2ºC rise in temperature is limited to strictly that – some are saying even limiting global temperatures to a 1.5ºC rise might be too little too late – the subsequently increased volatility of our climate, going from intense droughts to severe rainstorm events; extreme cold to extreme heat would not be stoppable in our lifetime.

Another planning concern is the amount of sediment reaching the coast. Some parts of the world have a shortage of sand. This can at least in part be traced to rivers, which are the natural means of transport for sediment from the mountains to the sea, being dammed extensively. This thereby traps the sediment and little or no provision gets made for the need of long shore drift, which works the sediment along the coast enabling the replenishing of sand beaches after big storms. A failure to restore the balance somewhat would mean that coastal regions that are vulnerable would be more and more exposed to the sea, meaning properties would have to be abandoned.

Moving forward, one has to wonder what sort of future other coastal communities face. Maybe planners have a solution, but for the time being, councils and insurers alike are being faced with hard questions that no one really knows the answer to. And time might not be on their side.

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