Expensive lessons from Mother Nature

Last updated 13:00 16/12/2013

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OPINION: It's hard to believe, during this balmy start to summer, that two years ago today, parts of the region were waterlogged disaster areas.

For many, it's a misty memory; for an unlucky few, it's become an ongoing battle over the future of their land and homes.

But there are still implications for everyone in the wake of both the December 2011 floods and the violent downpour that saw parts of Richmond and Stoke awash in April this year.

The Insurance Council is warning that the $50 million in claims from those two events will probably flow on to increased costs for flood cover.

That is unlikely to be a surprise, given the impact disasters such as the Christchurch quakes have had on Earthquake Commission levies and insurance premiums.

But on top of this, there are wider cost implications for the Nelson and Tasman councils, and therefore ratepayers.

The two councils have already spent more than $15m on infrastructure repairs from the 2011 floods, and the city council has budgeted another $790,000 for repairs from this year's deluge.

The issue they now have to grapple with is how much they should spend on protective measures to lessen the impacts of future events.

The Insurance Council says climate change projections point to Nelson receiving higher levels of rainfall. It says that unless measures are taken to minimise flooding, the likely increased severity and frequency of severe weather events will raise insurance costs.

The multimillion-dollar question is: what type of event should councils prepare for?

The 2011 floods were classed as a one-in-500-years event; the floods on April 21 this year were more than one-in-100-years, as 214 millimetres of rain fell across Stoke and Richmond in 24 hours.

Drainage infrastructure around the region was built to cope with much lower thresholds, and although upgrades are heading towards the one-in-100-years standard, they would not have been able to cope with either event.

A Tasman District Council manager says councils could build to cope with such extreme rainfall, but it would be "ridiculously expensive, and you'd use half your land in building drainage".

At the other end, there is the hope that the two events were a coincidental and unfortunate cluster, and that we have had our share of extreme downpours for another half-century.

Of course, you cannot rely on that, particularly given the region's susceptibility to northwesterly deluges.

The middle ground is probably an acceleration of upgrading old systems, or fixing known trouble spots. In areas like Golden Bay, for example, the floods have led to protection works that should see the area better able to cope. Around Champion Rd and the Orphanage Creek catchment, both councils are getting engineering advice about how to proceed. To that extent, the floods have been an expensive wake-up call, but at least we can be thankful that they were a non-lethal one.

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