Thames and Thames Coast Likely to be in “Imminent Risk” Category

More details have emerged about a draft NIWA Report which describes the extent of risk of coastal property to sea level rise.  Local Government NZ is soon to release a separate report on sea level risks to Council infrastructure and buildings. When these two reports are released the detail on the most at-risk areas to sea flooding and erosion is going to be of intense interest to Thames-Coromandel Council and local coastal property owners.

Back in September 2017, I reported how Thames was the eighth most at risk town or city in New Zealand from sea level rise.  This was based on a desktop risk census carried out by NIWA which took a broad brush approach by looking at half metre increments in sea level rise and the estimated value of properties within those elevation bands.

The new study carried out by NIWA breaks New Zealand down into regions and 10 cm increments of sea level rise.  NIWA have incorporated natural hazard risk modelling from GNS, more extensive LiDAR satellite imaging, and aerial maps showing the number of houses and commercial buildings in the at-risk area.  This will produce a far more comprehensive picture of the extent of risk and the potential cost of climate change on the coast.

Details of the draft NIWA report were revealed to an Insurance Council conference by Rob Bell, New Zealand’s leading expert on sea level rise.  Bell told the conference that $38 billion of New Zealand’s residential and commercial buildings may be at risk of flooding if sea levels rise 1 m.

NIWA estimated the size of the risk zone using what insurers and councils call the 1 percent AEP flood risk, which indicates that a building currently has a one-in-a-hundred-year likelihood of flooding based on what’s happened during the past few decades. However, the frequency of floods will increase on the coast as sea levels rise. The study will model how the potentially at-risk area increases after 10cm, 20cm, 30cm and so on of sea level rise up to 3m. 

Thames and the Thames Coast was severely inundated in January 2018 under current sea levels so it will be of great interest to see how at risk our coast will become with just 10 cm or 20 cm of sea level rise.  The study has also promised to take into account local land subsidence so it will be fascinating to see what conclusions the study comes up with for the Thames foreshore where land subsidence is occurring at probably the fastest rate in the entire country.

Bell told the conference that adding the effects of sea level rise to today’s flood risk in 10cm increments revealed that some areas – like Tamaki Drive in Auckland – were at imminent risk already.  It is likely the same “imminent risk already” description will apply to Thames and Coast settlements.

Of particular relevance for TCDC’s proposed aquatic centre near the Thames airfield Bell told the conference that early 2018 was the “summer of coastal storms” with floods in January, February and March. “There is still ongoing development around hazard prone land and we need to be careful we are not locking in future risk. Past events are not a reliable guide to future.”

Local Government New Zealand is carrying out a separate study of local authority infrastructure and assets which are at risk from sea level rise.  The results of this study are expected to be released in late 2018.

Read the full report by Eloise Gibson in Newsroom  here