Sea rise & shore boundary properties

I walk on Lyall bay beach and watch as new properties being built along the foreshore. I wonder how these will be managed with sea level rise. There has been work on the sand dunes and rocks added to try and reduce scouring at East End on beach last year.

Lyall bay would be exposed for a number of challenges, Tsunami’s and also high tides and storm waves/surges at the same time.

There was a very good article in Stuff on Sunday, July 11, 2021 , With seas rising and storms surging, who will pay for New Zealand’s most vulnerable coastal properties? and it rings up some interesting points about who has to manage this and how do they do it. Is it private owners or do the Council/Government need to step in and do something?

As a quick remark I would like to say that the comments section of the article are quite vociferous and sometimes nasty. I’ve noted that the comments section in some articles are not moderated very well and some of the more inconsiderate ones are not called out or culled. Maybe a lack of tolerance, tending to black/white rather than a sliding scale of gray.

I’ve been thinking about what type of building you would look to build in this situation and what can be done in the future. I remember a remark by Gavin on flooding in Wales and people building flood proof buildings, and when questioned on this Gavin said Garages at ground floor and habitable spaces upstairs.

Some topics

  1. increased frequency of storm events
  2. Storm events coupled with high tides (neap, spring etc)
  3. general rising of seal level
  4. erosion of coastal edge
  5. Property insurance
  6. Council approving consent to build on land & sub-division
  7. Who’s responsible for protecting property, owner or council/government?
  8. Who funds remedial protection, shore property owners, general rate payers or government tax
  9. future consents for housing at foreshore- what type? Fixed or transportable
  10. Access at edge of sea, the Queen’s chain & public property.
  11. The land ownership – who owns it if its underwater? What is a viable plot of land?
  12. Talk of leasing land for a specific duration.
  13. Retreat from edge-with erosion, how to manage
  14. Public buildings such as Surf Clubs etc on sea shore- some being relocated.

There are more issues but I want to scope the limited thinking I have on the topic at the moment

March 2, 2020 article Study of Wellington & Harbour Dam for Sea Level Rise. City roads app & scripts was a fun exercise looking at sea level rise in Wellington and how to limit issue in harbour.

Increased frequency of storm events Items 1,2 & 3 above

What information is available on this topic?

The NIWA site has some models and pages on looking at specific areas in NZ here, using RCP’s (Representative Concentration Pathways For Greenhouse Gases In The Atmosphere) of 2.6 , 4.5, 6.0, 8.5 so a number of models. This is Greenhouse gasses for rainfall and temperature, not sea level.

For Sea level rising issues click on image below to be taken to NIWA article

Other areas/articles:

Another area of information is Greater Wellington Regional Council (click on map to follow link)

It doesn’t look that bad in the near future but the Council work around the harbour being done by WCC or GWRC on foreshore protection will be remedial work for immediate future.

An interesting takeaway from the map is Petone inland is vulnerable to flooding, I suppose being low lying and the Hutt River & Artisean well system (saturated ground so water nowhere to go), it was a marsh originally.

From the Beach article “New Zealand has the world’s ninth longest coastline, and millions of people living within 5km of the coast” and “More than three-quarters of the major population centres are coastal, and tens of thousands of people live within 50cm of the mean high tide mark, the area most at risk of sea-level rise. New Zealanders love the coast, and have manoeuvred their communities to live as near to it as possible.

Perhaps the best evidence of this is found in the country’s most common street name: Beach Road. The consequence is that billions of dollars of infrastructure, including residential housing, is in areas most immediately threatened by rising seas. They include airports, roads, underground pipes, parks and reserves, community facilities and social housing.

The most recent estimates, based on a draft report set to be published next year, show that around 125,000 buildings – both commercial and residential – would be at risk of flooding with 1m of sea-level rise. The replacement value of those buildings is around $38 billion.

Another metre of sea-level rise on top of that would put a further 70,000 buildings at risk, with a replacement cost of $26b.The speed at which the sea rises is vitally important, because it dictates how much time is available to relocate these assets. Based on the amount of greenhouse gases already in the atmosphere, scientists project with high confidence around 20-30cm of sea-level rise by 2065, regardless of how emissions are reduced.  

This article on Wednesday, July 14, 2021 in stuff Kiwis overestimating sea-level rise rate may hinder climate action also discusses sea level rise

Insurance on coastal properties & properties prone to flooding

This is the nub of the issue and from the top article link “Insurance is based on uncertainty and is reevaluated annually. When the chance of damage rises beyond what an insurance company is prepared to bear, it withdraws.

ICNZ cost of natural disasters here. From downloaded CSV from 1968 to 2020 I made this graph in Excel from pivot table. So over time there are more natural disasters and costs associated with those disasters. I filtered the disasters to only ones mentioning FLOOD (a bit crude I know) and you can see greater frequency and cost

End comment

I moved onto some other distraction and didn’t follow this up. Interesting what this article pulled up though.

I’m thinking of Wellington Harbour, lots of coastline. Better to put flood barriers in at entrance and do stuff along South Coast, Lyall by etc to protect from Storm/flood damage.

How would you calculate amount of property protection and foreshore?

What about dam/bridge across to Pencarrow? Access to land over there? A link to that side of the coast and also close off harbour? That way flood protection barriers can protect entrance. overall infrastructure costs reduced as 2 things happen and can benefit each other- Access to Airport. 2nd route out of Wellington for major earthquake, not the Nauranga gorge bottleneck. Big money to be put in to make that happen.