Orewa Madness! Trying to Defy Sea Level Rise?

How can Auckland Council have approved this multi-million dollar apartment development on Orewa’s waterfront? These luxury apartments are being built barely twelve metres from an eroding shore, and have the ground floor only about three metres above sea level with a basement below that. With escalating risks from erosion due to rising seas such development surely should be avoided?

Orewa 1

The above artist’s impression on the cover of a recent North Shore Property Press is based on a real oblique aerial photo, which clearly shows the erosion problem on the shore, the public footpath undercut on the right, and a steep erosion scarp with rocks placed in front of the proposed apartments.

Who will foot the bill for ongoing foreshore erosion control? Will it be the developer? I think not. No wonder they are selling the apartments as quickly as possible. As soon as the apartments are built and sold the developer will be gone taking his profits with him. Ultimately the new apartment owners will be left with worthless rubble, or perhaps an apartment block stranded in the middle of the beach with the waves lapping around it, and Council will be blamed for allowing the building to be developed in the first place.

Another scenario could be that Council, ie. the ratepayers, will be expected to fork out for continuing foreshore erosion control so the apartment owners’ investment is not destroyed. How long could that go on? We know sea level is rising, and at an increasing rate, so sooner or later that option will become unworkable. I would expect insurance companies to do a rapid backtrack at the first sign of serious erosion threats.

The new apartment blocks under construction at Orewa.  The basement floor must be virtually at mean high water level, with the ground floor barely three metres higher.

The new apartment blocks under construction at Orewa. The basement floor must be virtually at mean high water level, with the ground floor barely three metres higher.

Eventually the beachfront properties will have to be abandoned. Why allow expensive re-development in the first place? Have there been some dodgy deals going on between developers, who stand to make large amounts of money, and Council planners to allow this re-development? The land is clearly at great risk of erosion from rapidly rising seas and increasing severity of storms under a changing climate regime.

Under the NZ Coastal Policy Statement (2010), Councils are obliged to take into account risks for at least 100 years hence, and need to plan for a sea level rise of 0.7m and to at least consider a rise of 1.0m in that time. Some researchers would consider that projected rise an extreme under-estimate. In fact nearly every review seems to escalate the estimates.

Clearly this is an eroding shore, yet Auckland Council continues to allow increasingly opulent redevelopment of houses right on the beachfront.  The fence, sales office and crane mark the construction site.  The sand cliff is where the undermined public footpath has been “repaired” with loose sand and has started to erode out again in the storm of 17th April 2014.

Clearly this is an eroding shore, yet Auckland Council continues to allow increasingly opulent redevelopment of houses right on the beachfront. The fence, sales office and crane mark the construction site. The sand cliff is where the undermined public footpath has been “repaired” with loose sand and has started to erode out again in the storm of 17th April 2014.

There have already been severe erosion events on Orewa’s foreshore, and expensive movement of sand by earthmoving machinery from one end of the beach to the other at Council expense. Those problems are only set to get worse. In the past century there has already been sea level rise of about 0.2m which has no doubt contributed to the current erosion problem.

There has already been a rise in sea level of about 0.2m in the past century, which has likely contributed to the current erosion problem at Orewa and some other beaches. (IPCC, 2013).

There has already been a rise in sea level of about 0.2m in the past century, which has likely contributed to the current erosion problem at Orewa and some other beaches. (IPCC, 2013).

There does not seem to be widespread understanding within sectors of Council which make decisions on these matters that sea level is rising now and will continue to rise well beyond the turn of the century when conservative estimates put the level at about a metre above its present height.

Perhaps one metre rise does not sound like much. If the water comes a metre higher up the beach so what? To understand the serious implications of a one metre rise in sea level, we need to understand a bit about the dynamics of what is going on near the shore and in shallow water offshore. On this type of shore it is not simply just a matter of the sea extending further up the beach and a bit of inundation of low-lying ground.

Recent pre-history.

Around 15000 years ago toward the end of the last ice age sea level was 120 metres lower than it is now and you could have walked to Great Barrier Island! From around 12000 years ago to 6000 years ago sea level was rising rapidly at an average rate of about two metres per hundred years as the earth bounced back from the last ice age.

During that rapid rise, although humans were on the earth they were nomadic and rising sea level and its associated severe coastal erosion and inundation was of little consequence. Our towns and cities only sprung up when civilization as we know it became established roughly 6000 to 8000 years ago after which sea level has remained essentially static. So from that time coastal towns and cities have been built close to sea level in apparent safety. We have become complacent and take it for granted that sea level remains stable, apart from daily tides which are normal in most parts of the world.

As post-glacial sea level rise came to an end about 6000 years ago all the beaches with low flat sandy areas behind them developed. Also spits like Omaha are only 6000 years old. We have been blessed with relatively stable sea level (and temperature) over the past 6000 years. Sandy flats and spits are common around our coast and have been prime targets for development of our coastal towns and beach resorts. They are recently deposited unconsolidated loose sand and very easily eroded.

There is a dynamic interaction between the sand on our beaches and the sand on the shallow seabed offshore. Over the last 6000 years of stable sea level, in many places there has been an equilibrium between erosion and deposition, with the shoreline being relatively stable. Any change in sea level will alter that equilibrium and change the dynamics.

Consequences of sea level rise on the “coastal zone”.

On an open coast beach like Orewa, essentially if sea level drops, sand will be eroded from the seafloor offshore and deposited on the beaches. Conversely if sea level rises, sand will be eroded from the shore and deposited on the seafloor offshore. The depth at which the seafloor “feels” the waves above determines the depth to which this dynamic interaction with the beaches occurs. This area is called the “coastal zone”.

Let’s take a conservative example of what would happen when we have a half-metre rise in sea level, which is likely within about 50 years. This will de-stabilise the system which will try to find sand to build up the seafloor offshore to satisfy the dynamics of the system. It will need enough sand to raise the seafloor by half a metre, out to the maximum depth offshore where waves can be “felt” by the seabed. In the sea off Orewa this depth would be at least 10 metres, which on this gently shelving sandy seafloor is out to approximately three kilometres offshore (see chart NZ 5321).

Part of hydrographic chart NZ 5321, showing the gently shelving seafloor off Orewa Beach and 10-metre depth contour between the pale blue and white areas, approximately 3 kilometres offshore.

Part of hydrographic chart NZ 5321, showing the gently shelving seafloor off Orewa Beach and 10-metre depth contour between the pale blue and white areas, approximately 3 kilometres offshore.

So the system will try to scavenge sand from somewhere to build up the seafloor by half a metre out to three kilometres offshore. That is an awful lot of sand to find, and the sea will take it from wherever it is easiest. At Orewa this is firstly the beach itself, and then the unconsolidated sand behind the beach to as far inland as satisfies the requirement.

Most of the Orewa commercial and residential area is about three metres above sea level (according to the Auckland Council GIS maps). A simple calculation suggests that half a metre of sand out to three kilometres offshore is equivalent to three metres of sand for 500 metres inland! So without massive erosion protection along the shoreline, the sea could progressively erode the sandy flat land behind the beach to a distance of 500 metres, or about to Centreway Road.

200 years ago such erosion would have been of little consequence, but now there is a vast amount of expensive infrastructure at great risk of destruction. Nature’s boundaries are dynamic. There is no respect for Man’s fixed artificial boundaries.

With sea level rise set to accelerate, and at least one-metre rise likely by the end of the century, the situation could easily get a lot worse than the conservative example above suggests. There may be an unpredictable time lag related to frequency and severity of storms both of which will increase due to climate change, but the trend is undeniable.

Auckland Council should be planning a managed retreat from low shore areas like Orewa, not approving new development or expensive re-development! We are setting up for a fight with the sea which we cannot win. There simply will not be sufficient resources to protect all the at-risk areas around the country from massive erosion and inundation caused by un-stoppable sea level rise.

Avoidance of future risk is the most cost-effective response to rising sea-level in most cases. Decisions on development should not increase the risk as this new apartment block on the Orewa foreshore clearly does.

Roger Grace,
9 April 2014. Revised 23 April 2014.

Further reading.

There is quite a lot available on the subject of climate change and sea level rise. In this context I would particularly recommend Bell (2011) and Hart (2011), and the brilliant series of articles by Cimino Cole in Mahurangi Magazine. Most of these reports are available on the internet.

Australian Government 2009 Climate Change Risks to Australia’s Coast. A First Pass National Assessment. Department of Climate Change 2009. 172 pages.

Bell, R.G. 2011 Sea-level rise synthesis for Auckland (2011). NIWA client report no. HAM2011-092 for Auckland Council.

Bell, R.G. 2014a February’s King Tides, part 1. King Tides Auckland on Facebook, Feb. 26, 2014.

Bell, R.G. 2014b February’s King Tides, part 2. King Tides Auckland on Facebook, Feb. 28, 2014.

Cole, C. 2013 New Unitary Authority Not Going to Plan. Mahurangi Magazine, 8 May 2013. http://www.mahurangi.org.nz (This also has a listing of 14 previous articles on sea-level rise, drawing on global information and experience but also discussing a specific local issue. Some brilliant stuff here!)

Craig, C. 2010 The effects of sea level rise in coastal environments. Auckland City Council.

Department of Conservation 2010 New Zealand Coastal Policy Statement 2010. New Zealand Government, DOC, Wellington.

Hart, G. 2011 Vulnerability and adaptation to sea-level rise in Auckland, New Zealand. NZCCRI 2011 report 08 October 2011. The New Zealand Climate Change Research Institute, Victoria University of Wellington.

IPCC, 2013 Summary for Policy makers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group 1 to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

IPCC, 2014 Climate Change 2014. Mitigation of Climate Change. Intergovernmental Panel on Climate Change.

Ministry for the Environment 2009 Coastal hazards and climate change: A guidance manual for local government in New Zealand. Wellington: Ministry for the Environment.

Nicholls, R. and Cazenave, A. 2010 Sea-level rise and its impact on coastal zones. Science, 328:1517-1520.

The Royal Society of New Zealand 2010 Sea-level Rise: Emerging issues. Wellington.

Comments

  1. Ron Cooper says:

    At last, we are able to read an expert account confirming the lack of wisdom in permitting this development to receive consent. I attended the hearing and made a submission pointing out the folly of this proposed development in the light of sea inundation. What astonished me was the comment by an ‘expert’ witness, a director of Tonkin and Taylor, a coastal engineering company, who stated that sandbags would be able to prevent the sea from entering and flooding the underground car park in the event of inundation from the sea. There were two commissioners who gave consent. One has, I subsequently discovered, had a number of his decisions overturned by the Environment Court and the other, a young man who, somehow was elected as a Rodney District councillor and who, it seemed to many of us, lacked sufficient knowledge of the issues relating to the effects of inundation and climate change. Having seen what storms are capable of doing to massive sea walls, this decision defies belief. Orewa has been exceedingly lucky over the past few years in that the heavy storms have not coincided with a 3.6m high tide nor with a significant low pressure. Nevertheless, as this article points out, erosion occurs with increasing frequency and Auckland Council appears to have no answer. During a site visit to Orewa by the Judge and his two commissioners, as part of the Plan Change Variation 101 hearing in the Environment Court, one of the latter expressed surprise that Moana Avenue was only about 1m above the high tide level. Auckland Council would do well to talk to Roger Grace and take note of his concerns. Alas, I doubt whether this would arise as there is far too much money at stake with the developers wanting more and more high rise in Orewa. Even after the Environment Court decision turned down plan Change Variation 101 which would have permitted buildings up to 12 storeys along the coast road, developers are, yet again, seeking high rise development in this low lying area under the Proposed Auckland Unitary Plan. Roger Grace hits the nail on the head when he asserts that the developer will not be around when the building is affected by sea inundation and it will be a battle between the residents and Auckland Council as to who should foot the bill for repairs or compensation. After all, it was the commissioners who granted consent so Auckland Council will probably have to be held liable. Thank you Roger Grace for putting together this well-thought article. I only wish that someone in Auckland Council reads it.

  2. Roger Grace says:

    Thank you Ron for your supportive reply. At the time of writing this article I sent it to several Councillors and other people. Interestingly I did not get one comment or reply from Councillors.

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