A new report from the State of California projects up to 2/3 of their iconic southern beaches may completely erode back to the landward limit of coastal infrastructure or cliffs by the end of the century because of sea level rise. Consider for a moment what the impact will be if up to two thirds of Coromandel beaches are progressively erased off the face of the earth within one generation.
Sure, there will be differences between here and California in terms of the topography, wave action and the other factors which influence erosion. But even if the impact was at the lower end of projections and one third of Coromandel beaches were eradicated, the effect on the local economy would be devastating. The possibility exists that the impacts here will be greater than in California? When we talk about Coromandel beaches we often think, Buffalo Beach, Cooks Beach, Hot Water Beach Tairua, Pauanui and Whangamata. But this scenario would also include beaches on the western side such as Te Mata, Tapu, Te Puru, and Waiomu etc.
These are very hard to comprehend and inconvenient truths, and it is understandable that some people refuse to face up to them. Seeing a memorial plinth to Capt Cook topple into the tide due to beach erosion is one thing. The speed and extent of the erosion already underway is plain to see from these photos.
Having entire beaches progressively stripped of their sand back to the cliffs within one generation is an entirely different beast.
But if we are serious about adaptation and sound planning, we cannot continue with “business as usual” and allow rampant development near our beaches. We have the warnings staring us in the face that within many of our lifetimes, and certainly within the lifetime of our children and grandchildren, many of our iconic beaches will be lost forever.
We will also have to completely rethink the basis of our local economy. One of the main reasons why so many people come to visit the Coromandel may no longer exist or be seriously curtailed. We will still have a reasonably pleasant (although warmer and much wetter) climate, some fertile soils, some excellent recreational activities inland on conservation land. Boating should still be an attraction? So long as road transport links can be maintained, we will still have a desirable place to reside and visit. But we would be very foolish indeed to think that the devastating effects projected for Southern California’s beaches will not happen here.¶
Here is a direct quote from the report –
“In a recent study, researchers use the CoSMoS model to simulate the long-shore and cross-shore transport of sand and other processes, and to estimate the dynamic, long-term impacts of SLR and waves on 500 km (312 miles) of coastline in Southern California. The simulation of the historical period (1995-2010) shows excellent agreement with observations. The future simulations estimate that 31 to 67 percent of Southern California beaches may become completely eroded to the landward limit of coastal infrastructure or cliffs by the end of the century, assuming SLR scenarios from 0.9 to 2 m (3 to 6.6 ft) and limited human intervention”
Denis Tegg - teggtalk 
It is also important to note that any changes accompanying projected sea level rise are likely to take decades to occur. We are not talking about “overnight” change.
At present we are dealing with beaches that largely just fluctuate backwards and forwards (when viewed over periods of decades). As noted above, that will likely change with sea level rise. While those longer term changes could be very significant (as you and I note above), the rate and scale of change will depend critically on the rate of sea level rise AND actual beach response to this (i.e. whether beaches erode as predicted or more/less).
The rate of sea level rise over the next century and beyond is hugely uncertain and the current central government guidelines recommend the use of various alternative sea level rise scenarios. These alternative scenarios all involve sea level rise but range from about 0.3m (lower bound scenario) to 0.6m (towards upper bound – 85th percentile) over the next 50 years; and from 0.55m (lower bound) to about 1.35m (high – 85th percentile) over the next 100. As I have outlined above there is also uncertainty about beach response. While there is general agreement that eastern Coromandel beaches are likely to erode, the response may be considerably less than the 1cm = 1m erosion in the article. In fact, current setbacks suggest it could be only 20-30% (varying from beach to beach) of that rate.
So, we have a lot of uncertainty and we also have time to work through the details with affected landowners and communities and decide together the best way forward; develop adaptive management strategies for each beach. Council have already kicked off this process. It is important that we properly inform coastal communities about existing and potential future risk and identify and plan for the full range of possibilities, not just the more extreme scenarios.
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Hi Denis
It is correct that sea level rise is likely to give rise to permanent retreat on the sandy beaches of the Coromandel. The actual retreat will likely vary from beach to beach and we only have crude models (e.g. Bruun Rule) to estimate this effect at present.
The existing TCDC erosion hazard setbacks (which a colleague and I developed) use figures of approximately 20-30m retreat for every 1m of sea level rise. These figures are only 20-30% of the 1cm SLR =1m beach retreat used in the article you quote. However, there are quite well known coastal scientists who argue that the existing models under-estimate the likely effect and that the erosion could be 2-3 times higher than predicted by the Bruun Rule (which would give similar results to the figure used in the article). Significantly, it will also be permanent beach retreat; unlike most present erosion on our east coast beaches which is largely temporary (i.e. associated with shoreline fluctuations); even though sometimes persisting for 2-3 decades or more.
It is important to note however that such erosion will not necessarily destroy the beaches – that will depend on other factors, including how the erosion is managed. If the retreating beaches are free to erode AND encounter sand (which extends well inland at most but not all eastern Coromandel beaches) then the beaches will persist. Under these conditions, all erosion does to the beach is move it landwards. Beach loss will only occur where the retreating beaches encounter hard surfaces such as old sea cliffs under the sand (which occur at Hahei and some other sites) or sea walls. At these sites, significant beach loss will occur with erosion.
It is this clash between high value public beaches and high value nearshore properties that lies at the heart of the difficulty in managing coastal erosion.
Regards
Jim Dahm
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