Sea-Level Rise – Should Whitianga Waterways Be Expanded?

 

New Government Guidelines on Sea Level Rise are a Gamechanger

The new Ministry for the Environment’s Guidelines on Sea Level Rise which were mistakenly released last week are a game-changer for Thames-Coromandel District Council and Councils throughout New Zealand.  New coastal “greenfield” development such as subdivisions will now have to be “stress tested” out to at least 2150 against a sea level rise of at least 1.9 m above current high tide levels.  A case in point is the Resource Consent application (SUB/2017/26) recently lodged by Whitianga Waterways for 72 new canal housing lots.  This application and many others like it will have to be assessed right now, against this new benchmark of a potential sea level rise of 1.9 m. This crucial decision-making must be made today, not next year or next decade.   Councils can no longer pretend that climate change and sea-level rise is something that future councils must deal with.

To be clear, this blog is not about whether the Waterways Project per se is a good or bad thing for Whitianga. There are a variety of opinions about that. Rather this blog concentrates on whether the Waterways developer and the District Council are giving sufficient and serious (even any?) attention to the potentially catastrophic effects of climate change and sea level rise for new long-term coastal developments such as this one.  

Millions of dollars will be sunk into new capital investment and infrastructure by both the developer and the Council.  Unwary buyers will be invited to purchase very expensive canal properties which could potentially be submerged by sea level rise within their lifetimes, or the lifetimes of their children. Many purchasers will take their cue from the Council if the Council consents to a new subdivision.  “If the Council has just given its OK – why should I be worried?  

The new Guidelines have changed all that.  They make it very clear that extreme caution needs to be applied to new subdivisions such as this which are at potential risk from intolerable coastal hazards.

What Do The New Guidelines say?

There is more detail in my previous blog but a quick recap of the new Guidelines shows the Ministry has set 3 “minimum transitional sea-level values”  to assist councils in the short term.  The sea-level value which is relevant to the current subdivision resource consent application is Category A –  1.9 m above the baseline of mean sea level 1996 – 2005.  

Slide 12.1

Category A is described as “coastal greenfield developments, change in land use, redevelopment (intensification), and major new infrastructure (or have potential to be staged to this level).   The new Guidelines also require that a longer planning timeframe to 2150 and beyond should apply to the upper range value of 1.9 metres. 

What does 1.9m sea level rise above high tide look like?

The Waikato Regional Council Coastal Inundation Tool   provides a ballpark indication of the effect of sea level rise.   For Whitianga Wharf, the Regional Council has provided a predefined level of for existing MHWS sea-level of 0.98m.  If 1.9m of sea level rise is applied above this existing MHWS level a total level of 2.88 m is indicated.  The approximate areas which would be inundated in Whitianga from 2.88 m are shown in the following graphic.  Note: The storm tide range and wave effects are not included.

Inundation Map of Whitianga with 2.8m SLR – no storm tideWhitianga 2.8m SLR

Storm Tide Effects

The Parliamentary Commissioner for the Environment (PCE)  has concluded that even a modest 40cm -50 cm of sea level rise will result in current “1-in-100-year” severe storm tides becoming an annual or six-monthly event.  1 m of sea level rise will result in the equivalent of a current “1-in-100 year” severe storm tide happening every day.  Severe storms may of themselves not be more frequent, or only marginally so.  But the effect of sea level rise will be to make a storm tide equivalent in force and intensity to today’s 1-in-100-year event –  a daily event.  A “stress test” for 1.9m SLR carried out by the Council must, therefore, include the effect of exceedances of 1-in-100-year storm tides for 1.9m SLR using the same methodology carried out in the PCE Report.

If the upper range of a Whitianga storm tide is added the total level indicated is 3.89m resulting in approximate “bathtub” inundation shown in the following graphic.  Again, wave effects which the WRC acknowledge can exacerbate the risk level are not included.

Inundation Map of Whitianga 3.8m with Max Storm TideWhitianga 3.8m with max storm tide

The result from either scenario is that the future viability of Whitianga as a functioning town would be seriously called into question.  A large area of the town would be inundated under the first scenario and almost the entire town would be submerged under the second scenario.  As well, several kilometres of the State Highway access from the west would be submerged.   A “stress test” considering this intolerable level of potential hazard would emphatically suggest that new “greenfield” development such as this should be avoided?

Best Available Information – Other Latest Sea-level Projections.

The H + scenario for Category A development in the latest Ministry Draft Guidelines requires that a sea-level rise of 1.9m be considered.  However, these guidelines are already conservative when compared to recently published guidance from the US National Oceanic and Atmospheric Administration (NOOA January 2017), and the California Ocean Protection Council (COPC) (April 2017).  NOOA is the equivalent institution to our NIWA.  These reports meet the test of “the best available information”, and therefore should be considered by Council.

Both NOOA and COPC have reviewed the latest peer-reviewed literature and have both concluded that a H++ scenario of 2.5m of SLR by 2100 is plausible and should be used to “stress test” Category A type development.

NOOA –  “The growing evidence of accelerated ice loss from Antarctica and Greenland only strengthens an argument for considering worst-case scenarios in coastal risk management” ……

Decisionmakers charged with planning for upgrades to existing long-life critical infrastructure, or building new infrastructure, need to consider the risks across a broad range of possible outcomes, including those associated with high-consequence, low-probability situations.”

  The COPC report came to almost identical conclusions: –

 “When decisions involve consequential infrastructure, facilities or assets, we advise that extra consideration be given to this upper end of potential sea-level rise outcomes”.

New ice-sheet projections suggest the rate of rise could accelerate sharply later in this century, with the potential for two meters or more of total sea-level rise by 2100. While the uncertainty in these projections remains high, the risk is not negligible given the stakes to future society, development, and infrastructure. Given the level of uncertainty but also the potential impacts, significant investment in any major new coastal development with long lifespans needs to be carefully assessed.”

The very clear conclusion from both US reports is that major new coastal development such as proposed in this current resource consent application needs to be carefully assessed against a potential sea-level rise of 2.5 m by 2100

 

Whitianga 4.49m with 2.5m SLR
Inundation with Max Storm Tide and 2.5m SLR by 2100 as per NOAA

The following table from the NOOA Report shows projected sea-level rise at 2150 with the Intermediate, Intermediate/High, High, and Extreme scenarios highlighted at 1.8m, 3.1 m, 4.3 m and 5.5 m respectively.

NOOA Global SLR Scenario HeightsNOAA SLR to 2200

If the latest draft Ministry Guidance is followed, including the requirement to consider Category A development out to 2150 and beyond, and the latest NOOA projections are used, then the current resource consent application would need to be assessed against a potential sea-level rise of between 3.1 m and 5.5m

Canal Sea Wall Already Being Overtopped

overtopping

Local Whitianga resident Thomas Everth has documented that the sea wall in the existing canal development is routinely overtopped during regular spring tides.  Thomas has raised legitimate concerns about the longevity of both the existing and future canal projects.

 

 

 

 

Conclusion

These are issues of immense significance for the town of Whitianga and the whole District. They have not been given even cursory consideration in the documentation filed in support of the subdivision application.

The applicant must be required to provide further detailed expert reports on sea level rise and coastal hazards risk, and/or the Council must commission such reports itself.  The application should be publically notified so that expert evidence can be presented and assessed. There is too much at stake to continue pretending we can have “business as usual.”

Note: there are some legal issues relating to the location of the “coastal environment line” which in turn has implications as to whether Government directives in the New Zealand Coastal Policy Statement on sea level rise and climate change apply.  I hope to cover these in a later blog.  In the meantime see Whitianga Waterways Stage 10 Paper

 

 

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