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ashley estuary

Where will estuaries be allowed to go?

I don’t normally spend my weekends trolling through policy statements, but here’s a little food for thought.

The 2014 National Policy Statement for Freshwater Management doesn’t cover estuaries, which are of course vital for many braided river birds. Estuaries are instead covered in the 2010 Coastal Policy Statement. In it, Policy 26 Natural defences against coastal hazards (1), states that it is necessary to, “Provide where appropriate for the protection, restoration or enhancement of natural defences that protect coastal land uses, or sites of significant biodiversity, cultural or historic heritage or geological value, from coastal hazards.” 

Since the biggest hazard identified by the 2010 Coastal Policy Statement is rising sea levels, let’s skip across to the Ministry for the Environment’s information on ‘Adapting to sea-level rise’. Here you’ll read that regional and local councils are obligated to prepare for the impacts of rising sea levels.

A key tool for doing so is over on the DOC website: Coastal Hazards and Climate Change – A Guidance Manual for Local Government in New Zealand (2nd ed) 2008. It’s an excellent guide, and the online version has updates as recent as 2010. However, the emphasis is on risks and adaptation strategies to property and infrastructure. Where biodiversity is mentioned, it conflicts with social and economic factors. Case in point: Policy 3: Precautionary Approach – I’ll explain why in a moment.

If rising sea levels sits in your mental ‘too hard basket’, it’s worth taking a few minutes to watch the Parliamentary Commissioner for the Environment, Dr Jan Wright, explain in a video I’ve loaded to the BRaid website. As Dr Wright points out, knowledge of the basic science is fundamental to understanding the problem. 

In the Ministry’s defence, it’s hard to keep up to date when it comes to rising sea levels. Because of the staggering implications, peer-review research is being published at a breathtaking pace, with the latest evidence published this year making the IPCC AR4 ‘worst case’(A1F1) scenarios that underpin both the 2008 Guidance Manual and 2010 Coastal Policy Statement seem wildly optimistic. Even the IPCC AR5 prognosis for rising seal levels is considered conservative, at best.

So what does this mean for braided river estuaries? Where coastlines are undeveloped, soft shore ecosystems including estuaries adjust naturally to sea level rise through spatial reconfiguration. Simply put, they migrate inland, inundating and/or eroding landward ecosystems as they go. That may seem obvious, and probably acceptable (unless you’re trying to protect rare-and-about-to-be-drowned freshwater and terrestrial ecosystems), until you realise that most braided river estuaries are not on undeveloped coastlines. Instead, they’re surrounded by unstable dune systems (made unstable by) exotic forestry, agricultural and commercial lands, private and public properties, and critical infrastructure such as roads, bridges, and wastewater treatment plants constructed and maintained through rates and taxes. And let’s not forget that any time these are lost or damaged by floods, our rates and insurance premiums hike up another notch.

As McGlone et al point out, ‘It is unlikely that people will readily allow new areas of dunes, marshland or estuary to form behind those now present. The most probable response to sea-level rise will be to protect assets and infrastructure by erecting new hard barriers to prevent erosion, planting sand dunes to stabilise them, and infilling encroaching wetlands and installing new drainage. This scenario (often termed ‘coastal squeeze’ in the international literature,) means that rising sea levels will probably remove large areas of the rich biological habitat.’.

A quick look at the Ashley estuary drives this point home. NIWA scores coastal environments with a coastal sensitivity index (CSI) for inundation (from the sea) and erosion. This stretch of the Pegasus Bay coastline is in the CSI inundation red zone – one of the most vulnerable in New Zealand. It’s a ‘soft shore’ environment comprised of the odd remaining unstable dune planted with exotic forestry, agricultural lands and houses, and critical infrastructure including SH1. Just to the north, sitting barely above sea level is the Amberley wastewater treatment plant. In June last year, low lying properties in the area around Ashley estuary were flooded. SH1 was closed near Saltwater Creek for most of the day, just moments after I drove through water exceeding 1m deep in places.

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Saltwater Creek, (Ashley estuary) flooding SH1 June 2014

Council engineers were later criticised for not ensuring that drainage was up to scratch. While some of the drainage issues certainly were attributable to the unusual weather event, drainage is going to become increasingly problematic when outlets are below sea level at high tide. Flapper valves and pumps (presumably powered by generators mounted above floodwaters) might help, but the drains were not designed for the volume of water that storms turbocharged by climate change are already delivering. Unless a sea wall is built from one end of Pegasus Bay to the other, the ocean is simply going to flow up the rivers, something all the drainage in the world won’t prevent.

So, going back to the Guidance Manual Policy 3: Precautionary Approach. What takes precedence:  2(a), to ensure that, ‘avoidable social and economic loss and harm to communities does not occur‘ or 2(b), ‘natural adjustments for coastal processes, natural defences, ecosystems, habitat and species are allowed to occur‘?

If McGlone et al are right, and 2(a) ends up trumping 2(b), can anyone explain where the Ashley estuary will be allowed to go?

References  and  further  reading

See also the Canterbury Regional Policy Statement 2013, which identifies climate change as one of the two key issues facing the region.

 

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