Shifting Sands – the end of a Kiwi dream

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The Kiwi dream of owning a beachfront property with panoramic views of the ocean is under threat—and not just for financial reasons.

The inflated property market has put the kibosh on many beachside fantasies, but there is another challenge to the realisation of this dream—one that cannot be easily overcome.

Just ask the residents of Granity, Punakaiki, or Carter’s Beach on the South Island’s West Coast; or Oamaru, Ocean Beach, or Clifton on the East Coast. In fact, from Cape Reinga to Bluff, thousands of properties are affected by this threat and it’s only getting worse.

We’re talking about coastal erosion—an ever-present threat to our coastlines—and NIWA scientists are working against the clock to help residents and councils alike to manage the risk and save their beachside property.

A community united

NIWA’s Dr Murray Hicks, Principal Scientist—River and Coast Geomorphology, and Dr Michael Allis, Coastal Engineer, have been working extensively with communities on the South Island’s West Coast affected by coastal erosion.

For more than 20 years the ocean has been bearing down on the Coast’s isolated communities, claiming houses, garages, roads, and even a school pool. The issue came to a head in 2016 after several garages in Granity were damaged by large waves washing into people’s backyards.

Drs Hicks and Allis attended an emotional public meeting in Ngakawau in late 2016 lasting more than two hours in which ideas were thrashed around and an agreement reached between the residents of the Granity, Ngakawau, and Hector communities to work with the West Coast Regional Council on the best sea erosion protection for their individual circumstances.

“Coastal erosion is a really sensitive issue. When it involves people’s homes there is an extra emotional factor. After the Ngakawau meeting a woman came up and showed me photos of her property. The ocean is eating into her property, which is her home and livelihood. She has very limited options. As a researcher and scientist, [finding a solution] certainly keeps you up at night. In this case, I am confident that we have provided the best package of options for this community to combat the risk,” says Dr Allis.

“There is a grieving process that communities go through. First it’s denial—‘there’s no erosion, our property will be fine’, then sometimes anger and depression, but eventually there’s acceptance— ‘okay, let’s find a solution that works’. Our role is to partner with councils and communities through this process, providing advice where appropriate. Ultimately, the landowners have to pay for any protection works, so they make the decision; we are just informing them to make the wise decision. These Buller district communities are just some of the places around New Zealand that have large numbers of properties at risk from coastal erosion. We are trying to establish a best practice protocol for community engagement to work alongside them through this process.”

Blame the early settlers

Coastal erosion is not new, and it’s often cyclical. On a monthly to seasonal basis, sand and gravel is deposited on the coast during relatively benign wave conditions, then is eroded and cast offshore during stormy conditions. Over longer time periods, often spanning centuries, accretion/erosion cycles can occur in response to waxing and waning supplies of sand and gravel brought to the coast by rivers—associated with episodic earthquakes and large floods. Over thousands of years, glacial cycles and associated swings in sea level also force the coastline in and out.

In the case of the West Coast—and many other coastal areas around New Zealand and overseas—a major part of the problem lies in where communities have been established.

“The issue of coastal erosion on the West Coast has become critical recently as there has been a relative deficit of earthquakes and landslides since the development has occurred. Earthquakes and landslides from past centuries had stocked the beaches with sediment, and when the early settlers arrived the coastline appeared stable and they decided to build close to the beach. I completely understand. It was a nice place, I’d love to live there—great views, beach access—but they weren’t aware of the long-term cycles and built too close to the coast,” says Dr Allis.

Indeed, these early settlers were focused on getting the communities established and business booming, not the environmental risks associated with the area.

The Oamaru District Council has long had to factor in coastal erosion to its plans after the town was settled on a low coastal terrace. Research on the issue dates back decades, with geologist Jeremy Gibb describing the coast as in a “long-term state of retreat” back in 1978. Fast forward 30 years and Waitaki Boys High School lost 60m of its sports ground to erosion in 2008. Planting along the ridge has held back the risk (at least in the short-term), along with the school’s prudent decision to move its sports ground further inland.

In June 2007, the coastal cliffs at Oamaru lost a lot of ground, including a conservation area for blue penguins and the factory seen here. [Photo: Murray Hicks, NIWA]

“People like to live on the edge of water, which is a problem when the coastline is in a recessional phase, which is what we have found ourselves in over the past hundred years or so. Things are not looking as flash [now] in terms of coastal stability as they were when these communities were settled,” says Dr Murray Hicks.

“The sensible thing is for communities to retreat from the coast, but most property owners want protection over the next 10–20 years and to buy some time before they are forced to retreat, without having to spend a huge amount of money of course.

“One solution is sloping seawalls built from rock, but this is cost-prohibitive for most private owners, and regional councils can only undertake works if ratepayer funds are available. The general emphasis is on short-term measures with an integrated approach across the community, rather than have one person building a large seawall 20 metres long, which can have a disastrous effect on neighbours up and down the coast—with the seawall effectively becoming a breakwater and pushing the water around the wall onto neighbouring properties.”

In Punakaiki the community is banding together to fund an extension of an existing seawall by 160 m with the assistance of the West Coast Regional Council.

Hydro dams exacerbating erosion

While there is a natural component to coastal erosion, humankind has not helped matters in some locations with advances in technology and our insatiable need for power exacerbating the problem.

“Globally there is a shortage of sand on beaches. In part this is due to rising sea levels, but the effect of dams on rivers on coastal erosion has been significant around the world, and New Zealand has followed a similar pattern,” says Dr Hicks.

Over the past four decades Dr Hicks has established a sizable research cache on erosion in New Zealand and has provided expert guidance and assessments to councils and corporations on the impact of hydro dam developments on coasts.

“Rivers bring sand and gravel out to the coast and waves then move this material along the coastline. Dams can reduce coastal sand and gravel delivery in two ways: the first is simply by trapping this sediment behind the dam; the second is by reducing the size of floods downstream from the dams, which reduces the capacity of the river to transport sediment to the coast.

For scientists and researchers the decades-long time lag between dam construction and the arrival of the deficit in sediment load at the coast makes it difficult to provide a definitive cause-effect link with erosion of the adjacent coast. Researchers also have to ascertain how much sediment is stored in rivermouth bars, some of which may be large enough to buffer sediment supplies to the adjacent coast for many years. The initially controversial Clyde Dam on the Clutha River, together with the earlier-built Roxburgh Dam, provided researchers with a valuable case study.

“Back in the 1950s, about 570,000 cubic metres of sand and fine gravel was delivered to the coast by the Clutha River each year. The Roxburgh and Clyde Dams have in tandem reduced this by 95 per cent for the past 60 years. The issue of how this sediment deficit may be responsible for coastal erosion between the Clutha mouth and Otago Peninsula was significant in the re-consenting of the Clutha Hydro Scheme, but there were conflicting arguments as to how much of the Clutha sand naturally nourished the coastline and how much of it was dispersed offshore by waves and currents,” says Dr Hicks.

The effects of hydro dams are also being felt further north. Dr Hicks’ research in 2002 revealed that rates of coastal erosion north of the Waitaki River mouth increased over the first 40 years after the construction of the Waitaki Dam. This aligned with his estimates that damming the Waitaki River had reduced its delivery of gravel to the coast by 50%. However, more recent surveys show no consistent signal of a dam effect on the Waitaki coast.

“The eastern coastline by Oamaru was eroding quite severely even in a natural state. Naturally there is a strong northward longshore transport of beach gravel along this coast, with the bulk of the wave energy that drives this coming from the south; so Oamaru, to the south of the Waitaki mouth, never received much nourishment from Waitaki gravel,” says Dr Hicks.

Eroding our rivers

The long-term effect of commercial gravel extraction from rivers is another area of concern for Dr Hicks and his colleagues.

Across New Zealand there are numerous companies involved in riverbed gravel extraction, with the gravel used for concrete and roading aggregate. As well as providing economic benefits (i.e., with provision of raw materials for infrastructure, employment and business opportunities), gravel extraction often also has the added benefit of enhancing flood protection by removing excess sediment. While this may be seen as a “win-win”, as Dr Hicks found, the level of extraction is sometimes excessive.

Rivers naturally transport sand and gravel out to the coast, helping replenish beaches; however, dammed rivers reduce this process by trapping sediment and reducing the size of floods. [Photo: Dave Allen, NIWA]

Back in 2005, Dr Hicks, Dr David Kelly and Dr Alistair McKerchar researched the downstream effects of over-extraction of river gravels using biological and sedimentological data. The trio focused its research on the Kakanui River near Oamaru in Otago and the Waimea River and its tributary the Wairoa River near Nelson in the Tasman District.

“We found gravel harvesting can trigger severe physical and biological changes. Gravel tends to move downstream in pulses during freshes and floods. Gravel harvesting in the Kakanui appeared to have starved downstream reaches of gravel supply, thereby degrading the channel, fining the substrate, and exposing bedrock. Some of these same trends were apparent in the Wairoa River, but to a much lesser degree,” says Dr Hicks.

“Over the past 20 years there has been considerable over-extraction in some regions. Rivers around Nelson and in Southland have limited gravel-supply rates and past extraction rates have far exceeded the supply rates. In Southland, lowering of the Oreti River bed has caused concern about bridge pier stability. In Mid to South Canterbury the over-extraction of river gravel has likely contributed to accelerated coastal erosion.”

Seawall construction on the Kapiti Coast. [Photo: Dave Allen, NIWA]

Mining the science of sand extraction

Sand extraction is big business in New Zealand—iron-rich mineral sand (ironsand) is mined for domestic and steel manufacture, and Statistics New Zealand says iron and steel exports contributed more than $471 million to the New Zealand economy in 2015.

Coastal sand is also extracted for construction purposes and to renourish beaches where sand is naturally no longer present (such as Auckland’s Mission Bay, which is renourished with sand from Pakiri, and Wellington’s Oriental Bay, which is routinely replenished with sand from Golden Bay).

In a 2011 edition of Water & Atmosphere, Dr Alan Orpin detailed the approaches made to NIWA by mining companies wanting to know about ironsand reserves along the west coast of the North Island between Whanganui and Kaipara. In the article Dr Orpin stated: “There are some sedimentary bodies that are very rich in ironsands. But, to be economic, it’s all about volume. The scale of marine extraction we are talking about is unprecedented.”

Among the approaches was one from Trans-Tasman Resources, who commissioned NIWA to provide scientific data for their 2014 application to the Environmental Protection Agency (EPA) for a marine consent to undertake iron ore extraction and processing operations offshore in the South Taranaki Bight. The controversial proposal met with strong community opposition and the EPA ultimately rejected the application on the grounds “(Trans-Tasman Resources) did not consider the wider effect on the environment from digging up 50 million tonnes of sand per year.”

“There are certainly considerable public concerns around this project that are understandable. Several NIWA scientists were involved in the 2014 application assessing coastal circulation patterns, drift on the coastlines, and sediment plume movement. In this case there wasn’t a clear-cut link between the extraction project and coastal erosion. Trans-Tasman Resources are now trying again for consent and have another Environmental Protection Agency hearing in a few months’ time. NIWA staff have again been involved in this process,” says Dr Orpin.

RMA: Safeguarding our coasts

Solutions to New Zealand’s erosion woes are not straightforward, but steps have been put in place to ensure the issue doesn’t worsen through poor planning or building. Dr Hicks says the Resource Management Act (RMA) 1991 (and subsequent amendments) highlighted the effects of activities on the environment in the medium- and long-term, along with central and local government and iwi policies.

NIWA is integral in the approvals process, with scientists providing technical reports and evidence at hearings and Environment Court fixtures. In the past year alone NIWA scientists have provided myriad assessments and technical reports across all areas of inquiry, including aquaculture, atmosphere, climate, coasts, fisheries, freshwater and estuaries, and natural hazards. In some cases the findings have forced developers and policy makers to pause to reflect the impact of the respective projects' initiatives on the environment and communities.

NIWA’s impartiality is crucial to the process says Dr Orpin.

“NIWA scientists are regularly called upon to provide expert information for political and corporate decision makers. As scientists we are not for or against an issue; we are approached to speak to the science of an initiative,” he says.

Looking to the future

Our coastlines will continue to evolve and erode over the coming decades. In the face of rising sea levels, New Zealand’s coast will remain in a ‘recessional stage’ for some time, and pressures will persist on our rivers, with both sand and gravel extraction activities and dams permanent fixtures on the landscape.

There will be localised changes—as seen in the recent Kaikoura earthquakes, which dumped a considerable amount of sediment onto the eastern coast—but with rising sea levels and increasing storm ferocity, we cannot count on all our coasts being replenished anytime soon.

It’s time for a shift in focus—to look further inland to realise our “Kiwi dream”. It may still be possible to have a property with panoramic views of the ocean—just perhaps from up high on a hill.

This article appeared in Edition 17 of Water & Atmosphere.
Research subject: Climate Change