As a coastal defence, the Great Barrier Reef’s value to communities goes way beyond tourism



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Parts of the Great Barrier Reef’s outer reefs can form a natural barrier to coastal recession, thus protecting urban centres.
AAP

Mark Gibbs, Queensland University of Technology

Rising sea levels are widely recognised as a threat to coastal communities worldwide. In Australia, the Climate Council estimates that at least A$226 billion of assets and infrastructure will be exposed to inundation if sea levels rise by 1.1 metres. Another report recommended that global mean sea level rise of up to 2.7 metres this century should be considered in planning processes.

The Queensland state government has commissioned the QCoast2100 program. This program aims to help with the development of coastal climate adaptation plans for Queensland communities exposed to sea-level rise.

Although the largest population centres in Queensland are in the state’s southeast, several of the most populous regional centres in Australia are located along the Great Barrier Reef coastline between Gladstone and Cape York. These include Townsville, Cairns, Gladstone, Mackay and Port Douglas.

A major task in developing coastal adaptation plans under the QCoast2100 program is to model inundation from a range of scenarios for sea-level rises and assess how assets will be inundated in the future. However, another threat is on the horizon.


Further reading: What’s the value of the Great Barrier Reef? It’s priceless


How urban centres are protected

Urban centres along the reef’s coastline, which forms the majority of the Queensland coast, are protected from major ocean storms by natural deposits of coastal sediments. These include dunes and associated vegetation such as coastal forests, wetlands and mangrove systems.

These natural features continue to exist largely because the Great Barrier Reef’s outer reefs dampen incoming ocean waves. Although exposed to the occasional cyclone – which can lead to short-term erosion at specific locations – much of the coastal zone inside the reef is slowly growing out into the sea.

This increasing buffer zone can form a natural barrier to coastal recession.

A recently released report estimated the total economic, social and icon asset value of the Great Barrier Reef at A$56 billion. By design, this report did not include many of the ecosystem services the reef provides. One of these is its role in reducing the energy of waves that impact the coastline behind the reef.

However, an earlier assessment of the total economic value of ecosystem services delivered by the reef estimated the present coastal protection benefit is worth at least A$10 billion.

Despite the inherent uncertainties in such assessments, it is clear the reef acts to reduce incoming wave energy and its impacts on cities and towns along much of the Queensland coastline. The total economic value of these benefits is in the billions of dollars.


Further reading: Coastal communities demand action on climate threats


What role is bleaching playing?

The Great Barrier Reef’s ability to keep protecting the Queensland shoreline, and communities living along it, depends upon the ability of individual reefs in the system to grow vertically to “keep up” with rising sea level.

The jury is still out on whether the outer reefs will be able to keep up with predicted rises. This is an active area of research.

However, it is clear reefs that are extensively affected by coral bleaching will struggle to maintain the essential processes required for productive reef-building. Many reefs are now experiencing net erosion.

Predictions of ocean warming suggest that bleaching events will become even more common in coming decades. Increasing levels of atmospheric carbon dioxide are also making the oceans more acidic, which makes it more difficult for organisms such as corals to maintain their skeletons, which are made of calcium carbonate. This mineral dissolves more rapidly with increasing acidification, reducing the reef’s capacity to recover from storm damage and coral bleaching.

Therefore, as bleaching events and acidification continue, the outer reefs that protect the Queensland coast from ocean waves will increasingly struggle to perform this function.

The ConversationIn turn, over time the Queensland coast will potentially suffer from more coastal erosion, which may increase the vulnerability of coastal infrastructure. This effect, combined with rising sea levels leading to more coastal inundation events, multiples the risks to coastal settlements and infrastructure.

Mark Gibbs, Director, Knowledge to Innovation; Chair, Green Cross Australia, Queensland University of Technology

This article was originally published on The Conversation. Read the original article.

The Sydney Barrier Reef: engineering a natural defence against future storms


Rob Roggema, University of Technology Sydney

The risk of more severe storms and cyclones in the highly urbanised coastal areas of Newcastle, Sydney and Wollongong might not be acute, but it is a real future threat with the further warming of the southern Pacific Ocean. One day a major storm – whether an East Coast Low or even a cyclone – could hit Sydney. The Conversation

With higher ocean temperatures killing and bleaching coral along the Great Barrier Reef to the north, we could also imagine where the right temperatures for a coral reef would be in a warmer climate. Most probably, this would be closer to the limits of the low latitudes, hence in front of the Sydney metro area.

We should then consider whether it is possible to help engineer a natural defence against storms, a barrier reef, should warming oceans make conditions suitable here.

Ocean warming trend is clear

The oceans are clearly warming at an alarming rate, with the unprecedented extent and intensity of coral bleaching events a marker of rising temperatures. After the 2016-2017 summer, coral bleaching affected two-thirds of the Great Barrier Reef.

On the other side of the Pacific, sea surface temperatures off Peru’s northern coast have risen 5-6℃ degrees above normal. Beneath the ocean surface, the warming trend is consistent too.

The East Australian Current keeps the waters around Lord Howe Island warm enough to sustain Australia’s southernmost coral reef. The waters off Sydney are just a degree or two cooler.

With the East Australian Current now extending further south, the warming of these south-eastern coastal waters might be enough in a couple of decades for Nemo to swim in reality under Sydney Harbour Bridge.

This shift in ocean temperatures is expected to drive strong storms and inland floods, according to meteorologists.

On top of this, when we plot a series of maps since 1997 of cyclone tracks across the Pacific, it shows a slight shift to more southern routes. These cyclones occur only in the Tasman Sea and way out from the coast, but, still, there is a tendency to move further south. The northern part of New Zealand recently experienced the impacts this could have.

Think big to prepare for a big storm

If we would like to prevent what Sandy did to New York, we need to think big.

If we don’t want a storm surge entering Parramatta River, flooding the low-lying areas along the peninsulas, if we don’t want flash-flooding events as result of river discharges, if we don’t want our beaches to be washed away, if we want to keep our property along the water, and if we want to save lives, we’d better prepare to counter these potential events through anticipating their occurrence.

The coast is the first point where a storm impacts the city. Building higher and stronger dams have proven to be counterproductive. Once the dam breaks or overflows the damage is huge. Instead we should use the self-regenerating defensive powers nature offers us.

Thinking big, we could design a “Sydney Barrier Reef”, which allows nature to regenerate and create a strong and valuable coast.

The first 30-40 kilometres of the Pacific plateau is shallow enough to establish an artificial reef. The foundations of this new Sydney Barrier Reef could consist of a series of concrete, iron or wooden structures, placed on the continental shelf, just beneath the water surface. Intelligently composed to allow the ocean to bring plants, fish and sand to attach to those structures, it would then start to grow as the base for new coral.

This idea has not been tested for the Sydney continental flat yet. But in other parts of the world experiments with artificial reefs seem promising. At various sites, ships, metro carriages and trains seem to be working as the basis for marine life to create a new underworld habitat

The Sydney Barrier Reef will have the following advantages:

  1. Over decades a natural reef will grow. Coral will develop and a new ecosystem will emerge.

  2. This reef will protect the coast and create new sandbanks, shallow areas and eventually barrier islands, as the Great Barrier Reef has done.

  3. It will increase the beach area, because the conditions behind the reef will allow sediments to settle.

  4. It creates new surfing conditions as a result of the sandbanks.

  5. It will protect Sydney from the most severe storm surges as it breaks the surge.

  6. It will present a new tourist attraction of international allure.

Let’s create a pilot project as a test. Let’s start to design and model the pilot to investigate what happens in this particular location. Let’s simulate the increase of temperature over time and model the impact of a cyclone.

Let’s create, so when Sandy hits Sydney, we will be better protected.

Rob Roggema, Professor of Sustainable Urban Environments, University of Technology Sydney

This article was originally published on The Conversation. Read the original article.