The erosion at Collaroy following the devastating June storms.

This is the first in a 2-part article was written by Jon Fairall and originally published in the Aug/Sep 2016 Issue of Position magazine.

In June this year, huge waves and king tides combined to drive Collaroy Beach, one of Sydney’s best, back 50 metres. Bad luck for surfers. It’s even worse if you own one of the multi-million dollar beach-side mansions that are now at risk of toppling into the sea.

The Water Research Laboratory at the University of New South Wales had been running a long-term survey of the beach. In the days after the storm, Ian Turner, the head of the lab, told the Sydney Morning Herald that “in the area we surveyed, for every metre along the beach, we have seen up to 150 cubic metres of sand stripped off the upper beach. It is now sitting in the surf zone.”

WRL is part of the consulting arm of the University of New South Wales. “We have been flying drones along the beach for at least two and a half years”, says Chris Drummond from WRL.

Currently, the lab is using the Sensefly eBee RTK drone, which is produced by SenseFly SA from Lausanne in Switzerland. It is equipped with a consumer-grade camera produced by Canon in Japan. After the imagery has been acquired, it is processed into a geo-referenced ortho-mosaic, which is used to generate an ortho-photo, digital surface model and point cloud. It is also possible to output contour lines and 3D meshes, all of which can be further processed using industry-standard software.

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According to the manufacturer, the drone can cover 12 square kilometres in a single flight with an optimum flight plan. If you want to maximise resolution, it is possible to generate imagery with a ground sampling distance of just 1.5 cm but only by sacrificing the coverage area.

“Our system can generate results to better than 7 cm accuracy without control”, Drummond says. “And we can do much better than that if we have control points.”

“We knew the June storms were coming, so we flew one sortie in the days before the storm hit, and one immediately afterwards. That is one of the reasons we were able to generate such accurate metrics on the state of the beach so quickly”.

The aftermath

In the wake of the storm, NSW state premier Mike Baird appointed deputy police commissioner Dave Owens as the State Recovery Coordinator charged with overseeing the recovery effort. Making the announcement, Baird said, “I want to ensure their efforts are coordinated in a way that allows communities to rebuild and recover as quickly as possible.”

It is a moot point whether that is the best strategy. In the aftermath of the storm, Sydneysiders were transfixed by the question of whether taxpayers would, could or should pay to repair the damage and build a seawall to protect the buildings in the future.

This is no academic issue, nor is it Sydney’s alone. Fifty per cent of the Australian coast is composed of sand or mud. The shoreline is dynamic, building seaward or eroding landward in a battle between land and sea that has been going on for millions of years. It only becomes an issue when the movement of the shoreline comes into conflict with fixed infrastructure.

In fact, it seems that along much of Australia’s coast it’s a mistake to think of a shore ‘line’; a shore ‘zone’ is more apt. An iron law seems to apply. Build within the zone and you need a bottomless pit of cash to protect your assets.

Before and After drone photography of Collaroy acquired during the post-storm survey carried out by the Water Research Laboratory. (Click to enlarge)

Traditional coastal protection, such as breakwaters, groynes, or seawalls are no answer. They ‘harden’ the coast, says Andrew Short at Sydney University.

Writing on the Coastal Watch website, Short argues that these defences usually make matters worse. Seawalls reflect and concentrate wave energy and therefore erosion, while groynes starve the coast of the sediment that naturally washes along it, which has the same effect.

The problem is not even limited to sandy beaches. Short cautions that, while the rocky shores of New South Wales appear much more resistant to erosion than its sandy beaches, there are local concerns about rock falls and public safety at Bilgola, Newport and Narrabeen headlands in Sydney, as well as about the steep cliffs at Coalcliff on the Illawara Coast. Landslides there are associated with the claystones and shales that lie between the beds of sandstones.

For many years, Lawrence Hargrave Drive, which used to wander along the foot of the cliffs, was regularly closed by falling rocks. The final solution was the Seacliff bridge, a 665 metre stretch of road that was built parallel to the cliff face 40 metres above the sea, but only after $52 million had been spent. Even then, in June 2015, the government had to allocate another $3 million to stabilise the approaches to the bridge.

The question remains: who pays?

The question of expense runs through this issue. If we continue to place infrastructure within the dynamic zone, it will cost money to protect. Should we protect public infrastructure? Even more contentious: should we protect private property? The question remains: who should pay?

To a first approximation at least, the law would appear to be straightforward. The Doctrine of Accretion first appeared in English law in 1636. It defines the shore line as the Mean High Water Mark. Freehold can exist down to the MHWM. Seaward, beyond the MHWM, belongs to the Crown, presumably out to the Territorial Limits.

In those cases where the MHWM is used as a boundary, gradual and natural changes in the position of the MHWM imply gradual and natural changes in the extent of the freehold. Movements in the MHWM boundary have no effect on the boundaries with other freehold titles. In a typical seaside setting, the movement of the sea along the front boundary has no effect on the back boundary.

The reality is somewhat more complex that this account may suggest. In every jurisdiction in Australia, elements of the Doctrine of Accretion have been modified or expressly repealed by legislation. Because Australian states are responsible for laws relating to property, and land in particular, and because land law is far from consistent across states, the actual legal framework that governs coastal land is complex and made even more so by the application of other state legislation.

In NSW, for instance, while many of the common law principles of the doctrine of accretion have survived, others have been expressly modified or negated by statutes created by the NSW Parliament, most recently by the Coastal Management Bill that was enacted in May 2016. Among other things, the Act compels local government to develop coastal management programs and provides penalties for home-owners who carry out works on their properties that are not sanctified by these programs.

Erosion on the Gold Coast, Queensland. Credit: Bruce Miller, CSIRO; CC BY 3.0

In Queensland, although some elements of the common law have been substantially overturned and replaced by statute, other principles of the doctrine have been codified as provisions in legislation, and thus continue as part of the relevant ‘shoreline law’.

The law may be murky; but the actual decisions of judges are positively arcane. In courts, much turns on the definition of ‘gradual, ‘natural’, ‘sudden’ and ‘catastrophic’. There was nothing ‘gradual’ about the Collaroy incident, but it was certainly ‘natural’. Sea level rise is ‘gradual’, as well as ‘catastrophic’.

Judges will have to attend to these definitions, because the issues will not go away. It’s going to get worse. In a recent paper written for the Intergovernmental Panel on Climate Change, Kathleen MacInnes, the leader of CSIRO’s Marine and Atmospheric Research itemised the consequences of climate change for the shoreline: sea level rise; an intensification of tropical cyclones; bigger waves; storm surges; altered precipitation or run-off and ocean acidification.

“These phenomena will vary considerably at regional and local scales, but the impacts are virtually certain to be overwhelmingly negative,” she said.

Of all these, it is the propensity for more extreme weather that seems to be the most important. Sea level rise may well be negligible out to the current planning horizon, but the evidence seems to be that more extreme weather is already upon us.

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