Coastal erosion undercutting policy

By Costa Haritos. This article first appeared in Issue Three 2018 of Fire Australia.

The Australian dream of owning a beachside property is slowly falling apart as the threat of coastal erosion on our favourite Australian beaches becomes a primary concern for coastal managers. Severe storms can cause significant damage to coastal towns, infrastructure and properties. This is a threat to many of the 80% of Australians who choose to live near the coast.

Erosion can be a complex beast. For those who live at the beach, it is not always as simple as assuming what happens at one location is the same elsewhere—local geography can play a huge role in determining just how detrimental erosion can be. But researchers involved in the Bushfire and Natural Hazards CRC’s Resilience to clustered disaster events at the coast: storm surge project have now conducted fieldwork and modelling to help save Australia’s pristine beaches at two sites where beach erosion is an ongoing management issue. The research team, based at Geoscience Australia and the University of Queensland, has been conducting extensive research since 2015. They have now created a StoryMap as a way of explaining their discoveries, engaging coastal managers and interacting with communities.

“The StoryMap can be used by coastal communities to get an introduction to what causes coastal erosion, and how it can vary from location to location,” said project leader Dr Scott Nichol, from Geoscience Australia. Dr Nichol has worked as a coastal geomorphologist and sedimentologist for 25 years, specialising in marine geoscience research.

The research team conducted research at Old Bar on the NSW central coast and at Adelaide’s metropolitan beaches. Specifically, the project looked at the response of beaches to successive storms known as storm clusters, which can cause extensive damage to the coast over time. “These locations were active erosion hotspots that had posed some challenges for coastal managers,” Dr Nichol said.

Textile sheets, sandbags and dune stabilising plants had been placed before the study began along the Old Bar coast to mitigate wave undercutting. This occurs when the sand gets so wet that it collapses—a particular danger when a house or road is built on top. The saturation of soil and sand reduces the strength of the ground, increasing the chances of landslides and erosion. The two case studies are a way of demonstrating a national method to understanding coastal erosion in two distinct coastal environments.

“The important thing is that this information gets people thinking and asking questions,” explained Dr Nichol.

The StoryMap shows the dune crest at Old Bar continuing to shift further back over time. It predicts that more than 20 buildings will be at risk of damage by the changing sand dunes in the next 50 years, with a further nine buildings predicted to be within 10 metres of the dune crest in the same period.

For Old Bar alone, this has vast implications for these residents, as well as any future development in the town.

The researchers calculated the results by investigating the annual exceedance probabilities, which measure the amount of erosion from storm clusters over 12 months and the probability of that number being exceeded each year. The team analysed wave buoy data from Old Bar to classify any wave height exceeding 2.93 metres as a storm. They also conducted surveys on the size of sand grains, the height of waves, and the depth of beach sediment, which is measured by a radar that penetrates the subsurface of the ground.

James Guy, from South Australia’s Department for Environment and Water, is an end user for the project. He explained the research team has provided a body of knowledge around the shoreline response to clustered storms.

“The new data, modelling tools and summary information for the Adelaide metropolitan beaches and Old Bar are essential reference materials for coastal managers,” Mr Guy said.

While the modelling does not consider rising sea levels or changes in the intensity of storms, Dr Nichol stresses that the conversations occurring now are key.

“The project provides information for decision-makers, who will need to assess the risk of erosion in the context of other factors before taking action,” he said.

The research team hopes that the information will provide decision-makers with the tools they need to assess the risk of erosion and help fast-track policy formulation.

Coastal managers can use the methods presented in the StoryMap at other beach locations nationwide where sufficient data is available. This can improve their planning and response to severe storms.

Researchers on the team say there is a continuing need for data and a greater understanding of how successive storms can affect a beach. This will benefit the estimated 700,000 residents across the country who live within three kilometres of the coast and less than five metres above the average sea level, where erosion could have life-changing consequences.

The Department for Environment and Water in South Australia will begin using the outcomes of the research to refine its annual beach replenishment program in Adelaide. The program is part of Adelaide’s Living Beaches Strategy, which identified beach erosion as an ongoing management issue in the 1970s. The Strategy, which aims to reduce the impact of erosion by continuing beach replenishment and recycling sand more effectively, will reduce the cost of managing Adelaide’s coastline by up to 20%.

The Victorian State Government will also use some of the research methods from the project as part of a coastal compartments study led by its Department of Environment, Land, Water and Planning. The Victorian study is funded for four years, with $3 million pledged by the state government. This will provide communities with information on coastal conditions and the long-term impact of climate change on the beach landscape.

Dr Nichol said the open data and tools developed through the research need to be matched with the right support and technical expertise from governments.

Through sustainable development and the right actions, the Aussie beachside dream can still be alive for future generations. For now, though, it is up to policy-makers to prevent that dream from washing away.

The research project concluded in June 2018. 

View the StoryMap here.