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Tropical storms or cyclones are often to blame when beaches are severely eroded. But on the north coast of Australia’s New South Wales at Byron Bay, another force is at play.
For the past six months, tourists and locals have been surprised to see Byron’s famous main beach literally disappear, inundated with water and debris. In October, lifeguards were forced to temporarily close the beach because they were unable to get the rescue team to the sand. Resident Neil Holland, who has lived in the area for 47 years, told ABC:
It’s the first time I’ve seen it so bad in all the time I’ve been here, and it hasn’t stopped yet. The sand is being removed by the meter.
So what’s going on? To find the answer, we combined a brief analysis of satellite images with previous knowledge about the process behind the erosion and how it has been occurring in Byron Bay. Erosion is due to a process known as “head drift” and is quite different from erosion caused by storms.
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The beautiful Byron Bay of Australia is located in New South Wales.
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What is headland diversion?
Head diversion occurs when sand moves from beach to beach around a solid obstruction, such as a rocky headland or headland. This process is driven primarily by wave energy. Along the southeastern coast of Australia, the waves generate currents that move the sand mainly north along the north coast of New South Wales and into Queensland.
However, the sand does not flow evenly or smoothly along the shoreline: when the sand reaches a beach just before a rocky headland, it accumulates against the rocks and the beach widens. When there is too much sand for the headland to hold, or there is a change in wave conditions, some sand will be pushed around the headland, bypassing it, before continuing your journey down the coast.
This large piece of moving sand is called a “sand pulse” or “sand slug”. The sand pulse needs the right wave conditions to move towards shore. Without these conditions, the beach in front of the pulse is deprived of sand and the waves and currents near the shore erode the beach.
Headland diversion was first described in the 1940s. However, only about 20 years ago it was recognized as an important part of the process of controlling sand moving along the coast. Since then, with better technology and more data, researchers have studied the process in more detail and have helped shed light on how headland drift could affect long-term coastal planning.
Recent studies have shown that the direction of the waves is particularly important in deflecting the headlands. Importantly, wave-producing weather patterns are affected by climatic factors, including the El Niño Southern Oscillation and the Pacific Interdecadal Oscillation. So future changes in the way these drivers behave will affect the waves and currents that move the sand along our coastline, which in turn affects headland drift and beach erosion.
Advice from Byron Shire
Byron Bay’s beaches have eroded a lot in recent months.
What’s going on in Byron Bay?
In October and November of this year, there was a large amount of sand just north of Cape Byron, from Wategos Beach to The Pass Beach. As this pulse of sand grew, Clarkes Beach, and then Main Beach, were deprived of their usual supply of sand and began to erode.
The sand pulse is visible on satellite images around April 2020. Each month, it slowly moves west towards the bay. As the sand pulse grows, the beach in front of the pulse gradually erodes. Currently, Main Beach is in the erosion stage.
Similar erosion was observed on Main Beach in the early 1990s. The beach widened again from 1995 to 2007. Beginning in 2009, shoreline erosion started slowly again and became very noticeable in the last six months. .
The effect of sand pulses on beach erosion is not unique to Byron Bay. It has been previously described elsewhere, such as Kingscliff Beach in New South Wales in 2011. In that case, erosion risked damaging a nearby holiday park and bowling club.
When will this end?
Gentle waves from the east to the northeast, which generally occur from October to April of each year, will help some of the sand pulse move towards Clarkes Beach and then Main Beach. This usually happens for several months to a year. But it’s hard to say exactly when the beach will be fully restored.
This uncertainty underscores the need to better forecast these processes. This would help us to predict when sand pulses will be avoided and to manage beach erosion.
Climate change is expected to affect wave conditions, although the exact impact on the headland drift process is unclear. However, better predictions would allow the community to be informed early on expected impacts, and officials could better manage and plan for future erosion.
Meanwhile, Byron Bay waits and watches, knowing at least that the erosion problem will eventually improve.
Thomas Murray is a researcher (coastal management) at Griffith University; Ana Paula da Silva is a doctoral candidate at Griffith University; Darrell Strauss is a Senior Research Fellow at Griffith University; Guilherme Vieira da Silva is a researcher at Griffith University and Rodger Tomlinson is the director of the Griffith Center for Coastal Management at Griffith University.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
