Images in the wake of violent coastal storms usually focus purely on the extensive damage caused to beaches, dunes, property, and surrounding infrastructure. However, a new international study has shown that extreme weather events could help protect beaches from the impact of sea level rise – by bringing in new sand from deeper waters or from nearby beaches. The study, led by Dr Mitchell Harley from UNSW Water Research Laboratory, is published today in Nature Communications Earth & Environment.
“We know that extreme storms cause major coastal erosion and damage to beachfront properties,”Dr Harley says.“For the first time we looked not just above water, where the impacts of extreme storms are easy to see, but also deep down below the water as well. “What we found was that hundreds of thousands of cubic metres of sand was entering these beach systems during these events – that’s similar to the scale of what engineers use to nourish a beach artificially.“This could potentially be enough to offset some of the impacts of sea level rises caused by climate change, such as retreating coastlines, and by several decades in the long-term. “It’s a new way of looking at extreme storms.”
Wave after wave
In collaboration with researchers from University of Plymouth and Autonomous University of Baja California, the study examined three coastlines across Australia, the United Kingdom and Mexico. Each was subject to a sequence of an extreme storms or extended storm clusters, followed by a milder period of beach recovery. In Australia, researchers studied Narrabeen beach in Sydney in the wake of a 2016 storm which famously ripped a swimming pool away from a property overlooking the coastline. Using high-resolution measurements of the beach and seabed, they were able to show that sediment gains were sufficient to theoretically offset decades of projected shoreline retreat.
Bruun rule
Exactly how much a coastline might change due to sea level rise is a key question facing coastal managers as they plan for the escalating impacts of climate change. In the past, this has been estimated using a simple approach known as the Bruun rule. This rule states that for a given metre of sea-level rise, the coastline is expected to retreat between roughly 20 and 100 metres, depending on the steepness of the coast. Using the Bruun rule, global sea-level rise caused by climate change has been projected to result in a large retreat or loss of almost half of the world’s sandy beaches by the end of this century.
Looking past the eye of the storm
Dr Harley says there are so few measurements of the seabed immediately off our coastlines that it’s hard to tell how much sand could potentially be mobilised in the future. While these findings are from only three extreme storm sequences, it certainly potentially changes how people can understand the long-term future of our coastlines. “We’re only scraping the surface here. We need to repeat these types of monitoring measurements for more storms and different types of coastal settings under various conditions,” he says. “Only then, will we be able to get a clearer understanding of how much sand is stored off the coast that could potentially help buffer the impacts of sea level rise – and a clear picture of what our beaches could look like in the year 2100 and beyond.”
Sources:
FLORIDA STATE UNIVERSITY NEWS
Provided by the IKCEST Disaster Risk Reduction Knowledge Service System
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