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Extreme storms can not only erode beaches but also replenish them

Extreme storms can not only erode beaches but also replenish them

how extreme storms can replenish beaches, not just erode them

Environmental scientists see phenomena, flora and fauna in a way that the rest of us don’t. In this series, we’ve invited them to share their unique Photos from the field.


Extreme storms can cause severe erosion and damage beachfront homes. Teetering on cliff edge edges. However, our Research in progressThe article, published today, suggests that storms could also help replenish beaches through the introduction of new sand from deeper oceans.

We looked at three extreme storms that occurred in Australia, the United Kingdom, and Mexico. One, in Sydney in 2016. Famously, a swimming pool was ripped.A property overlooking the coast is not recommended.

For the first time, we’re able to show just how much new sand can be added to a beach in a single storm alone – over 400,000 cubic metres in some cases. That’s equivalent to the The typical volumes of sandEngineers use artificial fertilization to maintain beaches.

This natural form of beach replenishment could be a key factor in reducing the harmful effects of climate change on beaches. It is difficult to predict the future of beaches over the next decade as we don’t know how much sand is moving offshore.

Collaroy Beach, Sydney, was damaged by an extreme storm that struck June 2016.
UNSW Water Research Laboratory, Author provided

Extreme storms can cause serious erosion to beachfront properties, but they can also bring new sand from deeper waters.
UNSW Water Research Laboratory, Author provided

Wave after wave

Violent storms can wash beaches of sand just above the waterline, which can cause erosion of sand dunes. However, in deeper waters, these waves stir up sediment on the seabed that is still dormant. This sand is then pushed towards shore and settles as the storm passes.

We used high-resolution monitoring equipment to study the storms in Australia and Mexico. This included twin-engine airplanes, drones, and jet skis with an echo-sounder to measure the seabed.

The UK Survey Team measured the sand volumes along Cornwall’s coast.
University of Plymouth, Author provided

To measure beach changes, a combination of high-resolution equipment and survey equipment was used.
University of Plymouth, Author provided

We measured Narrabeen Beach in Sydney, Australia. We monitored the UK’s impact on Several storms occurred during the winters 2013-2014Perranporth beach in Cornwall, 2015-2016 We also recorded the 2018-2019 impact on La Mision Beach in northwest Mexico.

The time-lapse video below shows how fast the water can reach beachfront homes during severe storms. Under the water surface, however large volumes of sand are still moving around.

Time-lapse of severe coastal erosion at Narrabeen Collaroy Beach (SE Australia), during the June 2016 East Coast Low.
Source: Mitchell Harley (author provided)

We were able capture the three-dimensional seabed changes of each event and quantify the sand volumes mobilised by these extreme storms for the first time.

To give an indication of the scale of beach change, the amount of sand added to the beach resulting from the stormy periods was on the order of 100 cubic metres for every metre length of beach – that’s like 20 tip trucks pouring sand on every metre-wide strip.




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Because the beaches stretched for several kilometres, this was 130,000 cubic metres at La Mision beach, 420,000 cubic meters at Perranporth, and 400,000 cubic metres at Narrabeen.

Below is a time-lapse video of Wamberal Beach in 2020 during a storm. While it wasn’t included in our study, it’s another great example of how large storm waves cause abrupt changes to beaches.

Source: UNSW Water Research Laboratory (author supplied)

Rethinking coastal erosion

As they prepare for the increasing impacts of climate change, coastal managers need to know how a coastline will change from sea-level rise.

The Intergovernmental Panel for Climate Change Projekte global sea levels to rise up to 76 centimetres by 2100, under a middle-of-the-road emissions scenario where global temperatures rise 2.1-3.5℃.

The Bruun rule was previously used to estimate the coast’s response to sea-level rise. This rule states, for every metre sea-level rise, the coastline should retreat between 20m to more than 100m. Depending on the steepness and elevation of the coast.

Chris Drummond, UNSW researcher, launches a drone to survey Sydney’s beach.
UNSW Research Laboratory, Author provided

The Bruun rule has shown that global sea-level rising due to climate change has been Projected to result in losing almost half the world’s sandy beaches by 2100. However, Not all scientists on the coast share this view..

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Sea-level rise is a tragic result of climate change and poses a grave threat to many coastal communities, particularly those in the Pacific.

Mexico’s La Mision beach, on a calm day. Research has shown that 130,000 cubic metres of sand was pushed into the beach system by storms in the winter 2018-2019.
Autonomous University of Baja California, Author provided

What our new research confirms is that the Bruun rule approach is overly simplistic, as it doesn’t take into account The many complex local factorsLearn about the response of individual beaches to sea-level rise.

This includes the amount and potential for replenishment of beaches by sand in deeper waters off the coast.

It is crucial to understand how sand moves along the coast for better coastal planning.
UNSW Water Research Laboratory, Author provided

In an uncertain future, improving predictions

Although this research has been limited to three extreme storms, it shows that they can be quite powerful. Understanding how sediment moves along a coastPlanning for climate change impacts is essential.

Two ways are we able to significantly improve long-term coastal change predictions in this uncertain future.

  1. Increasing the scale of mapping the seabedTo find out how much sediment is currently in deeper coastal waters, click here

  2. Increasing routine coastal monitoring of all nearshore systems, from the sand dunes to the deeper waters. Currently, this is being done by UK coastal observatories.

Computer modelling and a better understanding about sand movements offshore the coast can make it possible to better predict future shorelines. This will allow coastal managers to make long-term planning decisions that benefit communities.




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