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Once again the summer holidays have arrived and many people will be jetting off to the beach. However, few tourists will notice the tonnes of sand and gravel that weren’t there the previous year.

Each spring, an army of bulldozers gets to work fixing storm and tidal damage on many of the world’s most famous beaches. Fresh sand or gravel (a term encompassing everything from tiny pebbles to chunky stones) is placed where necessary, allowing waves and tides to redistribute the material. It can be dumped in the right spots by bulldozers, or shipped in on barges. It can also be pumped in through pipes, as seen in the video below; the mixed-in water is allowed to drain off and the remaining sand is shoved into the right places.

All this is partly driven by the influx of visitors and their rocketing expectations of perfect sand. But beaches aren’t just eye candy for tourists – they themselves have an important role in combating erosion through soaking up wave energy before the sea smashes into the cliffs or seawall. So despite the expense, there’s more demand than ever for what’s known as “beach nourishment”.

If this seems artificial, as though something pristine was being unnecessarily tampered with, then don’t forget beaches weren’t always there. In fact most are relatively new, formed during the past 5,000 or so years after the modern sea level was established. However in recent decades rising sea levels and more frequent storms have led to rapid beach erosion. By the 1990s just 10% of the world’s beaches were still growing, while more than 70% were eroding – with the world still warming and sea levels rising, things will only have got worse since then.

To combat this, beaches such as Venice’s Lido or a number along Italy’s north-west coast are “re-nourished” each spring to repair the winter damage. Over the years this adds up. One analysis of the famous beach in Nice, south France, found 558,000 cubic metres of gravel was added during the 30 years to 2005 – that’s enough gravel to fill up Big Ben’s clock tower 119 times over.

Along the Costa Brava, on Spain’s north-east coast, entirely artificial beaches have been created, sustained by a combination of breakwaters, groynes (structures built out from the shore to prevent the movement of sediment) and a dump of fresh sand each year.

Perhaps the most famous example of all is the artificial beach in Barcelona, which has been nourished with sand from offshore over the past two decades. The loss of the sediment here is only partially due to storms, with the normal action of the waves causing slow erosion – the area simply isn’t meant to have a massive sandy beach.

In contrast to many other parts of the Mediterranean, the coastline in our home country of Croatia managed to remain more or less natural. Its rocky coastline isn’t ideal for the creation of large sandy beaches, and political upheavals in the 1990s interrupted the growth of tourism. Now the country has once again become a popular tourist destination, and the beauty of its small and well-hidden gravel beaches are a valuable part of its attraction.

Many beaches have therefore been extended or created from scratch, and our current research is focused on the resilience of artificial gravel beaches in Croatia. Their sustainability depends on factors including a continued supply of sediment, and how well they stand up to stormy weather.

Understanding the behaviour of natural and artificial beaches in different environmental conditions is crucial for their maintenance. A number of techniques are used to detect beach changes including advanced GPS surveys, laser scanning, or images from fixed cameras and drones

Our work in Croatia, for instance, uses a simple digital camera combined with advanced computing methods to understand the changing shape of the beach. We also study our nearby coastline in Fylde, Lancashire. With our help, both day trips and holidays to the beach should remain a pleasant feature of our lives into the future.

This article originally appeared on The Conversation

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