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Surf Ed

Beaches

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In Australia, we have the best beaches in the world. There are  11,915 beaches surrounding our island continent, and you can explore all of them through this website! Generally small and embayed, Australian beaches are  commonly separated by dominant headlands, reefs and inlets which create picturesque and sometimes dramatic landscapes.

Some may think that all beaches are the same, but this is far from the truth. Consider a tropical white sand beach  with no waves and tranquil clear water leading to a coral reef.  Then compare it to a black sand beach, covered in large pebbles and pounded by huge surf. This page teaches you a little about what makes these beaches different, and how they change over time. 

It’s all about the sand...

To understand how the coastline changes, it all starts with the smallest grain of sand, literally. Sand can get moved around pretty easily, just think about how people make sandcastles on the beach. Now think about how much sand can get moved by waves during a storm, wind, currents rain or rivers. That’s why the coastline is constantly changing.

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The sand can be very different across Australia. Some beaches may have very fine, white sand; while others may have large pebbles, stones and boulders. The sand size will vary dependent on a range of factors such as wave energy.

Coastal Erosion and Accretion

Because beaches are dynamic, sedimentary environments, they naturally experience regular phases of erosion and accretion which means;

Erosion: The movement of sediment (sand) offshore which causes the retreat of the natural shoreline. This usually results in the beach getting narrower.

Accretion: The movement of sediment (sand) onshore which causes the advance of the natural shoreline. This usually results in the beach getting wider.

The beach gets smaller...

Erosion mostly occurs when large, destructive waves impact on a coastline. These waves cause more sand to become suspended in the water and carried offshore by large, powerful rip currents called megarips. These megarips can carry the sand and sediment offshore and deposit it in large offshore sand deposits. This process can occur quickly and dramatically during a severe storm event such as a tropical cyclone or an iintense low pressure system  produce large swells.

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The beach gets bigger...

While erosion can be quick and dramatic, accretion is a much slower process. It occurs during a period of average swell conditions which deliver sand from offshore deposits back onto the beach. It can take years for a beach to recover the sand lost from a significant erosion event.

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Case Study: Coastal Erosion and La Nina

Longer erosional phases are linked to climatic cycles such as the Southern Oscillation. For example, erosional phases are correlated with La Nina events, which are years when there is a higher frequency of storms along the east coast of Australia. Alternatively, phases of positive sediment budget, when there is a lower frequency of coastal storms, are linked to the El Nino events. Fluctuations in beach morphology, from erosional to accretional forms, also operate over longer time intervals because the frequency of El Nino and La Nina events fluctuates over decadal periods. Long term trends in beach morphology are also related to changes in sea level, which can induce phases of erosion (rising sea level) and accretion (falling sea level).

Round and round, and round it goes!

As  sand moves around on the beach and in the surfzone where the waves are breaking, this can create different beach patterns and shapes which in turn influence the flow and behaviour of the surf.  

Surf scientists have conducted a range of studies and classified these beaches into different categories. You can learn more about the different beach types at the OzCoasts website.

Another element, the tides...

Tides are the gradual rise and fall of the ocean. They are caused by a combination of the gravitational forces of the moon and sun, as well as the rotation of the Earth. Because these forces are relatively stable and consistent, tides can be predicted long in advance and are entirely separate to other processes like waves and tsunami.

How the tides work can be quite complicated to explain, so here is a man with a biscuit, a pickled onion, and an orange to try to make it easier: 

The difference in height between a low tide and high tide is called the tidal variation. The larger  the difference, the greater the effect tides will have on the coastline. In Australia, depending on where you are, you can experience tides that range from 0.5m to 12m! High tidal variation is common across northern Australia. Because northern Australia doesn’t commonly receive significant wave activity, the beach types present are slightly different such as Shark Bay, Western Australia below which is a relatively flat featureless beach at low tide. 

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Case study: King of All Tides

There are two areas in Australia that experience particularly large king tides - far north Queensland and north-west Western Australia. Check out this documentary about a small town in Western Australia that experiences big tides from the ABC.

Coastal Development and Sand Nourishment

Australians have a profound love for the coastline, and use it for many things such as tourism, recreation and development. Many areas of coastline have become highly developed with, seawalls, groynes, breakwalls and piers installed to protect the coast. These structures can change the natural flow of sediment, and cause some areas to become starved of sand. In some areas, sand nourishment is necessary to replace sand lost from the beach. 

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