What Is a Beach?
A beach is a coastal landform made up of deposited material — usually sand, pebbles (shingle), or a mixture of both. Beaches form where waves have enough energy to transport sediment but not enough to carry it further, so they deposit it along the shore.
Beaches are found in sheltered bays where wave energy is reduced and deposition outweighs erosion.
How Beaches Form
Material is transported along the coast by a process called longshore drift:
- Waves approach the beach at an angle (matching the prevailing wind direction).
- The swash (rush of water up the beach) moves sediment diagonally up the beach.
- The backwash (water retreating) runs straight back down the beach under gravity.
- Each wave cycle moves sediment a little further along the coast in a zig-zag pattern.
- Where the coastline curves into a bay, the waves lose energy and drop the sediment — building a beach.
Longshore drift can transport enormous amounts of sediment. At Chesil Beach on the English coast, pebbles range from pea-sized at one end to fist-sized at the other — sorted by wave energy along 29 km of beach. Locals claim you could work out where you were on the beach in the dark just by the size of the pebbles!
What Is a Bay?
A bay is a curved indentation in the coastline flanked by headlands (jutting points of harder rock). Bays form through differential erosion:
- The coastline contains alternating bands of hard and soft rock.
- Waves erode the softer rock more quickly because it is weaker.
- The softer rock retreats, forming a curved bay.
- The harder rock on either side stands out as headlands.
- The sheltered bay collects sediment from longshore drift, forming a beach.
Famous examples: Swanage Bay (Dorset, UK) — a sandy bay between chalk and limestone headlands; Botany Bay (Australia).
Spits and Bars
Longshore drift also creates spits — narrow ridges of sand or shingle extending from the land into the sea. They form where the coastline suddenly changes direction (e.g. at a river mouth). The sediment continues in its original direction, extending out into the sea.
A bar forms when a spit extends right across a bay, joining two headlands and potentially trapping a lagoon behind it.
Groynes (wooden or concrete barriers built out into the sea at right angles to the shore) are used to trap sediment and prevent it being moved away by longshore drift. They protect beaches by keeping the sand in place, but can have drawbacks — they starve beaches further along the coast of their natural sediment supply.
Beach Profiles
Beaches are not flat — they have a profile:
- Backshore/berm: Dry area above the high-tide line, built up by storm waves.
- Foreshore/beach face: Exposed and covered at each tide cycle.
- Nearshore: Shallow water zone where waves begin to break.
Real world: Brighton Beach and groynes
Brighton Beach on England's south coast is a famous shingle (pebble) beach. Longshore drift moves sediment eastward along this coast, so without intervention the beach would disappear. The local council has built dozens of groynes (timber barriers extending into the sea) to trap the sediment and keep the beach in place. The beach is vital for tourism — bringing £700 million to the local economy per year — so maintaining it is a priority.
Real world: Swanage Bay — differential erosion creating a bay and beach
Swanage Bay in Dorset, UK, is a textbook example of differential erosion. The coastline around Swanage contains alternating bands of hard limestone/chalk (forming headlands like Ballard Point and Peveril Point) and softer sands and clays. Waves eroded the soft rock to form the curved bay, while the headlands stand resistant on either side. The sheltered bay has collected enough sediment to form a wide sandy beach — a popular holiday destination.
Real world: Beach nourishment in Miami, Florida
Miami Beach in Florida has been losing sand for decades due to longshore drift and rising sea levels. Rather than build solid sea walls (which destroy the beach), Miami uses "beach nourishment" — pumping millions of tonnes of sand from offshore to rebuild the beach. This protects the coastline and maintains the beach for tourism, but is expensive and must be repeated every few years. Miami spends around $15 million per km of beach to do this.
Where do you see this in real life? Next time you visit a beach, look for groynes in the water — they show how longshore drift is being managed. Notice how sediment piles up on one side of each groyne but is absent on the other.
Practice Problems
Explain how longshore drift moves sediment along a coastline.
Show answer
Why do bays often have beaches but headlands often do not?