Beach erosion can be a matter of perspective. What might be considered a natural and cyclical process at a remote undeveloped beach location could be a disaster for local residents and communities on a highly utilized or developed shoreline.

A healthy beach is a demonstration of dynamic equilibrium. This is can be defined as “A long-term condition where erosion and accretion are in balance and the net position of the coast, despite minor fluctuations, remains stable”.

Care needs to be taken when defining ‘short’ or ‘long’ term changes or patterns, as this can be a matter of perspective. A geological view of time is not very helpful when assessing the risk to human assets and property. A more realist view on ‘long term’ erosion may be to consider the life of human assets or the span of generations.
Five possible reasons for beach erosion are discussed below.

1. Climate change
The dynamic equilibrium shown on a soft coastline is very sensitive to changes in the forces that keep it in balance. Wave action is the main energy force acting on a beach. This energy force is controlled by wind strengths and directions, locally and from distant storms (on exposed coastlines).

The cyclical nature of weather patterns is mirrored by cyclical erosion and accretion phases on the beach face. This cycle can be as short term as a single storm event, to annual /seasonal weather patterns (such as monsoon seasons) or short-term global patterns that can span a number of years (El Nino).

There are also longer-term cycles to the earth’s climate patterns such as ice ages. Human influence on perceived global climate change is also a hotly debated subject. Any changes to the patterns of wind direction, strength or frequency could bring about a long-term erosion trend.
Local wind, rainfall and river flows also influence the availability and movement of sand on the beach face. Again, any changes to direction, strength or frequency patterns could bring about a long-term erosion trend.

2. Sea Level Change - real or apparent
Any relative change in long-term mean sea level will invariable have an effect on a ‘soft’ coastline such as a sandy beach. Rising sea levels and their possible link to global warming are being intensively studied around the world. If the current trend of sea level rise continues then the problems associated with coastal erosion will also increase.

Coastal settlement or plate tectonics (the movement of the Earth’s crust) could also give rise to a relative change to the sea level over a specific section of coastline.

3. Sediment supply
Sand is constantly on the move on the beach face and in the surf zone. ‘Littoral drift’ is the movement of beach material in the littoral zone (beach and surf zone) by waves and currents. This includes movement parallel (long-shore transport) and perpendicular (onshore-offshore transport) to the coast.

Beach erosion can be caused by a loss of sediment in the littoral zone.


4. Human influence / hard engineering
Human influence has and will invariably alter the natural balances in sediment supply as depicted above. Coastal development will often restrict the natural supply of beach material by armoring the coastline and preventing dune or cliff erosion.

Coastal erosion control structures such as sea walls and revetments are built to defend the shore, not the beach. They will always have a negative impact on a beach, as they will prevent any new material from entering the littoral zone from the shore and can induce wave reflection.
Groynes employed to capture material at a specific location may starve an adjacent section of coastline causing erosion. They may also induce wave reflection and refraction.

5. Headland Erosion
The erosion of headlands at either end of a beach embayment may also expose a beach to long-term changes that may include a corresponding coastline landward migration and beach erosion.  
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