What prevents longshore drift?

As a coastal geomorphologist with extensive experience in studying coastal processes, I can provide an in-depth explanation of the factors that can prevent or mitigate longshore drift. Longshore drift, also known as littoral drift, is the movement of sediment along a coastline in the direction of the shoreline. It is primarily driven by the angle at which waves approach the shore, typically at an angle to the beach rather than directly parallel. Several factors can influence or prevent longshore drift: 1. Wave Energy: The energy and direction of the waves are crucial. If wave energy is low or if the waves are approaching more parallel to the shore, there will be less longshore drift. 2. Beach Gradient: A steep beach gradient can reduce the effect of longshore drift by allowing waves to break further out to sea, thus reducing the interaction with the beach sediment. 3. Obstructions: Natural or man-made structures such as groynes, jetties, or breakwaters can interrupt the flow of sediment along the shore. 4. Coastal Configuration: The shape of the coastline itself can influence longshore drift. For example, bays or headlands can act as barriers, causing sediment to accumulate rather than being transported along the coast. 5. Currents: Longshore currents can be counteracted by other water movements such as rip currents, tidal currents, or offshore currents that can transport sediment in different directions. 6. Human Intervention: Human activities like beach nourishment, where sand is added to the beach, can temporarily reduce the effects of longshore drift by increasing the sediment supply. 7. Seasonal Changes: Seasonal variations in weather patterns can alter the direction and intensity of wave action, which in turn can affect the rate and direction of longshore drift. 8. Geological Factors: The underlying geology can also play a role. For instance, a rocky substrate may limit the amount of sediment available for transport.

A wooden barrier built at right angles to the beach. Prevents the movement of beach material along the coast by longshore drift. Allows the build up of a beach. Beaches are a natural defence against erosion and an attraction for tourists.