Definitions
Longshore drift = the movement of material along a coast by waves that approach at an angle to the shore but recede directly away from it.
Longshore Drift Details
- The waves are approaching the shoreline at the angle of the prevailing wind direction. The strongest longshore drift occurs when waves approach the coast at an angle of 30 degrees to the beach.
- As the waves reach the shore, the swash carries sand and other sediments up the beach at the same angle as the approaching wave.
- The backwash of each wave then carries the same sediments back down the beach at right angles to the shore, under the influence of gravity.
- The backwash of each wave then carries the same sediments back down the beach at right angles to the shore, under the influence of gravity.
- We can see in the diagram that in this way, sediments slowly move in small zigzag steps along the beach until they meet a natural obstacle such as a bay or an estuary, or an artificial barrier such as a groyne. Groynes work by slowing down the waves and reducing their power thus forcing them to deposit their sediment and thereby reducing the loss of sediment from the beach.
Formation of Coastal Features:
- Over time, the continuous action of longshore drift results in the transportation of sediments along the coast. Sediments may accumulate in new areas, forming features such as sandbars, spits, and beaches.
Coastal Evolution:
- Longshore drift is an ongoing process that contributes to the dynamic evolution of the coastline. It plays a crucial role in shaping coastal landforms and maintaining the equilibrium of sediment distribution along the shore.
