A major disadvantage of using groins for beach erosion control is that they can negatively impact areas further along the coast by disrupting the natural movement of sediment.
Groins are structures built perpendicular to the shoreline to trap sand moving along the coast via a process called longshore drift. While they can be effective at widening a beach immediately updrift (on the side facing the incoming waves), they have a significant drawback. According to the provided reference, "One of the biggest problems with groynes is that they can have an impact further along the coast by stopping longshore drift."
Here's a breakdown of the problem:
- Sediment Interception: Groins act like barriers, accumulating sand on the side where the longshore current originates.
- Starvation Down-Coast: By trapping this sediment, groins prevent it from reaching areas located downdrift. The reference highlights this, stating, "By trapping the sediment, groynes starve towns and villages of sediment further down the coast."
- Increased Erosion Elsewhere: This sediment starvation can lead to accelerated erosion on beaches and shorelines located down-current from the groin field, often transferring the problem rather than solving it entirely.
In essence, while protecting one section of the coast, groins can inadvertently cause or worsen erosion issues on neighboring sections. This makes them a controversial solution that requires careful planning and consideration of the wider coastal system.
Potential Consequences of Groin Use Down-Coast:
- Narrower beaches or complete loss of beach area.
- Increased vulnerability of coastal property and infrastructure to wave action and storms.
- Need for costly additional coastal defenses or beach nourishment in affected areas.
This interconnectedness of coastal processes means that any intervention like groins must be evaluated based on its potential impact on the entire stretch of shoreline influenced by longshore drift.
