What role do groynes play in coastal defense?

Groynes serve a key function in coastal defense by interrupting the process of longshore drift, which is the movement of sediment along the coast due to wave action. When groynes are constructed at right angles to the shoreline, they act as barriers that trap sand moving along the coast. This sand accumulation leads to the build-up of beaches on the updrift side of the groyne, effectively helping to stabilize the shoreline and prevent erosion.

The design of groynes allows for the retention of sediment, creating wider and more robust beaches which can absorb and dissipate wave energy, further protecting the land behind them from coastal erosion. This is why they are considered effective coastal management structures.

While groynes may lead to some other effects, such as potentially affecting local ecosystems or altering sediment transport patterns further down the coast, their primary role is clear in the context of coastal defense.