Groynes are cross-shore structures designed to reduce longshore transport on open beaches or to deflect nearshore currents within an estuary. On an open beach they are normally built as a series to influence a long section of shoreline that has been nourished or is managed by recycling. In an estuary they may be single structures.
Erosion is the process of wearing away material from the coastal profile due to imbalance in the supply and export of material from a certain section. It takes place in the form of scouring in the foot of the cliffs or in the foot of the dunes. Coast erosion takes place mainly during strong winds, high waves and high tides and storm surge conditions, and results in coastline retreat.