How Jetties Protect Beaches: Interrupting Longshore Drift

Jetties are shore-perpendicular structures (rock, concrete, steel) that intercept longshore drift—the alongshore movement of sand driven by angled wave breaking.

How They Work

• Updrift side: Sand accumulates, widening the beach.
• Downdrift side: Sediment supply cut off → erosion (unless bypassed).
• Inlet stabilization: Jetties at tidal inlets/harbors keep channels open by blocking sand infill.

Trade-offs

• Can shift erosion downstream ("terminal groin effect").
• Alter natural sediment budgets & nearshore ecology.
• Require careful design, monitoring, and sometimes sand bypassing.

Effective coastal management uses jetties as part of a sediment-management system, not in isolation.