Which term refers to sand-trapping structures built along the coast to reduce shoreline erosion by interrupting longshore transport?

• A. Beach Replenishment
• B. Breakwater
• C. Groins
• D. Jetties

Answer: (C)

Longshore transport moves sand along the coast as waves wash up at an angle. Groins are built perpendicular to the shoreline to intercept that moving sediment. By catching sand carried by the longshore current, they accumulate material on the updrift side, forming a wider beach and reducing erosion there. But trapping sand means less sediment is available downdrift, which can shift erosion problems in that direction. That’s why groins are described as sand-trapping structures that interrupt longshore transport. Beach replenishment adds sand to the beach without blocking transport, breakwaters are offshore barriers to reduce wave energy rather than trap alongshore sand, and jetties at inlets stabilize openings and also affect sediment patterns but aren’t the typical coast-perpendicular sand-trapping structures along the open coast.