Which process transports sand parallel to the coastline, contributing to sand redistribution along a shore?

• A. Seawalls
• B. Breakwater
• C. Barrier Islands
• D. Longshore Drift

Answer: (D)

Longshore drift is the movement of sediment along a coastline driven by waves arriving at the shore at an angle. When waves break on the beach, the swash moves up the beach diagonally, while the backwash runs straight back down toward the sea. This creates a net transport of sand along the shore in the direction of the wave approach. Over many waves, sand is redistributed parallel to the coastline, reshaping beaches and moving material from one location to another.

Seawalls protect the shore but don’t promote along-shore transport of sand. Breakwaters alter wave conditions to protect harbors and can change sediment patterns, but they aren’t the process that moves sand parallel to the coast. Barrier islands are landforms built up by sediment and wave action, not the ongoing transport mechanism itself.