Groins are constructed perpendicular to the beach; they are designed to trap sand on the up-current side, that might otherwise keep moving along the beach.

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Groins are designed to trap sand on the up-current side, which helps to maintain the width of the beach and prevent erosion. By trapping sand, groins also help to reduce the amount of sediment that is transported further down the beach by longshore drift.

Groins Are Constructed Perpendicular to the Beach; They Are Designed