Use of Groins to Retard Beach Erosion

Two groins (jetties) made of large boulders extend from the Pacific Coast Highway across the beach into the surf zone here at Pacific Palisades. Notice the beach is wider on the near side of the groins than on the far side. Longshore transport of sand is southward, from the lower right to the upper left, and the view in the picture is also southward toward Santa Monica. Sand is deposited on the near side of the groins because the longshore current is stalled by the groins, and the power to transport sand along the shore is thereby reduced. Sand is eroded from the downcurrent side because the longshore current eddies. ©AGS1963.
Oblique aerial view of ship channel levees that interrupt the transport of sand along the southern California coast at Marina del Rey. The breakwater on the left edge of the photo prevents large waves from entering the channel. The longshore current flows from upper left to lower right in the picture. ©AGS1978.
Vertical aerial view of beach and en echelon rock groins, Pizzo Calabro, southern Italy, 10 June 1987. The longshore current is from the lower left corner to the right. Sand deposits behind the groin where the current stalls or eddies. ©AGS1987.

Back to Main Page