Groins
Groins are wall-like structures built into the water perpendicular to the shoreline for the purpose of trapping beach sand. Groins interrupt natural longshore transport and deprive beaches down the coast from groins.
This picture is an example of a groin in Sitges. Having wall-like structures help protect what the area that surrounds it from any permanent damage.
Jetty
Jetties cause similar effects like groins. Jetties are walls of concrete built to protect a harbor entrance from drifting sand.
As you see in this picture shows a Jetty in the area of The Indian River Inlet, DE. It created a way of transportation without having sand or other large materials cause further damage to the area.