A jetty is a structure that projects from the land out into water. Jetties are used to protect against erosion, to create a safe harbor, and to direct the flow of a river or stream. Groins are similar structures, but they are built at an angle to the shoreline instead of perpendicular. Both jetties and groins can be made from a variety of materials, including wood, stone, and concrete.
Jetties are commonly used in rivers and harbors. They help to protect against erosion by deflecting the flow of water away from the shoreline. Jetties can also be used to create a safe harbor for boats by blocking off areas of strong currents or waves. In some cases, jetties are built specifically to direct the flow of a river or stream. This can be done for purposes such as navigation or flood control.
Groins are most often used on beaches. They help prevent beach erosion by trapping sand that would otherwise be carried away by waves and currents. Groins can also be used to create artificial reefs which provide habitat for fish and other marine life. Like jetties, groins can be made from various materials including wood, stone, and concrete.