Usually constructed in groups called groin fields, their primary purpose is to trap and retain sand, nourishing the beach compartments between them.
Groins initially interrupt the longshore transport of littoral drift.
They are most effective where longshore transport is predominantly in one direction, and where their action will not cause unacceptable erosion of the downdrift shore. When a well designed groin field fills to capacity with sand, longshore transport continues at about the same rate as before the groins were built, and a stable beach is maintained. Groins are suitable erosion control measures where a beach is desirable, and they are compatible with most recreational activities. Filled groins provide this protection during normal weather conditions but offer only limited protection against storm-driven waves. Glossary of terms highlighted in the text above.