Groynes limit costal erosion by interfering with the process of longshore drift. This will stop most of the sediment to get past the groyne. Sometimes the groyne is fully underwater in which case it is a submerged groyne this will mostly stop sediment being transported by traction , saltation and suspension however will stop less solution than everything else. Groynes are mainly made of wood, concrete or rock piles and placed in groups.The area between groups of gryone are called groyne fields. They can be used to create beaches too. It is usually paired up with beach nourishment. On the downside  groynes may make a shore line to be seen as unnatural.