Jetties and groins run PARALLEL to the shore
and extend out into the water, serving as structures to prevent erosion of the shoreline. Jetties are long narrow structures made of rocks or concrete that are built to protect harbors, navigation channels, and river mouths from the effects of waves and currents. They may also be built to prevent the accumulation of sand in these areas.
Groins, on the other hand, are structures built perpendicular to the shore and jut out into the water. They are typically made of wood, concrete, or rocks and are designed to trap sand and prevent it from being washed away by the waves. By doing so, they help to maintain a stable beach profile and prevent shoreline erosion.
Both jetties and groins have their advantages and disadvantages. While they provide protection against erosion and improve navigation in some cases, they can also disrupt natural sand movement and lead to beach erosion at other locations. It's essential to carefully evaluate the need for and potential impacts of these structures before constructing them.