A groin is an erosion-control structure built perpendicular to the shoreline. Often used on a small scale along the shores of North Carolina's sounds and tidal rivers to protect individual properties, wooden and riprap groins offer protection from gradual erosion by slowing wave action and trapping sand. (Groins are not authorized along the oceanfront.)

Figure 4.12

However, the effectiveness of groins for reducing erosion is limited. While they do trap sandunder normal conditions, groins also may accelerate erosion of nearby shorelines. And they provide little protection from erosion during a major storm. In addition, groins can impede navigation and threaten water quality unless they are properly designed, located and maintained.

To receive a CAMA permit for your wooden and riprap groin projects, you must meet the general CAMA rules for coastal wetlands, estuarine waters and public trust areas as well as the following specific regulations {15A NCAC 7H .0208(b)(9)}:

    • Groins must not impede boat traffic. 

    • Groins may not extend more than 25 feet waterward of the normal high water or normal water level unless a longer structure can be justified by site-specific conditions and with sound engineering and design principles (see Figure 4.12A).

    • Groins must be at least 15 feet from the adjoining property lines (see Figure 4.12B). The 15-foot setback requirement may be waived by a written agreement of the adjacent property owners or when adjoining owners apply for a CAMA permit together.

    • You may not construct more than two groins per 100 feet of shoreline unless you can provide evidence that more structures are needed for shoreline stabilization (see Figure 4.12C). Generally, groins should be set apart a distance at least four times their length in order to interrupt water currents and trap sand.

    • The height of a groin must not exceed one foot above the normal high water or normal water level (see Figure 4.13). The purpose of a groin is to trap sand, which happens at the water bottom — not the surface. In addition, if a groin is built too high above the water level, storm waves won't wash over it, and the groin could be damaged or could collapse.

    • "L" and "T" sections are not allowed at the end of groins, because they can impede navigation and accumulate pollutants and debris.

    • Riprap material used to build a groin must be free from harmful quantities of loose dirt and other pollutants, and should be large enough to withstand waves or currents.

    Figure 4.13