They are usually built to protect buildings threatened by landward retreat of the shoreline. Seabeach amaranth never occurs on shorelines where bulkheads, sea walls, or riprap zones have been constructed. Not only does construction of these structures occur in the primary habitat of seabeach amaranth, but water and wind erosion lower the profile of the beach seaward of the armoring. Groins are concrete or riprap structures built out into the surf zone or beyond, perpendicular to the shoreline, and designed to catch lateral flow of sand and deposit it on one side of the groin. On some beaches in South Carolina and New Jersey, a series of groins has been placed at regular and close intervals the length of the island.
Groins have mixed effects on seabeach amaranth.
Another beach-hardening structure, the breakwater, generally consists of a riprap barrier placed offshore and parallel to the beach, intended to intercept and break the erosive force of waves. Widespread use of sea walls, jetties, and other hard stabilization structures in New Jersey, New York, and other northern States is associated with the extirpation of seabeach amaranth in those States. Of all the States in the former range of seabeach amaranth, North Carolina has made the least use of sea walls. The continued presence of seabeach amaranth in North Carolina and in the parts of South Carolina and New York which lack sea walls is probably not accidental or coincidental. In many cases they have been placed in stretches of coastline which were naturally unstable and subject to overwash, in order to protect buildings and roads.