How do groynes help to prevent coastal erosion?

Question:
How do groynes help to prevent coastal erosion?
Answer:

Groynes were originally installed along the coastline in 1915. Groynes control beach material and prevent undermining of the promenade seawall.

Groynes interrupt wave action and protect the beach from being washed away by longshore drift. Longshore drift is the wave action that slowly erodes the beach.