Groyne:
a low wall built out from the coast into the sea, to prevent the repeated movement of the waves from removing parts of the land [Cambridge Dictionary]
Noted in “Rising seas could submerge Rio and Jakarta by 2100 – what can we do?” Simon Usborne, NewScientist (26 February 2022, paywall):
But physical defences like these are expensive, impermanent and, in some cases, unintentionally harmful. Take groynes, structures built perpendicularly out from beaches into the sea. A series of these is good at stopping protective sediment such as sand from being washed away along the coast through a process called longshore drift, but it can actually increase erosion after the last groyne because this area receives less sand than it would otherwise.
