These are cool shaped but they don’t actually work; coastal armoring in general does not work as it does not prevent erosion. Sand replenishment is increasingly the path taken. Australia has an amazing pumping system (a jetty blocked longshore sand transport so they pump it around to the other side).
> coastal armoring in general does not work as it does not prevent erosion.
Not that simple. Example: east of Lauwersoog (north shore of the Netherlands) there's a dyke reinforcement project underway. Roughly 2/3 of the dyke's seaside is covered with regular rows of interlocking concrete blocks (~25 x 25 cm top view). At the base of the dyke, there's stone rubble to dissipate wave energy. These are heavy stones: 100s of kg each on average. But loose - some even wobble if you step on them! There's probably some other things in there like layer(s) of geotextile & such.
I'm pretty sure if those rubble stones weren't there, waves would 'eat' some rows of the smaller blocks, wash away a few metres of sand, then rows above would collapse, expose more sand, etc.
So it's not like those stones aren't doing anything.
In other places on the Dutch coast, it's more common to pump sand onto the beach every X year to replace what the sea eroded. 'Must read' in this context:
Sorry I was unclear. By erosion I meant beach erosion. I do agree that armoring can help preserve a structure like a dyke. The issue is the sand as you mention with the sand engine.
In my neck of the woods armoring is falling out of favor as sand replenishment takes over as the primary strategy.
We could just stop building so close to shore…