Not sure about how this reef will break, the tidal range is massive in Borth. But here is sweet physical modeling video for you reef fanatics.
Nice link :)
I guess they would actually see some pretty solid waves there from time to time so will be interesting to see how it performs! Good to see some progress on the Artificial reef front!
I think that rock may be the answer -sandbags seem too uncertain and unreliable?
the problem of waves tossing rocks around is another matter - their weight is diminished by each rocks volume (M***3) in tonnes.
That is one cu.m of rock underwater weights 1t less than the 2.x t it might be above water.
Borth coastal defense construction photos