You can quite accurately predict when a wave is going to break. When it will break depends on its steepness, which depends on the slope that it is running up on. So due to the funny beach shape caused by the differential erosion on the upstream and downstream sides of groynes we can watch one and the same wave crest break several meters apart depending on the side of the groyne we look at. Kept me fascinated for the better part of the three days we spent in Hastings, and would have kept me entertained for a lot longer, I am sure, had I not had to go to a conference (and win a poster award there, so it was all worth it in the end ;-))

Here we see a wave breaking on the right side of the groyne, while at the left side the previous wave is still breaking and the one breaking on the right side hasn’t even developed a clear crest yet:

It’s a lot easier to see in a movie. Have fun!