LOL.
Have you even tried to walk along the beach at high tide?
If that photo in the OP is actually of Hua Hin, you can see for yourself the encroachment at left side where the embankment does a right angle towards the sea.
Hardly a small section of the beach.
Only on the southern beach, and the bit where the palace is wasn't encroached when I was there.
However, encroachment is illegal, far as I know, so how was it allowed?