Mrs. B's story reminds me of when I used to live in Hastings:
There is a section of the concrete promenade near the pier which has surface rain drains near the edge whose outlets are about half way down the seaward side of the promenade.
It all used to work as intended and with no drama unless there was a combination of a high tide, rough sea, and ladies of a certain age in their floral frocks unlucky enough to be standing right on top of one of the drain holes when a big wave hit the aforementioned outlet and was forced upwards at great speed!
(I'd like to claim I did used to warn them about their imminent and unexpected douche, but I was only in my teens and somehow always seemed to forget.
)