I understand a freak tidal wave hit the East coast of England in the late 1800's. The East Coast is not noted for such things.
Yarmouth is almost certainly South of Scarborough, but ill informed singers have found it much easier to sing Yarmouth "down" to Scarborough instead of the correct "up to" Scarborough. Maybe synoymous ? with another well known song "won't you come down to Yarmouth town "