Many, many thanks, ClaireBear!! I will look up the anecdotalcity site as soon as I finish this post!! I THINK that site was where I originally found the story, but forgot the site name and have been unable to find it again!! (Until now, thanks to you!) I've googled and googled for Grangetown Whale without being alerted to that site. (So Google is not perfect after all!) I emailed the Grangetown city information bureau (Can't remember offhand the exact name and don't want to take the time to look it up) but they were very vague about the whole thing. I'm still not sure where I heard that the flood occurred about Christmas time, and I had a vague notion about the year 1879, but that may be 'way off base. (The 1940s sounds more likely except for the war going on then, so maybe it was 1970-something that I buried in the dustbin of my mind. Hopefully, Frank Hennessee may see some of these posts and clear away the fog. I suspect that only he may have all the answers.
Anyway, thanks muchly for the anecdotalcity site, ClairBear. I'm going there now.