The story of the drowned land known as Cantre’r Gwaelod is best known in a later version of it where the drunkeness of Seithennin caused him to forget to close the sluice gates when the tide was coming in. The less well-known earlier version from The Black Book of Carmarthen is discussed elsewhere on this site [~>]. If the later version has become the version most repeated in popular folklore in English, the earlier version seems to have become transformed in various strands of local folklore in the Welsh language. For instance, the tale of ‘Nodon’ and ‘Merid, which also contains elements of the later version relates that a giant called Nodon lived on a flat expanse of land which is now under the sea in Cardigan Bay.  He used both to drink from and to bathe in this well but otherwise it was kept covered and looked after by a well maiden called Merid. One day a stranger came past on his way back from a feast with a drinking horn full of wine. He asked Merid for some water from the well for his horse, and while the horse was drinking he gave Merid the drinking horn so she could taste the wine. He then goes on his way leaving Merid to get drunk and she forgets to close the well. Water flows out of the well while she is sleeping and she is drowned as the land all around is engulfed by a flood, and remains flooded to this day. Another version in English  says that man in a drunken state gave her wine then violated her with the same outcome. The tale ends by saying that she was transformed into a seabird and her descendants still inhabit the well-known seabird nesting colony on Craig yr Adar (Birds Rock) near to the village of Newquay on Cardigan Bay.
I was struck when I found this story recently as it chimes with my own attempts to re-write Mererid’s story both in interpreting the significance of the Black Book of Carmarthen poem [~>] and in a short narrative of my own written some time ago [~>].
Clearly this is a ‘version’ of the Cantre’r Gwaelod story and Merid must surely be the same character as Mererid in that story. Interestingly, the collection of local folklore in Welsh from the Cardigan Bay area where the story is reproduced also contains another story about a mermaid called Morwen who lives in the already drowned land of Cantre’r Gwaelod, and who causes further permanent flooding in order to capture a young man she wishes to carry off into the depths and marry him. A drowned land called Maes Maichgen is mentioned elsewhere in the medieval Triads in Latin  which describes it as the land of Helig son of Glannog and locates it in the central part of Cardigan Bay, apparently encompassing but stretching further than the lands of Maes Gwyddno (Cantre’r Gwaelod). The references to the inundation in this triad is to different kingdoms being flooded over a large area in the distant past. References elsewhere also refer to inundations that have taken place in the past: “there were but two rivers …. but the deep water grew wider and overflowed the kingdoms” as the Mabinogi story of Branwen has it. That is, there are both legends of specific inundations as in the Cantre’r Gwaelod story, but also references to a general rise in sea level over a long period of time.
But what of Nodon? If, as seems likely, he is the Brythonic god Nodens, represented here as a giant, what is the significance of him appearing in this tale and should it suggest a connection between him and Gwyddno Garanhir of Cantre’r Gwaelod? Nodens certainly has associations with the sea, but as both Welsh Lludd/Nudd and the Irish Nuada he is also associated with loss of sovereignty. The shrine of Nodens at Lydney overlooking the tidal River Severn with its bore – a powerful tidal rush of water running against the natural flow of the river – is also associated with healing and dogs feature in his iconography which has also led to suggestions of a link with hunting. He is a complex god with varying functions not the least of which is transformation. Such a god, appearing in later folklore as a giant, might well be associated with deluges that turned the land into sea bed. If these stories are embedded memories of land loss transformed into specific inundation legends and in the process mixed with themes from other stories, they embody just such a set of features as might be expected as ancestral memory is passed on and re-shaped in the mythos.