Greengrounds

The Green Grounds are a legendary, now-submerged area off the coast of Mumbles, Swansea, believed to be a former wooded, agricultural landscape swallowed by the sea, potentially during a 1607 tsunami.

Evidence, including a 19th-century court case, suggests it once featured a farmhouse, large meadow, and "Silver Wood". 

Key Details about the Green Grounds:

Location: Submerged land in Swansea Bay, with remnants located near Mumbles Head and the Swansea Docks entrance.

The Legend: Local stories tell of a fertile, cultivated area, sometimes called Grove Island, that was destroyed by a violent storm or tidal wave.

Historical Evidence: In the 1890s, the "Misses Angels" won a legal battle regarding land ownership by producing an old map that depicted a farmhouse on the Green Grounds.

Submerged Evidence: At very low tides, remnants of carbonized earth, tree trunks, and old stone structures have reportedly been visible.

Modern Day References: The area is still recognized in nautical terms, such as the SWIGG (South West Inner Green Grounds) buoy near the Swansea docks entrance.

Association with Disaster: The site is often linked to the 1607 Bristol Channel floods, a devastating event that destroyed villages along the South Wales coast

This event was the backdrop to a novel I read recently, called The Drowned City. Quite a good read, actually. 

In January 1606, exactly a year after the execution of the conspirators who tried to blow up Parliament in the failed Gunpowder Plot, a towering wave sweeps up the Bristol Channel, leaving a scene of devastation. Whole families are drowned, buildings are swept away and farmland is destroyed. As the survivors try to come to terms with what has happened, rumours begin to arise. Some say the wave was summoned by witches, others that it was God’s way of taking revenge for the executions. 

Not a bad review here 

Sources:-

https://www.storyofmumbles.org.uk/stories/articles/landmarks/the-story-of-the-misses-angels-and-their-farm

https://www.walesonline.co.uk/news/local-news/swansea-village-washed-away-tsunami-17058088