Sudbrook, and the nearby port of Portskewett, would have been coastal in the past, the area eventually silting up to form Sudbrook Pill. The Kitchin and Baldwin 1748 map still has the coast extending to near St Mary’s Church Portskewett*. while records have the sea coming to Sudbrook mill (c. 400 m inland and c. 600 m downstream of the port) in 1711*.
The whirlpool in question is marked on the edge of this area on the Aram map of 1777*. It was just under the current railway line near Southbrook Farm (where the footmap in the centre of this Map hits the railway line). The whirlpool appears inactive by the first OS maps and has been lost from local memory - it is, therefore, harder to say it acted as a spring, as well as a sinkhole (if, actually, it was the latter). Nonetheless, it is a strong candidate, simply because we know the area would have been coastal at the right time.