The Severn Sea, The Bristol Channel, The Atlantic Ocean, East Nash Buoy, Nash Point, St. Donats, Llantwit Major, 51º23'53.02"N 3º34'13.92"W
I found this fantastic chart of the Severn Sea, prepared for someone called Sir Rob Southwell.
A bit of research coming on..
Where it says Naze Sand (now Nash Sands) is the location of the work. Notice it says dry on the sand patch; The Severn Sea (or the Bristol Channel) has the highest tidal range in the world, so for a part of the day, at low tide, the sand is exposed. I've played cricket on it, which wasn't easy, as the surface is like a mini sand dune system, undulating and peaking much like the surface of the sea that surrounds it. In the troughs, sea water gets trapped and during the summer, it warms up to create an island of hot tubs (or more like an island of lukewarm tubs).