No idea mate re the structures thought one was dragon teeth? Marsh road runs along the shoreline rough map ref along Marsh road,there are a few more structures but at the time it was a tad boggy https://www.google.co.uk/maps/place/51°37'47.4"N+4°08'11.5"W/@51.6299534,-4.139042,17.25z/data=!4m5!3m4!1s0x0:0x0!8m2!3d51.629821!4d-4.136527