In Thames Rd aka Strand On The Green, just west of the railway bridge is an
alley called Post Office Alley which contains a small old floodgate at the
river end. Set into one wall of this alleyway is a line of solid metal knobs
which are shaped like carpentry dovetails. The line is level (i.e. level
with a spirit level rather than level with the rather sloping ground). There
is nothing in the other side of the alley. I presume they serve some flood
defence purpose but I can't figure it out. Any clues?