John Rowland wrote:
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?

I can't help with your question, but just to correct one point in your post:

Thames Road is not "aka" Strand on the Green. The name Strand on the Green
is applied both to (a) the riverside village just downstream from Kew
Bridge, and (b) within that village the highway along the river bank. That
highway starts as a road but the road soon veers away from the river at
which point it becomes Thames Road. Strand on the Green (the highway)
continues along the river bank as a mere towpath, but still has houses
fronting on to it (with postal addresses of xx Strand on the Green) whose
land reaches back as far as Thames Road, sometimes with separate buildings
fronting on to Thames Road.

Buildings or gates on the south side of Thames Road may therefore carry
either Thames Road numbers or Strand on the Green numbers, usually without
specifying which. As far as I remember, the situation is not helped by the
numbers on the two roads running in different directions.

Finding house number X in Thames Road can be difficult!
--
Richard J.
(to email me, swap 'uk' and 'yon' in address)