Stamford Brook
 

I was in Furnival Gardens in Hammersmith yesterday, and I stumbled across
the Berlin streetlamp that the mayor of West Berlin brought as a present in
1961... must be one of the strangest presents ever. Then again, I suppose it
went with the Harburg roundel which used to be at Victoria station (where is
it now?).

But I digress.

The Stamford Brook flows into the Thames just downstream from Dove Pier.
Above the outflow is a brick column containing a grille at head height,
facing toward the river. What's the grille for?