@spendius,
Quote:The larger the ponds to hold excess water upstream the less the levels rise for a given amount of rain.
True dat.
Quote:We often see pictures of churches above the flood line which seems to suggest that the builders of them knew all about floodplains hundreds of years ago.
Probably true dat too, but I think most old churches are built on pre-christian sites. Same thing applies of course.
Quote:There was more than a hint from an expert that water in the Thames is being held upstream to prevent London flooding.
I suspect that is so. Izzy is right that the barrier is there to stop tidal surge, and I don't think the river is tidal above Teddington Weir, but a large volume arriving from upstream would negate the effect of the Barrier, if closed. And tend to flood the City. And we wouldn't like that to happen, would we? Just think what the Lord Mayor would say.