"Denis McMahon" wrote in message
.com...
On Fri, 19 Aug 2011 01:20:55 -0700, CJB wrote:

tl;dr: there was a lot of rain in a short period, some buildings that
cover a lot of area don't have enough drainage on their roofs to cope.

Roofs are generally designed such that normal levels of rainfall are
carried away by pipes. However, these pipes have a capacity limit, and
can be blocked by all sorts of debris that ends up on the roofs.

The area in question, above platform 12, isn't really a roof, it's the
underside of the old parcels deck, (the London St deck) which is currently
undergoing major work to convert it into the new taxi rank. To look at from
below it is more like the underside of an old style railway bridge, with
arched brick infill between girders. Perhaps the work on the deck above has
progressed to the stage where whatever waterproofing there was has been
removed - and they've been caught out by the heavy rain?

Paul S