Rob Gray gave the FORCE AGM on 10th November 2011 the inside story: the cause was a jammed ‘penstock’ (a sluice or floodgate for regulating the flow from a pent body of water, as in a watermill) at the point where two 2m sewage pipes join to become a single 3m pipe. It jammed after had been closed to allow Thames Water (TW) to inspect the 3m tunnel using a remote controlled camera on a ‘surf board’.
The TW engineers worked through the night to try to free it; it is lifted by a screw gear; when this sheared off they asked the Army if they could use explosives to free it. In the end they attached jacks to it somehow and jacked it up.
Before this the sewage had backed up into a hotel basement and was forecast to flood a much larger area when Heathrow woke and went to the loo en masse. So TW decided that they had no choice but to open an emergency gate and discharge it into the river; it would in any event have overflowed into the river before long.
TW have removed, they say, c. 10,000 dead fish which they have taken to Mogden so that the range of species (more than 20) and ages can be recorded.
The last time a London river was fouled like this was a discharge of bleach into the Wandle by TW a few years ago: they paid £0.5 mn. into a trust fund to pay for the cost of bringing the river back to life. So it is expected that something similar will be agreed this time, before TW come to court in a year’s time or later.
— from Christopher J Squire