Looking at the latest reports of flooding started me wondering how many of
the incidents (excluding those from rivers bursting their banks and people
ending up with metres of floodwater coming into their homes) were due to
ill-maintained drains and gulleys, already been mentioned in the Press, and
whether the general drive to conserve water may now be having an effect.

All drainage systems rely on a good flow of water to flush them through and
if the normal flow is generally reduced - by using showers instead of baths
and reducing the flush in WCs, for example - then solids and silt are more
liable to build-up, and the ability of the drain to cope with a sudden,
abnormal, high intensity flow is reduced.

In a slight twist to that, a colleague here has just told me that he ended
up with 1m of water in his basement rooms in his west London home on Friday
morning because of a partially blocked yard gulley, which normally takes
very little flow and silts-up quite readily. He routinely counteracts this
by flushing the silt through in Autumn and Spring but he'd not done so this
year, as there was a hosepipe ban in force. Once he'd paddled around in the
rain and had found and rodded the offending gulley, the water all went down
with a vengeance, so the drain would have coped, but the damage had already
been done.

IME, as much damage is done by lack of maintenance of drains and gulleys
around the home as there is by the designed capacity of drains being
overwhelmed by heavy rain (you can get a hell of a lot of water down the
75-100mm pipes that domestic separate drainage comprises). A
partially-blocked drain will often still cope with moderate rainfall, which
will normally seep through the blockage, and won't show that anything is
amiss. It's only when the (say) once in 10 years event takes place that the
problem shows up.

By then, it's usually too late.


- Tom.