LETTERS: Heath Dams – More than a drop of rain

Published: 6 February 2014

• IN response to your interview (Heath dams: Expert defends double role, January 30), I don’t find Dr Andy Hughes’s defence of his double role particularly convincing and this is why.

Dr Hughes persistently conflates two wholly unrelated issues. The first is uncontested – the need to ensure existing dams are safe. The second is debatable – the claim that engineering works should take place on the Heath sufficient to safeguard lives against a storm of such intensity that it is predicted to occur only once in 400,000 years.

Let’s take seriously for a moment the professional advice that we need to safeguard ourselves against a storm of such a magnitude.

According to his report the maximum rainfall that it is physically possible for a cloud to discharge is 0.67 inches per hour. The inundation against which Dr Hughes advises we must safeguard ourselves is one where the maximum downpour that is physically possible will persist at this maximum rate for 14 consecutive hours and across every single point on an already saturated Heath.

The overall effect of this deluge would be approximately nine inches of rain, 40 per cent of London’s annual average, in just 14 hours. Is that really credible?

If so where else and when has a storm of similar intensity occurred in south east England?

One way of putting this in context is that in the 400,000 years between such inundations 800,000 people will have died jumping off Archway Bridge. This puts into perspective the 1,400 it is claimed would lose their lives in such a flood.

Another way of putting this in context is to imagine the catastrophic effect of what would happen elsewhere in London supposing nine inches of water were to fall in half a day. How many other reservoirs would Dr Hughes recommend be built against such a contingency?

A third way of putting this in context is to consider how many of the 400,000 years will elapse before we are able either to prevent a storm of this intensity occurring or to predict it well enough in advance to take appropriate remedial action.
I sense overkill in these recommendations.

King’s College