The SENDRA committee has just received this valuable clarification about non-return valves from Alan Alcock. We think it may be useful for all members to read it.

Dear Chair,

I don’t know who suggested the installation of non-return valves.  No doubt the committee’s advice is well-intentioned.  However, it seems to me to be misguided.

I shall try to explain.  In my front garden is a manhole where the soil and waste pipe from my house joins the drainage system.  Everyone has something similar.  Now, imagine that the river level rises to such an extent that it fills up the system and overflows into my garden, your garden, the street etc..  Let us suppose it eventually reaches the level of my ground floor, our ground floors.  Note that this is the level of the effluent inside my soil pipe which can rise about another 40cm before the ground floor WC overflows inside my house.  Note also, however, that the effluent is already starting to enter my/your house via the front door, or any other door at ground floor level.  Any non-return valve fitted on my soil pipe has been by-passed.  So the installation of one of these gadgets achieves nothing.  I therefore think that you and your committee should withdraw your advice.

On a more general note, I was encouraged by Chris Knight’s recent paper on flooding.  It seems to me both sensible and positive.  So why are we making questionable proposals to mitigate flooding as if it is likely?  Old habits….?

Best wishes.

Alan Alcock