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Oops, you missed a bit

The recent flurry of news about flooding and development in flood plains has not fully examined one important issue with which engineers are closely involved – control of run-off from development.
The most important piece of guidance on this subject for a number of years is PPS25. It is extremely prescriptive in some areas but when it comes to reducing peak surface water run-off from brownfield sites it is long on rhetoric and short on guidance.

Although these brownfield sites should present an ideal opportunity to reverse the practice of 100% run-off,
PPS25 and its companion practice guide make little reference to the issue.

There are several references to "not increasing flood risk", to "reducing risk where practical" (unspecified) and there is a cross-reference to a CIRIA document, which says: "It is preferable for brownfield solutions to provide run-off characteristics which are similar to green field behaviour."

But it also says that "run-off from urban developments should replicate or achieve a reduction from the greenfield response". In other words, the guidelines are so diverse that developers can find justification for almost any drainage scheme they choose to submit.

Floods minister Phil Woolas released a statement about water butts and permeable patios, which are not bad ideas but will not solve the problem. If he re-visited and strengthened PPS 25 it would make a much more significant contribution to reducing future flooding.

HOWARD GLENN (M), howard@howardglenn2.wanadoo.co.uk

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