Sir – Dr Peter Rawcliffe writes (Letters, March 5) that speeding up flood water in Oxford does not increase the water passing downstream.

This is not strictly true, as it allows for less time for water to evaporate or to reach the groundwater store. Moreover, the water does arrive downstream in a shorter time, increasing peak flow.

I remember specifically asking the Environment Agency hydrologists whether the flood relief channel to protect Maidenhead and Windsor (the Jubilee River, built 1990) would adversely affect London for this reason. They replied that modelling had indicated that a 2mm increase in peak flow was all.

However, the following year, floods in Chiswick were the worst on record. Some coincidence.

Michael Dean, Abingdon