From a hydrologist via Twitter
@JakeZackAndy: 300mm rain
= 300,000,000 litres per km2
= 15 billion litres of water for a 50km2 catchment
He also points out that no fixed flood defences which are environmentally and financially feasible could possibly cope with that amount of water that quickly.
I’m sure that won’t stop the media blaming the EA and other government agencies