It is understood a second barrier would be located farther east than the Woolwich defence system.
A review of the flood defences at all major police, fire and power stations and other vital infrastructure was now under way, he added.
"The important question is whether the critical infrastructure sites have adequate defences. The protection they have is predominantly against terrorism and security assault," he said.
Mr Woolas told the Sunday Telegraph that the government had come close to ordering the mass evacuation of parts of Gloucestershire after the Walham power station, near Gloucester, nearly flooded last month.
"It was one-and-a-half inches from flooding and had it flooded it would have been the biggest peace-time evacuation in this country in history," he said.