Seven inches of rain fell on the village of Boscastle in two hours, overwhelming the nearby river, knocking out electricity and leaving people stranded on rooftops.
The county council co-ordinated the rescue operation, which involved more than 150 people, 17 fire engines, and eight helicopters. More than 30 county highways staff worked overnight to keep the road network safe.
Emergency planning officer John James said the operation was the biggest and most complex implemented in the county.
'We lost electrical power, water courses were affected, drains were affected and we required military aircraft.'
The government doubled annual funding for emergency planning in this year's spending review, following a campaign by the Local Government Association and the Emergency Planning Society against year-on-year real-term cuts in the emergency planning grant.
Cornwall CC emergency planning staff have been cut from 12 to eight, and Mr James said they would have been unable to cope if the disaster had continued for much longer.