Via http://www.internationaltrusts.org/wp-content/uploads/2015/09/living_wit...

"Hydrology consultants HR Wallingford recreated the flood using a computer model. The results suggested that the rapid blocking of the lowest bridge on the Crackington Stream would have made the water level rise rapidly by about 3m (10ft)"

"We commissioned consultants HR Wallingford to make an initial assessment of how severe the floods were and the chances of a repeat.  Their initial findings, published in January 2005, were that while the Boscastle flood was among the most extreme experienced in Britain, the risk of a similar or worse flood was one in 400 in any given year."

"One of the lessons we’ve learned is the need for better information about vulnerable catchments. We’re compiling a national register of catchments where heavy rainfall is likely to make river levels rise very rapidly and the depth and speed of floodwaters could endanger lives.

The register of vulnerable catchments will help us to:
 - review and adapt our flood warning systems;
 - focus our public awareness campaigns;
 - influence local authorities’ planning decisions and emergency response plans"

https://www.gov.uk/government/uploads/system/uploads/attachment_data/fil...