Great article from the Guardian here explaining how half a million houses in the UK will be at considerable flood risk.  The cost of defending them will be far less than the cost of dealing with the floods when they occur.  The cost benefit analysis has to be 5 times the cost of the defences.  Apparently the average cost of a burglary6 in the UK is £1000 whereas the average cost to a home following a flood is £20,000 – £30,000!