The evaluation of flood risk policy in the Netherlands

Dams, dykes and coastal defences in the Netherlands have never been stronger: the probability of encountering floods from rivers or from the sea has substantially declined since the last flooding in the south-western part of the Netherlands in 1953. The risks of casualties and of economic damage from flooding have, however, become much greater since this event. This paradoxical situation is the result of a growing discrepancy between the existent set of design standards for the height and strength of dams, dykes and coastal defences set around 1960, and a steady social and economic development since that time. The average yearly economic expansion since 1960 has been twice as high as expected at that time and the population at risk in the Netherlands has more than doubled. In the period between 1960 and the present, the design standards have not been corrected for the increased economic value and population. Compared with other risks, the societal risk of flooding (the probability of large numbers of casualties) in the Netherlands appears to be several orders of magnitude larger than the sum of the societal risk of other known external hazards (e.g. industrial hazards and plane crashes). A further increase in flood risk is expected owing to further economic and social development.