Dutch dikes, and risk hikes; a thematic policy evaluation of risks of flooding in the Netherlands. Extended summary

23-06-2005 | Publication

Flood defences in the Netherlands are stronger than ever due to extensive improvement programs the past decades. However, flood risks have increased because the number of people and the economic values to protect have increased at a higher rate than the strength of the dikes. Compared to the risks associated with other hazards (external risks) flood risks are much higher. At the moment protection levels have hardly a relation with the values to protect. Other options than present policy (everywhere the same standards for flood defences) can be much more cost effective. The full report has been sent to Parliament last year.

Dams in the Netherlands have never been stronger so the probability of encountering floods from rivers or on the coast similar to the great flood in the south-western part of the Netherlands in 1953 has declined. However, the risks of casualties and economic damage from flooding have become much greater since this event. 

The controversy intimated here (decreased probability of flooding vs. increased risks of casualties and economic damage) has been largely attributed to a creeping discrepancy between the existent set of design standards for dike strength (used for dam assessment and reinforcement programmes in the Netherlands) and continuing social and economic development. These standards, set down in national law, are, to a large extent, based on insights gained in the 1953-1960 period. The present spatial distribution of economic interests attached to the “dike-ring” areas (vulnerable lands protected by a single ring dike) is no longer in proportion to the spatial variation of security standards. Besides, the public no longer seems to consider flooding in the Netherlands as a natural hazard but rather as a sort of external risk such as industrial hazards and plane crashes. The risks of casualties due to flooding in the Netherlands are much greater than the known combined external risks. Compared to other countries in Europe, and the USA and Japan, the safety levels of dams in the Netherlands are already much higher, based as they are on the high vulnerability of the population in the Netherlands, with its low-lying areas, dense population and large investments. 

A further increase in flood risks is expected due to the rise in sea level, climate change, and further economic and social development. Technical solutions no longer form the sole answer to this increase. Up till now focus has been on reducing risks of dike breaches by technical means, while efficient solutions in spatial planning have been overlooked. Solutions presented here include avoidance strategies for floodprone areas and the construction of compartment dams for splitting up large floodprone areas into smaller ones. Political support is essential, however past experience has shown that political interest has the tendency to rapidly decline after disasters. 

English translation of the summary of report 500799002