Compartmentalisation: flood consequence reduction by splitting up large polder areas


Correspondence: Frans Klijn, Deltares|Delft Hydraulics, PO Box 177, NL 2600 MH Delft, The Netherlands


River and coastal floodplains are often protected by vast systems of connected embankments. In the Netherlands, about 55% of the country is protected in this way, by some 3600 km of primary defences. The protection level is probably the highest in the world, and annual mean flood risks are low. Nevertheless, the consequences of a major flood event might be unacceptable. This is a reason to consider whether and how the consequences of floods could be reduced in a cost-effective manner. Splitting up large polder areas into smaller portions, the so-called compartmentalisation, would reduce the area subject to flooding, and thus the economic damage, the number of people exposed and the fatality risk. We carried out a policy analysis for the national authorities in order to establish whether, where and under which conditions a further compartmentalisation of the country would be desirable. This paper gives some results, discusses our experiences in four case studies and finally focuses on the fundamental questions of assessment and the trade-off between better flood protection and the benefit/cost ratio of reducing consequences.