Mitigating the levee effect – Spatial planning approaches to address residual risk

The levee effect poses a challenge for flood risk management. While there is research on the consequences of the levee effect in general, a detailed understanding of policies addressing residual risk is lacking. The aim of this research is to understand how coercive and cooperative policy designs are applied in spatial planning provisions dealing with residual flood risk and which context conditions influence planning authorities when deciding on a certain policy design. We applied a qualitative research approach, including expert interviews and examining relevant documents. The results show that coercive planning policies can regulate the use of areas with residual risk either by limiting the extension of building land or by prescribing flood adaptation of buildings. However, the formulation of such regulations is connected to the spatial context, the actors involved, past flood events and risk awareness. Cooperative planning policies address residual risk either as recommendations or by providing local authorities scope for decision-making when it comes to land use planning in residual risk areas. The interview partners also discussed possibilities that go beyond spatial planning, such as emergency management. The research shows the variety of policies that can offer ways of dealing with flooding beyond the expected level.