Flood Risk Mitigation by Spatial Planning—Lessons Learned From Municipal Consultation

Abstract

The paper investigates which information on flood risk is needed for local land-use planning and how a risk-based planning approach can be implemented. The article is based on the results of a municipal consultation meeting at which German municipalities presented their planning cases in flood-prone areas. These cases included the conversion of existing settlements and buildings and new developments on previously undeveloped land. The team of researchers conducted pluvial and fluvial flood risk assessments based on water depth and flow velocities and analyzed the planning documents. On this basis, we advised the municipalities regarding risk-based planning. The flood event that hit the German states of Rhineland-Palatinate and North Rhine-Westphalia in mid-July 2021 increased municipal awareness for flood-sensitive planning. The consultation has confirmed that the biggest challenge is managing flood risk in existing built-up areas. The extreme event changed the flood statistics and thus the assessment basis, but municipalities seek legal certainty for decision-making. Currently, the lack of a clear planning basis creates uncertainty but also poses opportunities for change. In this context, we recommend, with reference to good examples from other European countries, an orientation towards the precautionary principle and the consideration of extreme flood scenarios.