Urban River Restoration, a Scenario for Copenhagen

Abstract Urban flooding is an increasing hazard and expected to aggravate with climate change. The opening of a piped urban river in Copenhagen is explored to mitigate urban flooding as a result of a rising groundwater table. In the Copenhagen case study, a hydrological model has been used to calculate the effect of reopening a currently piped river to its natural environment as a nature-based solution (NBS). From the results of modelling scenarios, we have set up a simple damage function to calculate the avoided costs for the river basin by comparing difference in groundwater levels with and without NBS. Stakeholders were engaged from the first stages of the case study. The integration of stakeholder’s knowledge in the co-design and implementation process of NBS to support complex decision-making processes was carried out by (1) participatory modelling activities to elicit and structure stakeholder’s risk perception, (2) mapping the interaction among decision-makers and stakeholders, and by (3) deriving Fuzzy Cognitive Maps (FCM) from Group Model Building. The results show that by reopening the river, an economic benefit is obtained because the river now functions as a drainage channel which prevents flooding by groundwater of subterranean structures, notably housing cellars, and receives stormwater from cloudburst rainfall events. The FCM simulation showed that NBS implementation requires effective cooperation among different decision-makers to define potential interventions and to reduce the level of conflicts and to facilitate collaborative decision-making.