Integrating nature-based solutions in flood risk management plans: A matter of individual beliefs?

Nature-based solutions on floodplain restoration with coupled propagule dispersal simulation and stepping-stone approach to predict mangrove encroachment in an estuary

The mangrove ecosystem is significantly affected by human activities, climate change, and rising sea level. The propagules of mangroves dispersal with tide and river currents that extend upstream habitats are why mangroves are the dominant species in the tidal area. Bridging critical knowledge gaps can help to create restoration plans for mangrove extension. However, studies on the hydrodynamic and propagation trajectory model (PTM) simulation of propagule long-distance dispersal (LDD) and mangrove growth potential are scarce. By combining various numerical methods and empirical formulas and verifying them with the data obtained through field surveys, this study established a comprehensive model to assess the dispersal and growth of the propagules of Kandelia ovobata. The stepping-stone approach (SSA) and habitat suitability index (HSI) model were also employed to determine the location of the appropriate new habitats through iterative simulation in propagule dispersal. Dike removal was proposed as a nature-based solution and modeled to evaluate the benefits of ecological conservation and flood prevention. The PTM simulations indicated that the deterministic process of horizontal advection accounted for >80 %, and that the remaining variability in the model could be explained by stochastic processes in predicting mangrove propagules pathways. The integrated model of the PTM and SSA proved that propagules have LDD in an estuary. There were few matches in the regions for mangrove growth when comparing the suitability of habitat distribution and the probability of propagule movement. We suggested that the mangrove spread model incorporating the SSA and HSI models predict the potential for mangrove dispersal into new habitats. In addition, the removal of levees aids floodplain regeneration and allows propagules to disperse across the floodplain at high tide and establishment at low tide. The Guandu floodplain restoration with dike removal supplied a cobenefits on ecological demands and flood risk reduction. Future research could thus utilize the adaptation and mitigation strategies presented in this study by incorporating socioeconomic considerations to enhance practical feasibility.

Deliberating options for nature-based river development: Insights from a participatory multi-criteria evaluation

To address societal challenges in river landscapes, various options are conceivable that differ in the degree of adopting nature-based solutions (NBS) and the respective impacts on people and nature. Multi-criteria evaluation (MCE) can aid participatory deliberations about the performance and significance of such options. However, little experience and evidence exist from the application of participatory MCE in planning NBS in river landscapes. This study aims to expand the understanding of individual and collaborative judgments of agency representatives about river development options with varying levels of NBS interventions. A process tracing approach with a rigorous participatory MCE for four alternatives to develop an exemplary river in Germany is adopted, as well as weighted linear aggregation, descriptive statistics, principal component analysis, and decision tree modelling for data analysis. The results reveal a wide agreement among participants on the positive impacts of NBS on biodiversity and water quality. Participants also tended to judge those ecological dimensions as more important than non-ecological ones. The rankings of alternatives differed when elicited individually but seemed to converge during the deliberation process. Overall, the results indicate a relative preference of participants for medium NBS interventions, but also shed light on potential implementation hurdles. The study closes by proposing key questions to consider for MCE of NBS.