Mapping functional fluvial spaces for river restoration: a spatial analysis approach to floodplain reconnection

Urbanization and economic activities in floodplains have altered river dynamics, increasing flood risks, environmental degradation, and ecosystem services loss. This study explores river-floodplain restoration as a sustainable solution to mitigate urban flooding, using the rectified lower part of the Macaé River Basin, Brazil, as a case study. Conventional flood control strategies, like levees and channelization, have often exacerbated flooding downstream by disconnecting rivers from their floodplains and reducing water retention. In contrast, Nature-based Solutions (NbS) allow rivers to restore natural functions, while providing social, economic, and ecological co-benefits. This research proposes a systematic approach for mapping a functional fluvial space, by integrating GIS analysis, historical cartographic records, satellite imagery, and a multi-criteria decision-making (MCDM) method. Flood susceptibility, terrain features, and fixed points that constrain river flow are evaluated, to identify possibilities of river-floodplain restoration. The findings emphasize the role of peri-urban areas, highlighting a solution that prioritizes re-meandering and floodplain reconnection over engineered interventions. Integrating river restoration into urban resilience frameworks indicates the need for adaptive water management policies that balance flood mitigation, ecological restoration, and urban safety. In this context, strategic river restoration enhances resilience and biodiversity, providing long-term flood protection while fostering coexistence between natural and built environments.