Ryuiki-Chisui in local practice: a case study of Rokkaku River basin and Takeo City, Saga Prefecture, Kyushu region, Japan

Earlier disaster research has often assumed that the primary agent of choice is the autonomous human individual, overlooking how such decisions are shaped through relationships, notions, infrastructure, technologies, institutions, residential choice, and non-human environments. Following two major flood disasters in 2019 and 2021, local volunteer groups, municipal officials, and residents in Takeo City, Saga Prefecture engaged in various collaborative efforts to rebuild livelihoods, navigate administrative systems, and prepare for future events. This study examines how Japan’s emerging basin-based flood management policy, Ryuiki-chisui (River Basin Disaster Resilience and Sustainability by All), is implemented and reinterpreted in everyday practice through an ethnographic case study of Takeo City. Drawing on “logic of care,” “saikan (in-between disaster),” and “fluid,” the study analyzes how flood governance unfolds not as a sequence of rational choices or top-down directives, but as ongoing socio-technical tinkering shaped by relational labor, uncertainty, and situated forms of expertise. The findings show that Ryuiki-chisui operates as a dynamic set of practices that bridge the gaps between hydrological models, administrative frameworks, and residents’ embodied knowledge of the Rokkaku River basin. Volunteer intermediaries are critical in translating institutional categories, coordinating support for disaster certification and emergency repairs, and addressing the grey zones that fall between formal systems. Through these practices, flood governance has become a care-intensive process involving continuous adjustments across human and non-human actors such as pumps, gates, tides, homes, legal documents, and community networks. By highlighting the relational and ethically charged dimensions of life amid recurring disasters, this study advances international discourse on inclusive and transdisciplinary water governance. It demonstrates that effective basin-based flood management relies not only on technical measures, but also on cultivating forms of collaboration and care that sustain communities within continually changing environments. Practically, the findings suggest that Ryuiki-chisui will be more effective when intermediary work for translation, coordination, and grey-zone problem solving is recognized and resourced as part of basin governance, alongside conventional hard and soft measures. Conceptually, the study provides a practice-oriented specification of socio-hydrological coupling that can inform future interdisciplinary research integrating socio-hydrological modeling with ethnographic and participatory approaches.