In July 2017, an unusual train of rainfalls triggered an unprecedented set of hydro-meteorological hazards, which brought a compendium of landslides, debris-flows and floods, eventually reaching the city in the lower part of the forested catchments of the North Kyushu area. Surprisingly, spatially and temporally averaged rainfalls were not out of the ordinary, but the concentration over a short period of time along rainfall corridors triggered more than a thousand landslides. If lower amplitude events have usually driven the regional and local authorities to build protection systems in the catchment, the amplitude of the 2017 disaster has called for a full remodelling of it, interrupting waterways, reshaping slope shapes and structures, etc. In the light of the shear-scale of the means deployed by the central government for this reconstruction, it seems that the 2017 event has triggered a full “re-construction” (if not rethinking) of the area, which is set to deeply modify the functioning of the catchment’s hydrosystem. Thus, the aim of this contribution is to explain how the 2017 disaster forced to rethink the Akatani catchment’s organization.

The present research relies on (a) field surveys in 2019 and in 2022, in combination with (b) interviews with local, regional and national officials, and (c) Geographical Information System analysis based on historical aerial-photograph interpretation and geospatial data.

For the river floor and floodplain, the results of this research have shown that the planform geometry of the channel has been fully redesigned and straightened, while at the same time the size of the channels has been increased to accommodate and match the amplitude of the 2017 event. On the slopes, sediment control structures, such as slit-dams and check-dams are now restructuring the slopes, breaking the slope angles in sub-catchments such as in the Otoishi River. Furthermore, the space in between the sediment control structures has also been controlled by concrete coffin streams. Finally, these structures are complemented with geotechnical work on the slopes surrounding the dams. The Akatani River case illustrates the full range of structural measures developed by the Japanese engineering, exemplifying the vision of River System SABO.