Relationships of bankfull channel width and discharge parameters for modern fluvial systems in the Japanese Islands

•We examined hydrological features of modern Japanese fluvial systems.•We estimated empirical equations between channel widths and water discharges.•The equations may have wider applicability for both modern and ancient rivers.

The relationships between the bankfull channel width and the mean, bankfull, and maximum discharges of Japanese rivers were examined using the hydrological and geomorphological data from 368 sites. The relationships between the bankfull channel width and the mean and bankfull discharges do not show any distinct regional variations. In contrast, the relationship between the maximum discharge and the bankfull channel width shows regional variations, and the lower and higher maximum discharges relative to bankfull channel widths are documented in the fluvial systems in Hokkaido and Southwest Japan, respectively. These variations are interpreted to reflect regional variations in precipitation intensity during the rainy season, and the magnitude and frequency of typhoon-related flooding. The relationship between the bankfull channel width and the bankfull discharge can be described by an empirical equation similar to that described from modern fluvial systems on the European and American continents. Consequently, this empirical equation may have wider applicability for the estimation of hydrological features of modern and ancient fluvial systems, not only in active margin settings influenced by mid-latitude temperate climates, but also in passive continental margins and continental interior basins.