Hydromorphological data including temporal and spatial river width dynamics, flow regime, and river gradient for 1.4 x 10⁶ Australian river reaches are presented. We propose a parameter which can be used to classify reaches by the degree to which flow regime tends towards permanent, frequent, intermittent, or ephemeral. This dataset provides fundamental information for understanding hydrological, biogeochemical, and ecological processes in floodplain–river systems.