Hydrologic and geomorphic impacts of dams in tropical northern Australia

This study examines the geomorphic impacts of damming across northern Australia, one of the world’s most ancient and geologically stable landscapes. Using long-term hydrological datasets and aerial imagery, we analysed geomorphic changes over decadal timescales in four contrasting catchments with reservoir capacities ranging from 64×106 to 492×106 m3. Our analysis focused on: (i) tracking pre- and post-dam hydrological and morphological adjustments along the river continuum; (ii) assessing these changes across each catchment; and (iii) identifying key controls on geomorphic change.Although the extent of adjustment varied between catchments, the predominant signal was reduced geomorphic activity rather than widespread erosional instability, contrasting with global studies that emphasise enhanced downstream erosion due to the ‘hungry water’ effect. Across the study areas, we identified four post-dam morphological changes: (1) reduction in active channel width (from 0-78%), (2) in-channel vegetation encroachment, (3) reduction in morphological changes resulting in increased channel stability and (4) shift from primarily erosional to depositional regime. These changes were strongly linked to (1) degree of hydrological regulation and (2) local geomorphic river setting i.e. extent of lateral confinement and alluvium. Catchments with stronger flow regulation and a greater proportion of unconfined alluvial reaches experienced greater geomorphic adjustment.Two of the study catchments, the Harding and Proserpine rivers, may represent approximate lower and upper endmembers, respectively, with contrasting degrees of flow regulation and lateral confinement. These findings provide insights for river management in northern Australia and contribute to broader understanding of global river science in sediment starved, geologically stable fluvial landscapes.