Geomorphology of gravel-bed rivers three years after high-severity bushfire

Geomorphic change after bushfires is a concern for the management of many Australian rivers. Many studies skip from broad-scale assessments of burn extent and severity to downstream water quality and/or to effects on large charismatic fauna. Comparatively little attention is given to fluvial geomorphology. This study assesses the geomorphic similarities and differences in four gravel-bed rivers three years after high-intensity bushfire. At eight locations per site, we performed Wolman pebble counts and mapped in-channel geomorphic units. Cross-sections were taken at three locations per site and used to compare low flow and bankfull channel width and depth. Sites with more severely burned catchments had wider bankfull dimensions and higher proportions of bars and riffles. Sediment size and proportion of pools were also different but did not show statistical significance. Overall, either the rivers did not change much after the bushfires, or those that were more severely impacted have since recovered. The lack of geomorphic differentiation between river reaches with vastly different upstream catchment burn severities demonstrates the complex relationship between geomorphology and catchment disturbance regimes. In this case, bushfire severity alone is not a predictor of significant geomorphic change.