Morphological and historical resilience to catastrophic flooding: The case of Lockyer Creek, SE Queensland, Australia

•Catastrophic flooding occurred in 2011 in Lockyer Creek•Since European settlement only 26% of river length has adjusted•Eleven forms of geomorphic adjustment occurred from the early 19thC to present•This system is relatively resilient to geomorphic change•Antecedent controls drive contemporary forms and processes

This study aimed to determine the extent of geomorphic change resulting from the catastrophic flood of 2011 in the Lockyer Valley in southeast Queensland and to place these impacts within a history of geomorphic adjustment. Aerial photographs dated from 1933 to 2011 and parish maps and historical on-ground photographs dating from 1865 to 1966 were examined for evidence of geomorphic adjustment since European settlement in the first half of the nineteenth century. Eleven forms of geomorphic adjustment were identified in three categories; erosional, depositional, and reorganisational. Only 26% of the Lockyer Creek channel length has been affected by some form of geomorphic adjustment since European settlement. Most of this adjustment was localised and dominated by reorganisation of geomorphic unit assemblages within the macrochannel and sediment deposition on floodplains. No wholesale river change in the form of lateral migration or avulsion has occurred, and the river's morphology has remained relatively characteristic over time (i.e., morphology remains relatively uniform in a reach-averaged sense). Geomorphic responses to extreme flooding have been minor, and the geomorphic effectiveness of floods in this system (including the 2011 flood) has been limited over the last several hundred years. The system is likely still adjusting to past flooding events that 'set' the morphology of the current system (i.e., the macrochannel). A form of event resilience has resulted in this system such that it is less prone to geomorphic adjustment during events than would normally be considered geomorphically effective. As a result, antecedent controls on macrochannel presence and capacity are considered to be first-order controls on contemporary forms and processes in this system. Work is required to test whether the resilience of this system will hold in the future, with more extreme episodes of flooding predicted to occur in this region under future climate change.