An approach for assessing geomorphic river sensitivity across a catchment based on analysis of historical capacity for adjustment

Contemporary river forms and processes can be heavily influenced by the legacies of anthropogenic disturbances to river systems. Knowledge of the historical range of river adjustment can be used to develop an understanding of a river's 'expected' character and behaviour. Drawing upon the case study of Richmond River Catchment, New South Wales, Australia, we track the history of geomorphic river adjustment from the time of European colonisation in the mid-late nineteenth century. We use this study to develop an approach, called the 'Behavioural sensitivity logical tree' that can be applied to assess and quantify reach scale behavioural sensitivity, defined as the ease with which geomorphic units and associated water, sediment and vegetation interactions adjust within the expected behavioural regime. We use the results to categorise rivers as Fragile, Active sensitive, Passive sensitive, In-sensitive and Resistant. Fragile rivers have a behavioural sensitivity >75% and have the propensity to undergo wholesale river change such that a new river type and behavioural regime is created. Active sensitive rivers have a behavioural sensitivity ranging from 50%-75% and have the ability to re-configure within their contemporary behavioural regime. The behavioural sensitivity of Passive sensitive rivers lies between 20%-50%. These rivers have the ability to maintain their behavioural regime and withstand adjustment. Insensitive rivers have a behavioural sensitivity ranging from 5%-20%. They do not readily adjust and may contain significant antecedent elements that limit geomorphic adjustment. Resistant rivers have a behavioural sensitivity <5% and because of the imposed geological setting cannot readily adjust. We further discuss the evolutionary nature of behavioural sensitivity itself and how rivers can dynamically evolve and shift to a different sensitivity category over time in response to different forms of direct and indirect disturbances. (C) 2020 Elsevier B.V. All rights reserved.