The Evolution of Corryong/Nariel Creek since European Settlement: Implications for On-going Management Prioritisation

Geomorphological stability is a useful starting point to inform river management priorities, as it is critical to other river health parameters such as ecology and water quality. A key debate in channel stability is the relationship between climate and human activity. Corryong Creek is an ideal setting to study the interaction between climate and anthropogenic changes on channel evolution as it has experienced significant levels of both. Catastrophic floods have been induced by high rainfall, the floodplain has been completely cleared, the riparian zone is almost entirely invaded by willows, and every reach of the channel has experienced some form of channel modification. The impacts of both climatic and anthropogenic factors are visible in our channel change data, although at different spatiotemporal scales. Higher flows during La Niña resulted in channel widening while lower flows during El Niño resulted in channel narrowing. In addition, land clearing had caused the river to evolve into a higher-energy, straighter channel, while spatially variable and temporally irregular factors such as river engineering, willow density and stock trampling tended to intensify erosion on a reach scale. As our analysis shows that periodic increases in erosion during La Niña are expected, the local community needs to first accept and adapt to some level of channel erosion in order to avoid catastrophic damage during floods. As the second priority, since the reversibility of these factors are limited, erosion risk can be mitigated through strengthening willow management, limiting river engineering, practicing bushfire management, and fencing the riparian zone

Interaction of ENSO-driven Flood Variability and Anthropogenic Changes in Driving Channel Evolution: Corryong/ Nariel Creek, Australia

This is an Accepted Manuscript of an article published by Taylor & Francis in Australian Geographer on 03/09/2015, available online: 10.1080/00049182.2015.1048595Understanding the relative contributions of climatic and anthropogenic drivers of channel change are important to inform river management, especially in the context of environmental change. This global debate is especially pertinent in Australia as catchments have been severely altered since recent European settlement, and there is also strong evidence of cyclical climate variability controlling environmental systems. Corryong/Nariel Creek is an ideal setting to further study the interaction between climate and anthropogenic changes on channel evolution as it has experienced both significant periods of flood and drought, controlled by the El Niño Southern Oscillation (ENSO), and extensive anthropogenic changes. Since European settlement the floodplain has been completely cleared, the riparian zone almost entirely invaded by willows, and every reach of the channel has experienced some form of direct channel modification. Through the combined analysis of channel evolution, climate changes and anthropogenic history of the river it was found that both the ENSO-driven climate and anthropogenic drivers are significant, although at different scales of channel change. Significant straightening in response to land clearing in the early twentieth century occurred before any records of direct channel modifications. Following this, most river management works were in response to instabilities created in the clearing period, or to instabilities created by flooding triggering a new phase of instability in reaches which had already undergone stabilisation works. Overall, human activities triggered channel instability via land clearing, and management works since then generally exacerbated erosion during high flows that are driven by climate fluctuations. This research raises the interesting question of whether rivers in Australia have become more responsive to the ENSO cycle since the clearing of catchment and riparian vegetation, or whether the past response to climate variability was different