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.