The use of long-term monitoring data to inform the analysis of, and prognosis for, an incised stream system: The Cann River in Far East Gippsland, Victoria, Australia. (#85)
Ross E Hardie
1
,
Alex Sims
1
,
Sean Phillipson
2
- Alluvium Consulting Australia Pty Ltd, Cremorne, VIC, Australia
- East Gippsland Catchment Management Authority, Bairnsdale, VIC, Australia
- Why: The floodplain reach of the Cann River, located in far East Gippsland, is a sand bed river that has been transformed by large-scale channel incision triggered by post European settlement floodplain clearing and removal of large wood from the channel. Following a large flood in 1998, a long-term program of management, aimed at limiting the scale and extent of channel incision, and its impacts on the waterway values, public and private assets, was initiated by the East Gippsland Catchment Management Authority. The subsequent monitoring and evaluation program provides a rare opportunity to evaluate the effectiveness of this extensive program of grade control, implemented over a river length of tens of kilometres, and to guide future management.
- What we did: We used Cann River monitoring data (repeat LiDAR, longitudinal bed profiles, aerial photo imagery and vegetation mapping) collected and analysed over the last 25 years, together with stream power analysis and information for similar stream systems, to describe the geomorphic, and implied ecological, response in the Cann River to both catchment processes and the management interventions. We use these insights to predict the ongoing response of the system in the absence of management intervention, and to explore potential management options to address ongoing channel adjustments.
- What did we learn: The monitoring program revealed channel recovery within the subject reach of the Cann River including developing instream, bench and bank vegetation communities. However, the monitoring has also revealed persistent channel adjustments including an ongoing net loss of bed load sediment from the reach, and a pattern of decline in the bedgrade. Bed material upstream of the intervention reach has coarsened, which we interpret to be due to a decrease in sediment supply, suggesting the potential for a renewed phase of channel incision within the floodplain reach.
- Why does it matter: Programs to halt or slow incision in sand bed streams have been implemented across SE Australia. The causes and implications of renewed phases of channel incision in the Cann River, the role of successive phases of intervention in the Cann River and the implications for similar sand bed stream systems recovering from historic channel incision, are explored and are discussed. The investigation revealed the importance of long-term monitoring in the management of recovering incised stream systems.
Download Full Paper