Geomorphic differences in gravel-bed rivers three years after high-intensity bushfire (#206)
Carter T Lybeck
1
,
Timothy J Ralph
1
,
Kirstie A Fryirs
1
- Macquarie University, Macquarie Fields, NSW, Australia
- Geomorphic change after bushfires is a concern for the management of many Australian rivers. However, many studies skip from broad-scale assessments of burn extent and severity to downstream water quality, and/or to effects on large charismatic fauna. Comparatively little attention is given to fluvial geomorphology, microbial life, and links between physical and ecological changes. This study assesses the similarities and differences in four gravel-bed rivers three years after high-intensity bushfire.
- Dignam’s Creek catchment on the south coast of NSW burned during the Black Summer bushfires of 2019/20. Four subcatchments of varying burn extent and severity were compared to determine key physical differences between sites in the lower reaches of each tributary creek. At eight locations per site, we performed Wolman pebble counts and mapped in-channel geomorphic units. Cross-sections were taken at three locations per site and used to compare channel width and depth at low and estimated bankfull flow.
- Sites with more severely burned catchments had larger pebble sizes (less fine sediment), wider bankfull dimensions, lower proportion of pools, and higher proportions of bars/riffles. However, sediment size and proportion of pools were statistically insignificant. Overall, the four rivers either did not change much after the bushfires, or those that were more severely impacted have since recovered within a three-year timeframe.
- The lack of geomorphic differentiation between river reaches with vastly different upstream catchment burn severities demonstrates the complex relationship between geomorphology and catchment disturbance regimes. In this case, bushfire severity alone is not a predictor of significant geomorphic change.
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