Resource Management and Geography - Theses
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ItemSpatial distribution and scaling of avulsions on the King and Ovens River, Victoria, Australia( 2015)Anabranching is a multi-channel river system identified by in-stream vegetated islands or stable alluvial sediment. Avulsions require the abandonment of a river course in favour of a new, more efficient path, generally on the lowest point on the flood plain. Two styles of avulsions exist, progradational and incisional with the former requiring significant flood plain deposition (usually crevasse splays). The Ovens and King River of Northeast Victoria display characteristics of incisional avulsions which need overbank flooding to scour a new channel through surrounding flood plain. The study area of this paper provides a region, unaltered by human interference, to measure all avulsions and their relative distance downstream, an angle which previous literature has not taken up as yet. Results of longitudinal slope, stream discharge, relative flood plain height and sinuosity were based on analysing LiDAR data. Avulsion lengths and distance downstream showed very little correlation (R=2%) and although maximum lengths of avulsions showed greater correlation (R=54%) it still was not strong. Longitudinal slope decreased rapidly from -1.50 m/km to -0.29 m/km after approximately 70 km which correlated to the plateauing for maximum length avulsions. Although shear stress was not measured in this study, its ability to induce knickpoint migration is greater in lower slope regions, providing potential for longer avulsions. Valley-lengths of avulsions also exhibited similar patterns between the Ovens and the King with maximum in lengths at approximately 55 km, which correlated to a plateau in valley-length longitudinal slope. In conclusion, longitudinal slope was the main factor affecting avulsion length. Sinuosity of the Ovens River increased (1.34 to 1.65) whilst avulsion sinuosity decreased suggesting the current channel may avulse to new courses, or existing paleo-channels. The presence of paleo-channels on the wide expanse of flood plain of the lower regions, have a high tendency to attract flow into old conduits instead of scouring new channels for avulsions. Therefore, likelihood is high of reoccupation for avulsions along the Ovens River approximately from Wangaratta preventing the creation of long, whole-system avulsions. Finally, scale invariance of this study can be applied to expectations of avulsion lengths in other anabranching systems which must be considered for town-planning and risk-management. Therefore, providing the tools for predicting avulsions are necessary for future systems.