Assessing Rates of Bank Erosion in Regulated Rivers in South East Australia

This paper overviews the field investigations and numerical modelling of bank erosion rates in two regulated rivers in south east Australia. The first case study was the assessment of the rates of bank erosion under natural and regulated flows in the upper Murray River system downstream of Khancoban Dam to Jingellic. The field investigations and numerical modelling of flows and bank erosion are overviewed. It is concluded that: (i) regulation has caused important changes in the hydrologic regime of the Swampy Plain and Upper Murray Rivers in the reaches closest to Khancoban Dam and (ii) regulation has led to changes in bank‐erosion rates with increases in the reaches closest to the dam and decreases in the reaches farthest downstream, the former related to greater flow durations that exceed erosion thresholds. The second case study is the assessment of the rates of bank erosion under different and alternative flow releases along the Mitta Mitta River and the development of metrics to limit erosion downstream from Dartmouth Dam. The field investigations and numerical modelling of flows and bank erosion are overviewed. The magnitude and duration of flows above erosion thresholds exert strong influences on bank erosion rates and these were used to develop metrics for operational guidance to limit erosion. It is concluded that: (i) erosion rates modelled with BSTEM‐Dynamic ranged from 0.9 to 9.8 m³/m of channel length between 2006 and 2016 (ii) erosion thresholds ranged from about 5,200 ML/d to almost 13,000ML/d and (iii) bulk‐water transfers have the greatest potential to cause significant bank erosion because of high flow rates and durations above erosion thresholds.