Oral Presentation 9th Australian Stream Management Conference 2018

Rates of bank erosion under natural and regulated flows in the Upper Murray River system - Khancoban Dam to Jingellic (#14)

Brett Phillips 1 , Andrew Simon 2 , Jennifer Hammond 3 , Kimberly Artita 4 , Elizabeth Pope 5
  1. Cardno ENTRIX, Oxford, MS, United States
  2. Cardno, Oxford, MS, United States
  3. Cardno, Fayston, VT, USA
  4. Cardno, Clemson, SC, USA
  5. Snowy Hydro, Cooma, NSW, Australia

The Snowy Mountains Scheme provides for inter-basin transfers of water and for hydro-electric power generation in the upper reaches of the Murray River System. Since 1966, the magnitude, frequency and duration of discharges in the Swampy Plain and Upper Murray Rivers have been modified by the Scheme. Increases in mean-annual flows following regulation were determined to be 127% in the upstream-most reach on the Swampy Plain River, 68% above the confluence with the Tooma River and 16-19% downstream at Jingellic. The duration of half-capacity and channel-capacity flows at Khancoban showed an increase from 19 to 97 days and unchanged at about 3 days, respectively. Downstream at Jingellic, there was virtually no change. 

The hydraulic and geotechnical resistance of the banks was determined in situ at eight sites along the reach and disclosed relatively weak and erodible bank sediments. These data were used in the dynamic version of the Bank-Stability and Toe-Erosion Model (BSEM-Dynamic) to predict bank erosion under regulated and un-regulated conditions at hourly time steps for a 32-year period. The greatest difference between bank-erosion rates under un-regulated and regulated flows is in the reach closest to Khancoban Dam (increase of 255%). Differences in total unit-erosion along the study reach tend to decrease moving away from Khancoban Dam, becoming negligible below the Tooma confluence. In the downstream-most reaches, bank-erosion rates are lower than for un-regulated flow conditions. The majority of the other sites show a 22-129% increase in total erosion between the un-regulated and regulated flow series, largely attributable to the increased duration of flows above the erosion thresholds.

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