The Big Dry – From South Australia to California, USA

The effects of floods on riverbank and levee stability are well known and documented on global scales. Lesser known are the effects of extreme low-flow conditions due to prolonged drought.

During the Millennium Drought (1997-2009) the lower Murray River experienced catastrophic failure of it’s riverbanks, extreme low-flows (-1.5m AHD below sea level) triggering widespread failure in the alluvial margins, damaging infrastructure and posing a high-risk to public safety. Recently, research undertaken by Tom Hubble and Elyssa De Carli for the Goyder Institute for Water Research on the Millennium Drought Riverbank Failures, has been applied to the current drought gripping California, in order to assess the risk and threat to California’s levees. An article was published in Science Letter’s by Assistant Professor F. Vahedifard and co-authors, outlining this significant risk, drawing on Australia’s Millennium Drought Failures as a precedent.  Vahedifard et al 2015_CA Drought Levees_Science

Pool levels (y-axis) at Blanchetown, Mannum and Murray Bridge during the peak of the Millennium Drought (x-axis) (DEWNR 2013), and the occurrence of riverbank failures documented in geotechnical reports (red marker). Note an onset of failure events as pool levels dropped to -1.05m AHD from January 2009 (nb. normal operating range +0.75m AHD), and a continuation of failures post July 2010 as pool levels peak with flood waters.

Pool-levels (y-axis) at Blanchetown, Mannum and Murray Bridge during the peak of the Millennium Drought (x-axis) (DEWNR 2013), and the occurrence of riverbank failures documented in geotechnical reports (red marker). Note an onset of failure events as pool-levels dropped to -1.05m AHD from January 2009 (Nb. normal operating range +0.75m AHD), and a continuation of failures post July 2010 as pool-levels peak with flood waters.

 

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