Back analysis of Lower River Murray riverbank collapses

Riverbank collapses in the Lower River Murray threaten public infrastructure, private property and the safety of river users, and also provide significant challenges for environmental and river management. According to the inventory of the South Australian Department of Environment, Water and Natural Resources (DEWNR), between 2007 and 2010, 50 riverbank collapse-related incidents were reported at four very high risk sites: East Front Road, Mannum; Woodlane Reserve; River Front Road, Murray Bridge and White Sands. The objectives of this paper are to: (i) model four known and representative riverbank collapses at these four sites and (ii) determine the soil shear strength properties by undertaking back analyses. Adopting a GIS framework incorporating light detecting and ranging (LIDAR) digital elevation models (DEMs) and high-resolution aerial images, four cross-sectional models have been accurately established based on the examined historical collapses. Slope geometries have been determined using topographic information obtained from the DEMs. Finite element analyses based on a transient water model have been adopted to simulate the response of pore water pressure under dynamic variations of rainfall, evaporation and river level fluctuations. The limit equilibrium method has been used to undertake the slope stability calculations. The model results, which agree closely with the findings of historical incidents, demonstrate the efficacy of the framework and the accuracy of the predictions.