GIS-based Back Analysis of Riverbank Instability in the Lower River Murray

摘要

Over the last 4 years or so, unprecedented low river levels, combined with current loading conditions,rnhave adversely contributed to more than 137 riverbank collapse-related incidents and a long termrnmetastable condition along the Lower River Murray, which have recently been considered as therndominating factors inducing bank collapse. With high resolution aerial photographs and digitalrnelevation models (DEMs), this study has established the riverbank geometry prior to collapse of 26 2-rndimensional cross sectional models. In order to obtain appropriate soil parameters for the Lower RiverrnMurray study area, a series of back analyses have been conducted at 5 locations where failures wererndocumented adjacent to Long Island Marina, Murray Bridge, South Australia. The slope stabilityrnanalysis software SVSlope was employed in the back-analysis with soil data obtained from two nearbyrnsite investigations. Factors of safety were calculated to examine the potential for riverbank collapsernwith respect to varying river levels. The results indicate that, when the river levels return to 0 torn0.5 m AHD, a portion of the riverbank is close to collapse, whereas a large proportion of the banksrnremain quasi stable. A raised and maintained high river level will improve the stability but to a limitedrnextent. Several remedial works may need to be conducted when the river level is about to decrease.