The Burnett River experienced severe flooding in early 2011 and 2013, with the latter flood breaking all historical records. As a result of these floods, damage to assets from bank erosion was considerable. To develop a strategy for resilient and cost-effective protection measures, an understanding of both site-specific and system-wide stability conditions is essential. This is accomplished by quantifying the driving and resisting forces operating on the channel banks, and testing how alternative stabilization measures would perform over a range of flows. System-wide analysis then provides the spatial and temporal context to determine the suitability of conducting various types of channel works.
Combining analysis of aerial photographs from 2010 and 2013 with available LIDAR data, trends of channel stability and bank-erosion rates were determined for 300 km. The two dominant processes are fluvial deposition and mass failure of channel banks. Although the river has been recently impacted by flows with return periods of approximately 20 and 140 years, the Burnett River main stem has not been devastated. Channel stability, as determined through 9 diagnostic criteria display wave-like longitudinal trends related to the series of weirs and other structures along the river that alter flow hydraulics and the continuity of sediment transport. Maximum instabilities and rates of bank erosion are generally located just downstream of these structures and attenuate with distance downstream. An estimated 28 million m3 of material was eroded from the banks of the Burnett River between 2010 and 2013. About 75% of that material emanated from reaches downstream of Paradise Dam, representing 43% of the study length. Much of the 7 million m3 eroded upstream from the dam is likely trapped in its impoundment.
Data on the resistance of the banks were collected at 8 sites. Daily flow data were then used to generate a flow series to predict bank-erosion with and without protection to determine the effectiveness of a range of mitigation measures. Alternative strategies that were simulated included combinations of rock facing, vegetative plantings, battering and the use of Bendway weirs or engineered log jams (ELJs). Although failures are responsible for the bulk of the material delivered to the river, reductions in bank steepening through toe protection or reductions in applied stresses from bendway weirs or ELJs result in significant reductions in erosion (40-99%). The planting of vegetation on bank slopes without additional toe protection or battering was not sufficient to reduce erosion rates.