Assessment of Flood Impacts and Cost Effectiveness of Treatments to Mitigate Erosion, Burnett River, Queensland, Australia

The Burnett River, QLD Australia, experienced severe flooding in early 2011 and 2013, with the latter flood breaking all historical records. As a result, damage to infrastructure in Bundaberg and the loss of agricultural land from bank erosion was considerable. Exacerbated by the floods is concern about reducing sediment delivered to the Great Barrier Reef (GBR). It was determined that about 28M m3 of material was eroded from the banks of the Burnett River making it the single largest contributor of sediment (as opposed to a minor contributor as was earlier reported) and causing re-evaluation of sediment management strategies.

Data on hydraulic and geotechnical resistance of the banks, along with daily flows were input to the Bank-Stability and Toe-Erosion Model (BSTEM) 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 without additional toe protection or battering was not sufficient to reduce erosion rates. Overall, the scenarios involving rock in any form (rock toe or weirs) were the most expensive at any given site (about an order of magnitude higher than other measures at most sites, typically ranging from $1,000 to $3,000/m), and planting of vegetation was the least expensive (approximately $5/m2 of bank face or top). In general, however, mitigation runs including a rock component provided the greatest level of protection from bank erosion and sediment entering the channel, and those with vegetation alone, the least.