Victorian 2003 Bushfires reportsFollowing the 2003 bushfires, which burnt over a million hectares of forest and grazing land, a major study was commissioned to assess the likely impacts of the fires on water quality and quantity. This study produced six reports:
The work was commissioned by the Victorian Department of Sustainability and Environment and the Murray Darling Basin Commission (MDBC) with additional financial support from the North Eastern, West and East Gippsland Catchment Management Authorities and Gippsland Lakes Task Force. The study was managed by the Cooperative Research Centre for Catchment Hydrology and involved Sinclair Knight Merz, CSIRO Land and Water, the University of Melbourne (Department of Civil and Environmental Engineering and School of Forest and Ecosystem Science – formally the Forest Science Centre), Thiess and Ecowise Environmental.
Since this study was undertaken, another significant bushfire event occurred in the Great Dividing Range in Victoria. Lightning ignited a number of fires on 1 December 2006 that merged to form the “Great Divide Complex” fires in eastern Victoria, impacting 1,048,238 hectares of private and public land. Although the area impacted by the fires was generally to the south-east of the area burnt in 2003, most of the area burnt by the 2003 Alpine Bushfires in the Ovens River catchment was reburnt. It is important to note that one of the assumptions inherent in the yield estimates presented in this study is that no further bushfires occur. This assumption has been invalidated by the recent fires, which highlights the need for a probabilistic assessment of the water yield impact of a range of future fire scenarios.
The Water Yield Assessment component of the Bushfires Recovery Program was designed to quantify the impacts on water yield and water quality for the tributaries of the Murray River, the Gippsland Lakes (where the Tambo and Dargo/Mitchell Rivers were affected) and the Snowy River. The fundamental reports in relation to water yield are the ‘Broadscale water yield assessment’ and the ‘Seasonal streamflow response’ report. The report ‘Predicting the long-term impacts of bushfire on water yield’ applies the Macaque model to smaller sub-catchments to assess yield response in more detail.
An extensive network of short-term water quality monitoring sites was set up immediately following the 2003 fires to assess impacts and any possible recovery. Analysis of these data is shown in the report ‘Estimated changes in stream exports of sediment, phosphorus and nitrogen following the 2003 bushfires in Eastern Victoria’, while the report ‘Modelling the impacts of the 2003 bushfires on water quality in catchments in Victoria and New South Wales’ presents the results along with catchment modelling to extrapolate the likely water quality impacts to the relevant catchment scales.
The reports on each task include detailed discussions of uncertainty in the results. In the case of impacts on water yield most of the uncertainty stems from the more limited knowledge on the relationship between severity of burn, species and level of recovery. Uncertainty in the impacts on water quality stems from the representativeness of the sampling, variability in the measured concentrations, and the models used to compute loads from concentration and flow data and extrapolate across catchments.
While the information contained in these reports does not necessarily represent the position of the MDBC, the results and methods will be used to inform further investigations undertaken by the Risks to Shared Water Resources Program.