Quantifying water quality risks following wildfire

Fire poses an immediate threat to the water supplies of towns and cities because the key water treatment facilities in south east Australia (and often in other parts of Australia) are designed to treat relatively clean water from unburnt forested catchments.

For example, following the 2003 fires, Bendora reservoir (Canberra’s water supply) experienced turbidity values 30 times the previously recorded maximum, forcing water restrictions on the Canberra and the Australian Capital Territory. Melbourne’s water supply is also at risk, with approximately 80% of the cities water sourced from the (forested) Upper Yarra and Thompson catchments, with minimal treatment capacity. These catchments are prone to extreme post fire erosion events and debris flows. In the last decade post fire debris flows have been identified as a key erosion process resulting in extreme water quality impacts in the US.

In south east Australia the significance of extreme erosion events and debris flows generated from convective storm events has only recently been recognised. However the magnitude of the risk to water quality (ie. the probability of interruption to water supplies) and the degree to which this risk is modified by management actions (e.g. prescribed burning) is unknown.

The scientific aim of this research area is to quantify the relationship between burn severity and the probability of water quality impacts in excess of water treatment thresholds in Australian catchments. The methods include survey of extreme erosion events and field experiments to quantify the relationships between fire severity and hill slope hydrologic and erosion properties.

The management aim of this project is to help fire managers answer the question “What are the real risks to uninterrupted water supply if this catchment is burnt by wildfire, and can I reduce this risk with prescribed fire”.

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Fire in the landscape - Tarryn Turnbull
A group of fire managers and scientists this month went deep into the forests of north east Victoria to view research sites.
Perched 30 metres above the ground atop an outstretched former-MFB crane, Mana Gharun is carefully measuring the moisture content of the eucalyptus leaves in the tree canopy.
The Bushfire CRC is leading a Fire in the Landscape field excursion as part of its professional development event series, on Tuesday 27 March 2012.

External References

Gary Sheridan from the University of Melbourne is conducting Bushfire CRC research into bushfire threats to water quality.

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Water quality after bushfires. This project is being carried out in north-east Victoria in areas burnt on Black Saturday, 7 February 2009. The researchers are from the University of Melbourne. Interview with Petter Nyman.

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