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Bushfires and water quality

Bushfires in Australia can have devastating impacts on communities, the environment and economies. They can also affect the quality and quantity of water in streams, rivers and dams.

New South Wales landscape in bushfire conditions

Current bushfires in parts of the Basin

Bushfires are now impacting parts of the Murray-Darling Basin including areas in the Upper Murray catchment, which is above Hume Dam. The MDBA and state water authorities are keeping abreast of the bushfire activity. To date, the fires have not posed any significant risk to any MDBA operated structures and have not significantly impacted our river operations. The MDBA will continue to monitor the situation and work with relevant fire and emergency management agencies where necessary.

To stay updated on fire risks please visit:

Impacts of bushfires on water quality

Physical, chemical and biological processes in natural ecosystems are all disturbed when bushfires occur. The diversity of forest types, topography, soils and rainfall patterns across southeast Australia means that catchments respond to fire in different ways.

Water quality can be directly affected due to the replacement of forest litter by ash and charcoal, with materials then washed into streams when it rains or as atmospheric ash settles on the water. Loss of vegetation and ground cover means soil is more readily eroded by runoff.

Charcoal, soil particles and clay as well as dissolved materials such as nutrients and dissolved organic matter can all be washed into waterways. The extent to which this occurs depends on the severity of the fire, each catchment’s characteristics, and on the intensity, timing, volume and distribution of rain that falls after a bushfire.

Clay, ash and other constituents can alter the chemistry of water and affect water quality. Aquatic environments can experience highly variable effects, including the occurrence of blackwater events that can have devastating impacts on aquatic life. Sediment deposits can also affect habitats for aquatic animals. Poor water quality also requires additional treatment for human consumption.

Impacts of bushfires on water quantity

Bushfires are also known to affect the volume of surface water runoff. Depending on the topography and area affected, a temporary increase in runoff could be expected if rains were to occur in the first few months to a year following the fire before vegetation starts to regrow. As the vegetation returns, surface runoff has been found to reduce to levels below when the fires occurred. This reduction in runoff, or catchment yield, is due to the increased demand for water from the soil because of the vegetation regenerating.

As the vegetation matures, catchment yields begin to return to the pre-fire state. These processes occur over a couple of decades following the fire. The MDBA and states are aware of these impacts and consider these in water resource management.

Water storages and bushfires

Changes to water quality in dams is very complex and depend on many factors including how bushfire-affected water flows and mixes with existing water, the effect on dissolved oxygen levels (certain levels are needed by aquatic life to survive), and water temperature. An increased risk of algal blooms can occur when nutrients mobilised in sediment and ash wash into rivers and water storages.

Very large flows can result in existing colder or oxygen depleted deep water mixing with the new water, upsetting the natural water layers. This can result in reduced dissolved oxygen levels and turbidity.

 

Key facts

Bushfires can impact water quality immediately and for many years. The impacts can vary greatly in different areas.

Turbidity (amount of suspended matter) and a change in water chemistry can have significant consequences for aquatic animal and plant life.

Rainfall after a fire can trigger blackwater-like events as ash and other materials wash into waterways, impact on fish, animals and town water supplies.
Check with your local water supplier or state government regarding your local water quality, following a bushfire.

 

 

Water for communities

When using water following a bushfire in your area or in the catchment of your local water supply, please check in with your retail water supplier regarding any water treatment that may be required.

Contact your local water authority

New South Wales

Victoria

South Australia

Queensland

Australian Capital Territory

 

Updated: 14 Jan 2020