Water quality experts at WaterNSW have been working to maintain water quality in Sydney’s largest catchment after significant amounts of ash and debris were washed into Warragamba Dam following recent rainfall.
During December and January, more than 320,000ha of the Warragamba Catchment was ravaged by fire. Since then, WaterNSW experts have been working to understand the potential consequences of the significant fire damage on water quality.
Heavy rainfall commonly pushes sediment and debris into Lake Burragorang (Warragamba Dam), however the addition of unprecedented amounts of bushfire ash and the lack of ground cover to prevent soil erosion has resulted in increased levels of debris making its way into the lake.
Sediment, ash and debris are now clearly visible on the surface of Lake Burragorang and the inflow reached the dam wall on 12 February 2020. WaterNSW has established an incident response team of system operators and water quality experts to monitor water quality and develop contingency plans to address possible challenges. The team is working closely with Sydney Water and NSW Health.
WaterNSW CEO, David Harris, said he had complete confidence in his specialist team to identify potential challenges and address them accordingly.
“Our people are the best experts in the area of water quality. We are taking a range of precautionary measures on-site, including the deployment of a third floating boom in the Warragamba Gorge,” Mr Harris said.
“Raw water quality at Warragamba is improving, however more inflows may cause further deterioration in water quality at the dam wall.
“The intrusion is behaving exactly as our expert staff predicted – it is staying in the upper section of the water column. This means that we can safely draw good quality water from much further down in the water column if we need to supply from Warragamba Dam – which we are not doing at the moment.”
Water quality scientists continue to monitor the water using sophisticated, real-time technology pioneered by WaterNSW which can predict any change in the dam storage’s water quality.
Supply to Sydney Water’s Prospect Water Filtration Plant (WFP), which services Metropolitan Sydney, is running steadily with no issues. Water is being drawn from Prospect Reservoir and the Upper Canal, not Warragamba Dam.
WaterNSW actions intended to mitigate the potential risk to dam water quality include:
- The establishment of an expert incident response team who are constantly monitoring water quality
- Containment booms/silt curtains have been installed at three locations on Lake Burragorang (Warragamba Dam) to limit the amount of ash and debris near the dam’s supply off-take point
- Joint event response monitoring plans to characterise changes in water quality have been developed in consultation with Sydney Water and NSW Health
- Erosion modelling to determine areas of highest risk and inform further mitigation strategies
- Online monitoring and hydrodynamic modelling to pre-emptively assess ash movement and provide information on the duration, magnitude and location(s) of such an event
- Joint operational contingency plans to maintain supply in the event of poor water quality, such as offtake reconfiguration/supply from Prospect Reservoir and/or metropolitan storages
- Assessing weather predictions daily and identifying rainfall triggers that will activate additional management actions
- WaterNSW is in contact with other water authorities who have had recent experience managing post-bushfire water quality risks, such as Melbourne Water
- WaterNSW, Sydney Water and NSW Health recently completed an incident exercise to test responses in the event of a bushfire followed by significant rainfall