Utility reservoir modelling provides bushfire barrier

Australian water utilities have been quick to share learnings from the 2019-20 bushfire season, which put drinking water catchment risks in the spotlight. One Victorian utility has implemented modelling tools that find data is key to mitigating impacts on water supply. 

In partnership with Hydronumerics, Melbourne Water has been investing in sophisticated catchment and reservoir modelling over the past decades.

Melbourne Water Principal Hydrodynamic Modeller Dr Kathy Cinque said that while the utility was not impacted by the 2019-20 bushfire season, its water supply system makes bushfires a big risk to water security and water quality.

“The majority of our catchments are forested and protected from humans; there's no agriculture, there's no human access allowed,” she said.  

“We have no filtration barrier from catchment to customer, which means bushfires are our biggest risk.”

Melbourne Water partnered with Hydronumerics to devise and implement modelling tools for its reservoirs, which enabled the utility to prepare for and mitigate risks by accessing the right data at the right time.

“We need to know more about the risks bushfires pose and what we can do to mitigate these risks,” Cinque said.

“Modelling plays a large part in this. We have been using debris flow modelling coupled with reservoir modelling for the past 10 years.

“The models are now run in-house at Melbourne Water, which is rare for a water authority, but we found it helpful to operate this way.”

Hydronumerics Director Dr Peter Yeates said the models are created by coupling environmental forcing data.

“In the context of large reservoirs and lakes for drinking water supply, the concept of the models is to take the environmental forcing, including inflows and meteorological forcing, and then create a three-dimensional numerical model that predicts the response of the reservoir to this forcing,” he said.

“This allows you to make predictions about the fate and transport of inflows through the reservoir.

Enhancing decision-making

The modelling tools assist with real-time analysis, which helps support swift decision-making in the event of environmental issues in the catchment, including bushfire, Yeates said.

“We can tie together the model with routine monitoring data,” he said. 

“This gives the utility a picture of the reservoir’s health in real time. It also allows for a predictive capability, for example, how the reservoir is likely to respond to certain scenarios going forward.

“You can get a real-time understanding of what's happening now and what is likely to happen into the future. That's your objective with these models.” 

Yeates said using modelling in this way allows for immediate and long-term benefits for utilities and water authorities.

“If you're collecting data and providing a forecast, which may be seven or 14 days, you can certainly make better decisions when events occur,” he said. 

“Whether it’s a large flow event or there's a spill into a water body, utilities can make operational decisions about how best to manage those scenarios.

“The models also give utilities a means to bring together available information; water authorities can start to really understand where their uncertainties and risks are and how to plan and invest moving forward.”

Cinque said the modelling has definitely produced benefits when it comes to decision-making and planning, both in the short- and long-term.

“It provides the ability to quantify risk in terms of water quality deterioration and the timeframes,” she said.

“Regarding long-term scenarios, or worst-case scenarios, it helps us make decisions. We've done some worst-case scenarios and tried to estimate how long reservoirs would need to be offline for, or the impact on water quality and what that means for treatment.”