Researchers say the Thomson catchment is missing out each year on the amount of water used by 250,000 people

This article is more than 1 year old

This article is more than 1 year old

Logging is causing Melbourne’s main catchment area to miss out on about 15bn litres of water each year, equivalent to the amount used by 250,000 people, a peer-reviewed study has found.

If logging in Victoria’s Thomson catchment continues as planned, that number would increase to 600,000 Melburnians by 2060, according to the research from the Australian National University.

The researchers said logging in the catchment made little economic sense given the water lost was worth far more than the timber, most of which is used to make paper.

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The Thomson catchment, to the city’s north-east, is Melbourne’s most important, feeding a reservoir that makes up nearly 60% of the city’s water storage capacity. It is currently about half full. Melbourne’s total water storages were 56% full on Thursday, down from about 80% five years ago.

The study, published in the journal Science of the Total Environment, looked at how much old-growth mountain ash forest in the catchment remained intact, how much had been lost to bushfire, how much had been logged and how much was scheduled to be logged.

It found 42% of the forest has been felled by the timber industry and there were plans to log another 21%.

Chris Taylor, a landscape scientist and mapping specialist from ANU’s Fenner school of environment and society, said logging reduced flows into reservoirs as regrowing forests required more water than established forests. Melbourne’s water yields in 2017-18 were 16% below the average for the past 30 years and about a third lower than the average for most of last century.

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“Climate change will only exacerbate this trend,” Taylor said. “We’re already seeing the amount of water consumed annually by 250,000 people lost. That’s the same as a city the size of Geelong.”

State-owned authority Melbourne Water warned earlier this year that storages had declined to their lowest level since the millennium drought. It attributed this to increased demand from the city’s surging population and reduced stream flows into reservoirs as climate change led to longer dry periods, higher temperatures and drier soils.

David Lindenmayer, an ecologist and the paper’s co-author, said nearly 15,000 megalitres of water was being lost annually due to logging in the Thomson catchment. Melburnians on average use 161 litres each a day.

ANU researchers have estimated it would cost $1,650 per megalitre to replace water lost from catchments with that from the state’s desalination plant. The government has ordered 125bn litres of desalinated water this financial year.

Lindenmayer said an earlier ANU economic assessment had found the value of the water was more than 25 times greater than the value of the timber and pulp from the catchment.

“If you didn’t care about water, if you don’t care about biodiversity, if you don’t care about forests, if you only care about cold hard cash you certainly wouldn’t be doing what we are doing now. You’re actually playing with the water security of the city,” he said.

Lisa Neville, Victoria’s water minister, said logging was allowed in less than 1% of the catchment each year. She said Melbourne was one of the few cities in the world with protected catchments that produced high-quality water.

“The majority of Melbourne’s water comes from catchments where no timber harvesting occurs and public access is not permitted,” she said.