The Age, 21/01/2007
Melbourne is losing out on a million litres of drinking water every year from continued logging in the city's main catchment area. And it comes at a cost to the taxpayer of at least $147 million — the difference between the royalties paid by the logging industry to the State Government and the value of the lost water, according economic consultants commissioned by Melbourne Water.
As the city heads towards stringent stage 4 restrictions, a host of scientific studies indicate the Thomson Dam, which supplies about 60 per cent of Melbourne's water, is losing up to half the potential run-off in the highest rainfall area owing to effects of logging.
"It's a big effect, it's not tiny," said Associate Professor Brian Finlayson, director of the Centre for Environmental Applied Hydrology.
It is estimated that if logging was stopped, water yields in the catchment would increase by 20,000 megalitres within two decades.
Despite the existence of studies dating to the 1950s, in 2004 the Bracks Government decided to conduct more research into the reduced water yields caused by logging. It is scheduled to be completed in May 2008.
All the scientists spoken to by The Sunday Age questioned the need for further studies, saying the numerous existing reports, many of which were commissioned by the Kennett and Bracks governments and on which this article is based, were sufficient.
The Government is also planning to bring forward the 2010 deadline to reconnect the Tarago Reservoir to increase Melbourne's supply by 21,000 mega-litres. It was decommissioned by the Kennett government because of problems with water quality and requires a new treatment plant costing $70 million.
The Government is also conducting a feasibility study into having a desalination plant online by 2015, which it conceded would cost more than $1 billion and require huge amounts of energy from carbon-emitting brown coal.
The Thomson, the largest of Melbourne's four water catchments, is the only one where logging is permitted. Logging in the 49,000-hectare catchment took place before the dam was built by the Bolte government to "drought proof" Melbourne.
Loggers are drawn by prized giant mountain ash, alpine ash and shining gum species. These trees are found in a third of the catchment area along the Mount Baw Baw escarpment, where most of the logging coupes are, and as the map shows, where about two-thirds of the rain in the region falls.
Physical research and theoretical modelling of the Thomson catchment shows that once an area has been logged there is an immediate increase in the water yield because there is little vegetation to draw up the rainfall. But once these water-guzzling species start to regrow, the amount of water they take from the soil doubles, cutting run-off by half, according to research by Australian hydrology expert Dr Fred Watson, an assistant professor of science and environmental policy at California State University.
"The place where you get the most wood is the same place you are going to get the most impact on water yield because they are using the most water to produce that wood," he said.
Water yields do not return to pre-logging levels for more than 150 years, Dr Watson said.
The time between the logging of coupes was also crucial to water yields. Favoured coupes in the Thomson are logged about every 60 years, by which time the water yield is still about 25 per cent lower than at pre-logging. "Rotating every 60 years is the worst thing you can do from a water yield impact," Dr Watson said.
A Department of Sustainability and Environment spokesman said the Government's new study would use an updated model for determining water yields, examine timber substitution and look at economic, social and environment issues involved in logging in the Thomson. "Using the latest modelling for hydrological studies (the Macaque model) will produce more accurate and far more useful results, as previous models had wide margins of error," the spokesman said.
However, Dr Watson, who developed the Macaque model, said when he applied it to the Thomson it didn't produce fundamentally different results from the previous "Kuczera curve" model. "Any improvements to the model you make will still give you a situation where over the first few decades after logging there will be a big decline in water yield and than over the next 100 or so years it will slowly recover," he said.
Original article
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