Spring rains nurture hope

The Age

October 26, 2009

THE reservoirs are swelling, and Melburnians could be forgiven for feeling dam(n) confused.

Just when we had got used to the notion of drought, strong spring rains have put the word ”deluge” back into the lexicon.

As excitement about dam spills and river flushes fades, what is the state of our drinking supplies, and has our rainfall gone back to its old ways?
The Upper Yarra Reservoir looks healthy.

The Upper Yarra Reservoir looks healthy. Photo: Craig Abraham

There’s a simple joy in watching a dam spill, but the recent scenes at O’Shannassy and Maroondah dams should be regarded as little more than that.

Both are small reservoirs that fill quickly because of their highly productive catchments. O’Shannassy could fit into Melbourne’s major reservoir, the Thomson, 356 times.

The Thomson is only 20 per cent full, and that figure is boosted artificially by environmental flows being withheld from the river behind the dam wall.

Not all the city’s bigger dams are struggling; Upper Yarra Reservoir, a crucial part of the network, is more than 87 per cent full. But there’s little point worrying about anything other than the overall result.

Melbourne’s dams were 37.3 per cent full yesterday and, using crude mathematics, holding enough water to supply the city for about 675 days.

That tally will almost certainly secure supplies until the major water projects start feeding Sugarloaf and Cardinia reservoirs, but historically it’s a poor state of affairs.

This brings us to the rainfall. September’s was above average, but every other month’s has been below and 2009 could yet be the driest year recorded at the Melbourne gauge.

The city gauge has received about 296 millilitres so far this year, less than the 332.3 millilitres recorded in 1967, the driest so far in 154 years of records.

With 10 weeks left in the year, most gurus think Melbourne will climb above that record low. But it’s no certainty.

Rain gauges in towns close to catchments (such as Noojee and Coldstream) are also below average for the year.

The flooding rivers and spilling dams of September seem likely to be the exception rather than the rule. Damn it.