A cotterdam used for constructing piers to support a bridge across the Mississippi River
A temporary cofferdam being used for constructing piers to support a bridge across the Mississippi River

I opened The Age on my iPad yesterday morning and there on the front page was the headline, Waterways may be dammed for toll road. There was a similar message on the front page of the web version: River may be dammed for new toll road.

The toll road in question is the planned Western Distributor, connecting Melbourne’s Gateway Freeway to Transurban’s City Link toll road. When I clicked through to the full story it was headlined River could be dammed, high-voltage towers moved for Transurban’s toll road.

Greens politician Colleen Hartland was quick to respond to The Age’s story. Yesterday morning she tweeted:

Damming Maribyrnong River & Moonee Ponds Creek?! New details on Western Distributor are very concerning!

A dam on the magnificent Maribyrnong in inner city Melbourne, less than 4 km from Southern Cross Station? Has Daniel Andrews gone mad? Was yesterday April Fools day? Has The Age turned into The Onion in a desperate bid to arrest falling circulation?

Actually, no to most of those. When I clicked through to the full article I found it says that if the dam is required, it would be temporary; it would only be needed while a bridge is being constructed over the Maribyrnong. Whew!

Still, damming the river, even for a year or so, sounds like it could do a lot of environmental damage. But no again; those who read the article found that in fact it’s a “partial” dam.

A partial dam? Since the purpose of a dam is to raise the level of water and store it, the idea that a dam could be partial seems like an oxymoron. But it sounds a lot less problematic for river health than a whole dam. Whew!

The Age says it’s relying on “fresh detail” revealed in documents Victoria’s Transport Department has submitted to the federal Environment Department. Unfortunately it doesn’t make the source documents available to readers.

But we can see from the Western Distributor business case documents released by the government that cofferdams are an option under consideration for bridging the Maribyrnong. That sounds like a more plausible description of what’s proposed.

Cofferdams – or coffers – enclose an area temporarily so that the water within can be pumped out (see exhibit):

(They) are temporary enclosures to keep out water and soil so as to permit dewatering and construction of the permanent facility (structure) in the dry.

But despite the name, a coffer isn’t a dam in the conventional sense; it doesn’t regulate the flow of the river and it doesn’t store water for later use. It isn’t permanent either.

Like any engineering intervention, coffers have potential environmental implications that have to be managed, but to portray them like conventional dams is misleading.

The key environmental issue is whether or not placing piers at the edge of the river is the right approach in this case; perhaps further investigation will show a longer span is a better solution.

There’s no denying though that a headline like River may be dammed for new toll road sends a powerful message. A dam is a potent idea, conjuring images of environmental disaster; but irrespective of one’s view of new motorways, in this context it’s a gross exaggeration.

The Age demeans public debate by making a political choice in the way it framed this news report. It appears it’s fast giving up any pretension to being a paper of record.