Gone with the flow.


A well-written letter extracted from the on-going correspondance published in the Gympie Times, -directly based on the downstream flow data published in the Environmental Impact Statement for the proposed dam .....

Nev Harrington (The Gympie Times, May 2) tells us that fears for the survival of the Lungfish in the Mary River are just “Greenie hype” and that the proposed Traveston Crossing dam will in fact be “beneficial” to this threatened species.

Now, fish biology is not my field of expertise (nor is it that of Mr Harrington) but I have read reports by many respected experts including Prof. Jean Joss from Macquarie University who express grave concerns for lungfish survival if the dam proceeds. Indeed, when commissioned by Peter Garrett to conduct an independent assessment of the project’s EIS, Associate Prof. Keith Walker from Adelaide University stated that the proposed dam “presents an unacceptable risk that the [lungfish] population would be severely impacted”. He also said that "In many cases, the EIS makes assumptions on the basis of scant evidence and draws conclusions about impacts with little or no justification" – a flaw also often evident in Mr Harrington’s letters to this newspaper.

One field where I am qualified to comment is that of flow calculation and modelling. As a former engineer Mr Harrington should know something about this too. He tells us that the proposed dam will “even out the flow situation, therefore being beneficial to lungfish (especially downstream)” and also “guarantee a more reliable flow for downstream irrigators”. That sounds great when you say it quickly, but does it stand up to scrutiny?

To test Mr Harrington’s assertions, one needs to look at the results of the detailed flow modelling produced by SunWater as part of the Traveston EIS. It compares downstream flows with and without the dam, based on 110 years of historical data.

The SunWater study shows that downstream of the dam, the average flow in the Mary would be reduced by 15% on average, compared to current usage. Average flow is not a very good indicator for highly variable systems, so one must also consider the dry periods.

The SunWater study shows that downstream of the dam, the average flow in the Mary would be reduced by 15% on average, compared to current usage. Average flow is not a very good indicator for highly variable systems, so one must also consider the dry periods.

n the driest 25 years of the 110 year simulated period, representing extended dry spells and droughts, the flows would be reduced by a massive 68%!

In the worst year of all, 1933, the dam would have reduced the downstream flow by 98%, from 156,342 ML with current water entitlements to just 3,798 ML

So, at the times when fragile ecosystems and irrigators are under most stress – dry seasons, dry spells and droughts – the SunWater study shows that the proposed dam would have a catastrophic impact on the already depleted downstream flows. This is not the flow regulation Mr Harrington talks about, but robbery.

In the words of my friend and fellow engineer, Steve Posselt, “our rivers are not drains”. The folly of previous generations and their engineers has no place in 21st century Queensland and must not be allowed to decide the fate of the Mary River.