Saturday, January 08, 2011

Two non-rhetorical questions

Given the current flood on the Mary River I have two serious questions:

1: Would the Traveston Dam have been ableto mitigate this flood in a meaningful way?

2: Is a major flood any LESS a threat than a dam is to the lungfish or any other endangered species of the river?

I suspect the answer to the first is possibly yes, even though the premise of it needing to be built was predicated on mitigating drought, the shallow nature of the valley it would have flooded would tend to at the absolute least flatten the peak of floods, and with a bit of luck and timing could have absorbed most of it.

With the second question, I suspect the flood would have done the lung fish little damage, but I am not aware of how it copes with floods. Most fish use it as an opportunity to spread. Endangered land animals already marginalised by drought and the encroaching humanity might have been better off with a mitigated flood, however.


Chris Fellows said...

1. If it was empty, yes; if it was full, no. As it would not have been built by now, no.

2. No.

Chris Fellows said...

2. Er, I got confused by how you asked your non-rhetorical question. The dam was much more of a threat.

Marco said...

I was probably expecting a more verbose answer than that I guess. It seems that dams are back on the agenda, with flooding on the back of drought (eg Tony Abbott). Although the Traveston dam will never be reconsidered - for emotional as well as scientific reasons, I wanted to revisit the whole pros and cons of it again. Although the Mary valley is arguably the premier spawning site for the lungfish, and the lungfish is endangered, my personal opinion is that it would not precipitate extinction. The essence of the issue is that wild river species are optimised to sporadic floods and drought and while in theory they should survive easily within a network of lakes connected by more controlled flows such as is with many dams - other species that are more optimised for such systems easily outcompete these wild species. It is not about how many die with a major flood such as the current one (I am sure a large portion of lungfish have been swept to their deaths) but about how well their population recovers in subsequent years. The flooding of the Mary valley (due to a Traveston Dam) would probably not kill many lungfish, but would kill their natural advantage and niche in the habitat. There would probably be a heap more fish and bird life quantity wise with a lake there, and my next question is therefore: If we could guarantee that the lung fish does not become extinct either way, how can we price the lung-fish-factor in our cost-benefit analysis of this and other dams?

Chris Fellows said...

I note that the Wivenhoe Dam is at "173% capacity" and thus not able to carry out its original primary (?) function of preventing a repeat of the 1974 floods. The two roles of dams in water storage/power generations and flood control are thus diametrically opposed to each other...

I can't find the link anymore :/ (think it was on the Courier-Mail website) but I read about concerns in Stanthorpe about upstream dams on private land failing... this is the risk you take whenever you build a dam.

The Mary River problem is not the small area of drowned river upstream of the dam, but the radically changed conditions in the river downstream of the dam and the division of the lungfish habitat into two smaller, less viable, reaches of river.

Marco said...

I reject the notion that seems to be going around that a dam's flood mitigation success can be judged solely on whether it can guarantee a maximum flood level downstream. Releases from the Wivanhoe started well in advance of the main upstream flood impulse - resulting in a much flatter peak to the flood. Better hydrological models and runoff predictions based on forward rainfall predictions could have made an even bigger difference, regardless of initial dam water level. Hydrologists substantially underestimated runoff from this well predicted rainfall event, and thought they would have caused an unnecessary moderate flood downstream had they initially released the current release (500,000ML /day) which they eventually had to resort to for dam safety margin reasons.

I take the view that the lungfish like, like the polar bear can be kept from extinction without resorting to infinitizing the value of having them in their current comfortable environment range. Ie. we should pick a finite value for that "asset" and use it logically in a cost benefit analysis of say radically reducing CO2 output and/or cancelling an otherwise cost effective dam. The answer one might get might be the same (ignore CO2 limits and stop the dam), but at least there is a logical framework to make the decision rather than tugging the heartstrings of voters.