We need to mop up some of the erroneous statements sloshing around about the Dunoon Dam, floods, and water security.
The following statements can be verified by references for anyone who is interested.
Flooding would worsen immediately below the Dunoon Dam.
Dunoon Dam would produce greater flooding in the first 3 km downstream from the dam. This is detailed in the Environmental Flows Assessment for the Proposed Dunoon Dam (9 November, 2012).
It states, on page 141: ‘Modelling shows that the magnitude of the largest floods may also be increased, with the largest flows in the natural regime of 17,280 ML per day shifting to 20,456 ML per day with Dunoon Dam operating’. This is an increase of 18.37 per cent! Sure, it is just modelling but for any living thing in that zone an increase of 18 per cent on the biggest flood would be catastrophic.
It is explained here: ‘When full, the dam acts to increase catchment runoff efficiency, with all rain that falls directly onto the water surface delivered directly into downstream flow when the dam is spilling. This phenomenon results in increased peak magnitude of the modelled flood events’.
The dam would do nothing to mitigate flooding in Lismore.
The figures on the relative catchments of Rocky Creek and the combined creeks that flood Lismore are provided by Rous County Council (RCC): Rocky Creek catchment is 50 km². The combined catchment upstream of Lismore is 1,400 km². So Rocky Creek is 3.57 per cent of the entire catchment.
Even a completely empty dam would intercept only 3.57 per cent of the flood water heading for Lismore.
An objection has been raised that part of Rocky Creek catchment is in the very high-rainfall Nightcap Range. That is true. However, so are the catchments of other creeks that also contribute to flooding in Lismore. According to Google, the highest rainfall areas in NSW are Nimbin, Dunoon, and Modanville (and Mullumbimby). Given that only part of Dunoon’s rainfall goes into Rocky Creek we can conclude that the high rainfall that floods Lismore comes mostly from catchments other than Rocky Creek.
All of this is backed up by the fact that RCC has never claimed that the Dunoon Dam would mitigate floods.
Dams are no defence against prolonged drought.
Yes, dams fill in flood rain. But that helps only in the short term – a full dam does not last indefinitely. Prolonged drought is the real concern as there is little or no dam-filling runoff.
Droughts have been decades long in the past and will be worse in the future, according to the NSW Water Strategy. It has made a detailed analysis of climate data and is very clear about the risks. That is why it is government policy to provide water security by spreading the risks.
We need measures that are not wholly dependent on rainfall. These can include: leakage and pressure management; change to the levels-of-service which, with the stroke of a pen, reduce the demand for water; wide-scale and comprehensive water audits and efficiency programs for residential and non-residential water-users; indoor retrofits and outdoor water-use programs.
Together these measures would be a fraction of the cost of a new dam but would provide more water more quickly (see The Rous Sustainable Water Program: Towards a secure, reliable and affordable water future, by Prof Stuart White).
If anyone wants more information feel free to contact me. You could also check the WATER Northern Rivers website, which has all of the references quoted above. waternorthernrivers.org.
For four decades The Echo has printed the stories some people loved, some people hated, and some pretended not to read. If you want us to keep telling the truth, the real truth, not the sugar-coated version. We’ll need your support to keep the presses rolling. 
