After four years of work, the CSIRO has come to the conclusion that multiple water detentions (dams), in the upper reaches of the catchments in the Northern Rivers, along with other flood mitigation engineering, could reduce future catastrophic flooding impacts in Lismore and elsewhere by as much as 2 metres.
This work, which was commissioned by the National Emergency Management Agency (NEMA), has been criticised for its limited scope, as well as its great public expense, which has come as affected communities continue to struggle to recover from the flood events of 2022.
Detention basins
While the CSIRO has acknowledged that no amount of hard engineering would ‘flood-proof’ Lismore, computer models suggest that 10 ‘detention basins’, along with changes to the Tuckean Swamp and a second river outlet at Boundary Creek would reduce 2022 style flooding in Lismore by 2.07m, Casino by 0.95m, Kyogle by 0.8m, Coraki by 0.42 and Ballina by 0.73m.
The dams in this theoretical model would be massive, and massively expensive, with a conservative estimate of $2 billion. Rock Valley alone, for example, would require a 93.4 gigalitre holding capability to deal with flooding Tuncester Creek, equating to a 39 metre wall height and a bank to bank width of 389 metres.
Numerous other dams are proposed in ecologically delicate natural areas high in the catchment, dwarfing the existing Rocky Creek Dam. There has already been extensive community opposition to a proposed Channon Gorge dam, lower on that same catchment.
Political response
While the idea of extensive flood mitigation has been welcomed by Page MP Kevin Hogan, and to a lesser extent Lismore MP and minister for disaster recovery Janelle Saffin, who described the CSIRO’s report as a ‘milestone’, Greens MLC and Lismore local Sue Higginson has been far more critical.
‘This report confirms what flood experts and the community have been saying all along, billions of dollars in new dams for the Richmond River will not prevent severe flooding and could make floods far more dangerous and long lasting,’ said Ms Higginson.
‘This project was commissioned and tasked with recommending hard-infrastructure like dams as flood mitigation – that’s why this report is only about pouring concrete in the upper catchment. Dams only offer false hope of flood mitigation, our community needs solutions and not just disinformation that will cause more harm.
‘Now that the science is in this report, it’s time for Kevin Hogan and the Nationals to admit that floods will continue to hit the communities of the Richmond River and that their favourite solution of more dams will make the problem worse.
‘There is incredible work happening throughout Australia and around the world that shows planned retreat and nature based solutions are the best, cheapest, and longest lasting mitigation measures for floods.
‘This is the tough conversation that our Richmond River communities need to be having.’
Slowing down floods
Sue Higginson said, ‘Replanting the forests of the upper catchment, revegetating and repairing the banks of our streams and rivers – these measures will catch more water and slow it down before it joins the major flood happening on the plains. We get a healthier river and more flood resilience – it’s a win-win.
‘Our community needs more investment in genuine climate resilience, and we have the opportunity to be a world leader by re-imagining our CBD as the wetland cultural market hub it can be – while cleaning up the river at the same time. We should be the region who fixed one of the most broken dirty damaged rivers in the country and made it a swimmable, drinkable, fishable world heritage rainforest-to-coastal river once again.
‘The Lismore CBD will still flood even if all ten new dams are built. Those dams will flood vast areas of the environment, destroy cultural heritage, and will create instability in new areas – and the floods will last longer and do more damage.’
When will Lismore learn to adapt?
Sue Higginson said, ‘It’s time to ask how many hundreds of millions of dollars need to be wasted before Lismore adapts to living on a floodplain?
‘Now that the proposed dam locations are in this report, I expect the communities directly impacted will be pretty concerned. The government will do a business case for these projects and realise the cost-benefit analysis doesn’t stack up.
‘The community must be actively and transparently included in consideration of other options,’ concluded Ms Higginson.
The complete CSIRO report is available to read here.
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