Flood Mitigation is arguably the key element of Lismore's future growth providing a base in which our city can thrive once again.

The CSIRO is the key stakeholder that will provide a number of flood mitigation options to the federal and state governments in 2026.

The Lismore App asked Jai Vaze, the Senior Principal Research Scientist for the Northern Rivers Resilience Initiative about the flood mitigation process.

There are two options for Jai and his team:

1. The Northern Rivers Joint Organisation create a vision document that the CSIRO team can use in their scenario planning.
2. Look at just flood mitigation.

The Northern Rivers Joint Organisation (NRJO) met last week and agreed to create a vision for the Northern Rivers with the help of a different arm of the CSIRO. This was confirmed by Member for Lismore Janelle Saffin on Friday afternoon.

The NRJO vision will identify what the seven local government areas (LGAs) want to achieve for the region. So, by the time Jai and his team build the flood model in 18 months, it gives them the guidance to find more than just flood mitigation solutions.

This is the preferred option by Jai Vaze.

"That can be multiple things like security from flood, maybe also security from drought. So, can you hold back that water from a flood like in 2017, so that there is little or no impact, and then help a drought situation like in 2019 when there were pretty severe water restrictions?"

These sorts of scenarios from the NRJO vision piece are dependent on funding from the federal and state governments.

"If it doesn't get funded, I will be looking at only flood mitigation. So, in Lismore where the flood level was 14.4m, is there a way I can hold it below the levee or can I hold it to 13m? So, a one-meter reduction and what intervention options could achieve this, is it upstream storage, is it detention basins or bypass flows."

"Once I do that, I also need to look at how can I get rid of that water. If it's a bypass, bypass Lismore to save Lismore to some extent, but is there a way I can take that water so that it doesn't wipe out Coraki, Wooburn, Wardell and Ballina. The same thing will start happening from Kyogle and Casino."

"There are more levers to play in Richmond. There aren't too many levers in Lismore, because the upstream catchment is much smaller in Lismore and it's really steep and that's the heaviest rainfall area. So about 1400mm upstream of Lismore, whereas if you go to upstream of Casino it's about 800 something."

"We will test all that and then again, provide a really rough costing. So, hypothetically, if we can reduce a flood by one meter throughout, how much roughly will cost? Before any government invests in a flood mitigation scenario or scenarios, they will do a proper business case. But, putting a case to reduce one metre overall, we might need 2 billion dollars. If you want to go 1.5, which is doable, but that cost goes up to 6 billion. And then the government makes the call because there comes a point where the returns that you're getting for the extra investment become so marginal that is not worth it."

"Secondly, as I have been saying right from the beginning, 2022 was an extreme flood. It can happen again, no one knows. But what level of protection is required? Take the 1974 flood, which we don't have data for, or the '17 flood, the impact will be minimal. So looking at the history of Lismore and the damages in recovery cost, even a one-in-two-year flood, it's a nuisance flood, that's what they define, but it does cost businesses and community because some of the CBD gets closed or whatever and then you lose one week, two weeks and the handouts for recovery cost $10, 20 or 30 million."

"Then you come to one in five years and it starts costing $100 million for the recovery. 2017, is a mixed bag because some of the numbers I have received are really different numbers from different people, but some of them are close to a billion dollars. One was $890 million, another was $420 million and for 2022 I had numbers before like $8.7 billion and today, I will not say the name, someone quoted $16 or $18 billion. And these numbers are increasing."

"If we can say that for Lismore, just giving an example, that we can make sure that one-in-five, one-in-10 will not have an impact, in the next 50 years you will be saving $3 billion or $5 billion and one-in-20, like the '17 flood, the impact is now equal to a nuisance."

"Minister Murray Watts said in one of his announcements that currently the ratio is, I think, 3-4% on proactive mitigation and 96-97% on recovery. If we can shift that, you don't need to spend all the money on recovery costs and we save on the trauma, the mental anguish and psychological impacts."

"At CSIRO we are science. We'll do the science and we'll put it out. The state and federal governments then make the decision to invest or not."

Once Jai and his team have finished the Richmond River catchment model, they will head north and build one for The Tweed. They have been asked to do a model parallel to the Richmond but Jai said he doesn't have enough skilled staff to build another first-class model at the same time.

"Everyone understands one thing, you need a full catchment model. When you have a small parcel area model, you really don't know what happens because what are the inputs? As your flood level rises, different flow paths start coming in. The catchment boundary changes depending on the size of the flood. So if you have a full Richmond model, you will know what will happen. At the moment you look at some intervention in Lismore using just the Lismore model, you don't know what is happening in Coraki, Woodburn or Ballina.

"I told the Ballina Mayor that during a flood, not all the rain is falling in Ballina. It's coming from up the catchment so if we can get rid of that water before, you might not need a levee or anything in Ballina."

"That's why we are collecting the best quality digital elevation model. It is every metre and think of it, metre by metre, it's getting sixteen (16) returns from different angles. That's the most accurate representation of the surface height. It is a hilly area, but still, it's about eight 900 square kilometres upstream of Lismore. So there are these valleys in there where you can try and hold back some water. It can be just temporary storage that lets the peak go, also you have Leycester, Terania joining it and the Wilsons and they joined here. In 2022, the peaks from both coincided. In 2017, they didn't. Wilsons had more flow, but it went through earlier.

As we know, 2022 was an extraordinary event where a blocking high, created constant dumping rain for 24 hours causing flood peaks in both Leycester and Terania Creeks and Wilsons River. Normally one would peak before the other as the weather system continues to move.

"So, is there a way, and these are all just ideas that I have, we can hold back one of the peaks and let one pass and then let the second one pass. Suddenly, you will be dropping the flood level by a metre or more. That's why the model is so critical. Once I have the model, we can test it. And then the question comes, what intervention to hold it back? And can it be done?

"Any business case, if the government is thinking of going ahead, will have to go through environmental approvals, community acceptance, all of that. I also see that maybe, for something like 2022, the model will show that nothing can be done. I can't remember the exact number but I think something like 3000 gig of water went through. That's a lot of water. Some of the rainfall numbers we are looking at is like a metre of rain overnight on a saturated catchment.

"I have this really strong opinion. First, you go with mitigation, look at what can be realistically mitigated, given the money available. Once you have done that, suddenly your impact area reduces a lot. Then go for adaptation.

"If your area impacted before was like, I'm just giving an example, 1000 houses. Once you have done these mitigations, if that's reduced to 900 only 100 can be saved. Then that's the adaptation, you buy out those 100 and the 900 can stay.

"It will also start showing, given it's a full model, very clearly which are those areas that are pretty much floodproof for good, and that will help the council to decide whether they want to release it or whoever owns the land.

Jai will be happy to answer any questions from any of the seven councils or the community for a year once the Northern Rivers Resilience Initiative model has been released in June 2025.

Jai fields about eight to ten calls from the community each week but knows that once they release the data on June 2024 there will be so many questions because people will be looking at it.

"Once we have the model in June 2025, we will run some public consultation and councils to show them how exactly the model is reproducing the history. Once I hold the scenarios, then there will be public consultations, where we will show that if you input this and this and this and this option, this is how the flow will change. And we can then take examples of houses or locations, before the intervention, that's the height, velocity and duration, it would have been recorded with the intervention and now it's reduced to this."

"That's where the community gets the confidence. If they can see my backyard was flooded and if the model shows that the backyard was flooded, and as I said, it can be one metre of water, but as long as the model is showing something like 0.8 to 1.2, that is fine. The model is 7000 square kilometres, not just modelling your house, but roughly."

"So, then they will have confidence and that's the only time they will start believing in the future scenarios."

As we learned from last week's story, the timing of the CSIRO model has been delayed due to ongoing poor weather conditions last year. If the CSIRO team know what scenarios they will be testing, can feasibility studies be started now to halt further delays in starting to build flood mitigation solutions?

"I do feel that it needs to be done now, but they are independent of the model. So, a region piece and feasibility study, which looks at what is the vision for the region and a feasibility study that starts looking at the soils, the structure, current land use, future land uses and all of that. If that's done, that will help a lot in building the scenarios."

"I actually feel if we go in parallel, that's the best option. A feasibility study will give you a more detailed insight into the possibilities. It will give you what options are there. Are they feasible and are they publicly accepted? So, if that is ready, then the scenarios I test might solve multi-objective purposes like protecting against flood and giving protection against drought. If I don't have that, the only thing in my Terms of Reference for NRRI (NRs Resilience Initiative) I will be just testing flood mitigations. But even better scenarios are available only for feasibility and that's what will be the basic output of the feasibility study."

Lismore and the Northern Rivers flood mitigation plans appear to lie with the federal state governments, just like the success of the Resilience Homes and Resilience Lands Programs. It all comes down to funding.