INLAND Rail builder, the Australian Rail Track Corporation, says it is continuing to work to understand why its computer modeled flood predictions are different to observed flood levels on the Condamine River floodplain in 2010.
In a statement issued to Queensland Country Life on Tuesday, Inland Rail chief executive officer Richard Wankmuller said flaws in the modeling were "of concern".
Mr Wankmuller's comment follows Ross and Bronte Harris's damning photo featured at the recent Senate Inquiry into the Inland Rail, which shows the current peak flood level to be above the top step of their farm house at Pampas.
The Harrises maintain they were initially advised that the modeling showed the maximum peak flood level was only at ground level. Incredibly, and despite the photo to prove otherwise, the modeling showed floods didn't impact on their farm house.
ARTC's advice was revised several times, Mr Harris said. Now it is in line with the Toowoomba Regional Council's requirement that new infrastructure has "no more than 25mm impact" on existing flood levels.
"How can you believe them," Mr Harris said.
"It's just too convenient. One day there's no flood, the next it's up and then surprise, surprise it's exactly in the range required by TRC.
"They're producing the outcomes to suit themselves to get the Inland Rail built as quickly as they can and bugger the farmers."
Mr Wankmuller said the hydrological modeling of the floodplain was an effort to build a picture of water flows, which would in turn inform the design of the Inland Rail.
"But there are areas, such as at Bronte and Ross Harris's Pampas property, where observed flood levels in 2010 are higher than ARTC's modelling currently predicts," he said.
Mr Wankmuller said there was a local abnormality in the Pampas area as well as other areas across the floodplain where past experience was not lining up with modeling. ARTC was trying to figure out what they were, he said.
"We're still trying to figure out exactly what happened," the statement reads.
"Was there a piece of machinery that pushed the water differently that the model doesn't account for?
"Was there an embankment or a levee we didn't know about?
"Did somebody augment their property and build a temporary dam that we didn't know about?
"We truly have to get this right and the only way to get it right is to talk to people and get the information they have.
"That's why we talk to people. That's why we have to figure out exactly what was happening."
But it is the "talk to people" which appears to have derailed ARTC's credibility more than anything else.
Multiple witnesses appearing at the Senate inquiry strongly criticised ARTC for failing to appropriately act on the information provided by local landholders.
This included criticism from Goondiwindi Regional Council and landholders on the Macintyre floodplain on the NSW side of the border, who say the current design will exacerbate flooding and threaten the Goondiwindi township.
Mr Wankmuller said while the engineers ARTC had engaged were "very smart people", ARTC needed local knowledge.
"We need to work together with the community if we're going to get this right. So our process is all about trying to find things that we don't know about," his statement reads.
"It's not this big problem when we find something we didn't know about. It's actually a good thing."
Despite Mr Wankmuller's acknowledgement of flaws in the modeling and his apparent willingness to act on local knowledge, Ross Harris said he remains disillusioned by ARTC's approach.
"It seems every time they talk to us they tell us something different," Mr Harris said.
"Now there there saying it could be a piece of machinery left in the paddock or some sort of temporary water structure could have changed the flood height.
"It's just crap."
Mr Harris said his greatest concern was the impact the mainly 3m high earth levy bank for the Inland Rail would have on flood flows.
"Sure, they are talking about increasing the amount of bridging, but the large number of culverts they are talking about will block with the stubble from our paddocks," Mr Harris said.
"There is no doubt about that. It already happens now. That is how we farm in this country.
"The straw is deliberately left on the ground to protect the soil and every time it floods, it floats off on the flood water like a massive raft and will block everything and wrap itself around any tree or structure on the floodplain.
"But ARTC says it is doing its modeling is on only 25 or 50 per cent blockages.
"Try modeling at 100pc blockages and see what the outcome is.
"That is going to be a lot closer to reality."