Design work for flood-mitigation measures to address future flooding events in Alice Springs are a step closer, six years after the Territory government first received the recommendations.
A report, prepared by water management consultants WRM Water & Environment, presented the government with various flood-mitigation options for the town: option A, B1, B2, B3 and C.
Option A was to build detention basins in the Todd River upper catchment areas at an estimated cost of $8.1 million; option B1, B2 and B3 called for the building of various levees, ranging in cost from $8.3 million to $164.8 million; and option C relied on an upgrade to trunk (major) drainage at an estimated cost of $4.7 million.
The government announced that the preferred option was C, which extensive modelling predicted would reduce the flooding impacts on 386 properties.
Graeme Finch, the executive Director for Land Development at the Department of Infrastructure, Planning and Logistics which commissioned the report, said that flooding in Alice Springs was very complex.
He said that the town was subject to both riverine flooding, when the Todd River broke its banks, as well as localised flooding, when the stormwater drainage system overflowed.
"Flooding in Alice Springs … a lot of it depends on where [the rain] falls and when it falls," Mr Finch said.
He said option C would not stop the Todd River from flooding, but would reduce the impact of the flood waters on the town.
"The trunk drainage deals with flooding and it's not going to deal with the riverine flooding but it does deal with the overland flooding associated with those heavy rainfalls through Alice Springs," he said.
"The reason that the water jumps out of these drains and then runs through residential streets and through the town centre is because the river is full.
"Which means that the local drainage network can't cope with the water that's running through those areas.
Flood modelling at work
Mr Finch said option A, which was not a preferred option, would protect an estimated 1,535 properties in a large rain event.
"[Detention basins are] not overly complex. It comes down to the effectiveness of them," he said.
"The detention basin that provides the most effectiveness sits on only about 17 per cent of the catchment.
"So you have 83 per cent of the rest of the catchment. If it rains anywhere else, you're still going to flood."
He said despite modelling, it was difficult to predict where the rain would fall.
"When you start to model our peak events and statistically look at where the rain could come from, Alice Springs could flood and those basins will be bone dry," he said.
Not enough progress
Araluen MP, Robyn Lambley has accused the Northern Territory government of displaying a lack of commitment and investment to protecting Alice Springs from a one in a hundred-year flood.
Ms Lambley questioned how much difference option C would have on the town during a flood, and its impact on the region's insurance premiums, which have risen substantially over the past 12 months.
"The government's had a long time to think about this and budget for adequate flood mitigation for Alice Springs," she said.
"It was given a comprehensive plan by the flood-mitigation committee in 2017 and there's been zero progress and there still will be zero progress until 2024 at the earliest."
The current report was produced in response to recommendations made in 2017 by the territory government-appointed Alice Springs Flood Mitigation Advisory Committee.
Insurance Council welcomes investment
In a statement, the Insurance Council of Australia declined to comment on the mitigation options outlined by the Northern Territory government but welcomed any investment that better protected communities.
"Given the large number of significant extreme weather events the nation has experienced over the past three years, it is positive to see governments around the country investing more in projects that better protect homes and communities," it said.
"The Insurance Council has long been calling for all Australian governments to invest in resilience and mitigation measures that better protect communities from worsening extreme weather because of climate change."
