The derailment of a freight train after heavy rainfall near Charters Towers highlights to rail infrastructure managers the importance of adequate and well-maintained drainage, according to the Australian Transport Safety Bureau investigation of the incident.
Eleven wagons derailed on a loaded Aurizon freight train while it was travelling over a drainage culvert about 110 km south-west of Townsville, in the early morning of 30 December 2020.
While the locomotive stayed on the track and neither of the crew were injured, damage to the track and rolling stock was substantial.
The ATSB’s investigation found the derailment occurred after a series of rainfall events the day prior.
“While the rainfall was heavy, the ATSB’s calculations did not indicate it exceeded the design flow of the culvert itself,” ATSB Director Transport Safety Dr Stuart Godley said.
“It is therefore likely the pipe’s throughput was restricted.”
Dr Godley noted the culvert had been cleaned and cleared on 6 December, just over three weeks prior to the derailment.
“The throughput restriction could have been due to sinking, debris blocking the pipe, collapse of the pipe itself due to an exceedance of its service life – or a combination of the three,” he said.
The pooling of rainwater on the upstream side of the culvert led to it over-topping the track, which very likely undermined the track infrastructure, such that it could not support the weight of the train early the next morning.
Since the incident the track owner, Queensland Rail, has significantly improved drainage at the site, with the single 1,050 mm pipe now replaced with three new 900 mm pipes.
Queensland Rail has also had a contractor conduct a hydrology study along the rail line from Stuart, through Hughenden to Cloncurry, Mount Isa and Flynn to Phosphate Hill.
It has also identified a further 44 sites for new and upgraded weather monitoring equipment, and progressed a business case for required capital expenditure.
“To minimise the risk of system inundation and track over-topping, rail infrastructure managers should ensure their drainage systems are fit for purpose, and are clear, open, and in a serviceable condition,” Dr Godley said.
Read the report: Derailment of freight train 9281, near Charters Towers, Queensland, on 30 December 2020