Inconclusive modelling was used to allow dredge spoil to be dumped within the Great Barrier Reef Marine Park, a green group says.

Dumped dredge spoil in the Great Barrier Reef Marine Park could travel farther than previously thought, affecting coral.

Three million cubic metres of dredge spoil will be dumped in waters 20km from the reef following a Great Barrier Reef Marine Park Authority’s (GBRMPA) decision on the expansion of the Abbot Point port in north Queensland.

The bid to create one of the world’s biggest coal terminals near Bowen was last month criticised by UNESCO’s world heritage committee meeting in Doha.

Now, the North Queensland Conservation Council has obtained freedom of information documents that they say show the dredge spoil could travel farther than had been anticipated, which could affect coral.

This was because modelling used to justify dredge spoil dumping had failed to factor in another set of modelling which can predict deep ocean current movements, spokesman Jeremy Tager said.

“The argument that wasn’t necessarily going to affect corals wasn’t necessarily correct,” he told AAP, adding the technology to forecast ocean currents has been around for two decades.

The North Queensland Bulk Ports Corporation modelling provided to GBRMPA showed the reef would be safe from dredge spoil.

Last month, it was revealed that GBRMPA had approved the dumping of 370,000 cubic metres of dredge spoil as part of a project to expand the Hay Point coal port south of Mackay, in central Queensland.

A GBRMPA spokeswoman said modelling was only one of many tools the authority used to make impact predictions.

“The Great Barrier Reef Marine Park Authority follows a transparent and rigorous environmental impact assessment process to evaluate the possible risks or effects on the environment of a proposed activity,” she said in a statement.

“This process uses the best available knowledge.”