Scientists were opposed to dumping millions of tonnes of dredged sediment but they were overruled

The government’s marine scientists warned against dumping millions of tonnes of sediment inside the Great Barrier Reef’s marine park, only to be overruled, according to a former government official.

Jon Day, who was until recently a senior director at the Great Barrier Reef Marine Park Authority, said the decision to dredge and dump 5m tonnes of seabed to expand the Abbot Point port in Queensland would prove harmful to the reef.

Day told ABC’s Four Corners on Monday that dredged spoil was having “adverse impacts” upon the reef.

“We’ve seen that elsewhere and there are alternatives,” he said. “Sure, they may cost more, but again we’re dealing with a world heritage area, the most important world heritage area on the planet, a magnificent marine protected area that the world wants us to protect.

“Our own legislative mandate says ‘the long-term protection and conservation of the values’ and we’re not doing that.”

According to internal documents obtained under freedom of information law, scientists at the GBRMPA were opposed to dumping dredged sediment within the marine park, with one calling it “environmentally and socially unacceptable”.

Despite this, the GBRMPA issued the dumping permit in January.

Alternatives, such as building an extended ship loading trestle, were rejected as unsafe and too expensive by the mining industry, which will use Abbot Point to export millions of extra tonnes of coal once it is expanded.

Russell Reichelt, head of the GBRMPA, said the dumping would cause “changes locally for a short time” but that it would not harm corals and other marine creatures such as dugongs and turtles.

Greg Hunt, the environment minister, who approved the dredging, told Four Corners: “I made the decision that this would be the last time that we were changing the practice and since then we have stopped four inherited proposals from proceeding which would have seen material deposited into the marine park. So five down to one.

“That was actually included in this decision. I remember the very words were, ‘This is a line in the sand.’”

Environmental groups dispute Hunt’s assertions, pointing out that the GBRMPA allowed the dumping of a further 378,000 cubic metres of dredged material into the marine park at Hay Point earlier this year.

Unesco has warned that the Great Barrier Reef may be placed on its “in danger” list next year, with the UN body expressing concern in June over the plan to dump sediment within the marine park.

A GBRMPA report released last week found that the overall outlook for the reef is “poor, has worsened since 2009 and is expected to further deteriorate in the future.” Climate change, pollution from land-based chemicals and coastal development were cited as the reef’s main threats.

Seabed sediment dumped near coral is a concern because it can smother the organisms, hindering their ability to feed. Recent research indicates dredging can double the risk of coral disease.

Although the dumping has been approved, the exact site has yet to be chosen. Hunt has placed a number of conditions on the Abbot Point dredging, with disposal only allowed when corals are not spawning.

He has also specified that the project results in a “150% net benefit” to water quality, achieved by cutting down the amount of sediment flowing onto the reef via rivers.

Terry Hughes, head of the coral reef centre of excellence at James Cook University, said this stipulation was “fanciful”.

“Around $400m has been spent in reducing sediment by about 10%, so it’s just not logical to expect it to be offset,” he told Guardian Australia. “The problem is that sediment doesn’t sink like a stone. Particles can travel up to 100km. The notion it will stay in a nice neat box is just not credible.

“The outlook report makes it very clear that the condition of the reef is declining. If the reef is not able to cope with the current level of impacts, what’s the rationale for allowing further impacts to take place?

“Climate change is the biggest threat and so logically to improve the prospects of the reef, you shouldn’t approve the opening of one of the world’s largest coalmines.

“It’s also not entirely logical to spend hundreds of millions of dollars to reduce sediment run-off from land and then turn around and allow millions of tonnes of it to be dumped directly into the reef’s marine park.”