TWO separate breakaways of containerships at the Port of Brisbane occurred after heavy rains produced floods, reported Australia's Mirage News.

This highlighted the importance of robust emergency and risk management arrangements, according to an Australian Transport Safety Bureau investigation.

The May 2022 incidents occurred after an unprecedented stretch of rainfall resulted in significant freshwater inflows into the Brisbane River following several controlled water releases from dams located upstream.

This resulted in strong currents through the Port of Brisbane, at the mouth of the river, which added strain to the mooring lines holding ships berthed there.

The container ship OOCL Brisbane broke away from berth 10 at Fisherman Islands. Four days later another container ship, CMA CGM Bellini, broke away from berth 6.

"Fortunately, the ships were brought under control in both cases, and there were no injuries or substantial damage in either incident," said ATSB chief commissioner Angus Mitchell. "But breakaways can have serious outcomes."

The ATSB investigation found that both breakaways occurred due to the strong currents following the high rainfall combined with the interaction forces created when a second container ships passed alongside and then berthed ahead of, each vessel.

"The high ebb current speeds and the interaction forces introduced by other vessels resulted in the mooring limits for both ships being exceeded," Mr Mitchell said.