Revealed: the reason for the catastrophic failure of new $15 million Gold Coast bridge

An investigation has shed new light on why an approach road to the $15 million John Muntz Bridge was swept away during 2017 floods, warning it could be damaged again.

AN investigation has found a $15 million Gold Coast bridge which catastrophically failed during 2017 floods, created downstream erosion now threatening parkland.

Gold Coast City Council consultants examining Coomera River banks at Oxenford concluded a huge increase in river flow was due to removal of the old weir for the new John Muntz Bridge and excavation of a flood plain directly upstream creating a quarry lake.

Council mapping showing the future erosion and parkland loss near the John Muntz Bridge at the Coomera River.

Aerial photographs on potential future erosion show homes are at low to moderate risk. But there is a high risk the Oxenford Pony Club at Charlies Crossing Park will lose most of its land.

The specialist investigation by Registered Professional Engineer Queensland effectively ends the debate about responsibility for loss of land after the floods which caused a stand-off between the council and State Government.

Scour protection near the John Muntz Bridge at the Coomera River.

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“The effects of the severe erosion as a result of these changes in the flood plain hydrodynamics were not fully realised until the weir and original John Muntz Bridge was removed,” the report said.

“Specialist advice from the RPEQ certified consulting engineer is that the original weir-bridge acted like a brake which slowed the water down and prevented the erosion impacts of upstream lakes.”

The Coomera River near the John Muntz Bridge prior to the 2017 floods.

The 2017 flood event was the worst recorded in the Coomera River in 50 years causing the “catastrophic failure of the northern bridge embankments” leaving a gap between the bridge and connecting road.

The old weir was removed in 2013, but between then and 2017 the new bridge and its surrounds had not been tested by a major weather event.

Aerial around the John Muntz Bridge at the Coomera River.

The new bridge contributed significantly to land lost at Charlies Crossing Park “thereby linking (State Government’s Department of Transport and Main Roads) as the owner of the bridge to any future repair or preventive works”.

If the riverbank remains unprotected, more parkland will be lost and the bridge is in danger of more damage during flood events, consultants concluded.

“There remains widespread community concern about the long term viability of the new bridge if the erosion is allowed to continue, as it is the critical road corridor to Tamborine Mountain,” the report said.

Coomera River in flood with old John Muntz Bridge.

Council’s solution will be to protect the recently eroded section of river with rock fill behind the armoured rock riprap, likely to cost at least $1.97 million.

Area councillor Donna Gates said the report suggested it would be possible to reclaim a portion of the land and there were works which could prevent it reoccurring.

The John Muntz Bridge at the Coomera River – the bridge failed on its northern side during the 2017 flood.

“The jury has been out on whether that actually has been the case prior to our considerations of that report (at committee),” Cr Gates said.

The Oxenford Pony Club upstream from the John Muntz Bridge has faced constant erosion from recent floods losing 6m of land.

“I’m just pleased there is funding there to resolve the matter. We are seeking joint funding because quite clearly the State controls the waterway, bridge, and Tamborine-Oxenford Road. “The lines have been muddied about who should take full responsibility.”