The worst case scenarios for the deepening of the entrance to Melbourne’s Port Phillip Bay are frightening. Tides out of hand, cars floating in the casino carpark, Southbank awash, the flooding of low-lying suburbs built on what was intertidal swamp from Mordialloc to Frankston, the loss of suburban beaches and even the inundation of the Werribee Sewerage Farm. If the project goes this disastrously wrong, the consequence for the Victorian government are obvious — political oblivion. Is that why Premier Bracks and Deputy Premier Thwaites — bayside members — both exited stage left on Friday?
When the opposition asked Minister for Ports Tim Pallas whether he was aware of ongoing studies into the impact of last year’s “trial dredging” he denied their existence, misleading Parliament. The fact is, the Port of Melbourne Corporation (PoMC) have already started preparing to start the project, booking dredges and the like.
Port Phillip Bay has a very narrow entrance that limits the flow of tidal water. Much of the rock at the entrance to Port Phillip Back is sand held together with shell lime. Exposed to weathering it hardens but beneath this brittle crust it is soft. Private divers told the PoMC the erosion at the heads was ongoing, months after the trial dredging.
The State Government is extremely keen for the project to proceed and allowed the PoMC to fudge many of the 130-odd specific recommendations from the first Panel. So they sacked that Panel and appointed their own Panel, then banned cross examination of expert witnesses. It’s all a bit Tasmanian.
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Consultants assessed what damage was still being done nearly 18 months after the trial dredging. They found that the rubble left behind was not only still falling into the Marine Park but scouring holes in the beds of the channel and in the Great Shipping Channel, deepening the cut.
There has always been concern that opening up the entrance of the Bay would have a dramatic impact on tidal flows, but now this scour hole development has pushed the depth estimates of the digging from 19 metres to 22 metres, and is predicted to continue for 10 to 30 years. Why 22 metres? Well, possibly because the consultants observed a harder layer at that depth. Yet, is that good enough given what is at stake?
Last Friday another 600-page report dropped on the Panel’s desk. It is meant to consider that document and deliver a decision on the project on 1 October. The documentation for this project has been produced by a conga line of consultants — to borrow a phrase — all of which look after their shareholders first and the public second.
Even so, their combined public risk insurance would be unlikely to cover the funds required if the tidal heights in the Bay rose significantly. It may not be possible to predict the impact of deepening the entrance because of the complex interactions of tidal flow and shifting seafloor profiles, let alone the impact of further dredging, likely booked already by the PoMC.
The Federal Environment Minister Malcolm Turnbull has a golden opportunity to intervene and demand proper modelling of the impact of the changes in tidal flow on the migratory bird fauna of Mud Island, which could easily be lost. and that would be a Federal issue.