Fine silt from Port Otago's off-shore dumping could have a "disastrous" effect on the coastal kelp forests on which rock lobster, paua and kina rely on for survival, Otago fishing interests say.
The effect of Port Otago's proposal to dump silt 6.5km off Taiaroa Head as part of its Next Generation plan to dredge 7.2 million cubic metres from the existing shipping channel and swinging basin in Otago Harbour to allow large ships entry, is being heard in the Environment Court in Dunedin.
The Otago Regional Council granted consent subject to conditions for Port Otago to carry out the project in 2011 and shortly after it was appealed.
While the East Otago Taiapure management committee, New Zealand Federation of Commercial Fishermen, Southern Clams and Otago Rock Lobster Association have settled most of their concerns with the port company, they continued to appeal conditions relating to the unproven effects of the sediment dumping on the disposal site and the rocky seashore to the west of the site.
Environment Court Judge Jeff Smith, of Auckland, who is hearing the appeal alongside commissioners Alex Sutherland and Anne Leijenn, said the goal of the hearing was to ensure the coast of Otago was kept free of the adverse effects of the sediment dumping.
The court was not concerned with whether Port Otago's model was right or wrong but how any potential effect could be avoided, remedied or mitigated in the event of it all going "belly up", he said.
"Once it's in suspension and onshore there is not a lot that can be done about it."
Phil Page, counsel for the fishing interests, said they were concerned about the unmanaged risk that fine sediment would find its way into the near-shore environment and the potential effects would be "disastrous" for the kelp forests and the shellfish that relied on the rocky habitat for survival.
"Modelling is not the same as monitoring. Modelling ... tells us nothing about what actually is happening to the environment."
They feared that by the time problems started becoming apparent, it would be too late to do anything about it, Mr Page said.
There was nothing in the conditions requiring Port Otago to conduct near-shore monitoring of fine-silt dumping.
Len Andersen, counsel for Port Otago, said the movement of the sediment plume from the dumping had been modelled under "worse case" scenarios and it was predicted any sediment ending up on near-shore would be in quantities too small to be discernable, "let alone cause adverse effects".
Monitoring at the dump site was proposed to verify that modelling.
The company could not categorically prove there would be no adverse effects on the near-shore as the model had not been verified with field data.
It could also not identify what would constitute a trigger level for dumping to stop, due to turbidity levels.
Alastair Logan, counsel for the Otago Regional Council, said the consent had been granted on the basis the modelling was correct and there would be no adverse effects on the inshore environment.
A staged approach to the disposal of dredged material at the off-shore site was appropriate with a verification stage, including monitoring of sediment dispersal, followed by an operational stage for both the small and large dredge.
At the end of the monitoring stage, the council would look at the data and consider whether to review the consent, he said.
The hearing was adjourned for the panel to visit the dump site via helicopter. It will resume today.