Peter Ker, The Age 24 Sep 09;
JASON Salter is trying to reacquaint himself with the tides. Years of taking diving groups into the deep at the entrance of Port Phillip Bay gave him a wealth of local knowledge. But his understanding of underwater drifts and currents counts for little these days.
"There's been some noted change in the way the bay behaves," he says. "There have been subtle differences like the direction that divers will drift in and out of dive sites. Over the years there have been solid and reliable patterns of drift and you could bank on them every single time.
"Now there are anomalies and they happen for no reason other than the water pattern has changed in and out of the heads."
In the north of the bay, the sea views at Williamstown have become slightly more authentic. Those seeking a waterfront lifestyle are being obliged, as the tides lap nearly one centimetre closer to their doors.
Port Phillip Bay is a changed place in the wake of the controversial dredging project - that much is indisputable. But as the project draws to a close, what remains unclear is how much those changes actually matter. Dredging proponents, the Port of Melbourne, believe the changes caused by shifting almost 23 million cubic metres of silts have not significantly damaged the bay's environmental health.
While several breaches occurred, Port chief Stephen Bradford argues the vast majority of the project was conducted within the limits outlined in the mammoth pre-project Supplementary Environmental Effects Statement document.
"If you look at the SEES, you would have to say they got it right. The number of areas where it was proved to be incorrect were very few, the number of areas where it was too conservative, were a lot. So I think they got it right," he says.
The few exceptions included a day when dredging occurred outside the area planned, and another incident where loose dredged rock was not fully cleared from the seafloor.
A section of the sensitive canyons at the bay entrance also suffered more rockfall than was predicted.
Environmentalists argue that dredging should not be viewed like a maths test, where getting most things right equals success. Opposing sides of the dredging debate have been claiming vindication for their pre-dredging stances for months.
Politicians such as Ports Minister Tim Pallas were declaring dredging at the entrance to be a success last October; a full 10 months before official reports showed rockfall exceedances and mysterious biological shifts in nearby communities of threatened species. On the other hand, anti-dredging campaigners have been blaming everything from beach erosion to beached seastars on the project.
Few people know more about the bay than Professor Michael Keough, the University of Melbourne expert who was hired to independently review the SEES before the project began.
Keough says it is far too early to tell what impact dredging has had on the bay.
"The monitoring things that are coming out were really to manage the operational parts of dredging … if there was a seagrass effect it would not have shown up yet and if recovery in the entrance were to take a long time we are not going to know that for a while yet either," he says.
Keough says he is encouraged the project has been completed without an obvious, major disaster in the bay. But he lists the health of seagrass beds, and the site off Mordialloc where contaminated materials have been buried on the seafloor, as the unknowns that must be watched.
Isolating the impact of dredging from other forces within the bay has become a major complicating factor in monitoring the project.
Many changes have been observed over the past 18 months, but proving the cause was dredging is often impossible.
Turbidity plume
A cloud of disturbed sediment billows behind dredging ships, blocking sunlight from penetrating the water and affecting some natural cycles. In the first few months of dredging, the plume did not behave as expected, according to the satellite images that were used to measure it.
The Port of Melbourne called a high-level meeting with state and federal governments over the issue and was given approval to change the way the plume was measured.
With the new system, the plume was measured by testing water quality around it, instead of using aerial satellite pictures. The Port of Melbourne and dredging monitors say this was a more accurate way to measure the plume, because satellite images can confuse turbidity plumes with shallow water and other suspended sediments.
After the change, turbidity remained within expectations for the rest of the project, with unwelcome spikes usually related to extreme weather events.
Seagrass
Experts say big changes are occurring in seagrass beds around Port Phillip Bay, with many symptoms noted years before dredging started. Certain beds near Blairgowrie have been deteriorating for more than a decade and causes remain unclear. Against this backdrop, the impact of dredging is hard to quantify. During the dredging period, some seagrass beds in the bay decreased in size and cover, while others increased. Importantly, light penetration to the beds remained good. Mick Keough says seagrass has the ability to survive on energy stores within the plant for periods of time, so if plants had been distressed during dredging, the effect might not show for years.
Bay entrance
Several unfortunate events - including oil spills, a failure to properly clean the seafloor after dredging, and elevated levels of rock falling into nearby canyons - made the sensitive bay entrance the most contentious aspect of the project. Most significant was the biological shift that occurred in deepwater communities living in the canyons. The community structure of the threatened canyon species, mostly sponges and coral, changed significantly around the time dredging occurred nearby. The dominant species suddenly showed much reduced range and a new, unidentified species arrived.
But scientists could not prove the cause of the change, saying that it could be either natural or from dredging. Rockfall into the canyon from dredging was more severe than expected in some parts, but less severe than expected in others. In a positive result, rockfall into the nearby marine national park was less than predicted.
Recovery of the damaged sponges was faster than expected in some locations while slower than expected in others. Scientists have told the Government that close monitoring of the canyon communities is required in the years ahead.
Tides
With a larger hole at its opening, the bay now has more water flowing in and out. The Bureau of Meteorology has reported water levels close to one centimetre higher in parts of the bay, with Point Lonsdale experiencing bigger increases than other parts.
Diving operators say tidal movements near the entrance are now markedly different and less predictable than before dredging. Anti-dredging groups have been inundated with people reporting localised coastal erosion they believe is unprecedented, but University of Melbourne coastal erosion expert Dr Wayne Stephenson says there is little chance the expanded bay entrance will hurt coastlines.
"Most of the metropolitan beaches in Melbourne are so interfered with through seawalls, groynes and renourishment interventions, that detecting any signal from that source would be just about impossible," he says.
Putting the sea level rises in context, the Victorian Government expects climate change to lift sea levels by about 80 centimetres by the end of the century.
Fish
Concerning trends have emerged for the bay's fish, but once again the impact of dredging is unclear. A recent trawl of the bay reported a significant decrease in the biomass of fish caught in intermediate depths since 2005. A similar trend was noticed for fish in the deep waters since 2007.
Curious results were also found in fish that inhabit the waters near the Yarra mouth. This year's official survey could not find a single yellow-eye mullet, forcing the official monitoring program to proceed with only one species, black bream. Those caught were found to be up to 30 to 40 per cent leaner than the black bream caught at the same spot in 2006. Dredging monitors said the difference could be due to fish reaching a different stage of their breeding cycle.
All the fish were caught close to where contaminated materials were dredged from the river at Newport. Tests of the bream showed chemical concentrations were either the same as, or lower than, 2006 levels. Trawls for anchovies failed to find any fish less than one year old; dredging monitors were confident that baby anchovies were still in the bay, and had been missed by a flaw in the trawl process.
Contaminated sites
Heavy metals and contaminants were shifted from the Yarra mouth near Newport to a dumping zone off Mordialloc without major incident. Investigators found the dumping zone - known as a bund - was constructed properly, effectively sandwiching the contaminants between layers of clean sand on the bay floor. Experts say ongoing monitoring of the bund's stability will be needed.
Penguins
Body-mass measurements for adult members of the Phillip Island colony have generally remained strong, as have overall population numbers. But the summer of 2009 was a poor season for chicks. Many were underweight, and survival rates were poor. Penguin experts could not determine what caused the poor chick season.
The health of the St Kilda penguin colony remains less clear because of a lack of funding for monitoring. GPS trackers showed that St Kilda penguins were feeding in regions affected by the dredging plume. Chemical testing on St Kilda penguin feathers are still awaiting funding to go ahead.
The good
Heavy dredging was completed faster than expected, after the Port changed its schedule to bring in a second dredger for works in the south of the bay. The move shaved months off the schedule, and means seagrass beds will not be affected by dredging during the spring and summer months when their growth is strongest.
Another legacy will be the enhanced monitoring of the bay, some of which will continue for years to come.
The bad
A number of mistakes emerged during the project. Midway through 2008, dredgers failed to clean up loose rock that was left near the fragile bay entrance; a computer error was blamed. Earlier this year, the dredging ship accidentally dredged outside the area it was supposed to be in. There were numerous small oil spills, with a significant spill of about 900 litres occurring near the entrance in August 2008.
