Annual Torrens Lake blue-green algae management program kicks off today
This program, which has run for over a decade, helps prevent the growth of blue-green algae in the CBD waterway but residents downstream have concerns for its impact on the beach and water quality.
The Torrens Lake Cyanobacteria Advisory Committee – which includes the City of Adelaide, City of Charles Sturt, SA Water, EPA, Department for Environment and Water and Green Adelaide – will begin the annual blue-green algae management program today to prevent the growth of poisonous algal blooms on the urban waterway.
The program, led by Green Adelaide, will see a small channel cut to excavate sand at the outlet of the River Torrens to pre-emptively prevent the growth of blue-green algae and keep the Torrens Lake open during summer.
This is done to assist in water flowing easily out to sea should a managed freshwater flow be required to keep blue-green algae levels low in the Torrens Lake – the section of the river from the weir to Frome Street bridge.
Blue-green algae often grow during summertime “particularly if the water is not moving” Green Adelaide director Brenton Grear told InDaily..
“So there’s no fresh water circulating and when the water is warm, there’s nutrients in it. That’s all the right ingredients to have a bloom.”
Grear said that blue-green algae is “not a healthy thing to touch or drink when it’s in high quantities” as he said it can cause people to get sick and have skin irritation.
He said “the way to manage the blue-green algae and the conditions in the lake – so you don’t get a bloom – is by having some flow through the lake”.
“What we’re doing is essentially circulating water through the Torrens Lake above the weir and so you’re getting movement, and then the water cools down,” Grear said.
“When there is movement of water, nutrients pass through, and the conditions for a bloom are negated.”
These flows might see “800 megalitres of water coming out of the Kangaroo Creek Reservoir”.
Local resident and Henley Ward councillor Kenzie van den Nieuwelaar said cutting a channel at the river outlet has “got its issues”.
“We’ve got a very highly eroded section of the beach there, so you bring big machinery in and moving sand around, that’s obviously going to have impacts on erosion and coastal processes,” she told InDaily.
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“That’s I guess where I’d like to see that tied in with effective beach management and sand management because we’ve already got the sand management replenishment program coming.
“I’d like to see what impact is that having on the current program.”
Grear said the channel volume is approximately 5000 cubic meters of sand which is “not an incredibly large volume of sand”.
“That sand is not taken away to do something else with,” he said.
“So this year, we’re going to use some of the sand out of the excavation to deposit in the Northward meander… – which is only a matter of 10, 20, 30 metres away – to stop the Torrens naturally breaking through and heading north, so make sure it keeps going out straight.
“It’s to do with longitudinal drift. It’s just the way sand moves on a coastline like Adelaide’s.”
Van den Nieuwelaar said “in 2024, there has to be a better way to deal with the [blue-green algae] bacteria at its source”.
This current method has been undertaken for more than a decade, beginning in the summer of 2013/14.
“Flushing it out to the Gulf in summer at some of Adelaide’s heavily used beaches is just inappropriate,” she told InDaily.
“I think we need to consider the impacts to the whole coast and the effects of the way the flushing occurs.”
Van den Nieuwelaar said the implications of this management program are “multi-faceted”.
“Obviously this area, we’re experiencing a lot of erosion, so if you’re flushing bacteria out directly into the Gulf, that’s obviously going to have impacts on sea grasses, which can assist with slowing down coastal erosion,” van den Nieuwelaar said.
“We’ve got quite a lot of bird life around there now, so of course, they’re going to be impacted by heavy machinery and trenching.
“And let alone humans that actually use the beach that time of the year for swimming, for water sports activities, because there’s always signs saying ‘don’t swim when the water discoloured’.
“I liken it to incinerators. Years ago, people had incinerators in their backyard to deal with excess rubbish and everything, and we now know that that was actually disastrous for the environment.”
Grear said SA Health and EPA do some monitoring if there’s a release at the outlet.
“There’s no implication for human health in terms of the volume that comes through… but it does discolour – so it’s discoloured water. It probably has a bit of vegetative material in it,” he said.
“You could even potentially get some carp washed out as well – I think that has happened – and of course, carp in full sea water will die.
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“But really, very minimal impacts for human health, other than it doesn’t look nice for a few days, and some positives for the aquatic ecosystems in the lower reaches of the River Torrens.”
Grear also said there is “very little” environmental implications to the shorebirds around the area, including the hooded plover.
“In excavating the channel, it’s made sure that there are no hooded plovers nesting in that area and then once the channel is established, the hooded plover won’t be impacted by it,” Grear said.
Van den Nieuwelaar said she would like to see “more of a collaborative process between all the parties coming together to move forward with a solution”.
Grear said “all the stakeholders and the local community get advised that this excavation is taking place”.
“The council and the dune protection team get involved in just working out how the excavation should happen as well,” Grear said.
Adrian Ralph, general manager of city operations for the City of Charles Sturt, said being a part of the advisory committee is “not really about being in agreement”.
“We’re there to advise and work with Green Adelaide who need to manage the Torrens River system as a whole,” he told InDaily.
“We’re there for support from a communications perspective, advise on the impact on our council area and potentially the beach. But [the] responsibility actually sits wholly with Green Adelaide to manage.”
Green Adelaide’s channel excavation will commence today and will last three to five days.
Grear said the reason the channel is cut without knowing if there definitely will be a release is because the blue-green algae is monitored in the lake regularly.
“As the levels of it increase, it can go from ‘all good’ to ‘there’s the potential of a bloom’, and we’re going to have to release,” Grear said.
“That can happen in 24 to 48 hours so you haven’t got time to excavate this channel at the outlet and so that’s why it’s done pre-emptively.”
Just because a “small channel will be cut at the outlet of the Torrens” doesn’t mean “there’ll be any flows down the river”, said Grear.
“That might happen in a week’s time. It might not happen at all. It might happen on March 10,” he said.
Grear said whether a flushing occurs “really depends on the weather conditions”.
“Some years there hasn’t needed to be any flows and other years, there have actually been multiple flows,” Grear said.
“If it’s going to be hotter than average, there’s a good chance we probably will need these managed flows. If it’s drier than normal, that’s another factor that you’ll likely need to do these managed flows.”
However, Grear said after analysing the long-range forecast, there is a “good likelihood” that there will need to be a managed flow this year.
“Even though there was a bit of rain with this humid condition, we’ve had a dry, dry winter and spring, so the landscape is dry. There’s going to be limited flow off of the catchment, particularly upstream in the more rural catchment,” Grear said.
“The long-range forecast is for a hotter summer than usual, but the mitigating bit on that is the forecast is also for slightly more rain this summer.”
