Montefiore: Flushing the Torrens for Tourism’s Sake

Now that Torrens Lake has become the centerpiece for the state’s $1 billion Riverbank vision, the challenge remains of how to keep the water as clean as the tourism images.

The notion of ‘wicked problems’ has it that, despite traditionally effective remedies, some still won’t go away. The worst-case scenario is when noone’s certain when the problem might need urgent attention – if at all. This keeps Town Hall’s water quality managers awake at night.

On Torrens Lake, an artificially created body of water familiar to every South Australian, the muddy waters lap quietly, as paddleboats, gondolas and the Popeye cruises ply leisurely trades – a picture of tranquility. But below the surface, a problem has joined the list of state challenges needing quiet, but constant monitoring. This is acutely so here, because since the government’s Riverbank vision was adopted by the city fathers (against their Rundle Mall-induced best judgement), the lake has become Riverbank’s tourism epicentre, flanked on one bank with multi-million-dollar developments, and on the other with pop-up commercial activities, attended by thousands of interstate and international tourists.

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The Riverbank Precinct has become a focal point for state and local government activity in recent years

Unfortunately, however, the lake has a propensity to get awfully polluted with blue-green algal blooms (cyanobacteria) when summer warms the murky waters. If you’ve never seen it, the water surface turns vivid green – and a pong wafts from the reedy edges. In recent years, the state government has been periodically (and quietly) flushing the lake with artificial surges of water spilled from upriver Kangaroo Creek Reservoir. Megalitres of flows, pushing the lake pollutants down into the gulf off Henley Beach south. Each flush came via a profligate dump of clean captured hills water at times when Adelaide’s suburban families have been paying dearly for similar supply. But now the flushes have had to cease. More on this later.

Torrens Lake pollution has two causes: in-stream pollution (organic matter, bird poo and toxic chemicals and heavy metals) and storm water pollution (introduced microbiological and chemical matter and nutrients from upstream agricultural pursuits). Ironically, while good rains are seen to be the alternative key to the reservoir flush solution, they also remain part of the problem, linked to climate change. A June 2011 Town Hall report stated: “…more extreme rainfall events are predicted, which will result in surges of storm water input with high levels of debris and pollutants.”

Adelaide experienced such a downpour in January, again in September 2016 and again in January 2017. Hills tributaries overflowed; flooding caused chaos, the lake swelled alarmingly, then high levels surged their way west. The water significantly refreshed the supply of runoff pollutants and topped up Torrens Lake like never before. The Kangaroo Creek reservoir flush idea emerged more than 10 years ago. It mostly worked, but the volume of water required demanded that, in a perfect world, the reservoir’s level should be raised to store more, to compensate for the deluge requested. But to raise the level was seen as risky because it could compromise long-established one-in-200-year flood-protection (spillover) risk protocols. A 2007 report said that the decision would be up to the politicians. “Ultimately there would need to be a political decision and risk to public property and life is expected to rate higher than restrictions to Lake use and negative media on recreational water quality problems,” it stated. The source report Summary of Findings: Progress Update reflected three years’ work by water experts, mayors, bureaucrats and state politicians. It was compiled by the state government’s Torrens Taskforce and re-examined in November 2009.

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Blue green algae; enemy of health and tourism alike

Around the same time Town Hall discussed the ‘amenity flow’ flush plan but voted that it be kept secret because disclosure “would divulge information provided on a confidential basis by or to a minister of the crown, or another public authority or official…” and that it “would, on balance, be contrary to the public interest.” This only served to illustrate how bureaucracies work when the public interest is in fact paramount.

Fast forward seven years and the quandary is worse. Although the idea to install new infrastructure to raise the reservoir level wasn’t endorsed, flushing continued. As late as 2015 the Adelaide Park Lands Authority indicated that several flush events were planned for 2015–16. They occurred until January 2016 but on completion of a reservoir safety upgrade, flushes were deemed no longer feasible.

Three alternative solutions now remain – chemicals, revegetation and a fishing spree like no other. The chemical is to be hydrogen peroxide, in dose form of sodium percarbonate to kill algae cells, but doesn’t kill the all-important plant growth that adds oxygen to the water. The re-vegetation plan seeks to boost aquatic native plant growth on the lake floor (much of which was destroyed during in a 1990s council dredging exercise). However, a November 2016 progress report noted that, of a trial of 17 species, only two survived – a brutal illustration of the lake’s poor water quality. Option 3 – the fishing exercise – is to try purge the lake of big populations of European carp, the exotic, invading enemy of clean water and native fish and plants and unwitting ally of algal blooms. So seriously do experts view the fish problem that they plan ‘targeted electrofishing’, a quiet declaration of war against the hardy pest.

While each of these tactics may have some effect, the end to lake flushing exposes lake managers to fresh risk. Adelaide summers have in recent years seen multiple heat waves and lately the weather has taken on ‘sub-tropical’ characteristics, complete with atypical downpours, refreshing the pollutant buildup in the lake. Fortunately, there is at least one benefit of the very evident quality of the water – tourists might take home many images of it as they promenade the water pathways, but they aren’t tempted to swim in it.

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