Weir delays

Weir delays could cost Lower Murray and lakes region dearly

22 September 2009

Ken Jury 

Senior Journalist (Marine & Aquatic Ecology). 

The delaying tactics with the construction of the Pomanda Weir could result in a toxic legacy with some of the lower Murray and Lakes region being gradually destroyed by acid.

Considered to be one of the world’s worst acid sulphate soil regions, the festering concern about the lack of official progress is increasing every day. The installation of the weir is necessary to enable the lakes to return to an estuarine feature, to deal with acidification and to save precious river water for food security upstream. These are the subjects that have become the overriding topic of the region.

The facts are that the delays in building the weir have heightened the awareness for many South Australians and they are not only concerned for the well being of the region, but also with our food security from South Australia’s ‘Riverland.’

Downstream, locals throughout are realising that there’re two options left to save their region; a dried out system full of acid or a seawater solution. While both are contentious and neither is entirely palatable, most agree they certainly don’t want to see the huge lakes region dry up, only to be destroyed by acid. Most say that a seawater solution to return the lakes to an estuarine feature is now inevitable and urgent.

While grappling with this realisation, there’s an increasing concern today about the condition of the Murray River between Wellington and Lock 1 at Blanchetown.

The physical erosion and deposition reshaping the lakes shores has been well documented but further up in the system there are increasing cost implications from collapsing (slumping) river banks with the potential collapse of buildings as water heights return to sea level. Upstream of Wellington, very expensive ‘shacks’ and the real estate they precariously sit on, are destined to become part of the river bed.

The physical consequences of low water levels are as bad as the chemical mix of acid sulphate soils (ASS) and water in terms of costs and long-term damage to both the natural environment and the human built environment.

Consequently, there is wide support for the concept of holding water back in the river for critical human use and for servicing wetlands and backwaters. This support overshadows a preference to allow river water to flow down the river and into the lakes, only to become acidic and toxic, to eventually evaporate and waste.

In the meantime, there’s little coming from the government about the weir and how temporary the Pomanda structure is. There’s increasing dissatisfaction about the site for the weir and whether a narrower opening and bedrock base should be part of the discussion. Many agree, to build another wall across the Murray without a solid base and locks or gate’s is unthinkable.

What really needs to be raised is the level of continual procrastination over the weir and everything that goes with it. This has caused a situation where dried out wetlands have become a serious threat to the health and ecology of the river, which in turn threatens water supplies destined as a top up for Adelaide’s reservoirs during low rainfall catchments.

Lessons learned from acidification of Currency Creek and Lake Alexandrina to-date should be warning enough to highlight further potential risk in the river and its wetlands. This is particularly so, given the weather forecasts for next summer.

The implications of draining wetlands with resultant acidification of soils and run-off should have become more widely understood, particularly in the last ten years or so. When considering the past 120 years and the engineering solutions we used to alter the environment to the way we thought it should be, and looking at results of about 100 of those years, it reveals we have not really understood how we’ve been literally poisoning waterways and estuarine environments with acid run-off laden with toxins and heavy metals.

These have played a role in the decline of productivity and health of these systems over many years. Not only are we dealing with a crisis with our River Murray, Lower Lakes and Coorong, in a wider picture we’re also draining and diverting nearby coastal swamps and samphire flats, allowing potential acid sulphate soils to dry out and leach the acids and heavy metals into the poorly flushed marine environment, with help from occasional seasonal rain.

In one case not connected with the Murray River and lower lakes, there is some doubt concerning the coastal lands north of Adelaide where serious and urgent remedial work is required with soil disturbance, river flood plain drainage and creek runoff reaching coastal estuarine and mangrove features. This is a similar but smaller ASS crisis but no less serious from what we are doing (or not doing) along the Murray and Lower Lakes where implications due to poor knowledge in the management of acid sulphate soils is evident, even-though its existence has been known for decades.

This gives rise for concern in the Barker Inlet estuary north of Adelaide which is home to dolphin communities. It was also home to ‘Billy’ the much loved dolphin that died recently. Recent reports suggest sulphuric acid is entering over the levees and fords into the St Kilda drain cross-overs, north of Barker Inlet. This should not be ignored.

Meanwhile, between Lock 1 and Wellington, there’re increasing concerns that heavy metals from dried out wetlands may eventually reach the river intake pipes when pumping from the river to supplement our Adelaide potable water supplies.

This raises the question of moving the intake pipes from Murray Bridge, Mannum, Swan Reach and Tailem Bend, and repositioning a single feed from Morgan where water is much cleaner and safer, and the threat of acid and heavy metals is much lower or practically non-existent. This would provide a solution to the acidification of the lower river and its 80 wetlands from Lock 1 to Wellington.

Today, only three of those wetlands remain wet. We are told officially that 25 more wetlands will be inundated as a result of the construction of the Pomanda weir but the rest will remain dry through lack of water. Fourteen wetlands are in dire need of serious acid sulphate soil management right now, to stop acid moving through soil profiles to release heavy metals and other toxins. 

Dried out wetlands and back waters are becoming a threat to the health and ecology of the river. What was once wet mud with the potential to cause catastrophic damage when it dries out, has now become a very real threat because of the chemical changes of drying out and becoming ‘aired’ with oxygen.

We are still ignoring the implications of mismanaging acid sulphate soils.

There are some doubts concerning the path that heavy metals may take when dried wetlands are eventually flushed out. Albeit, readings from future food chains will however, leave us in no doubt.