Bunds, regulators, weirs, dams. They go by different names but the engineering interventions that cut Lake Alexandrina off from Lake Albert and cut the fresh water flows of the Finniss River and Currency Creek off from Lake Alexandrina are blocking walls. Pumps may be mounted on them. Siphons may be strung over them. Water may be pumped across them but they disconnect and segment a system that relies on connectivity for its resilience and ultimately for its recovery.
So it was with great joy that we gathered at the ferry at Narrung on Monday morning this week (20/9/2010) to witness the breaching of the 300 metre bund that has separated Lake Albert from Lake Alexandrina since April 2008. We live around the lakes and know their rhythms. Before the bund was built water would gush through the Narrows, the 13 kms stretch between the lakes. Now, as we predicted, the Narrows have silted up. The bund has thwarted the wind driven movement of water through the Narrows, movement that keeps water oxygenated. That same wind has been battering the bund and with good environmental flows and steady rainfall, the water levels have risen in Lake Alexandrina. Locals began predicting the bund could breach naturally.
Signs of weakness in the structure have been apparent for some time. The bund has been patched up and reinforced but this month it was time for the structure to go. The SA Government prepared for a partial removal. Excavators would scoop out 100 metres worth of bund and trucks would whisk the spoil away. Last week steel pylons were removed from the bund but the structure was too unstable to proceed with the excavations. The bund needed to be reinforced. For a week, our regular updates had been predicting the breach was imminent.
Sunday we received the news: official time for the bund breach was set as Monday 10.30am. Instructions: Gather on the Meningie side of the bund for safety. Don’t rely on the ferry operating. Champagne would flow as the fresh water of Lake Alexandrina with levels around 0.7m AHD rushed into Lake Albert where water levels were about 0.35 m AHD. I set off before first light to drive to Narrung.
Mother Nature had other ideas. Sunday afternoon the bund gave way and the water flowed. By the time the excavators began work on Monday, a 50 metre gap had opened up. The locals had gathered. The pelicans massed overhead. A lone swamp hen struggled against the current only to be sent shooting downstream with the new water that was swirling into Lake Albert. Helicopters hovered overhead. By 10.00am the gap had opened to over 70 metres and the excavator was beginning to bring up silt. The second excavator began to remove the sand and silt being dumped on the Lake Albert side of the bund by the first machine. The spoil was trucked away. The champagne popped. The cameras clicked. Life was coming back.
Questions remain.
- How long will it take for the water levels to equalise? A matter of weeks or over a month? On Monday it was obvious that the backwater wetlands were filling up and as we drove back along the Narrows, we could see trickles of water creeping through the grassy lowlands. A thirsty country was getting the drink it so needed.
- Will the Narrows need dredging? A line of silty sand that extended from the diminished bund into the Narrows was clearly visible by noon on Monday. The current will probably disperse that material but there is the build up of the past two and a half years. There is also the build up of silt that the construction of the causeway in the 1960s occasioned. That should have been a cautionary tale but it seems we do not learn.
- Will there be sufficient movement of water between the lakes for the salinity levels in Lake Albert to fall to tolerable levels? It is not only water levels that have been impacted by the blocking walls, water quality has also been compromised. Before the breach, salinity levels in Lake Albert were three times those of Lake Alexandrina.
- Should the entire bund be removed? It would certainly facilitate movement of water and demonstrate that diversion levels up stream are going to be set sufficiently low to ensure flows through the Murray-Darling River system to the Murray Mouth, a most desirable outcome.
- Did we need the bund in the first place? The official reason for the bund was to maintain water levels above the tipping point at which the acidification on Lake Albert was predicted. Could the acid sulphate soils have been managed without disconnecting the lakes from each other? We may never know the answer to that question but we have consistently maintained that the threat posed by the presence of acid sulphates has been over-stated. We have repeatedly asked for the reports on which the decisions were based to be released to the public. We have maintained that strategic liming of ‘hot spots’, mulching and encouraging native vegetation across exposed lakebeds could mitigate the problem.
Most of all we have advocated for fresh water flows. Even the most meagre rainfalls have been sufficient to refresh the country but blocking walls like the bund prevent this water moving through the system. Yes we have been in a drought but, we have argued, it is over-allocation that has reduced the lakes to such a desperate state. And, even in the depth of the water crisis, there was still water that could be purchased on the water market. But who would buy it for the environment? Would it not just evaporate? What is the environment worth? Our position has been that a healthy environment, a healthy river and healthy lakes are a prerequisite for healthy communities and economies.
Now we are turning our attention to the so-called ‘regulators’ at Clayton Bay and across the Currency Creek. It is time for them to be removed. It is time for the river to flow to the sea. The floodwaters currently coursing through the system on their way to the lakes are our opportunity to ‘reset’ the system. Those floodwaters have the potential to flush the accumulated salts and nutrients through the Murray Mouth and out to sea. Work will begin on the partial removal of the regulator at Clayton Bay on 29 September. If we are wise and allow the floodwaters to do their work, if we reconnect the tributaries, lakes, river, mouth and Coorong, we will really have something to celebrate as a community and as a nation.
Have we learned yet?
