Why can’t they let more water out of the barrages before the floods come?

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Considering how much water is coming down the River Murray, why isn’t more being let out of the barrages and into the sea?

A number of Murray Bridge News readers have asked the question this week, including a shack owner at Zadow’s Landing.

“We’re very well prepared for bushfires and everyone is well informed about how those decisions are made, but with floods we’re left a bit in the dark,” he said.

“They know the water’s coming, but...”

So why aren’t the Lower Lakes being drained more quickly to make way for the floodwaters?

Garry Fyfe, SA Water’s senior River Murray operations manager, said there were a few factors at play.

The biggest one: the barrages had gates, not pumps.

If the water level in Lake Alexandrina fell below sea level, salty water would simply flow in and fill it up again.

On Tuesday, for example, the high tide reached 1.1 metres and no water could be let out for a time.

Windy weather also changed SA Water’s calculations by pushing water one way or another.

The water level at the Tauwitchere barrage had gone up and down by 40 centimetres in a four-hour period on Tuesday, Mr Fyfe said.

“What we’re trying to do is make sure that whatever gets in (to the Lower Lakes) goes out,” he said.

“Every single day we’re monitoring the lake level and maximising the capacity of the barrages to let water out.

“We’ll continue to do that three times a day, seven days a week.”

What was important to know, he said, was that floodwaters would not be allowed to build up in the lakes and back up the Lower Murray.

So long as the water level in the lake was higher than sea level, SA Water could let out a whole lot more water than it had been doing lately.

Fewer than 250 of the 579 openings in the barrages had been in use in recent days.

“We have a lot of capacity to open additional openings if we need,” he said.

“We also have a one-kilometre open stormway, set above lake level, so … the water gets to a certain level and spills over.”

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Clarification: This story has been updated to more precisely reflect the number of openings in the barrages.

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