Late release of dam water sparks brawl over downstream flooding

Flood specialists say water should have been released earlier from Warragamba Dam, as driving rain led to the dam spilling on Sunday threatening homes.

Water gushes from Warragamba Dam on Sunday. Picture: Water NSW

Flood control specialists say water should have been released earlier from the Warragamba Dam, as driving rain led to the dam spilling on Sunday for the second time in two days, threatening thousands of homes in low-lying areas downstream.

The failure to reduce water ­levels in the dam in recent months despite predictions of destructive weather has sparked a brawl ­within the NSW government.

Modelling by WaterNSW shows that on current rainfall estimates about 1500 gigalitres of water will flow into the dam in just seven days — 75 per cent of the dam’s total capacity of 2000GL.

More than 450GL of water is now spilling from the dam every day, with the rate increasing and likely to result in widespread flooding. But WaterNSW has ­released just 130GL from Warragamba Dam since November.

The Australian has obtained figures showing that in November 48GL was discharged in a controlled release to draw the storage down one metre below full supply level for operational and maintenance purposes.

Another 43GL was released during a second drawdown from full supply level in January, followed by another 28GL earlier this month.

Warragamba dam has started to spill. With heavy rainfall persisting, we are also expecting to see spills at Nepean, Cataract, Cordeaux and Avon dams.
For weather forecasts and flood warnings, visit https://t.co/2GW553xMtn
For emergency information, visit https://t.co/7v9ukIZgQBpic.twitter.com/eainGUuCaw

— WaterNSW (@WaterNSW) March 20, 2021

NSW Police and Emergency Services Minister David Elliott, whose Baulkham Hills electorate has been severely affected by flooding, was reported to have been furious at Water Minister Melinda Pavey’s reluctance to more significantly reduce the volume of water.

Mr Elliott refused on Sunday to be drawn on the issue but noted that “you don’t have to be a Rhodes scholar to work out that a litre of water in the dam today is a litre of water that will flood somebody’s house tomorrow”.

However, both he and Premier Gladys Berejiklian were at pains to point out that an earlier release of water would have made little difference because of the sheer volume of rain being experienced.

“If the statistics we’re hearing at the moment are correct you’d have to empty half the dam to truly mitigate what we’re seeing at the moment,” Mr Elliott said.

Water scientist Ian Wright from Western Sydney University said releasing more water from the dam would have helped to ­reduce river levels, but pointed out that under current rules Warragamba Dam’s only function is to store water; it has no mandate for flood mitigation. That might have to change, he said.

“I think we’re going to need to have a very thorough analysis after this, and for me that would have to be on the table. This was predicted.”

Mr Wright said his biggest concern was that many people now living in the area downstream of the dam had no experience of flooding and didn’t realise how quickly the often single-lane roads could become choked.

Flood expert Jamie Pinnock, from the Australian National University, said he was “a bit surprised” there weren’t earlier efforts to release the water.

“This rain event has been forecast for a number of days and I think there would have been the opportunity to reduce some water. But this really highlights why using dams to control flood waters is very difficult to get right — if you want to control a flood, you’ve got to keep the dam at least partly empty; if you want to supply a city with water, you’ve got to keep them as full as you can.”