Helpful video shows exactly how Sydney’s Warragamba dam works during floods as new calls are made for its level to be raised by 14metres to protect thousands of people
- Authorities renew calls to raise Sydney’s Warragamba dam level by 14 metres
- The catchment is located in Western Sydney and supply’s 80% of the city’s water
- During floods dam gates automatically open & close based on water levels
- In extreme weather events, an auxiliary spillway is used with dam’s flood gates
A video that reveals how Sydney’s main dam manages flood levels was released as authorities renew calls for its level to be significantly raised.
An east coast low is expected to dump up to 120mm of rainfall over a six-hour period in NSW, bringing with it the possibility of flash flooding from Sydney down to Bega.
The deluge has already caused Sydney’s Warragamba Dam to spill, which could continue for up to two weeks.
Sydney’s Warragamba dam was built to manage floods and the city’s water supply (pictured, water spilling over the Warragamba Dam in March 2021)
The catchment located 65 kilometres west of Sydney, built to supply 80 per cent of the city’s water, has spilled more than 50 times since it was built in 1960.
During floods the gates work automatically, opening and closing based on the lake’s water levels – a process also known as the H14 protocol.
When the supply level reaches capacity after heavy rainfall, the dam’s five flood gates open sequentially, starting with the ‘drum gate’.
When the supply level reaches capacity after heavy rainfall, the dam’s five flood gates open sequentially, starting with the ‘drum gate’ (pictured)
The remaining four ‘radial’ gates progressively open in stages once water levels exceed 230mm.
When all gates fully open, the dam has reached 1.83m above the full supply level.
Flood gates can usually be manually operated after extreme flooding to reduce the dam’s water level.
In extreme weather events, an auxiliary spillway is used in conjunction with flood gates to safely pass the floods.
In the coming weeks, Warragamba’s spill rate is up to 250 gigalitres a day, roughly half the amount leaked during the floods that devastated western Sydney 12 months ago.
‘The spill rate will ultimately be determined by the intensity of the rainfall and the inflow generated,’ WaterNSW said.
In extreme weather events, an auxiliary spillway is used in conjunction with flood gates to safely pass the floods (pictured)
‘Nonetheless downstream river level increases are likely and will also be influenced by the volume of inflows from tributaries downstream of the dam.’
When the dam spilled in November last year, authorities said raising the dam’s level was the only way to reduce the risk of ‘catastrophic flooding’ in the Hawkesbury-Nepean Valley.
‘The proposed raising of the Warragamba Dam wall is the only feasible flood mitigation option,’ Floodplain Management Australia President Ian Dinham said.
‘For a 1 in 100 chance in a year flood raising the dam would reduce the number of people needing to evacuate from 55,000 to 14,000.’
On Wednesday, Stuart Ayres, NSW minister for Western Sydney, told 2GB: ‘The water inflows into the dam are not as high as first anticipated so that is a good sign.’
‘But it is incredibly dependent on where the rainfall actually takes place.’
The Warragamba Dam spillway is seen outflowing in November 2021 after heavy rains across the Sydney catchment
Mr Ayres renewed calls for a flood mitigation level to be added to the top of the dam, raising it by 14metres.
He expressed particular concern for regions that have been issued major flood warnings such as the Hawkesbury-Nepean, Colo and MacDonald rivers.
However, environmental impacts and future development plans have held up any chance of the dam walls being raised.
‘We don’t have a flood mitigation option in the way that we run the dam, that’s why we’ve got to increase it’s capacity,’ Mr Ayres said.
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