Image: SA Water
After nearly four years without a release, water is once again flowing through the spillway gates at Mount Bold Reservoir following a huge influx of water from Adelaide’s recent record-breaking rainfall.
The reservoir was sitting at just 69 per cent capacity heading into the weekend, but has since captured more than 13 billion litres of water, sending its storage level soaring to around 95 per cent.
That hit the threshold for SA Water to begin a controlled release down the Onkaparinga River, with four of the reservoir’s eight spillway gates now open.
It’s a dramatic turnaround for Mount Bold, which has more than tripled its storage since the beginning of winter and was holding around 44 billion litres of water before the gates opened on Friday morning.
SA Water Senior Manager of Environment and Energy James Crocker said, “Dam walls, gates and spillways are designed to manage water within a reservoir in a controlled manner, to ensure we can protect the structural integrity of the dam and its surrounding communities.
“Proactive water releases such as that now happening at Mount Bold are a perfect example of this type of dam infrastructure in action.
“In the case of Mount Bold, its dam has 8 gates that can be controlled to release different volumes of water from the reservoir based on its storage level and expected inflows from the catchment.”
At present, four gates have been opened to 10 centimetres, allowing a controlled amount of water to flow downstream.
SA Water will continue monitoring the reservoir and reassess how long the gates need to remain open, with the timing informed by rainfall forecasts and expected inflows.
The utility has been working closely with the Bureau of Meteorology to monitor incoming weather systems and determine when water should be released.
Once the reservoir reached its 95 per cent trigger point, on-site rangers opened the gates remotely from the control room using an electronic panel.
And while plenty of water is making its way into the Onkaparinga River, locals downstream aren’t expected to see a significant change in river levels from the release.
Some of the water will also be diverted at Clarendon Weir through an underground tunnel into Happy Valley Reservoir, allowing SA Water to make the most of the additional water within Adelaide’s supply system.
The bumper rainfall has delivered a major boost to Adelaide’s water storages more broadly, with more than 85 billion litres captured by SA Water’s metropolitan reservoirs since the beginning of winter.
A massive 18 billion litres flowed into metropolitan storages in the 24 hours to 8am on Monday alone.
Adelaide’s metropolitan reservoirs are now sitting at 79 per cent capacity, compared with just 54 per cent at the same time last year.
For those keen to see Mount Bold’s impressive response to the rainfall for themselves, there is also a new reason to head out to the reservoir reserve. While the dam wall remains closed to public access during the release, visitors can safely view the reservoir’s pop-up waterfall from the viewing platform.
The lookout is accessible via a 1.4 kilometre return walk from the car park off Razorback Road, offering views down towards the dam as water makes its way through the spillway.
So, while Adelaide’s recent rain may have made for a very wet few days, it has delivered a seriously welcome boost to the city’s water supply.
