Myponga abuzz with activity as spillway gate upgrade has lift-off

Major work is now underway at Myponga Reservoir as part of SA Water’s $3.7 million upgrade of the dam spillway gates, to ensure the long-term safety of the structure and secure the Fleurieu Peninsula’s water supply.

Sitting atop a section of the dam wall, Myponga’s three spillway gates facilitate controlled releases of water from the reservoir, based on its capacity and rain inflows from the catchment.

Earlier this month, the three gates were carefully removed by a large crane located on Reservoir Road, with each lift taking around 30 minutes and involving 12 crew members across the delicate operation.

SA Water’s Senior Manager of Infrastructure Planning and Strategy Dr Daniel Hoefel said the dam’s spillway gates have made for spectacular pop-up waterfalls in recent years, and were earmarked for refurbishment.

“Myponga Reservoir’s arch dam is an impressive engineering feat and 60 years on, the wall remains in sound condition with our routine inspections identifying the dam’s spillway gates require an upgrade to ensure they keep operating reliably,” Daniel said.

"The gates are curved steel plates, reinforced with a series of beams that can be opened at varying heights depending on the amount of water being released, and are critical to our ability to maintain the reservoir’s water level and protect the dam’s structural integrity.

“Along with Mount Bold, Myponga is our only other gated dam and requires manual operation by our reservoir rangers from an on-site control room, with the gates operated via a hoisting system either electronically or hydraulically.

“Before we were able to crane the gates off the dam wall, we released water from the reservoir for two weeks until the water level was sitting below the top of the spillway crest – which was around 71 per cent of capacity.

“Our crews then constructed scaffolding to enable safe access along the spillway and prepared the gates for lift-off by attaching lift points on the gate arms, removing the wire ropes, and disconnecting the arms.

“The project includes refurbishing the gates’ arms and bearings, along with replacing their seals, rollers, and sill plates, to ensure the gates operate reliably when water is released from the reservoir.

“All three gates have now been transported off-site for full refurbishment, with our crews starting work to restore the concrete around the seal plates, which is the section that makes contact with the wall to hold in water.

“Importantly, we scheduled our work during late summer and autumn when the reservoir is at its lowest level to limit the amount of water we had to release, while maintaining a secure supply for our customers and ensuring the gates are back in action to maximise water capture across winter and spring.”

To safely accommodate crews and heavy machinery, pedestrian, and vehicle access to Reservoir Road, between the Myponga Reservoir Lookout and Forktree Road, will be temporarily closed during the work.

Work on the spillway gates will be undertaken between 7am and 5pm, Monday to Saturday, and is expected to be completed by mid-2024.

Mr Hoefel said there’s even more activity at Myponga with upgrades at the reservoir reserve’s main entrance, in response to visitor feedback.

“As part of our ongoing work to enhance the recreational experience across our reservoir reserves, we’ll soon be commencing a number of upgrades at Myponga in direct response to what visitors have told us,” Daniel said.

“This includes installation of a new kayak drop-off loop via the Eatts Street entrance, to make it easier for visitors to get as close to the water’s edge as possible, and new BBQ and shelter facilities in this area of the reserve.

“We’re also upgrading the service road off Eatts Street by applying a bitumen seal to improve dust suppression for neighbouring residents, along with creating a series of stormwater retention ponds surrounding the car park to capture stormwater and protect the reservoir’s water quality.

“Additional temporary car parking will be available at both entrances during the work, which has now started and will take around six weeks to complete.”

There will be a two-week closure of on-water access at Myponga during the Eatts Street access road upgrade from mid-April, with the car park and nearby launch area currently temporarily closed to enable this work.

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