Myponga Dam safety upgrade

Background

Myponga Reservoir, nestled near the township of Myponga, is a critical piece of SA Water’s infrastructure, supplying safe, clean drinking water to the majority of Adelaide’s south.

The reservoir was built between 1958 and 1962, at a time of rapid economic expansion in South Australia.

Its construction increased the state’s storage capacity, supporting population growth and the expansion of industry in Adelaide’s south.

Its capacity is managed via the Myponga spillway gates. When a rainfall event exceeds the dam’s capacity, water is released via the spillway gates into the Myponga River.

Water from the reservoir is treated at the nearby Myponga Water Treatment Plant before it is supplied to homes, businesses, schools and hospitals on the Fleurieu Peninsula.

The broader Myponga Reservoir Reserve is open to the public for recreational use, including fishing (with PIRSA permit), kayaking and canoeing.

Myponga Dam safety upgrade

In February 2024, together with major construction partner John Holland Guidera O’Connor joint venture, we will undertake remediation works to the spillway gates and associated infrastructure. This is the first time since the spillway gates were commissioned in 1962 that they will be removed. Remediation will extend the serviceable life of the gates for 50 years.

To safely undertake works, the Myponga Reservoir water level needs to sit below the spillway crest level. These works are scheduled during late summer and autumn when the reservoir is naturally at its lowest level. Depending on water levels at the time of construction, a controlled release of water may be necessary. If so, water will be slowly released via the dam’s scour valve to gradually introduce water into the Myponga River watercourse. The gates will then be opened incrementally to release water to the spillway crest level, before being closed again.

Environment

We have worked with the Hills and Fleurieu Landscape Board ahead of the planned release on measures including a Water Affecting Permit and implementing a controlled release.

The release mimics a summer rain event, providing water to vegetation higher up on the banks of the Myponga River and flushing the system with freshwater.

Summer rain events improve water quality downstream, which can deteriorate during long dry summers. This benefits many aquatic species.

Road closure

To safely undertake works, access to Reservoir Road between the Myponga Reservoir Lookout and Forktree Road will be closed to all vehicles and pedestrians during the upgrade.

The area directly adjacent to the dam wall will be occupied by machinery, cranes and scaffolding.

Reservoir Reserve access

During the works, Myponga Reservoir Reserve will remain open for all recreational activities. Advance notice will be provided of any unexpected restrictions.

As the reservoir level will be lower than usual, please bring a trolley to get your kayak or canoe to the water's edge more easily. We will use a combination of sand and matting to improve access to these areas as a result of lower water levels during the upgrade.

The kayak launch pontoon at Pink Gum Hub will not be available due to the lower water level. It will be available again when inflows re-float the pontoon.