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Topics > River Murray floods

Lower Lakes and barrages

Why isn’t there any flood information for the Lower Lakes?

It is expected that barrage operations will be able to safely pass the forecast flood peak and maintain average lake levels below 1.0 m AHD. Because flooding is not expected to occur at the Lower Lakes, flood warnings for the River Murray and flood inundation maps only extend as far downstream as Wellington.

How will the barrages be managed during the flood?

Barrage releases will continue to be managed to provide airspace in the Lower Lakes when conditions allow. Rapid increases in water level (such as what occurred early November 2022) should be expected during periods of storms/high tides/swells, followed by more gradual decreases in level as barrage releases are increased and airspace is created. There are 593 available openings over the combined five barrages. If required all openings and spill ways will be used to safely pass the expected flows.

Why are lower lake levels fluctuating?

The barrages are operated to not only manage lake levels but also to prevent excessive amounts of sea water from entering the Lakes. Winds and tides are important considerations in planning daily operations. Barrage gates may need to be closed for short periods during storms and high tides to prevent seawater ingress into the Lakes, which can lead to rapid increases in water level while high flows are entering the lakes from the river. Additional barrage gates will be opened to release the surcharged water when it is next operationally possible.

During strong weather events, persistent wind over the lakes can also cause water levels to increase on one side of the shoreline temporarily, sometimes spiking above 1.0 m AHD in localised areas.

Lake communities and users should be aware of the potential for rapid, temporary rises in lake level.

Why aren’t the Lower Lakes being drained to help with flood mitigation?

The Lower Lakes are being managed to target a water level of 0.65 m AHD as much as possible, which is lower than normal for this time of year when the lakes tend to be surcharged to hold extra water in the lead-up to summer. However, there may be times that lake levels rise temporarily due to local weather events or short closures of barrage gates during very high tides. Additional gates will be opened (when operationally possible) to release more water to maintain this target water level.

It would be ineffectual to target a level lower than 0.65 m AHD at the present time because of elevated downstream water levels in the Coorong North Lagoon and Murray estuary, which would make it difficult to make releases from the barrages at levels below 0.65 m. The water level in the weir pool below Lock 1 also needs to be maintained above certain levels so that irrigators, SAWater and other users can continue to access water supply.

Lowering the lake level below the normal operating range is no tan effective strategy for managing water levels during the flood. During floods, the distance that the lake level will influence upstream water levels is substantially reduced compared to regulated flow conditions.

Why aren’t more barrages open?

SA Water operates the barrages on behalf of the Murray-Darling Basin Authority and in consultation with the Department for Environment and Water. Decisions on the number of gate openings at each barrage are made daily, with releases currently being made to target an average Lake level of 0.65 m AHD. If too much water is released too quickly, water levels will drop too low. Current barrage operations are successfully passing the River Murray flow entering the Lower Lakes from Lock 1. On a daily basis, barrage outflows can vary considerably due to tide and weather conditions, but over a longer period, outflows are matching inflows.

As the flow into the Lower Lakes increases over the coming weeks, the number of barrage gates open will be increased to pass the higher volume of lake inflow and minimise any unnecessary rise in water levels and inundation of foreshore areas.

Why aren’t barrages operating on the weekend?

There are hydraulically operated gates installed at most of the barrages and these can be/are operated over the weekend. Traditionally there is only one barrage attendant rostered to work weekends and the task of operating the manual barrage gates is a minimum 2 person task. However, if gate changes are necessary over a weekend as the flow increases, more staff will be rostered on.

While the general public only has viewing access at Goolwa barrage, there are four other barrages that are releasing flows to the Coorong, even when the Goolwa barrage is closed.

Why has the dredging of the Murray Mouth stopped?

The Murray Mouth is currently in a good condition and with the sustained high flows this is expected to be maintained over the coming months. A dredge has been maintained on standby should it be required at the site.

SA Water is undertaking fortnightly surveys of the Murray Mouth and will monitor its condition and resume dredging should conditions require it.

How often is the Murray Mouth being assessed to ensure that it doesn’t fill with sand?

Fortnightly surveys are being undertaken to assess the condition of the Murray Mouth. This will continue throughout the high flow event.