Water quality issues prompt MDBA to trial Hume Dam releases through ga

MDBA

The Murray-Darling Basin Authority (MDBA) is trialling a different method of water releases from Hume Dam using the spillway gates in a bid to improve downstream water quality.

MDBA acting Executive Director River Management Dr Andrew Kremor said dissolved oxygen levels remained low immediately downstream of the dam for several kilometres​, even though the MDBA had been releasing water through the valves to increase aeration, and compressed air has been added to water releases through the power station since earlier this month.​

“The very high levels of bushfire residue which entered the lake over the past few years has led to complex processes that use up a lot of the available oxygen in the lower layers of the lake,” Dr Kremor said.

“A drop in oxygen can make it difficult for fish and other aquatic animals to breathe, so we have tried valve releases to create a spray which aerates the water as it hits the river, and air has been added to releases through the power station.”

Impacts from these low dissolved oxygen levels to aquatic organisms or town drinking supplies have not been observed at this time and by actively maintaining or increasing the dissolved oxygen levels it is hoped that this will continue to be the case.

While the valve releases to date have improved low DO levels a little, from today (Friday) the MDBA will trial releasing a small volume of water through the spillway gates until Monday when the effectiveness of this method will be assessed.​

“This trial is being considered as recent water quality monitoring has shown that dissolved oxygen levels are much better in the upper layers of the lake, compared with the lower levels where water is released through the power station and outlet valves,” Dr Kremor said.

“These spillway releases will only be during the day and the valves will be used overnight which we hope will optimise an improvement in dissolved oxygen levels.

“If successful, the MDBA may consider continuing to use the spillway to assist with improving dissolved oxygen levels.”

Another water quality issue is also affecting the lake. WaterNSW has issued a red alert for blue-green algae (BGA) for all of Hume Dam.

However, these water releases are not expected to transfer significant amounts of algae downstream as the released water is not drawn from the surface levels where the BGA is typically present during the daytime to carry out photosynthesis.

Other Hume Dam operations

Hume is effectively full, at 99% capacity and the MDBA is actively managing the storage in close consultation with the Bureau of Meteorology and WaterNSW.

Releases to meet downstream demand for water will overtake inflows in coming days and the storage level is starting to decline.

Current forecasts indicate only light rain or dry weather until Monday next week.

Releases were increased to 19 GL/day last Friday and have been steadily reduced as inflows have steadily receded. Today they are starting at 10.5 GL/day.

Since the 1960s, when Hume Dam was expanded to its current size, this is only the 4th time the dam has been above 99% capacity in January. The previous occasion was 28 years ago in January 1994.

The situation is quite dynamic, and our river operators are working round the clock and in close consultation with the Bureau of Meteorology and WaterNSW to manage releases from Hume Dam.

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