Questions raised about Wyangala Dam releases following Lachlan Valley floods

Following last November's devastating floods, which caused widespread damage to the tune of an estimated $10 million for producers in the Lachlan Valley, one local farmer has raised concerns about the timing of releases from Wyangala Dam.

Lance Graham, who owns "The Junction", a property near Wyangala, believes there was a lack of action ahead of the rain and subsequent flooding late last year, which only exacerbated the situation.

Looking at WaterNSW statistics, Wyangala Dam was 97 per cent full on October 29, 2021, a week before the floods.

During the next ten days, 1442ML was released from the dam however the dam level increased, reading at 97.7 per cent on November 7.

WaterNSW statistics comparing the two dams between October 29, 2021 and November 7, 2021.

WaterNSW statistics comparing the two dams between October 29, 2021 and November 7, 2021.

Mr Graham said, in comparison, Burrinjuck Dam, which was "likely to spill" at the same time according to WaterNSW, had a total of 106,218ML released and fell from 98.1 per cent on October 29 to 94.4 per cent on November 7.

Graphs show the percentage of effective full storage and daily releases for the two dams between October 29, 2021 and November 7, 2021.

Graphs show the percentage of effective full storage and daily releases for the two dams between October 29, 2021 and November 7, 2021.

"Obviously, the rains and the floods are linked but it was an expected rain event predicted by many and understood by all," Mr Graham said.

"[The data] shows flooding along the Lachlan could have been prevented as was, and proven by, the Burrinjuck Dam management.

"Both [dams] had similar issues and outlooks. Both needed active management to avert disaster - as they said they were doing. However, this only happened for Burrinjuck.

"Wyangala did not receive the same considerations or actions for the same event."

Mr Graham believes water management - rather than continuous debate around the raising of the wall at Wyangala Dam - should be in focus.

"The whole issue of the Wyangala Dam wall raising has been used to disguise a massive problem with the management of this dam and the recent disastrous flooding of the Lachlan," he said.

"I do not have a bias on whether the Wyangala Dam wall gets raised or not. Right now it doesn't matter what comes out of that discussion.

"It only matters that we have the right people and procedures in place to control the dams and river flow."

In response, WaterNSW said substantial releases had been made for several months between rain events to safely lower the Wyangala dam storage level and capture as much of the inflows from the next forecast as possible.

"WaterNSW works closely with the Bureau of Meteorology and regional stakeholder reference panels - comprising local farmers, peak industry bodies, irrigators and local councils as well as relevant government agencies - to plan any changes to storage levels in anticipation of rain-generated inflows, in line with strict operating rules," a spokesperson for WaterNSW said.

"These decisions must also consider future water security and can only occur with high certainty that water released will be replaced by the resulting inflows."

The spokesperson said "it is very difficult to compare operations at the different dam storages as they have different catchment areas and therefore respond very differently to rainfall events".

"Additionally, the Murrumbidgee River valley can handle much larger dam releases without impacting on downstream communities, in comparison to the Lachlan River valley where towns are inundated at much lower release volumes," they said.

"The intense storm event principally responsible for the initial Lachlan valley flooding was well outside forecast expectations and generated huge flows into the dam - reaching a peak of 110 gigalitres (GL) per day - as well as in uncontrolled downstream tributaries.

"With only days since the previous rain event, and the dam storage at capacity as a result, dam operators had little opportunity to lower the storage without impacting downstream.

"Even with significant storage reduction the inflows in the days after the storm event would have resulted in the dam exceeding capacity and spilling."

According to WaterNSW, from July to November 2021, the dam received inflows of 1355 GL, compared to 1110GL of outflows over the same period.

"Not only was 245GL held back from the flooding downstream, but months of temporarily holding back inflows from the dam's catchment served to reduce flood peaks," the spokesperson said.

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