Balancing act at Lake Glenmaggie

SOUTHERN Rural Water is balancing flows out of Lake Glenmaggie based on current inflows, in anticipation of late winter and spring rains.

SRW water supply east manager Terry Clapham said staff were following a strategy that was designed to have the storage full at the beginning of the irrigation season, while maintaining some storage space in anticipation of more rain.

“Glenmaggie is close to 90 per cent full, so we are now releasing about 2800 megalitres per day,” Mr Clapham said.

“A wet start to the season means that irrigation demand from the storage will be slow to kick off, and releasing water now allows us to maintain some storage space in the reservoir in anticipation of further winter and spring rains.

“We are also closely following a filling curve so that the reservoir will be full when our customers need the water for irrigation.

“This is a balancing act that we perform most years with Lake Glenmaggie.”

Mr Clapham said the catchment had received more than 200mm of rain since June 1, which meant it was quite wet.

“We estimate it will only need 10mm or so of rainfall to see substantial run-off into Glenmaggie,” he said.

“Our current releases are well below minor flood levels, which start at 7500 megalitres per day.

“Because Lake Glenmaggie is such a small storage compared with the catchment behind it, it has limited capacity to make a big difference during major floods,” Mr Clapham said.

“However, maintaining some storage space gives us some ability to reduce the impact of minor or moderate floods on areas downstream.”

Mr Clapham said Southern Rural Water was monitoring the situation constantly and would make allowances for inflows as well as irrigation demand once the season opened on August 15.

He said the irrigation district allocation was sitting at 65 per cent, but expected this to change.

“Because the storage is now spilling, customers on the Thomson, Macalister Rivers and Rainbow Creek are eligible for spill entitlement now,” he said.

“If current conditions continue, we expect spill entitlement to be available for district customers from August 15.”