Water

Lake serves many purposes

By Geoff Adams

Lake Mulwala was created by the damming of the Murray River in 1935 to raise the water level for gravity irrigation in NSW and Northern Victoria.

It has become a centrepiece of Yarrawonga and Mulwala’s development as thousands of people enjoy water sports and fishing on the lake.

Many people have opted to retire to the town, pushing Yarrawonga’s population to 7000 with an average age of 48, about 10 years older than the Australian average.

The river’s annual flow is diverted to the Yarrawonga Main Channel and the Mulwala Canal.

According to Goulburn-Murray Water, the Yarrawonga Main Channel services the Murray Valley Irrigation Area of Victoria, which extends from Yarrawonga to Barmah and south to the Broken and Nine Mile Creek systems.

The channel has a discharge capacity of 3100Ml/day and distributes water to an area of 128000ha via a network of six main channels and 261 spur channels.

The Mulwala Canal is a much larger structure and has an off-take capacity of 10000Ml/day.

Water diverted through the Mulwala Canal supplies the Berriquin, Denimein, Deniboota and Wakool irrigation districts in southern NSW. The total annual water allocation to these districts exceeds 1000000 Ml over an area of 700000ha.

A unique feature at Yarrawonga Weir is the fish lift located adjacent to the power station. Constructed in 1994, the lift provided the first opportunity in 60 years for fish to travel upstream of the weir.

A hydro-electric generation facility at Yarrawonga Weir was commissioned in June 1994. The facility has a maximum capacity of about 9.6MW.

The lake was drained in 2011 to rid the water of an invasive weed.

It will be lowered by about 3.5m this winter to facilitate works around the lake foreshore and weed control.

Murray-Darling Basin Authority’s river management head Andrew Reynolds said locals and visitors to Lake Mulwala and Yarrawonga Weir might notice changes to water levels from the end of April.

‘‘We’re undertaking this work in conjunction with Goulburn-Murray Water to improve infrastructure at the lake and to control invasive aquatic weed,’’ he said.

‘‘We plan to have the lake back to its usual level in early August.

‘‘Lake levels will start to fall slowly from April 30 by about 70cm until mid-May when the irrigation season ends.’’