Water

Irrigators point to lower lakes issue

By Geoff Adams

If you want to get up the nose of Murray Valley irrigators facing low or zero allocations, ask them about the amount of water flowing into the lower lakes of the Murray River in South Australia.

They will tell you that gigalitres of water are currently being emptied into the river to keep the lakes fresh and to prevent the Murray Mouth from closing.

They will also tell you that the system is propping up a false notion that the lower lakes should be freshwater, when there is plenty of historical evidence that the lakes are in fact estuaries which were saltwater.

This view was raised several times at a Speak Up Campaign meeting at Cohuna last week, when about 50 irrigators gathered to work out strategies to get their needs recognised at a political and community level, and to hear about European carp control in the Murray Darling basin.

Lake Alexandrina, in the lower lakes, was described by one person as the fourth largest storage on the Murray system, but one which never delivered water for productive use.

The Murray-Darling Basin Authority reports about 1200Gl of environmental water from a number of water holders, including return flows from environmental watering events upstream, was co-ordinated to target continuous barrage flows and fish movement, improve water quality and lower salinity in the Coorong and Lower Lakes in the 2016-17 year.

Documents held by the authority state:

‘‘Prior to European settlement, the Lower Lakes were predominantly fresh, with river water discharging to the sea keeping the Murray Mouth open.

‘‘Saltwater intrusion to the Lower Lakes was not common until after 1900 when significant water resource development had occurred in the River Murray system. Only small areas of the Lower Lakes, around the mouth and channels, would be impacted by saltwater intrusion during periods of low river flow or significant storm surges.’’

But the Speak Up Campaign people point out that explorer Charles Sturt, who navigated the Murrumbidgee and Murray rivers in 1839, found the Murray Mouth closed. Other examples are quoted supporting the idea that the lakes were once estuarine.

The irrigators also point to a historic drainage system which redirected overland flows of water away from the Coorong, thus reducing the inflow into the lower lakes.