WaterNSW has released figures confirming that evaporation and losses due to seepage consumed the majority of the water that made its way into the Menindee lakes system since 2016.
Of the 1937 gigalitres (GL) of inflows received into the lakes since mid-2016, evaporation and seepage accounted for 851GL, or 44 per cent, of the inflows over that period.
386GL or 20 per cent was released specifically for the environmental well-being of the Lower Darling River and Lower Darling Anabranch. Of that 386GL total, 142GL was delivered under the Lower Darling Water Sharing Plan, and a further 244GL via deliveries to government environmental entitlement holders, largely to benefit native fish species.
Lower Darling customers received a further 45GL, while less than 18 per cent – or 340GL – was delivered to the Murray-Darling Basin Authority by the end of January 2018 to meet the demands of NSW, Victorian and South Australian water users.
In the past six months flows into the lakes has decreased significantly with less than 35GL entering the system.
As a result of the low inflows, in December 2017 WaterNSW enacted its Lower Darling Drought Operations Plan to extend supply to landholders and the riverine habitat downstream of the lakes as the upper Darling Catchment continues to receive below average rainfall.
WaterNSW could begin pumping water from Lake Tandure into Lake Wetherell as soon as March 2018 if the prevailing drought conditions continue to dry the Darling River.
Under a worst-case scenario of zero inflows, the WaterNSW Operations Plan ensures the Menindee lakes would still provide water for Lower Darling landholders and environment until at least December 2018, and provide supply to Broken Hill until at least August 2019.
Transferring water from the shallow Lake Tandure to the comparatively deeper Wetherell reduces the surface area of the water storage and thereby cuts evaporation losses.
Without significant inflows, the plan’s next major action would be transferring water from Lake Pamamaroo to Copi Hollow, with the construction of an earthen block bank to separate the two bodies of water.
WaterNSW has implemented a reduced release regime from the lakes to maximise supply to both the Lower Darling and Broken Hill.
Releases into the Lower Darling continue at a rate of 200 megalitres per day (ML/day), with flows at Burtundy of 50ML/day.
The operations plan will endeavour to maintain at least 20ML/day at Burtundy should drought conditions persevere over summer and beyond.
