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Water resource issues in the Lower Murray Darling Basin. Dr John Tibby Senior Lecturer Geographical and Environmental Studies john.tibby@adelaide.edu.au. Murray Darling Basin. Identified as key threatened system in global scale assessments. Kundzewicz et al . in IPCC (2007). Key questions.
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Water resource issues in the Lower Murray Darling Basin Dr John Tibby Senior Lecturer Geographical and Environmental Studies john.tibby@adelaide.edu.au
Murray Darling Basin • Identified as key threatened system in global scale assessments Kundzewicz et al. in IPCC (2007)
Key questions • Will a weir be built across the River Murray at Wellington? • Can it be justified in terms of the “natural” state of Lake Alexandrina
A weir: why? • Construct across bottom of River Murray to raise/maintain water levels upstream • Karlene Maywald, Water Security Minister, recently said a 30% chance of being built (The Australian, 6th Aug) • Up from 10% last year
Australia is becoming warmer… • Most of the last 20 years have been warmer than average… Source: www.climatechangeinaustralia.gov.au
And drier… • Drying trend for last ~ 50 years Source: www.climatechangeinaustralia.gov.au
Predicted to get worse… • 50% chance of 5% rainfall decline • Perhaps a 25% reduction in stream flow % change Source: www.climatechangeinaustralia.gov.au
Water balance in MDB: 2006 • Average natural flow to the sea: 14,000 GL: • Average irrigation extraction: 11,000 GL source: Ladson (2008) Open channel cotton irrigation near St George, southern Queensland
Water “users” in MDB in 2020 • Canberra bushfire regrowth: 130 GL • Revegetation: 550-700 GL/yr • Climate change: 1100 GL • Living Murray Initiative: 500 GL/year? source: adpated from Lawrie and Williams (2004) Revegetation near Myponga Reservoir, southern Fleurieu
Sth Australian use of Murray • Have a “guaranteed” allocation of 1850 GL • 570 GL: irrigation • 170 GL: domestic water (mainly Adelaide) • 1110 GL: environment • Total storage volume in Basin: 2300 GL
Adelaide water balance • 2003 water use: ~280 GL • Groundwater (bores): 6% • Rainwater tanks: <1% • Desalination plant: 50-80 GL/year • average: 60% from Adelaide Hills catchments, 10% in drought years Mannum: Adelaide water offtake
So… • Will a weir at Wellington be constructed? • My money is on “yes” • Can it be justified in terms of the environment?
Lake Alexandrina: naturally estuarine? • Many claim Lake Alex would have had regular marine incursions • Don’t have a time machine… • Not quite…
Little marine incursion in 7000 yrs Lake Alexandrina diatoms Modified, with permission from Fluin et al. 2007, Hydrobiologia591
In conclusion • Can’t justify letting in marine water in terms of naturalness • However can prevent other environmental problems • Now your questions… Swanport wetland, Murray Bridge
References • Fluin, J., Gell, P., Haynes, D., Tibby, J. and Hancock, G. 2007. Palaeolimnological evidence for the independent evolution of neighbouring terminal lakes, the Murray Darling Basin, Australia. Hydrobiologia591(1): 117-134. • Ladson, A. 2008. Hydrology-An Australian Introduction. South Melbourne, Oxford University Press. • Lawrie, K. and Williams, M.A.J. 2004. Improving salinity hazard predictions by factoring in a range of human impacts in the context of climate change. In: I.C.Roach (ed.) Regolith 2004: Proceedings of the CRC LEME Regional Regolith Symposia, 199-203. Cooperative Research Centre for Landscape Environments and Mineral Exploration • Climate change in Australia: http://www.climatechangeinaustralia.gov.au/ • The Intergovernmental Panel on Climate Change, 4th Assessment Report: http://www.ipcc.ch/