1. Water resource issues in the Lower Murray Darling Basin Dr John Tibby Senior Lecturer Geographical and Environmental Studies john.tibby@adelaide.edu.au

2. Murray Darling Basin Kundzewicz et al. in IPCC (2007)  Identified as key threatened system in global scale assessments

3. 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

4. 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, 6 th Aug)  Up from 10% last year

5. Australia is becoming warmer…  Most of the last 20 years have been warmer than average… Source: www.climatechangeinaustralia.gov.au

6. And drier… Source: www.climatechangeinaustralia.gov.au  Drying trend for last ~ 50 years

7. Predicted to get worse…  50% chance of 5% rainfall decline  Perhaps a 25% reduction in stream flow Source: www.climatechangeinaustralia.gov.au % change

8. 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

9. 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

10. 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

11. 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

12. Water level is going below offtakes…

13. So…  Will a weir at Wellington be constructed? My money is on “yes”  Can it be justified in terms of the environment?

14. Lake Alexandrina: naturally estuarine?  Many claim Lake Alex would have had regular marine incursions  Don’t have a time machine…  Not quite…

15. The answer is in the mud…

16. Lake Alexandrina diatoms Modified, with permission from Fluin et al. 2007, Hydrobiologia 591 Little marine incursion in 7000 yrs

17. 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

18. 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. Hydrobiologia 591(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/ http://www.climatechangeinaustralia.gov.au/  The Intergovernmental Panel on Climate Change, 4 th Assessment Report: http://www.ipcc.ch/