Water resource issues in the Lower Murray Darling Basin

Dr John TibbySenior LecturerGeographical and Environmental Studiesjohn.tibby@adelaide.edu.au

Murray Darling Basin

Kundzewicz et al. in IPCC (2007)

Identified as key threatened system in global scale assessments

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…

Source: www.climatechangeinaustralia.gov.au

Drying trend for last ~ 50 years

Predicted to get worse…

50% chance of 5% rainfall decline Perhaps a 25% reduction in stream

flow

Source: www.climatechangeinaustralia.gov.au

% change

Water balance in MDB: 2006 Average natural flow to the sea:

14,000 GL: Average irrigation extraction:

11,000 GL

source: Ladson (2008)source: Ladson (2008)

Open channel cotton irrigation near Open channel cotton irrigation near St George, southern QueenslandSt 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 source: adpated from Lawrie and Williams (2004)Williams (2004)

Revegetation near Myponga Revegetation near Myponga Reservoir, southern FleurieuReservoir, 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 Total storage volume in Basin: volume in Basin: 2300 GL2300 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 Mannum: Adelaide water offtakewater offtake

Water level is going below offtakes…

Water level at Morgan (m above sea level)

2

4

6

8

10

Jul-74

Jul-77

Jul-80

Jul-83

Jul-86

Jul-89

Jul-92

Jul-95

Jul-98

Jul-01

Jul-04

Jul-07

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…

The answer is in the mud…

Lake Alexandrina diatoms

Modified, with permission from Fluin et al. 2007, Hydrobiologia 591

Little marine incursion Little marine incursion in 7000 yrsin 7000 yrs

In conclusion

Can’t justify letting in marine water in terms of naturalness

However can prevent other environmental problems

Now your questions…

Swanport wetland, Swanport wetland, Murray BridgeMurray 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. 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/

The Intergovernmental Panel on Climate Change, 4th Assessment Report: http://www.ipcc.ch/