Taming the Mighty Murray

Environmental significance vs economic benefits?

The natural system

Spatial interaction?

Supporting our local wildlife

Under natural conditions:

• Regular, yet unpredictable floods and droughts

• Replenished ecosystems- flood plains and wetlands (which need to be alternatively wet and dry)

• Habitats for birds, fish, invertebrates, plants

• What else?• BUT….

The Murray-Darling is one of the most regulated rivers in the world

What do you notice?

Murrray Darling System

Barrages

Weirs • Weirs with adjacent locks, raise the

water level an average of 3.1 metres, creating a series of stepped pools along the river.

• They were built to provide permanent navigation between Wentworth and the Murray Mouth.

• Pools retained relatively constant levels to help with pumping for irrigation and water supply and storage weir 9 raises the water level high enough to allow for gravity diversion to Lake Victoria.

• South Australia operates weirs locks 1-9. There are 13 navigation locks on the Murray and 2 locks are on the barrages at the Mouth.

Lock and Weir 9

Locks

• Locks allow boats to be lifted or lowered from one level to another along the river.

• There are 2 sizes in the locks on the Murray. Those upstream of the Darling Junction are shorter than those between Blanchetown and Wentworth.

Lake Hume

Why?• Initially for transport of commercial goods e.g.

wool by Paddle steamer to Goolwa (at mouth). Up to 240 steamers used by 1870s. Later became defunct due to rise of cheaper and efficient rail

• Rise of irrigation for crops e.g. Renmark and Mildura- river unregulated and anyone could take water. Desert starts to bloom. Frequent dry years (1896-98 and 1901- Federation drought) called for weirs and reservoirs to control flow

• Variable climate across basin requires variety of ways of water use to meet different needs. E.g. cotton, rice, fruit, veg, cattle etc

• Peak demand for water in summer didn’t match natural flow (snow thaw in spring)

Brief History…• 1915- River Murray Agreement established• 1917- River Murray Agreement signed, water sharing with

NSW and VIC, SA guaranteed minimal quality of water.• 1919-36 Hume Dam built and Lake Victoria• Over next 40 years, many weirs and dams built to provide

water supply for irrigation. Now important agriculture area with 39% Australia’s gross value in agricultural production

• Barrages built at mouth to prevent sea water from entering lakes during low flow- increase land productivity in area

• Snowy mountains scheme diverted water into the Murray catchment 1949-66, increase amount of water

• 1998- Cap on water diversions for NSW, SA and VIC (p166 NP)

• Native Fish Strategy (2003), Living Murray initiative (2005)

Circle of viewpoints

Turn to page 173 of NP

• Discuss the strengths and weaknesses of river regulation in the MDB.