Location
The Murrumbidgee River is in central NSW, Australia. It starts in the Fiery Range of the Snowy Mountains, 1600 m above sea level.
The total catchment area is 84,000 km2, with the main river reach from its source to its confluence with the Murray River stretching 1479 km.
The Lower Murrumbidgee Catchment has a 948 km reach. It starts downstream of Burrinjuck Dam, north of Wagga Wagga and finishes at the confluence with the Lachlan River at Redbank Weir, near Balranald in South-Western NSW.
The Burrinjuck Reservoir catchment area is 13,000 km2. Below the dam that was built in 1913, the river flows through a rugged narrow gorge before emerging into the western plains near Gundagai.
The other major surface water storage in the area is Blowering Dam, built on the Tumut river in 1968. The dams can hold 1026 GL and 163 GL respectively. The Snowy scheme can also store water and provide flows to the Murrumbidgee system via Blowering Dam and the Tumut River. There is also an en route storage at Tombullen (113 GL) upstream of Gogeldrie Weir.
The largest tributary below Burrinjuck Dam, Tumut River has a contributing catchment area of 4,000 km2. Several other minor unregulated tributaries join the Murrumbidgee River between Burrinjuck Dam and Wagga Wagga, before the alluvial flood plains of the river widen into broad plains below Berembed Weir, 30 km upstream of Narrandera.
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Climate
The Murrumbidgee valley's climate varies from cooler high country in the east to the hot plains of the west.
Its annual rainfall varies from more than 1500 mm in the high country to less than 400 mm on the western plains. The annual evaporation averages about 1000 mm to 1800 mm, respectively, for the same regions.
Under average climatic conditions about 24% of the rainfall in the 28,000 km2 river catchment above Wagga Wagga appears as runoff.
Below Wagga Wagga, the runoff coefficient is less than 2%.
Estimated groundwater storage in the Murrumbidgee Basin is around one million GL, of which around 98% is in alluvial deposits. About 270,000 GL of this is of good quality (EC <1.5 dS/m), with an estimated safe yield of about 1600 GL/year.
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Water delivery
The major diversion structures in the study area include Berembed, Yanco, Gogeldrie, Hay, Maude and Redbank weirs.
The main water users, who account for 85% of total consumptive use in the study area, are Murrumbidgee Irrigation Ltd (average annual allocation >1200 GL) and Coleambally Irrigation Cooperative Limited (CICL) (about 500 GL average annual allocation).
The Murrumbidgee Irrigation Area and Districts (MIA) comprises 2,408 farms (480,444 ha) in five sub-districts - Mirrool, Yanco, Benerembah, Tabbita and Wah Wah. The Coleambally Irrigation Area consists of 332 farms stretching over 79,000 ha.
Total surface water abstractions from the Murrumbidgee from 1988 to 1994 constituted 23.5% of all surface abstractions in the Murray Darling Basin, according to a 1995 MDBC report. The current total groundwater abstraction downstream of Narrandera is more than 100,000 ML a year from the good quality and high yield aquifers, which have bore abstraction rates of up to 400l/sec.
Both temporary (between the Murrumbidgee, Murray and Lower Darling systems) and permanent transfers of regulated flow entitlements can occur within the Murrumbidgee catchment.
Possible further storage sites to improve flow regulation in the Murrumbidgee River include Lake Mejum off-river storage, immediately north of Narrandera, which would have around 450 GL capacity).
Natural yearly flows in the Murrumbidgee average about 3,800 GL, two thirds of that in the five months from June to October.
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Outputs
Agricultural production in the Murrumbidgee Catchment is worth $1 billion a year, more than 16% Australia’s total agricultural production.
Combined irrigated agriculture is worth around A$408 million, with the region serviced by more than 10,000 km of irrigation channels.
The MIA is Australia's largest wine grapes producer and home to about 80% of NSW carrot and 90% of potato production.
More than 520,000 people live in the Murrumbidgee catchment, including 305,000 people in the Australian Capital Territory, with an annual population growth rate of 1.5%.
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