2. Rivers of the Murray-Darling Basin

When all the rivers, creeks and water courses are plotted on a map, the Basin appears to have a mass of waterways. However, many of these only carry water at times of flood - for the rest of the time, they are dry.
The nature of the Murray-Darling Basin means that, for much of their lengths, the majority of the rivers flow over plains. One consequence of this is that their individual courses are far from simple, as they meander across their floodplains. The actual course of the Darling is about three times as long as the direct distance that is involved.

Another consequence of the nature of the Murray-Darling Basin is that the rivers generally have extremely low gradients. As a result, under normal conditions, changes in flow propagate down them relatively slowly. Table 3 provides approximate travel times in sections of the River Murray and the Darling River, when flows are contained within the river banks. During floods, the travel times of the flood peaks are slower due to the effects of the floodwaters spreading out over the floodplains.

Section of river	Distance (km)	Time (days)
Hume to Yarrawonga	237	4
Yarrawonga to Torrumbarry	358	7
Torrumbarry to Swan Hill	220	4
Swan Hill to Euston	294	4
Euston to Wentworth	289	7
Wentworth to Lock 9	60	1
Lock 9 to Lock 7	69	1
Lock 7 to Lock 1	422	4
Lock 1 to Wellington	203	5
Menindee to Wentworth	507	13

Table 3 . Illustrations of travel time of flow wave in the Murray and Darling Rivers (source: MDBC RMW)

The Darling is the longest river in Australia, measuring 2,740 km from its source to its confluence with the Murray at Wentworth. The Murray is 2,530 km long from its source in the Australian Alps to its mouth on Encounter Bay in South Australia. For 1,880 km of its length, the river marks the border between New South Wales and Victoria. The actual border is defined as the top of the bank on the Victorian side of the river, meaning the main river channel itself is in NSW. The Murrumbidgee is 1,545 km long. The Darling, Murray and Murrumbidgee are among the world's longest rivers. The longest continuous stretch of river is from the source of the Condamine, about 100 km south-west of Brisbane, to the mouth of the Murray, less than 100 kilometres south-east of Adelaide, a distance of approximately 3,750 km.

While the Darling, Murray and Murrumbidgee are the longest rivers, they are but three of the twenty three major rivers in the Basin (Table 4). Between them, these major rivers have hundreds of tributaries. Each of the rivers have unique features with different hydrology and ecology according to the natural climatic and biophysical conditions of the region, and recently due to the human impacts of urban and water resource development

State	River	Length (km)	Area (km2)
Queensland - New South Wales	Border	557	49,500
	Moonie	390	15,800
	Condamine - Culgoa	690	15,000
	Warrego	800	72,800
	Paroo	530	76,200
New South Wales	Lachlan	1,484	84,700
	Macquarie -Bogan	960	73,700
	Castlereagh	549	17,700
	Namoi	858	43,100
	Gwydir	668	25,900
	Macintyre	321	22,550
	Murrumbidgee	1,575	84,000
	Darling	2,740	174,800
Victoria - New South Wales	River Murray – upstream of Hume Dam	306	15,300
Victoria	Mitta Mitta	219	4,720
	Kiewa	184	2,050
	Ovens	227	7,850
	Broken	192	7,330
	Goulburn	563	16,800
	Campaspe	245	4,020
	Loddon	392	15,400
	Avoca	269	12,000
	Wimmera-Avon	290	23,400

Table 4 . Major rivers of the Murray-Darling Basin (source: MDBC) (To be revised)

System	Runoff (GL/year)	Inter-Basin Transfers (GL/year)
New South Wales
Border Rivers	586
Gwydir	910
Namoi/Peel	716
Macquarie/Castlereagh/Bogan	1,656
Barwon-Darling Lower Darling	106
Lachlan	1,054
Murrumbidgee	4,184	550
Murray	2,084	284
Western Plateau
Total NSW	11,295	834
Victoria
Goulburn Broken Loddon	4,243
Campaspe	305
Wimmera-Mallee	316	79
Kiewa Ovens Murray	4,455	284
Total Victoria	9,319	363
Total South Australia	132
Queensland
Condamine/Balonne	1,500
Border Rivers /MacIntyre Brook	586
Moonie	116
Warrego	419
Paroo	483
Total Queensland	3,104
Total Murray-Darling Basin	23,850	1,196

Table 5 . Average Annual Run-off and Inter-Basin Transfers

[top]

2.1 Surface water resources in detail

Detailed information on the water resources of the Basin's major catchments is shown in Table 5, with the catchments shown in Figure 1.

There is considerable variation in runoff from one part of the Basin to another. Further, runoff bears little relationship to catchment size (Figure 1). The catchments draining the Great Dividing Range on the south-east and southern margins of the Basin make the largest contributions to total runoff. For example, the Murrumbidgee and Goulburn, Broken, Loddon river catchments account for 35 per cent of the Basin's total runoff from 12 per cent of its area. The Upper Murray catchment alone accounts for 17.3 per cent of runoff from 1.4 per cent of the Basin. By contrast, the Darling group of rivers contribute 31.7 per cent of the Basin's mean annual runoff from 60.4 per cent of its area. The Darling catchment itself accounts for 10.9 per cent of the Basin's area but only 0.4 per cent of mean annual runoff.

Interbasin transfers are also a feature of the system with water being transferred into the Murray-Darling Basin via the Snowy River scheme and the Wimmera-Mallee scheme from the Glenelg River system. However, these flows are only equivalent to 5 per cent of the natural run-off.

Except during very wet years some 86 per cent of the Basin contributes virtually no runoff to the river systems, except during floods (Figure 3). It is perhaps not surprising that the name of the Warrego river in the north-west of the MD basin means "river of sand".

[top]

2.2 Variability of river flow

Australia's climate, compounded by the variability of its rainfall, means that virtually all of Australia's river systems are subject to considerable variability of flows from one year to another. In fact, on a global scale, Australia (together with Southern Africa) experiences higher runoff variability than any other continental area (McMahon et al. 1992). The Murray-Darling Basin is no exception to this, in spite of the fact that much of the river system is now highly regulated. By way of illustration, Figure 4 shows natural inflows into the Hume Reservoir over a period of one hundred and thirteen years, showing not only the normal seasonal variations in any one year, but also the very great variations from one year to another. Over the period 1894-1993, the annual discharge at the mouth of the Murray-Darling system has ranged from 1,626 GL to 54,168 GL, with a mean of 10,090 GL and a median of 8,489 GL (Maheshwari et al. 1995).

The storages and other regulatory structures smooth out many of the smaller flow variations, but they have only limited impact on the major floods. In times of drought, the storages, provided they contain water, add to river flows.

For the Murray and Murrumbidgee, the high and relatively reliable precipitation in their source areas means that stream flow is much more reliable than in other parts of the Basin. But even for some of their tributaries, there are significant exceptions, notably the Broken and Avon Rivers. However, these variations are small in comparison with those of the Darling River and its tributaries (Table 6 & Figure 5). These rivers not only experience massive floods, as indicated above; they can also cease flowing for extended periods. The Darling provides some of the most extreme examples. At Menindee, between 1885 and 1960, it ceased to flow on 48 occasions. The longest no-flow period was 364 days in 1902-03. Flowing now?

Major flooding can affect particular catchments or groups of catchments, such as on the King, Ovens and Broken Rivers in early October, 1993. Because much of the Basin is in effect a vast floodplain, flooding can be very extensive. In April 1990, large areas along the Darling and a number of its tributaries, as well as other areas to the north in Queensland, were inundated. The flooding was among the most extensive and dramatic recorded, covering in total (within and beyond the Basin) more than one million km2, with a total damages bill well in excess of $250 million. Record floods on the Warrego and Bogan Rivers resulted in the total inundation of Charleville and Nyngan (respectively) (NSWDWR 1990). Floods, like droughts, are part of the Basin's environment, the extreme manifestations of Australia's climatic variability. Fish, trees, and waterbirds, as well as most native flora and fauna, are dependent for key parts of their ecology on floods. In order to better manage them, strategies are being developed which take account from the human impacts and the ecosystem benefits they bring.

Figure 4. Natural inflows to the Hume Reservoir, 1891-2004, in GL per month


Figure 5. Variations in average annual streamflow for selected rivers in the MDB (source: MDBMC 1987)

System	Current Conditions Average Flow (GL/year)	Natural Conditions Average Flow (GLyear)	Current Average / Natural Average (%)
Hume Reservoir Inflows (Including Snowy Transfers)	4750	4183	114%
New South Wales Tributaries
Border Rivers1 2	155	258	60%
Gwydir at Yaraman, Garah and Collarenebri less d/s use	439	726	60%
Namoi River at Mollee Weir less d/s use	598	833	72%
Darling River at Wilcannia	2150	3590	60%
Lachlan River at Oxley + Willandra	338	439	77%
Murrumbidgee System - Balranald + Darlot	1476	2782	53%
Lower Darling River at Burtundy	1137	2120	54%
Victorian Tributaries
Kiewa River at Bandiana	672	682	99%
Ovens River at Wangaratta	1614	1640	98%
Goulburn River at McCoys Bridge	1428	3538	40%
Campaspe River at Rochester	162	300	54%
Loddon River at Loddon Weir	120	241	50%
Queensland Tributaries
Culgoa	231	512	45%
Bokhara	32	53	61%
Narran Lake Outfl ow	61	156	39%
Border Rivers1,2	155	258	60%
Moonie River1	98	140	70%
Warrego River1	63	71	89%
River Murray
Albury	5402	4907	110%
Yarrawonga	4988	6463	77%
Euston	6646	12588	53%
South Australian Border	6702	13871	48%
Barrages	5071	12896	39%

1 Draft Water Resource Plan Limits
2 Half outflow attributed to NSW and half to Qld
Note: The average annual current or natural conditions flow is the average of 109 years (1891-2000) of modelled current or natural conditions flow. The modelled information comes from the MDBC River Murray model and the States' tributary models.

Table 6. Average Annual Flows at Selected Sites in the Murray-Darling Basin

	Natural Conditions (GL/year)	Current Conditions (GL/year)
Runoff 1	23,850	23,850
Inter-Basin Transfers2	0	1,200
Diverted3	0	11,580
Evaporated from Reservoirs4	0	1,430
Consumed by wetlands, floodplains etc	10,960	6,970
Outflow to Sea5	12,890	5,070
Outflow to Sea as a % of Runoff	54%	21%

1 Table 3 Page 25, National Land and Water Resources Audit, 2000.
2 Average Inter-Basin Transfers from modelled output from Snowy Hydro Limited and historical data from Wimmera-Mallee Water.
3 MDBC Water Audit Monitoring Reports.
4 Average for 1998-2002 from MDBC Water Audit Monitoring Reports.
5 Output from the MDBC MSM_Bigmod model May 2003.

Table 7. Average Annual Water Balance for Murray-Darling Basin Rivers

[top]

2.3 River Losses and End of System Flows

Much of the Murray-Darling Basin is in arid or semi-arid areas. The Avoca, Gwydir, Macquarie, Narran, Warrego, Paroo and Lachlan all flow into large wetlands, floodplains and floodplain lakes systems in which a large percentage of the water is evaporated or transpired by vegetation. Using computer models, it has been estimated that under natural conditions almost 11,000 GL/year is consumed in wetlands, on the floodplains or by evaporation from the river surface and that only 12,890 GL/year or 54% of the runoff reaches the sea.

Some of the water that would have been consumed by wetlands and the floodplain under natural conditions is now used for irrigation or is evaporated from reservoirs. For this reason, there is not a one-for-one relationship between an increase in diversion and a reduction in outflow to the sea. Table 7 summarises the water balance in the rivers of the Murray-Darling Basin under natural and current conditions.

[top]