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Lack of rain or too much extraction?
This article is part one of a series on Murray Darling water and implications for sustainability. You may wish to view other posts related to this issue, below. I have used information from the following:
MDB is short for Murray-Darling Basin.
Gl means 1,000,000,000 litres of water - approximately the size of 400 Olympic swimming pools
Ml means 1,000,000 litres of water. This enough to cover a hectare to a depth of 10cm on a quarter acre block (~0.1 hectares or 1000 sq m) to 1 metre high.
Given the extensive coverage of fish kills and water shortages below the upper Darling river regions, I thought it would be useful to analyse the likely cause of the non-flowing river. The first source for this analysis is the Barma Water Resources, ‘Northern Basin Historic Flow and Usage Report’ (April 2018)
The most important conclusion for this analysis is that rainfall has been lower than average over the five year period to 2017. The rainfall has not been as low as that during the millennium drought. However, mid basin flows (Bourke) have been about the same as in the millennium drought.
See also this more detailed map from the MDBA
Water is therefore disappearing. Part of that is through evaporation and part is through extraction. One of the most vexed issues with extraction “entitlements” is that State Governments have allowed for the “entitlement” to be extracted even when flows in the rivers are low and to allow overextraction (up to 300%) under some circumstances. The details of these arrangements vary across borders as do interpretations across local authorities. What we see as a result is a mess that renders glib statements that extractions are “within the cap” fairly meaningless. The most common reason given for irrigators not using their entitlement is “that there was no flow in the river to allow extraction”
What really matters is the science. Also a bit of economics and understanding of social impacts.
What does this mean? Firstly lets work out how much water goes onto a Ha for these farm uses. A Hectare is 100m squared or 10,000 sq metres. It takes 1000 litres (1 kl) to cover a square metre to a depth of 1 m. 10,000 kl or 10Ml would cover a hectare to a depth of 1m. We can see that cotton is the second most intensive use for water. Rice uses much more and vegetable production is very efficient with large yields per Ha. Viticulture is also very efficient and profitable.
Fortunately for the health of agriculture across the Basin, water to the Southern Basin comes mainly (around 86%) from the South.
Also some statistics and facts:
72% of irrigated farming is in the Basin
43% of farms are in the Basin
50% of crops are in the Basin
50% of fruit and vegetables come from the Basin
92% of cotton comes from the Basin
almost 100% of rice comes from the Basin
74% of grapes come from the Basin
50% of sheep/wool comes from the Basin
34% of dairy cattle are in the Basin
34% of wheat is grown in the Basin
Rafting, Skiing, water sports, fishing, cruising, sailing golf and much more
This is worth more than double the value of cotton and unarguably has less environmental impact
About 2.8 million people live within the Basin itself. Canberra, Toowoomba, Bendigo, Albury and Wagga Wagga are notable. 3.5 million people use water from the Basin
The basin is home to representatives of the oldest living cultures and early evidence of agriculture dating from 40,000 years ago
Without water, Basin communities cannot survive – economically nor physically
Population distribution is in line with water availability. The mid to lower Darling is sparsely populated by comparison with the North East of the Basin and the Southern Basin. The low population in the mid to lower basin means there is less political clout to counteract wealthy lobbies.
Intensive agriculture is practiced in the northern basin and along the east and south margins adjacent to the Great Dividing Range.
Irrigated farming is seen across than 70% of the Basin, however only 2% of the basin land is in fact irrigated. For a Basin that is a million square km in size, that is still quite a lot.
Milling, wineries, tourism/recreation, commerce, agribusiness canning plus other manufacturing and service industries are dependent on water.
80 species of mammals, with 62 extinct and 10 endangered
55 species of frogs, with 18 endangered
46 species of snakes, with five endangered
5 species of tortoises, with none endangered
34 species of fish, with up to half either threatened or of conservation significance
Cubbie Station uses over 90% of cotton irrigation water. Its dams hold up to 200,000 Ml
Total private storages could contain as much as the Public storages and is at least half 2
The major tributaries of the Darling River are the Border Rivers in NSW (35% of inflows), Namoi (25%), Condamine (20%), Gwydir (10%), Castlereagh & Macquarie (5%), and Paroo and Warrego (5%).
All tributaries except the Macquarie are summer-flowing rivers, that is, their flows are derived mainly from summer rainfall
The Darling River provides about 12 percent of the total annual flow of the Murray River.
The Paroo and Warrego rivers are highly unpredictable, and usually do not reach the Darling River.
Average flows past Menindee in the 21st Century have been 1,800,000 Ml per annum. Around 60% of that in the 20th Century.
For full details and authoritative data see: http://www.bom.gov.au/water/nwa/2017/mdb/index.shtml
The catchment of the Murray has been in a severe drought, but not the Darling catchment. BoM records show that for the five years to 2017 rainfall over the whole Darling catchment has ranged from slightly below average to very much above average. But water flows down the Darling have dropped right off, and Menindee Lakes are down to much less than 20 percent.
Lets consider the value of water for two regions. First the Northern Basin and then the combined mid and lower Darling communities.
The farming communities in the Northern Basin get first use of the water in the tributaries to the Darling. They use it for high value intensive farming and cotton. They can get their domestic and industrial water from dams located in local valleys. The rainfall is generally sufficient to provide tank water and grow most crops, horticulture and graze animals. Irrigation water is therefore to increase production of higher value produce.
In the mid and lower Basin, below Bourke, water is scarce with low and inconsistent rainfall. There are few places to build dams for towns. Communities are generally smaller and scattered because of the climate and low productivity of the land. Without water in the Darling, these communities have almost nothing. Irrigation in this part of the river is more to maintain subsistence than make larger profits – as in the Northern Basin. Basic needs like drinking, washing and cooking water are met by the river.
So where has the water disappeared to?
Average annual runoff into the tributary rivers in the Darling Basin is about 7,000,000 Ml. In 1960, about 50,000 Ml were extracted for irrigation. By 1991 extraction increased to 1,400,000 Ml. By 2012 the annual surface water used in the Darling Basin was about 4,200,000 Ml . Most of this increase in water extraction is due to expansion of the cotton industry. Cotton farms like Cubbie Station extract water from rivers and store it in large, shallow dams that have high evaporation rates. The water is not used until the next cotton growing season starts. Cotton fields are flooded several times to saturate the soil and promote growth for the cotton plants. That water cannot be returned to the rivers, because it contains fertiliser, pollutants and salt.
See also: State of the Darling Report 2007 – Webb, McKeown & Associates Pty Ltd and ABARES and BoM. One Gl is the same as 1,000 Ml.
A more insidious cause of water disappearance is theft. In MDBA and National Water Accounting there is an allowance for errors. Those errors should more rightly be referred to as potential illegal extraction. There will be some errors resulting from calculations around groundwater and evapotranspiration, however, any thorough investigation into water theft will undoubtedly result in discovery of more ways farmers have diverted water that they should not have been entitled to.
Tragedy of the Commons
It appears to me that we have a classic example of The The tragedy of the commons is a term used in social science to describe a situation in a shared-resource system where individual users acting independently according to their own self-interest behave contrary to the common... More; where a common resource can be consumed by a small number of powerful and early exploiters of the resource to the detriment of others without the means or access to use the resource themselves. This is a human failing that has been observed over millennia and it is happening in the Murray-Darling Basin. Yes, there is a drought. The low rainfall is not the actual cause of the low water flows. It is over extraction of water. That simple.
What can we say about the fish kills due to blue-green algae? Low water flows are the largest root cause for these events, high temperatures contribute and the load of phosphates in the water plays its part. The algae thrive in warm water, phosphate rich but nitrogen poor water. This is exactly what you get when there is a low flow rate in a large river running through agricultural land. More water in the river would dilute the concentration of algae and move it on and it is not the whole story. The whole story includes climate change, agricultural practices, and water resource in a complex interaction.
Bottom line: Water extraction has continued in the upper Darling basin at unsustainable levels. If extraction of High Security Water had been limited and marginal to illegal extractions been stopped, then there would have been sufficient water in the Darling to allow for the river system to survive. As it is, the extraction of water to make private economic gains has directly led the Lower Darling Basin to the brink of An ecosystem is considered collapsed when its unique biological and other natural features are lost from all previous occurrences.Ecosystem collapse could be reversible and is thus not completely equivalent to species extinction.1 Ecosystem collapse can... More.
Now we can take a look at the economic value per Ha for each of the farm use types. I have done an analysis to update the early 2000s estimates. There will be a separate post on this analysis that considers what might be the best use of water.Notes and Further Reading
- MDBA latest figures
- there is difficulty accounting for all farm dams because they are unregulated and depth cannot be adequately measured form aerial data