Murray Darling Basin and downstream irrigation
by Mike Young, Ret. DEH and horticultural expert
and Ken Jury, Ret Journalist (Marine & Aquatic Ecology)
26 April 2010
The majority of reference books dealing with Australian natural sciences, be they flora, fauna, pre-colonial wild-life in general or even the fossil record; most deal with the progressive drying out of this continent over time.
Desertification has been occurring here for a very long time. There is often speculation regarding the role of early aboriginal man and the fire-stick in the changes to both vegetation and fauna. However, the past 200 years has seen enormous changes to the demands put on the environment by colonisation.
For much of that time, an attribute of ‘populate the new land’ has been taken. Today, the question arises ’by how far?
We have plenty of land area, but we also have the driest continent!
Ability to make the best use of the little water we have to reliably sustain ourselves in hard times, land is not the limiting factor here, but quality fresh water is.
We must have food production where water and arable land is sited. Piping water enormous distances is both un-practical and un-defendable if the need to defend our country were to arise.
The Miocene history of the lower half of the Murray Darling Basin and the saline nature of soils bordering the river, particularly in South Australia dictates that the Murray’s water will progressively become more saline as one travels downstream. Much of the lower MDB was inundated by the sea for thousands of years, and this legacy remains today.
A truism of horticulture is that a plant can be grown with less water in a low salinity medium when using low salinity water; lower than more saline soils which require relative saline water. A plant must be irrigated heavily enough to flush salt from the root zone to prevent build-up, during irrigation with higher saline water.
This constant leaching is not required with low salinity water and highlights how less water is used when the quality off the water is good.
Obviously, irrigators in South Australia relying on the River Murray have learnt to deal with more saline water than their counterparts upstream in other states.
They still need to be productive, but they also need to be more astute with the selection of crops or similar food industries which can best tolerate the salinity we know to exist here.
Irrigation practices have to be designed around the water quality known to the area. Conservation of water during irrigation has rarely been a consideration and denying food grower’s water is denying food for the community. There is no other serious option.
It is alarmingly obvious that we will not continually receive adequate rains year after year without fail throughout the Murray Darling Basin.
On occasions there may be enough to fill the catchments and even fill the lower lakes for a short period. However, as the population increases, the demand on the basin as a food supplier increases.
Water allocations and buybacks fix the ledger for how much is allocated compared to ten years ago but its not fixing the river, the environment and the wetlands along the river.
It is frustratingly obvious that governments both Federal and State are spending large amounts of money, our money on temporary solutions throughout the drainage. None of these will have permanency except perhaps for the theory of allocation purchase which only show on paper, and then only in the river in times of plenty.
Many in South Australia insist on calling for water to be sent on down the river for the Lower lakes.
Very few recognise that for each 100 gigalitres sent down the river, only about 20 gigalitres will make it to the Lower Lakes. Once in the lakes, it is lost from the river forever. But then during a period of 12 months, water in the lakes is lost to evaporation and so it’s a ‘no win’ situation.
Once past Blanchetown, river water levels are dictated by the levels in the lakes. With uncontrolled flow to the lakes from Blanchetown, the backwaters and lagoons along the river for a 200 km stretch, cannot be flooded to restore them and they become lost as wetland habitats.
The urgent building of a permanent, regulatory weir at Wellington to manage the pool between Blanchetown and the lakes is the only practical option for freshwater management in the river.