WATER POLICY by Jan BeerNews Weekly
450 gigalitres upwater not feasible on Murray-Darling
, February 25, 2017
The consequences of the 2016 flood flows should now make it blatantly obvious to the Murray-Darling Basin Authority (MDBA) and even to Tony Burke, Shadow Minister for Water, that the extra 450 gigalitres (equivalent to about one Sydney Harbour) of environmental water simply cannot be delivered with neutral or beneficial socio-economic impacts. Nor can that water be recovered mainly through on-farm efficiency measures, due to the vastly diminished critical mass of irrigation water left in the irrigation districts.
As Agriculture and Water Resources Minister Barnaby Joyce has stated, the reality is that sending an additional 450 gigalitres down the river without hurting people cannot be done, and there is not “a hope in Hades” of recovering that water under the specified legal requirements.
As a result of major flooding in September and October 2016 in the Murrumbidgee, Murray and mid-Goulburn rivers, flows to South Australia were of the volume or in excess of the volumes proposed by the MDBA under the Constraints Management Strategy, that is in excess of 60,000 megalitres a day for over five weeks. Flows of 60,000 Ml/day over the South Australian border began on November 11, 2016, peaked at 94,246 Ml/day on November 30 and were then in excess of 65,000 Ml/day till December 18, 2016.
That is, South Australia experienced the highest water levels since 1993, when the flow over the border was 110,000 Ml/day.
Yet, a newspaper notice in South Australia, issued by the Minister for Transport and Infrastructure, Stephen Mullighan, on December 26, 2016, stated that dredging works at the Murray mouth were to start again on January 9, 2017. This dredging was to be continuous night and day and work would take place across the Goolwa Channel, Coorong Channel, on the seaward side of the Younghusband and Sir Richard peninsulas, 1.5 kilometres either side of the Murray Mouth and 100 metres seaward of the high-water mark.
The fact that dredging has recommenced can only mean that the five weeks of flows across the border in excess of 60,000 Ml/day had little or no effect on clearing the Murray River mouth of sand bars.
The flows that are needed to deliver that volume to SA, from upstream in the Murray, Murrumbidgee and Goulburn and their tributaries, are greatly in excess of the so-called “small overbank flows” that the MDBA proposes.
In 2016, peak flood flows in the Murray River at Tocumwal, north of Shepparton, reached a huge 204,000 Ml/day. Yet, with attenuation and evaporation as flows slowly wend their way seaward, less than half reached the SA border, where flows of 40,000-100,001 Ml/day are defined as minor flood level.
The major flood flows in NSW and Victoria in September and October 2016 caused millions of dollars of damage to farmland, crops, infrastructure, both public and private, and were responsible for massive loss of farm and business income.
Floods in Australia are the most costly of any natural disaster, yet these are the flood-flow volumes required to send the MDBA’s proposed environmental flows of 60,000-80,000 Ml/day to SA to achieve the desired environmental outcomes of keeping the Murray Mouth open 95 per cent of the time without the need for dredging or flushing the Murray of salt loads, and maintaining appropriate salinity levels in the lakes.
The MDBA surely cannot believe it has the ability to manipulate flows from the upstream catchments in at least three of the four major river systems, coincide releases from major dams, “piggy-back” them on top of high tributary flows, and deliver these into the major rivers downstream so that they combine to deliver flows over the SA border of specifically 60,000-80,000 Ml/day for a sustained period of five to six weeks.
As we have just seen, volumes in excess of the proposed flow of 60,000-80,000 Ml/day at the SA border have been totally inadequate to flush the Murray mouth clear of sand bars. Moreover the flows would also have needed to coincide with high outgoing tides to have any effect whatsoever.
It is completely pointless attempting to deliver computer-modelled environmental flood flows through very extensive hot, flat, arid areas where the river system simply does not have the ability to force flows through the lakes and out the Murray mouth with sufficient energy to scour the sand bars. Once the Murray enters the drowned estuary of Lake Alexandrina, the waters creep to the sea with a fall of an inch per mile.
As geologist Neil Motton explained several years ago, we have “a mature river system coming off an old Palaeozoic (200-600 million years old) continent, where the erosional nature of the continent has reached a low-energy system”.
“As always these systems have barrier estuaries clogged by years of sedimentation. Sediments held in suspension by freshwater systems invariably drop out of suspension when they hit the saltwater interface of the sea, thus creating these clogged estuaries.
“As a result at the Murray River mouth we have at least 100 kilometres of the Younghusband Peninsula, which is made up of sand dunes. These dunes and beaches are like a large sponge where 90 per cent to 100 per cent of the water coming down from the river seeps out to the sea, apart from the water that doesn’t evaporate in the large shallow basin known as Lake Alexandrina.”
The MDBA has based its computer-modelled environmental flows on a fundamentally flawed perception of how the river and its estuary system works.
It is time that the federal and state governments called an end to the Constraints Management Strategy and the requirement for the additional 450 gigalitres upwater, which can neither be recovered nor delivered without creating huge adverse social and economic impacts.
Jan Beer represents the Upper Goulburn River Catchment Association.