Significance of Murray River

A Historical Snapshot

To understand what's happening in the Murray River system today we need to look at history, of a time long ago and of the time since 

European settlement. Here is a very brief overview.

  • The Murray River has existed for more than 60 million years.

  • 6 million years ago Swan Hill would have been a coastal town; the sea had covered large areas of continental Australia. 

  • By about 2 million years ago the sea had retreated leaving behind sediments. Also ancient river streams discharged into a very large lake - Lake Bungunnia - that stretched from Euston to Mannum. This lake persisted until about 500,000 years ago.

  • By about 900,000 years ago, the sea had retreated to a level about 130 metres lower than it is today. The Murray cut through deposited sediments - 65 metres deep at Lake Alexandrina - and all the way out to the edge of the continental shelf.

  • Uplift at sections along its course have caused re-routing of the Murray. The Cadell Fault between Echuca and Deniliquin occurred about 25,000 years ago.

  • The Murray generally oscillates about 4 km across its journey downstream, except for a narrow gorge - the "Murray Gorge" - that stretches from Overland Corner to Mannum.

  • Sea level rise at the end of the last glacial period - 17,000 to 6,000 years ago - caused the Murray to deposit sediments for half the gorge depth.

  • Humans have occupied the river valley for about 40,000 years.

  • Europeans began using the Murray River commercially a little more than 150 years ago when the first paddlesteamers were used for trade.

  • Victoria began irrigation from the Murray in the 1870s.

  • Disputes about irrigation versus navigation between Victoria and South Australia, and the involvement of NSW and the fledgling commonwealth government, resulted in the River Murray Waters Agreement in 1915, but only after 13 years of argument and negotiation. Has anything changed today?

  • The Agreement provided for water-sharing, water storages, 26 locks and weirs extending up to Echuca, but was amended in 1924 and 1934 respectively to allow for 14 locks and weirs, flood diversion weirs on the Murrumbidgee, and 5 barrages near the Murray mouth.

  • Menindee Lakes storage, Hume Dam, and the Snowy Mountains Scheme were all constructed in the years after 1949, and concluded with the opening of Dartmouth Dam in 1979.

  • Construction of the barrages was a concession to South Australia for the exclusion of some of the original 26 locks and weirs, so as to prevent ocean intrusions into the lower lakes thereby making them fresh-water bodies for land development and irrigation purposes.

  • In the space of a few decades the Murray became a totally regulated system.

Source : "The Murray", Murray-Darling Basin Commission, 1990

Impacts of Man on the Murray

The next link in understanding the Murray River's condition today is about how natural flows have been changed and the consequences that have resulted.

Major impacts include :

  • native vegetation clearance throughout the Basin catchment, including in South Australia, where in many areas rising groundwater has resulted because of the diminished interception capability from vegetation loss

  • diversion of water to irrigation channel systems - first diversions began in 1870 at Kerang in Victoria, and have continued right up to the present day

  • a "Cap" on water extractions was introduced in 1994 with the agreement of NSW, Victoria, and SA

  • reservoirs and dams affect the flow regime, and locks and weirs have caused artificial water levels that have resulted in flooding and death of large areas of redgum

  • irrigation water diversions have reduced river flows substantially; the effects have been almost catastrophic in recent years years as witnessed by the impacts of the long drought on thge Lower Lakes of the Murray

  • storages and weirs have resulted in the reversal of natural seasonality of flows 

  • the frequency of natural mid-range flows has diminished by up to 5-fold

  • feral fish species have resulted in the decimation of the native fish species

South Australia - A Dry State 

In the drought years to 2009, falling water levels in Lake Alexandrina and Lake Albert exposed acid sulphate conditions in the bottom of the lakes.

  • One response was to allow the return of the estuarine system with sea water, however the problem with this approach would be to destroy the existing freshwater ecosystem that had been favoured since the installation of the barrages in the 1920‘s.

  • Average rainfall in the MD Basin is 480 mm/year; in SA the average rainfall along the Murray River corridor varies between 275mm and 400mm annually. 

  • Average annual inflow into the Murray is 508,000 GL/year. Compare this with potential evaporation of 1,968 mm/year or 2,070,000 GL/year

  • Reduced rainfall produces much greater reduction in run-off (possibly in the order of a 3 times reduction)

  • During the long drought ending in 2009, the period 2004 –2006 produced rainfall and runoff lower than long-term means almost everywhere in the Basin. The mean annual rainfall was 384mm, significantly lower than long term mean, and mean annual runoff at 16.7mm was 39% lower than long term mean of 27.3mm.

  • Very little runoff enters the Murray River in the SA section of the Basin; most runoff that enters the River is produced in Queensland, NSW, and Victoria. 

  • During the period 1997 – 2006, mean annual rainfall declined to 440mm, 4% lower than the long-term mean of 457mm. Mean annual runoff was 21.7mm, 21% lower than the long-term mean 27.3mm.

  • Runoff in the southern portion of the Basin during 1997 – 2006 was unprecedented in the historical record, and was much lower than similarly dry ten-year periods in the past. 

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