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The Old Mundoo Barrage/Dam

In September 1914, Mr H Eaton (from the Engineer In Chief’s Department) was requested to inspect a suggested site at Mundoo Channel for a temporary dam to be constructed.  In his report to The Engineer In Chief, Mr Eaton stated that because the distance to the lake by the Mundoo Channel being so much less than by the other channels, there is no doubt that the Mundoo Channel would be the medium through which salt water would first be discharged into the lake.

Mr Eaton also suggested that the dam should be constructed when the water in Mundoo Channel was fresh, otherwise the salt water would be locked in and the residents along the Mundoo Channel would be deprived of fresh water in the channel for some time.

This proposal came about as a means to decrease the quantity of salt water entering the lakes. Mundoo Channel is the shortest distance between the sea and the lakes and there was no doubt that a large quantity of fresh water was drained off from the lakes by this channel and also that a large quantity of water entered from it.  They were not sure as to the extent that this action would affect the salinity of the lakes but there was little doubt that it would improve it. 

The Old Mundoo Barrage (Mundoo Dam) was commenced in October 1914.

A severe storm damaged the Mundoo Dam overnight on 1st March, 1915.  The damage was repaired and the earthwork completed with the face and top covered with 12 inches of stone.

The Mundoo Channel was officially closed in March 1915.

By September 1915 there were 34 men on the employment list at the Mundoo Barrage.  Some young men had bid farewell and headed off to assist the allied forces in WW1. 

On 20th December, 1916 the officers of the Irrigation Department were of the opinion that the Mundoo barrage was responsible, to a large extent, for the high level reached by water in the Murray between Mannum and the mouth. They contended that the channel was the natural outlet for floodwaters, because it was the shortest route from the lakes, and therefore the one which would be taken.  The Engineer In Chief’s Department took the opposite view, maintaining that the barrage could not possibly have the bad effect alleged, because there were two or three other outlets.

 The Government considered the matter and generally admitted that the removal of the barrage would have made no difference to the high waters, and their effect upon the reclaimed swamps.  However, in view of the possibility of still higher floods coming down in the future, it was decided that automatic gates should be placed across the channel.  The present barrage would remain until the gates were erected, which could not be done until the water level had gone down considerably.  The proposed gates were to be fitted with floats, which would cause them to close when there was an inrush of sea water, so that it should be held back.  When the salt water returned to the ocean the gates would automatically lower and a flow of fresh water backed up by the gates would find an outlet.  The saltwater would therefore be held back from the lakes.

The Observer 8th March, 1919: “Keeping The Lakes Fresh – Progress with the Mundoo Bridge”

“The construction of the barrage across the Mundoo Channel is an important experiment.  It is the first chapter of what is expected to be a happy story of conquest over the advancing forces of salt water.  If Lakes Alexandrina and Albert are to be kept fresh, the Mundoo, which is the direct gateway from the sea, must be equipped to resist the destructive encroachment; and not only this stream, but others that link the lakes to the ocean.  Mundoo is the test.  Officially, the Engineer-in-Chief’s Department, which is doing the work, knows nothing of future operations.  That is a matter of policy.  All that is disclosed at present is that the Mundoo will be blocked; but, as the Goolwa and Boundary Creeks and Tauwitcherie Channel would remain sources of danger, unless a general scheme of effective prevention be adopted, it may be assumed that more projects are contemplated.  The whole question has been an intermittent controversy for a number of years.  It is one of the established river topics, and enough “expert” opinion has been expended on it to fill several blue books – with a fair proportion of blue language!  The explosives which blew up the temporary Mundoo barrage in 1917, did not blow the argument out of sight.  The advisableness of that action is still keenly debated.  The departmental view was that the demolition of the barrage was not justified.  The same objection was raised by Capt. Ritchie, MP, during a vigorous speech in the Assembly, but the Director of Irrigation (Mr S McIntosh), backed up by protest from settlers on the lower Murray, between Wellington and Mannum, who said the effect was to increase materially the height of the maximum flood, carried the day.  So the wedge came out.

The Coorong Barrages

The ensuing years heralded many debates regarding the decision to build the barrages.  There were concerns that low lying land would be flooded for too long, the mouth would partially close up and that the fishing industry in the lakes would be jeopardised. 

In 1930, the River Murray Commission recommended the construction of five barrages across the channels leading from the lakes to the Murray mouth in order to maintain the freshness of the River Murray as far down as Wellington, to maintain the water level for irrigation purposes and to prevent the ingress of salt water from the sea into the Lower Lakes during periods of low Murray River flow.

The benefits of a barrage scheme were debated over many years and it was ultimately agreed that the barrages should be built to maintain fresh water in the Lower Lakes and lower reaches of the River Murray.

Our islands are dissected by the Coorong Barrages that were commenced in the mid 1930s.

The Mundoo Barrage and Boundary Creek Barrage adjoin Mundoo Island and the Boundary Creek Barrage and Ewe Island Barrage adjoin Ewe Island.

Our family history on Mundoo Island Station pre-dates the barrages. We have witnessed many changes through the years as a result of the barrages ... some good and some not so good.

The state government leased portions of Mundoo Island and Ewe Island from Jack Grundy so that a township and workman's camp could be constructed to house the workmen and their families during the construction phase. A school was opened on Mundoo Island to educate the children of the workmen's families. It was a thriving township for the period of construction.

The New Mundoo Barrage

May, 1935 – Erection of temporary buildings proceeded, the Machine Shop was completed, 2 two-roomed cottages were erected and the bathrooms for the staff and men’s quarters and work commenced on the office and school.  One 10,000 gallon tank was erected and connected up to the buildings to conserve all rain water.  A considerable quantity of material including Machine Shop plant was received.  Poles for the telephone line were erected between the office and the old barrage and a contract was let for the erection of the line in from the trunk line.

June, 1935 – Erection of temporary buildings proceeded, a further staff cubicle, a two-roomed cottage and office were erected.  The school building was partly completed.  The machinery and shafting for the Machinery Shop were assembled and the foundations finished in concrete.  The telephone line between the office and Hindmarsh Island was completed and the contractor erected all the posts from the old barrage to the trunk line.  Four steel piles were driven to test the possibility of using them for cofferdam purposes; they were afterwards withdrawn and demonstrated that the type of cofferdam was practicable.  The overhead tankstand was erected and a second squatter’s tank was assembled for the camp water service.  Cross sections at the site of openings in the barrage were taken for cofferdam data.

27 May, 1937 – The approaches with the stone protection were nearing completion and the girders and decking for the bridgeway over the concrete piers would be placed in position soon.

30 June, 1937:   Materials Placed in the Mundoo Barrage

  • Cofferdam                                  1,720 linear feet
  • Rock Excavation                       2,587 cubic yards
  • Concrete - plain                        384 cubic yards
  • Concrete – reinforced             2,587 cubic yards
  • Steel Reinforcement                217,873 lbs
  • Structural Steel                        119,278 lbs
  • Cast Iron                                    36,689 lbs
  • Non-corrodible Steel               715 lbs
  • W I Bolts etc                              2,760 lbs
  • Jarrah Timber                          1,248 sp feet
  • Earth Embankment                17,100 cubic yards
  • Stone Pitching                          6,716 cubic yards

Cofferdam – This structure was extended during 1937 to allow for an additional length of sluices.  The cofferdam was completely removed by 30 June, 1937. 

Sluices – This work was completed by 30 June, 1937.

Embankments – The earth formation for the embankments from each shore to the sluiceway were completed by 30 June, 1937 and the stone paving protection was about 80% complete.

23 July, 1937 – The work was well advanced and in a few weeks the plant and settlement would be dismantled and moved to the site of the Ewe Island barrage.

And so the construction of the Coorong Barrages continued until all 5 were completed.

The state government held a 6 day auction in 1940 to sell the plant, equipment, housing and vessels used for the construction of the barrages. Much of the equipment was utilized in the construction of the locks and weirs throughout the length of the River Murray, and transported on paddlesteamers and barges for use during their construction phase.

Murray Darling Basin Authority: All About The Barrages Fact Sheet

From its headwaters in the Australian Alps, the River Murray travels over 2,500 km to the Southern Ocean. In the final 100 km before entering the ocean, the river passes through Lake Alexandrina, the Murray Estuary and the Murray Mouth. Connected to Lake Alexandrina by a narrow channel is Lake Albert. These are the Lower Lakes, together holding approximately 2,000 GL of water, nearly four times that of Sydney Harbour. Between Lake Alexandrina, the Coorong and Goolwa Channel are barrages separating the River Murray from the sea. These are designed and operated to ensure the lakes
and lower reaches of the river remain fresh, not only for environmental reasons but as a water supply source.

There are five barrages that separate Lake Alexandrina from the Goolwa Channel and the Coorong — Goolwa, Mundoo, Boundary Creek, Ewe Island and Tauwitchere.

The barrages maintain the river level between the Lower Lakes and Lock 1 at Blanchetown, a distance of about 250 km. Adelaide, parts of the mid-north, Yorke Peninsula and south-east South Australia depend on water pumped from this weir pool. The water in this reach is also directly drawn for towns and agriculture around the Lower Lakes and River Murray up to Lock 1.

Why were the barrages built?

From the 1880s the South Australian Government was concerned about maintaining fresh water supplies for stock, irrigation and domestic purposes for settlements along the lower Murray and around the Lower Lakes. There was concern that due to increasing use of water all along the river, flows would not be sufficient to keep the lakes fresh.

The government also wanted to ensure there was enough water in the River Murray to allow navigation for river boats (and therefore trade) between New South Wales, Victoria and South Australia.

For many years, and throughout several inquiries and commissions, the barrages scheme was generally not supported by the other states.

The River Murray Waters Agreement (1915) established the River Murray Commission and water sharing arrangements between New South Wales, South Australia and Victoria. It also provided for the construction of the storages, weirs and locks that regulate the river for irrigation and allow navigation. South Australia was provided with flows to protect the settlements along the lower River Murray as far as Wellington from salinity, but Lakes Alexandrina and Albert were excluded.

The barrages were not included in the original scheme of works for the River Murray. South Australia continued to lobby for their construction on the basis of increasing salinity with general support from local landholders keen to secure fresh water. Salinity had increased from allowing the Lower Lakes to support a Murray Cod fishery in the 1800s, to supporting a salt water fishery in the 1930s.

Opposing concerns were raised that the barrages may impede navigation and cause the siltation of the Murray Mouth. Goolwa fishermen thought the barrages would prevent fish entering the river and lakes and reduce their catch. Some landholders were worried that during floods, more land and river townships would be inundated as a result of the barrages maintaining elevated levels in the Lower Lakes.

After construction of the barrages, South Australia finally had the confidence to connect Adelaide’s water supply to the River Murray downstream of Lock 1.

How do the barrages work?

The barrages are a series of 593 independent gates or stoplog bays across five structures – creating a barrier 7.6 km long. The barrages isolate the estuarine area (including the Coorong) from the Lower Lakes and artificially hold the lakes at higher than natural levels (about 0.75m above sea level).

Gates and stoplogs are opened progressively to pass the target flow to the sea. This target is calculated taking account of river inflows, rainfall, local catchment run-off, evaporation, consumptive use and required lake level. In many summer and autumn months — when river flows are low and

Fact Sheet: Barrages

Mundoo Barrage

Mundoo Barrage

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Ewe Island Barrage

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Old Mundoo Barrage (Mundoo Dam)

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Hand-operated lock chamber in the Tauwitcherie Barrage to allow passage of vessels from fresh to salt or salt to fresh

Fishway in the Tauwitcherie Barrage

Fishway in the Tauwitcherie Barrage

Floodwaters released from Tauwitcherie Barrage 2010

Floodwaters released from Tauwitcherie Barrage February 2012

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New Zealand Fur Seals have colonised the Coorong and often haul-out on the barrage structures

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Mundoo Island Township built mid-1930's for barrage construction accommodation

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A Mundoo Island Township Barrage Home bought at the auction by Mr McPherson. His family lived in this home for many years after he relocated it to Hindmarsh Island.

Ewe Island Barrage

Ewe Island Barrage