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Monitoring of the 2019 Northern Fish Flow

Throughout the duration of the Northern Fish Flow – a release of water for the environment to replenish critical waterholes along the Macintyre, Gwydir and Barwon Rivers – the Murray–Darling Basin Authority (MDBA) undertook monitoring and analysis of the flow event.

The release of 36 gigalitres (GL) of water for the environment from the Glenlyon and Copeton dams travelled more than 1,200 kilometres and provided much needed water to the native fish trapped in the disconnected waterholes of the Barwon River. After several months the flow reached the Brewarrina weir pool and travelled as far as the junction of the Barwon and Culgoa Rivers.

Compliance monitoring

Throughout the flow event, the MDBA worked with the Commonwealth Environmental Water Office (CEWO) and undertook monitoring and analysis at a number of gauge locations along the flow path, to determine what proportion of the flow had progressed, to where, and when that occurred.

We also made use of specialised algorithms generated from the Sentinel-2 satellite images to help determine the presence of water in the landscape and how the flow was actually behaving and how it moved through waterways and the surrounding landscape.

This data was then passed onto our colleagues at the CEWO and has been used, for example, in their regular Northern Fish Flow updates. It was also provided to relevant New South Wales compliance authorities for reference if unauthorised water take was suspected. This protected flow was also being monitored by the New South Wales Natural Resources Access Regulator using the gauge network and various on-the-ground compliance activities.

The responsibility for compliance related monitoring now rests with the Inspector-General of Water Compliance. However, the MDBA continues to monitor water flows and vegetation response using information collected from remotely mounted sensors and collaborate with Commonwealth and state government entities to assess conditions across the Basin.

Outcomes of tracking the Northern Fish Flow

The Northern Fish Flow was undertaken with the intention of refreshing fish habitat along the Barwon as parts of the river had gone for more than 200 days without flow. Through analysis of hydrological data and satellite imagery it can be confirmed that the Northern Fish Flow was effective in reconnecting isolated waterholes and providing much needed refuge to native fish.

Benefits of the flow were also evident in results from on-ground monitoring that showed a marked improvement in water quality. The monitoring of the Northern Fish Flow has reaffirmed that the analysis of satellite imagery is an effective technique for tracking flows, and it will continue to be implemented and improved upon for the analysis of future flow events.

The Northern Fish Flow’s starting point and corresponding monitoring areas

The reach area monitored by the MDBA is defined in the map below and we’ve provided a summary of key data as the flow reached each area.


Sentinel-2 satellite imagery

The images (featured below) from the Sentinel-2 satellites, use a water detection index across the landscape. The presence of water is traced in dark blue, with the landscape a yellow/gold colour. A light blue indicates areas of increased moisture. Throughout the flow event, the MDBA was interested in capturing significant changes in the landscape, particularly if any of the water storages within the proximity of the flow path changed to a darker blue.

Your eye across our skies – check out comparative images from the flow event

To see the type of satellite images the MDBA Remote Sensing team monitor, open the link below for an example of 2 satellite images taken on the 19 March and 28 May 2019. It shows an image taken over Mungindi in the Northern Basin and allows the user to slide between 2 contrasting images to see the differences in the landscape.

What the gauges are telling us

The plot graphs on this page are called hydrographs and they plot the measurement of the flow from several gauges along the river in megalitres per day. The hydrograph examples on this page show how the flow event progressed and how it changed. The MDBA is looking for sudden, significant and unexpected changes to indicate if any impact has occurred, which could include unauthorised take.

Border Rivers reach

The water for the environment releases began on 24 April from Glenlyon Dam and travelled down the Dumaresq River passing Bonshaw Weir and Glenarbon Weir. The flow arrived at Goondiwindi on 7 May and continued down the Macintyre River. During May, the front of the flow passed Boomi Weir and arrived at Kanowna.

The flow took approximately 30 days to progress through the Border Rivers system during April and May with changes to the flow properties highlighted on the plot. The flow can be seen to undergo a change in shape and undergo a large loss between Glenlyon and Goondiwindi, which was examined in detail by the New South Wales Natural Resources Access Regulator.

Gwydir flow reach

The water for the environment releases from the Copeton Dam for the Northern Fish Flow event began on 2 May and took approximately 30 days to progress through the Gwydir system – travelling down the Gwydir River, past Pinegrove (near Bingara), Gravesend and Pallamallawa, before it entered the Mehi River and passed Moree and Bronte. On 22 May, the front of the flow reached the gauge at end of the Gwydir system near Collarenebri and then proceeded to flow further downstream.

The hydrograph below shows the flow event from several gauges along the river across a period of approximately 30 days, the period it took to progress through the Gwydir system. Changes to the flow properties can be seen in the profiles.

The connection of the Mehi River and Barwon River

Throughout the week commencing 20 May, the flow travelled towards the Barwon River through the Mehi River. The before and after images below show the satellite images from 19 May, before the flow reached the Mehi, and the after – when water is visible in the Mehi and had reached the Barwon River.

Footage from sites along the flow

Water for the environment released from Copeton Dam on 24 April arrived at the Mehi River and Barwon River junction on 22 May.

Local Collarenebri resident and Walgett Shire Councillor Mr Kelly Smith was on-site to film as the water reached that part of the river on 22 May.

Barwon upper and middle flow reach

The flow from the Border Rivers first arrived at Mungindi on 23 May with the flow peaking at 159 megalitres per day where it travelled down the Barwon River. The flow from the Gwydir joined with the flow from Mungindi and reached Collarenebri in late May, where it peaked at 494 megalitres per day. It then travelled down the Barwon River, reaching Walgett on by mid-June. The flow took approximately 40 days to progress through the Barwon River with changes to the flow properties captured in the hydrograph below.

The flow refreshes dry river bed

As the flow progressed down the Barwon River, it inundated river beds that had been dry for a very long time. This can be seen in the below satellite imagery taken near Walgett. The satellite image on 7 June shows the parched river bed of the Barwon – this is in stark contrast to the full channel seen just 10 days and later on 17 June when the flow was measured at 423 megalitres per day.

Barwon lower flow reach

The flow arrived at Boorooma on 27 June where it peaked at 320 megalitres per day and reached a volume of 4.2 GL. As the flow travelled further down the Barwon River, it was measured at Brewarrina at a peak of 172 megalitres per day and a volume of 2.1 GL. While passing through Brewarrina, the flows appears to flatten out, which is expected (flow behaviour). As the flow travelled over dry river bed it experienced significant losses in the Lower Barwon River.

Brewarrina gets its highest recorded daily flow in more than a year

The flow peaking at Brewarrina at 173 megalitres per day on 11 July 2019 signified the largest daily flow measured at Brewarrina in more than a year. The last time Brewarrina had a flow of this size was in late June 2018 and since then the area has experienced sustained periods of no flow. The Sentinel-2 satellite images below show the reconnection of the Barwon River on either side of the Brewarrina weir, before the flow event in early April and the image from 15 July.

Expected reach

The Northern Fish Flow occurred along the Mehi and Macintyre Rivers and into the Barwon River. The flow travelled about 300 kilometres further downstream than expected and reached just upstream of the Bourke weir pool.

Updated: 21 Dec 2021