History Of Flooding

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History Of Flooding

The Gwydir Valley has a history of flooding that brings both devastation and life to the region.  While every flood is different in magnitude, duration and size they can be compared to help be prepared and predict possible behaviours.

Below is a key comparison of the big floods and these are generally ones that are regarded as 1:100 year flood events, our key events.

When a flood warning is issued, we often compare predicted heights to these key events which are largely reported by the Bureau of Meteorology in meters.

River Height in meters

Gauging Location

23 Oct 2022 Nov-21 Mar-21 2016 2012 2011 1976 1955
Gwydir at Gravesend

16.21 8.99 14.9 8.739 15.668 13.266 16.01 17.34
Gwydir at Pally

10.56 7.83 10.5 7.668 10.518 10.105 9.237 NA
Gwydir at Yarraman

7.53 7.06 7.35 6.95 7.512 7.326 7.5 NA
Mehi at Moree

10.50 3.84 10.43 4.172 10.68 10.206 10.59 10.87

The Gwydir River peaked at Gravesend at 11:45pm on Friday 21st October 2022 at a height of 16.20m. At 2:30pm on Sunday 23rd October 2022 the Gwydir was falling at Gravesend, steady at both Pally and Yarraman. The Mehi was steady in Moree at this time. 

River peak flow rate in megalitres per day

Gauging Location Nov-21 Mar - 21 2016 2012 2011 1976

Gwydir at Gravesend 65,918 58,058 341,849 181,547 264,662

Gwydir at Pally 58,387 162,263 56,006 169,186 141,701 145,838

Gwydir at Yarraman 50,962 85,804 47,100 141,136 78,017 N/A

Mehi at Moree 3,445 46,546 5,769 55,778 58,710 N/A

To understand the magnitude of these key events, the 2011 and 2012 floods were part of wide-spread significant and extended flooding in the north west.  The first in November/December 2011 and then again later in January/February 2012.  During this time 3,450 GL of total system flows distributed across the valley and floodplains. The Gwydir event was not isolated and 8,600GL was gauged at Bourke as many valley flooded simultaneously and Menindee Lakes filled and were surged as they were over capacity.  

We include 2016 in these records, as this event is a moderate flood level that created substantial flooding in the watercourse, along the lower Gwydir and Gingham area due to operational constraints within the river.  The volume of this flood was a third of that in 2011 and 2012 with the majority flowing towards the watercourse and wetlands.  Rivers and streams in surrounding valleys also flowed but flooding was limited in those areas.  River flows provided for water along the Barwon Darling delivered via water sharing plan rules and Menindee Lakes almost filled at 91% capacity.

The 2016 flood is important to understand the limitations in managing flows in the Gwydir Valley when the flow rate is higher than 20,000ML/day upstream of the Tarelaroi Regulator.  For safe operation of the river infrastructure, WaterNSW are required to remove of regulating infrastructure and allow flows to naturally pass.  This often results in a lowering of hydraulic pressure at the regulator and limits the management of water by the river operator until flow rates decline.  The result, there is limited ability for WaterNSW to direct this water down the Mehi River and flows remain within the Gwydir River system and naturally flows towards the watercourse area west of Moree. 

The current flood warning in the Gwydir was issued via the Bureau of Meteorology on 22 March 2021, is larger than the 2016 flood and is more wide-spread with rainfall across the catchment.  Its tracking very similar to 2012.  A comparison of the predication and actual is presented below as well as the records for December 2020.

Major flood warnings was made by the Bureau of Meteorology, updates are available here via the BOM website. 

River prediction and actual March 2021

Gauging Location Height prediction Actual peak
Actual peak flow rate 
Gwydir at Bundarra* 9.7  9.7  ML/day
Gwydir at Gravesend* 14.9 14.9  ML/day
Gwydir at Pally 10.5 10.48 162,263  ML/day
Gwydir at Yarraman 7.3 7.35 85,804 ML/day
Mehi at Moree 10.4 10.43 46,546 ML/day

* Moderate flood.

Comparison of March 2021 to 2011 and 2012 Flood Table

River prediction and actual December 2020

Gauging Location Height prediction Actual peak height Actual peak flow rate
Gwydir at Gravesend NA 7.2 40,000
Gwydir at Pally 7 5.7 33,159
Gwydir at Yarraman 6.5 5.4 21,432
Mehi at Moree 5.5 3.1 3,244

Flood Safety Advice:

In life threatening emergencies, call 000 (triple zero) immediately. If you require rescue, assistance to evacuate or other emergency help, ring NSW SES on 132 500.

  • Avoid drowning. Stay out of rising water, seek refuge in the highest available place.
  • Prevent damage to your vehicle. Move it under cover, away from areas likely to flood.
  • Avoid being swept away. Stay out of fast-flowing creeks and storm drains.
  • Never drive, ride or walk through flood water. Flood water can be deceptive and dangerous.

For more emergency information, advice, and access to the latest river heights and rainfall observations and forecasts:

NSW SES: www.ses.nsw.gov.au

RMS Live Traffic: www.livetraffic.com

Making Every Drop Count

Securing a future for the Gwydir Valley through Irrigated Agriculture.