Cease to flow periods in the Barwon-Darling

Summary:

The Barwon-Darling region naturally goes through wetting and drying cycles that can last decades.
We are currently going through a dry period. The last dry period was 1900 – 1950.
The cease to flow periods experienced in the most recent drought have been long and severe, but are not unusual when compared to conditions in historical dry periods.
There are clear differences between the cease to flow periods in the dry, compared to the wet periods.

Climate cycles

The NSW Government has collected rainfall data for approximately 130 years. This data helps us begin to understand some of the long term climate trends in the region. The north-western region of NSW cycles between wet and dry cycles with each cycle lasting decades:

1900s – 1950

Comparatively dry period
1950 – 2000

Comparatively wet period
Post 2000

A return to comparatively dry periods

The driest 10-year and 5-year droughts in all northern valleys and the western region have all occurred during the dry periods.

Cease-to-flow periods

The Barwon-Darling river has often stopped flowing for periods of time. The cease to flow periods in the dry periods of our climate are more frequent than in the wet period.

The cease to flow conditions we saw in the most recent drought were severe and had significant impacts on communities, ecosystems and industries, but they are not unique when compared to the historical record. Our lived experience is mostly drawn from the wet period when there were very few cease to flow periods.

Important information

For this analysis we have used the plain English definition of cease to flow which is zero recorded flow.

Graphs

Barwon-Darling

The graph below shows the number of cease to flow days per year across different points in the Barwon-Darling river.

Walgett

Period	Average number of cease	Average duration of cease to flow periods	Duration of longest cease to flow period
1900 – 1950	0.5	50 days	270 days
1950 – 2000	0.1	60 days	156 days
2000 – 2021	0.7	42 days	326 days

Brewarrina

Period	Average number of cease	Average duration of cease to flow periods	Duration of longest cease to flow period
1900 – 1950	0.54	51 days	296 days
1950 – 2000	0.02	127 days	127 days*
2000 – 2021	0.15	74 days	114 days

^{* this occurred July – November 1995}

Wilcannia

Period	Average number of cease	Average duration of cease to flow periods	Duration of longest cease to flow period
1900 – 1950	0.44	66 days	130 days
1950 – 2000	0.16	34 days	80 days
2000 – 2021	0.64	104 days	309 days

Weir 32

Period	Average number of cease	Average duration of cease to flow periods	Duration of longest cease to flow period
1900 – 1950	0.6	66 days	263 days
1950 – 2000	0.06	3 days	4 days
2000 – 2021	0.5	32 days	97 days