Ord: Climate and water

  • Total annual rainfall was above average following a very dry 24-month period.
  • Inflows into Lake Argyle were above average for the first time in four years.
  • Despite above-average wet season rainfall, flow in the lower Ord River was below average.

Schematic representation of the Ord region. In 2020–21, rainfall was 927 mm, above average for the first time in four years. Streamflow in lower Ord River in 2020–21 was 3,047 GL compared to the average value of 6,170 GL. Soil moisture was above average.

For further information on the region's climate and water conditions during the 2020–21 year scroll down this page or click on the links below:

 

About the region

  • The Ord region lies within the wet–dry tropics of northern Australia. Almost all rainfall in the region occurs during the wet season (November–April). As a consequence, flow in the rivers is strongly seasonal.
  • Many of the region's rivers, including those that flow into Lake Argyle, cease to flow during the dry season (May–October).

 

Climate conditions

Rainfall

Figure C1 Annual and monthly rainfall deciles for the Ord region during the 2020–21 year

 

  • Total area-averaged rainfall for the year was 927 mm, above the mean value of 683 mm.
  • The above-average rainfall in 2020–21 follows the region's driest 24-month period in 50 years.
  • The climate across northern Australia was influenced by weak La Niña conditions in the Pacific Ocean, the first La Niña event since 2012.
  • Heavy rainfall associated with several tropical lows that crossed the region in December 2020 and March 2021 contributed to the above-average rainfall during those months, particularly over the southern part of the region upstream of Lake Argyle.

 

Figure C2 Total monthly rainfall for the Ord region during the 2020–21 year compared with the average and percentiles for the region

 

  • Rainfall was above average throughout December 2020–March 2021, typically the wettest part of the year.
  • Total rainfall in December 2020 and March 2021 was above the 90th percentile and double the average for those months.
  • Pre–wet season rainfall in September–November was above average.

 

Actual evapotranspiration

Figure C3 Annual and monthly actual evapotranspiration deciles for the Ord region during the 2020–21 year

 

  • Total area-averaged actual evapotranspiration was above average across most of the region.
  • Evapotranspiration was below average during July–September 2020 prior to the 2020–21 wet season. This was due to very dry conditions across the region following two consecutive years of poor wet-season rainfall.
  • Evapotranspiration was above average over most of the region during December 2020–April 2021 due to increased water availability following high rainfall throughout the 4-month period between December 2020–March 2021.

 

Soil moisture

Figure C4 Annual and monthly soil moisture deciles for the Ord region during the 2020–21 year

 

  • Soil moisture in the root zone (0–1 m depth) was above average across almost the entire region.
  • Very low rainfall during the previous 24-month period between 2018–20 meant root-zone soil moisture was well below average during July–August 2020.
  • By the start of the 2020–21 wet season, soil moisture was average to above average across the region following late dry-season rainfall during September–October 2020.
  • Soil moisture remained above average during the 2020–21 wet season due to above-average rainfall occurring throughout the 4-month period between December 2020–March 2021.
  • More information on soil moisture distribution across the Ord region is available in the Australian Landscape Water Balance.

 

Streamflow responses

Map of key gauging stations. In the southeast upstream of Lake Argyle are Ord River at Old Ord Homestead, station number 809316, and Negri River at Mistake Creek Homestead, station number 809315. Ord River at Tarrara Bar, station number 809339, is downstream of Lake Argyle in the north.
Figure C5 Key flow gauging stations along the main rivers within the Ord region

 

  • The upper Ord and Negri rivers are two primary rivers that flow into Lake Argyle.
  • Streamflow in the lower Ord River below Lake Argyle is influenced by hydropower releases, diversions for consumptive use, dam operations, and the dam spilling.

 

Figure C6 Total monthly flow for major rivers in the Ord region during the 2020–21 year compared with the average and percentiles

 

  • Total annual flows in the upper Ord and Negri rivers were above average throughout most of the wet season. This follows three consecutive years of very low inflows into Lake Argyle.
  • Very high streamflow occurred in March 2021 due to heavy rainfall over the upper reaches of the Ord and Negri river catchments in mid-March 2021.
  • Despite above-average wet season rainfall, total annual flow in the lower Ord River at Tarrara Bar (Station 809339) was 3,047 GL, below the average value of 6,170 GL.
  • The below-average flow in the lower Ord River was influenced by Lake Argyle not filling during the 2020–21 wet season, which meant no spills from the dam contributed to the flow. In addition, rainfall associated with the tropical lows that crossed the region during December 2020 and March 2021 was higher over the southern part of the region than the lower reaches of the Ord River (see Rainfall).

 

Major water reforms

Ord–East Kimberley Expansion Project

Map of proposed expansion in the Ord River Irrigation Area. The 3 current irrigation areas are the Ivanhoe Plain and Goomig Farmlands, north of Kununurra on the eastern side of the Ord River, and the Packsaddle Plain, south of Kununurra on the western side of the Ord River. Irrigation expansion is proposed around these 3 current areas. Other potential irrigation areas include Carlton Plain and Mantinea in the region's northwest, Ord West Bank, south of Kununurra on the western side of the Ord River, Knox Creek Plain and Keep River Plain in the region's northeast.
Figure C7 Proposed expansion in the Ord River Irrigation Area

 

  • The Ord–East Kimberley Expansion Project is a major initiative of the Western Australian Government.
  • The first stage of the expansion will develop 74 km2 of irrigated farmland in the Goomig Farmlands, with an option to develop a further 60 km2 in the Knox Creek Plain area. The portion of irrigated land in the Goomig Farmlands has been increasing each year since the first planting of crops commenced in 2015.
  • The Ord Irrigation Cooperative currently holds a licence for diversion of 335,000 ML/year for the Ivanhoe and Packsaddle plains. Kimberley Agricultural Investment Pty Ltd currently holds a licence for diversion of around 72,000 ML/year for the Goomig Farmlands, which is expected to increase to the total commitment of 120,000 ML/year in the next few years.
  • Additional water demand for the planned Knox Creek Plain area is expected to be 60,000–110,000 ML/year.
  • Development of other proposed areas could take place in the next 5–10 years. Further details on these potential irrigation areas are given in Chapter 3 of the Ord Surface Water Allocation Plan.
  • Further information on the Ord–East Kimberley Expansion Project can be found at the Department of Primary Industries and Regional Development and Office of Northern Australia websites.