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Ord: Supporting information

  • Above-average wet season rainfall contributed to average annual runoff across the region.
  • End-of-year storage volume increased to 76% full, the first annual increase in storage in four years.
  • 61% of the allocated water was taken in 2020–21, primarily for irrigated agriculture.

Schematic representation of the Ord region. In 2020–21, runoff was 6% less than average. Storage volumes at 30 June 2021 were 76% full, much higher than the previous year. 61% of the total surface water allocation (448 GL) was taken. 82% of the total groundwater allocation (9 GL) was taken.

For further information on the region's water accounting statements scroll down this page or click on the links below:

 

Water assets

Kununurra Diversion Dam, Ord region (Water Corporation © Darryl Perroni)

 

  • Water asset volumes in the region at 30 June 2021 were 8,250 GL, more than 99% of which is water held in storages. The remaining amount is water held in rivers.

 

Bar graph of annual storage volume in the Ord region at 30 June for the years 2010–2021. Accessible storage plus dead storage is plotted against the storage capacity to show percentage full at 30 June each year. Storages at 30 June 2021 were 76% full, much higher than the previous year. Between 2010 and 2018, end-of-year storage volume was consistently above 70% full. Only in 2019 and 2020 was the end-of-year storage below 70% full (when it dropped to 54% and 40% full respectively).
Figure S1 Total storage volume in the region at 30 June 2021 compared with the previous 11 years

 

  • Storage volumes increased from 40% full at 30 June 2020 to 76% full at 30 June 2021, the first annual increase in storage in four years.
  • Water in Lake Argyle makes up more than 98% of the region’s total surface water storage.

 


Figure S2 Percentage-full volume on 30 June 2021 for each storage and total daily storage volume from 2013–2021 (inset)

 

  • At the end of the 2020 dry season, storage volumes had dropped to 27% full, the region's lowest level since early 1993.
  • Average to above-average rainfall throughout most of the wet season resulted in a stready rise in storage levels throughout December 2020–March 2021, which peaked at 83% full in late-March 2021. This was the first significant rise in storage since 2017.
  • More detailed information on the individual storages within the region is available on the Bureau of Meteorology's Water Storage website.

 

Water liabilities

Lake Argyle, Ord region (istock © anonymous)

 

  • Water liabilities in the Ord region refer to the volume of allocation remaining on licence entitlements at the end of the 2020–21 year.

 

Table S1 Volume of surface water allocation remaining at 30 June 2021
Description Individual users (ML) Urban system (ML) Irrigation scheme (ML)
  Opening balance at 1 July 2020 10,128 670 290,694
add Allocation 39,732 700 407,754
less Allocated diversion 23,955 425 247,069
less Adjustment and forfeiture 15,779 275 146,298
  Closing balance at 30 June 2021 10,126 670 305,081

 

Table S2 Volume of groundwater allocation remaining at 30 June 2021
Description Individual users (ML) Urban system (ML)
  Opening balance at 1 July 2020 1,155 2,252
add Allocation 6,092 2,700
less Allocated extraction 5,407 1,778
less Adjustment and forfeiture 685 922
  Closing balance at 30 June 2021 1,155 2,252

 

  • Most of the water supply licences for the region do not have a water management year that ends on 30 June. Therefore, the allocation remaining is the unused component of the annual allocation for these entitlements.
  • A more detailed description of water allocations in the Ord region is given in the Water use section below.

 

Water flows

Champagne Springs, Ord region (istock © samvaltenbergs)

 

Figure S3 Water inflows and outflows for the region's water stores during the 2020–21 year

 

  • Total surface water flows into the region's storages was 5,789 GL. The key item contributing to surface water inflows was runoff, which made up 89% of the total surface water inflows for the region.
  • Runoff was close to average (based on modelled data from 1971–2021) due to above-average wet season rainfall across the region.
  • The key item contributing to surface water outflows from the region's storages was river outflow, which made up 69% of the total surface water outflows. Despite the high wet-season rainfall, river outflow was below average, which was influenced by the lack of spills from the dam at Lake Argyle contributing to the flow in the Ord River (see Streamflow responses).
  • Water taken for consumptive use was 279 GL, around 5% of the total outflow (see Water use section below).

 

Water availability

Bar graph of annual surface water availability in the Ord region for the years 2011–2021. Accessible storage at 1 July plus estimated inflows during the year is plotted against the mean water availability (based on 1970–2021 data). Surface water available during 2020–21 was well below average, similar to the previous year. Surface water availability has been below average for 6 of the last 7 years. Water availability was well above average during 2011–12.
Figure S4 Annual surface water available in the Ord region, 2011–12 to 2020–21

 

  • Physical surface water availability is calculated as the sum of accessible storages at the start of the year and the inflows (precipitation, runoff, and inter-region inflows) into storages and rivers during the year.
  • Despite above-average rainfall in 2020–21, surface water availability was below average, primarily due to the very dry conditions across the region during the previous 24-month period between 2018–20.
  • As physical water availability is much higher than the region's water needs, water allocations vary little between years.
  • Water taken during the year is typically higher when water availability is low, reflecting an increased demand from customers when conditions are dry (see Water use section below).

 

Water use

Irrigation channel, Ord region (Bureau of Meteorology © Dene Moliere)

 

Figure S5 Water taken during the 2020–21 year in the region's water management areas

 

  • Total surface water diverted in the region was 271,449 ML.
  • 91% of the total diversion was for irrigation scheme supply, all within the Main Ord River management area; 9% was for individual users and less than 1% was for the urban system.
  • Total groundwater extracted was 7,185 ML.
  • 75% of the total extraction was for individual users while 25% was for the urban system.

 

Bar graph of annual surface water allocation and diversion for different users in the Ord region from 2011–12 to 2020–21. Most of the surface water allocations are associated with the irrigation scheme. In 2020–21, allocations for the irrigation scheme were higher than previous years. 68% of the allocation was taken. Allocations for individual users and the urban system change little from year to year. 74% of the allocation for individual users was taken. 61% of the allocation for the urban system was taken.
Figure S6 Surface water allocations and diversions in the Ord region for the years ending 30 June, from 2012–2021

 

  • In 2020–21, total surface water allocation was 448 GL, mostly for irrigated agriculture in the Ord River Irrigation Area; 61% of the allocated surface water was taken.
  • Water allocation for irrigation scheme supply was slightly lower than the previous year due to the expansion of irrigation in the Goomig Farmlands (see Major water reforms).
  • During the last three years, water taken for irrigation scheme supply has been much higher than previous years. The increase in irrigation scheme supply has been influenced by the very dry conditions across the region during the last two years, as well as the continued expansion of irrigation in the Goomig Farmlands.
  • Surface water allocations and diversions for individual users and the urban system remained relatively unchanged. Town supply in particular changes little from year to year.

 

Bar graph of annual groundwater allocation and extraction for different users in the Ord region from 2011–12 to 2020–21. The groundwater allocations are associated with individual users and the urban system. In 2020–21, the allocations for individual users were similar to the previous 2 years. 85% of the allocation for individual users was taken. Allocation for the urban system has remained the same for the last 10 years. In 2019–20, 66% of the allocation was taken for the urban system.
Figure S7 Groundwater allocations and extractions in the Ord region for the years ending 30 June, from 2012–2021

 

  • In 2020–21, total groundwater allocation was 9 GL, mostly for mining purposes; 82% of the allocated groundwater was taken.
  • Water allocations and extractions for individual users increased from last year.
  • The large decrease in allocations for individual users in 2017–18 was due mainly to an adjustment in water entitlement for the Argyle Diamond Mine, one of the larger groundwater licences in the region.
  • Allocations and extractions for the urban system remained relatively unchanged. Town supply changes little from year to year.

 

Water market activity

Ord River Irrigation Area (istock © John Carnemolla)

 

 

Cultural and environmental water

Cathedral Gorge, Purnululu National Park, Ord region. Source: istock © Photon-photos

 

Cultural benefit

  • Periods of low flow in the lower Ord River are administered to support traditional hunting and fishing activities (see the Cultural water management section in the 'Region description'). This occurs when maintenance or inspection works on dam infrastructure are required.
  • During the 2020–21 year there were no reductions in flow administered in the lower Ord River.

 

Environmental benefit

Environmental water provisions

  • Environmental water provisions in the region are defined for the lower Ord River and include baseflow and wet season flood event requirements.

 

Example line graph of daily flow in the Ord River at Tarrara Bar, station number 809339. The flow is compared with the required environmental water provisions: a minimum baseflow and 4 flood peak thresholds. The flood peak thresholds include: flow greater than 100 cumecs for a total duration of 18 days; 4 flood events with peak discharges greater than 125 cumecs for a total duration of 10 days; 2 flood events with peak discharges greater than 200 cumecs for a total duration of 5 days; and 1 flood event with a peak discharge greater than 425 cumecs for a total duration of 2 days.
Figure S8 Example water provisions for the lower Ord River; required baseflows and wet season flood events are also shown

 

  • The required flow regimes are maintained from a combination of water releases from Lake Argyle and Lake Kununurra, and unregulated catchment inflow.
  • Larger, less frequent wet season flood events are also a component of the environmental water provisions, but are not shown on the figure above. These events occur as a result of runoff from the catchment downstream of Lake Argyle and cannot be managed by water releases from the storages.
  • A more detailed description of the environmental water provisions for the lower Ord River is provided in Chapter 4 of the Ord Surface Water Allocation Plan.

 

Environmental water outcomes

Line graph of daily flow in 2020–21 in the Ord River at Tarrara Bar, station number 809339. The flow is compared with the required environmental water provisions: a minimum baseflow and 4 flood peak thresholds. Key aspects of the daily flow graph are described in the text below the figure.
Figure S9 Flow in the lower Ord River compared with the required flow regime during the 2020–21 year

 

  • In 2020–21, flow in the lower Ord River exceeded the minimum baseflow requirements and all of the wet season peak flow requirements.
  • A larger flood peak in late-January 2021 met the required 1 in 2-year flood event (average daily discharge >750 m3/s). A flood peak that met the required 1 in 4-year flood event (average daily discharge >1,400 m3/s) occurred during the 2019–20 wet season (see the 2020 Account).