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Perth: Supporting information

  • Rainfall during the 2021-22 year was below average for the fourth consecutive year, although a wet winter contributed to high runoff and storage inflows across the region to start the 2021-22 year.
  • Total storage volumes increased by 13% during the 2021-22 year to finish at 55% full by 30 June 2022 to finish at 55% full by 30 June 2022 - the highest end-of-year storage since June 1993.
  • 60% of surface water allocations and 75% of groundwater allocations were taken in 2021-22, primarily for individual users.

Schematic representation of the Perth region. In 2021–22, runoff was 35% more than average. Storage volumes at 30 June 2021 were 55% full, marginally higher than the previous year. 60% of the total surface water allocation (184 GL) was taken. 75% of the total groundwater allocation (406 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

Wellington Dam, Perth region (Water Corporation © Darryl Peroni)

 

  • Total water asset volume in the Perth region at 30 June 2022 was 501 GL, around 94% of which was water held in surface water storages.
  • Just under 6% of the water assets are part of the irrigation scheme's claims to surface water, while the remaining volume of water assets was held in rivers.

 

Surface water assets

  • Surface water assets were 472 GL at 30 June 2022, representing around 94% of the total water assets for the region.

 

Table S1 Accessible storage volume (ML) at 30 June 2022 compared with the previous ten years
  2022 2021 2020 2019 2018 2017 2016 2015 2014 2013 2012
Canning 51,579 48,332 54,325 52,925 68,580 49,129 22,183 22,056 17,514 16,589 26,204
Churchman Brook 714 1,197 687 892 570 602 494 581 588 853 871
Drakes Brook 2,012 1,892 1,870 2,013 2,237 1,783 1,462 1,643 1,975 1,505 1,996
Harvey 32,331 15,362 12,087 22,051 19,167 15,576 16,823 29,642 31,500 17,872 21,215
Logue Brook 14,561 12,349 13,064 14,717 11,842 8,180 6,653 7,474 6,745 3,323 3,132
North Dandalup 42,405 35,380 35,765 38,275 28,282 15,114 25,703 34,501 20,631 11,934 19,289
Samon Brook 3,937 3,635 2,938 2,417 3,524 2,477 1,848 672 1,340 430 798
Serpentine 72,841 64,334 63,172 62,477 47,191 31,145 29,820 37,696 39,651 30,870 32,810
Serpentine Pipehead 1,525 1,533 1,687 1,665 1,555 1,497 1,557 1,506 1,718 1,648 476
South Dandalup 15,155 6,991 9,822 15,411 6,285 266 (663) 5,304 5,006 8 102
Stirling 36,588 22,203 20,142 24,673 24,914 12,235 6,175 12,652 25,393 20,880 19,561
Victoria 4,830 5,500 4,263 2,849 4,576 4,428 4,145 3,875 3,878 4,222 4,771
Waroona 7,577 6,995 7,875 10,663 10,909 6,356 4,053 6,190 6,087 4,050 2,953
Wellington 121,420 70,636 66,536 101,143 97,263 89,943 93,308 130,407 138,115 103,841 108,063
Wungong 39,188 42,767 38,246 35,909 37,560 34,122 26,035 16,113 20,936 22,717 29,887
Accessible total 446,663 339,106 332,479 388,080 364,455 272,853 239,596 310,312 321,077 240,742 272,128
Dead storage 23,098 23,098 23,098 23,098 23,098 23,098 23,098 23,098 23,098 23,098 23,098
Total storage 469,761 362,204 355,577 411,178 387,553 295,951 262,694 333,410 344,175 263,840 295,226
Total capacity 860,840 860,840 860,840 860,840 860,840 860,840 860,840 860,840 860,840 860,840 860,840
% full 54.6% 42.1% 41.3% 47.8% 45.0% 34.4% 30.5% 38.7% 40.0% 30.6% 34.3%

 

  • Storage volumes increased from 42% full at 30 June 2021 to 55% full at 30 June 2022 - the highest end-of-year storage volume since 1992-93.
  • The higher storage volumes over the previous few years are not only attributed to wetter winters, but also lower diversions and increased 'banking' of desalinated water in the storages. The Water Corporation's reduced reliance on surface water in recent years is a result of their adoption of a range of demand management strategies and continued development of climate-independent water sources in response to the long-term decline in storage inflows.
  • Three storages (Canning, Sepentine and Wellington) make up more than 55% of the region's total surface water storage.

 

Map of Perth region showing the status of each storage at 30 June 2022. The storages are colour coded into eleven categories of volume as a proportion of capacity. An inset line graph shows the time series of percentage-full storage volume between 01 July 2009 – 30 June 2022. Perth storages at 30 June 2022 were 55% full, 13% more than last year.
Figure S1 Percentage-full volume on 30 June 2022 for each storage and total daily storage volume from 2009–2022 (inset)

  • Storage volumes rose steeply in the first four months of the 2021-22 year, peaking around 70% full in November, following above-average rainfall during late-winter and early-spring.
  • Low rainfall from November 2021 to April 2022 resulted in storages dropping to roughly 50% full.
  • By the end of June 2022, storages had increased slightly to 55% full.
  • More detailed information on the individual storages within the region is available on the Bureau of Meteorology's Water Storage website.

 

Groundwater assets

  • Volumes of water stored in aquifers cannot be quantified due to a lack of available data, however, information on the total annual change in aquifer storage is available.

 

Table S2 Total annual change in aquifer volume in the region at 30 June 2022 compared with the previous eight years
  2022 2021 2020 2019 2018 2017 2016 2015 2014
Change (ML) 196,871 (70,695) (191,841) 50,556 206,060 114,320 (98,089) (52,075) 284,160

 

  • High rainfall during winter 2021 resulted in an increase in groundwater storage during 2021–22.
  • This was the first year, since 2019, where the aquifer volume increased within the region.

 

Water liabilities

Perth desalination plant, Perth region (Water Corporation © 2009)

 

  • Water liabilities in the Perth region refer to the volume of allocation remaining on licence entitlements at the end of the 2021–22 year.

 

Table S3 Volume of surface water allocation remaining at 30 June 2022
Description Individual users (ML) Irrigation scheme (ML)
  Opening balance at 1 July 2021 8,522 31,798
add Allocation 45,580 98,468
less Allocated diversion 44,093 66,112
less Adjustment and forfeiture 0 34,290
  Closing balance at 30 June 2022 10,009 29,864

 

Table S4 Volume of groundwater allocation remaining at 30 June 2022
Description Individual users (ML)
  Opening balance at 1 July 2021 102,376
add Allocation 303,993
less Allocation extraction 304,017
less Adjustment and forfeiture 0
  Closing balance at 30 June 2022 102,352

 

  • Many 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 Perth region is given in the Water use section below.

 

Water flows

Serpentine Reservoir, Perth region (Water Corporation © Darryl Peroni)

 

  • Total water inflows into the Perth region was 4,785 GL, 69% more than last year.
  • Surface water inflows contributed 2,603 GL (54%) of total water inflows. Runoff contributed to 63% of the total surface water inflows.
  • Groundwater inflows contributed 1,603 GL (34%) of total water inflows. Recharge from landscape contributed to 92% of the total groundwater inflows.
  • Urban water inflows contributed 513 GL (11%) of total water inflows. Wastewater collected contributed to 28% of the total urban water inflows.
  • Irrigation scheme inflows contributed 66 GL (1%) of total water inflows. Allocated diversion from irrigation scheme contributed to 100% of the total irrigation scheme inflows.
  • Total water outflows from the Perth region was 4,577 GL, 65% more than last year.
  • Surface water outflows contributed 2,504 GL (55%) of total water outflows. Outflow contributed to 76% of the total surface water outflows.
  • Groundwater outflows contributed 1,489 GL (33%) of total water outflows. Discharge to landscape contributed to 24% of the total groundwater outflows.
  • Urban water outflows contributed 517 GL (11%) of total water outflows. Supply of drinking water to urban users contributed to 44% of the total urban water outflows.
  • Irrigation scheme outflows contributed 66 GL (1%) of total water outflows. Irrigation delivery contributed to 72% of the total irrigation scheme outflows.

 

Water availability

 

Table S5 Annual surface water available in the Perth region at 30 June 2022 compared with the previous eight years
  2022 2021 2020 2019 2018 2017 2016 2015 2014
Water availability 2,168,316 1,156,078 995,343 1,619,143 1,845,319 1,276,018 730,646 1,328,213 1,583,552
Water accessible 291,797 255,024 288,188 346,888 253,097 237,275 282,218 326,641 309,017
Water taken 170,066 114,673 137,996 192,422 112,489 89,596 127,902 152,241 156,794

 

  • Physical surface water availability is calculated as the sum of storage volumes at the start of the year (see Water assets) and estimated inflows into storages and rivers during the year.
  • Surface water accessible is calculated as the sum of surface water allocations and other statutory rights, plus carrover at the start of the year.
  • Surface water availability in the Perth region in 2021–22 was above-average for the first time since 2019.
  • Water taken during the year is influenced by the physical water availability. Typically, water taken from surface water resources is lower than water availability and water accessible.

 

Water use

Desalination plant infrastructure, Perth region (Water Corporation © 2013)

 

Consumptive use

 

Table S6 Surface water taken for consumptive use in Perth region for the previous four years
Surface water 2022 2021 2020 2019
Individual users 44,093 45,173 43,998 43,599
Urban system 59,861 19,799 20,171 74,014
Irrigation scheme 66,112 49,701 73,827 74,809
Total 170,066 114,673 137,996 192,422

 

Table S7 Groundwater taken for consumptive use in Perth region for the previous four years
Groundwater 2022 2021 2020 2019
Individual users 304,017 300,495 301,028 310,525
Urban system 130,256 137,064 135,516 122,318
Total 434,273 437,559 436,544 432,843

 

  • Water taken from surface water and groundwater resources for consumptive use was 604,339 ML.
  • Total surface water diverted in the region was 170,066 ML, 48% more than last year.
  • 35% of the total surface water diverted was to the urban system which included sub-surface water flows and desalinated water 'banked' in the storages.
  • 39% of the diversions from surface water were to the irrigation scheme from storages in the Harvey and Collie river catchments, while the remaining 26% of the diversions were for individual users (comprising allocated and non-allocated diversions).
  • Total groundwater extracted in the region was 434,273 ML.
  • 70% of the groundwater extractions were for individual users, including both allocated and non-allocated while the remaining 30% of extractions was for the urban system.

 

Allocations and diversions

 

Table S8 Surface water allocations and diversions in the Perth region for the year ending 30 June
Surface water 2022 2021 2020 2019
Individual users
Carryover 8,522 8,522 8,522 8,522
Allocated announcements 45,580 45,173 43,998 43,599
Allocated diversions 44,093 45,173 43,998 43,599
% used 81% 84% 84% 84%
Irrigation scheme
Carryover 31,798 31,831 40,634 38,141
Allocated announcements 98,468 79,366 102,164 113,333
Allocated diversions 66,112 49,701 73,827 74,809
% used 51% 45% 52% 49%

 

  • In 2021–22, total surface water allocated was 184,368 ML (54,102 ML for individual users and 130,266 ML for the irrigation scheme).
  • Overall, 60% of the allocated surface water was taken (81% of individual users allocation was used, while 51% of the irrigation scheme allocations were used).
  • Total allocations for individual users was similar to last year, meanwhile allocations for the irrigation scheme were 17% more than last year following a wet winter in 2021.
  • Total diversions to individual users were slightly less than last year, while total diversions to the irrigation scheme was 33% more than last year. A portion of these diversions is sub-surface water flows and desalinated water transferred to the reservoirs for storage (see Urban system supply section below).

 

Table S9 Groundwater allocations and diversions in the Perth region for the year ending 30 June
Groundwater 2022 2021 2020 2019
Individual users
Carryover 102,376 102,377 102,377 102,377
Allocated announcements 303,993 300,494 301,028 310,525
Allocated extractions 304,017 300,495 301,028 310,525
% used 75% 75% 75% 75%

 

  • In 2021-22, total groundwater allocated was 304,017 ML, all for private and commercial use.
  • 75% of the allocated groundwater was taken.
  • Total groundwater extraction was similar to last year as 'banking' of groundwater in the surface water storages was increased due to the low storage inflows.

 

Urban system supply

 

Table S10 Water sources used in Perth's urban supply system during the 2021–22 year compared with the previous ten years
  2022 2021 2020 2019 2018 2017 2016 2015 2014 2013 2012
Surface water 59,861 19,799 20,171 74,014 1,135 -8,532 20,100 47,519 49,082 46,475 44,969
Groundwater 130,256 137,064 135,516 122,318 131,948 139,598 136,878 122,128 124,851 139,622 157,789
Desalinated water 116,198 143,641 140,047 89,295 148,904 149,822 138,645 119,457 113,060 95,770 78,847
Inter-region delivery 1,996 2,006 1,938 1,906 1,795 1,832 1,953 1,922 2,121 1,939 1,422
Total urban water supplied 308,311 302,510 297,672 287,533 283,782 282,720 297,576 291,026 289,114 283,806 283,027

 

  • Total inflow to the urban water supply system was 308,311 ML, around 2% more than the previous year.
  • Around 19% of the total urban supply was from surface water storages, while 42% was from groundwater extractions. Desalinated water made up roughly 38% of urban supply. The remaining 1% was from inter-region delivery.
  • High storage inflows following a wet winter in 2021 meant the Water Corporation could rely on surface water rather than desalinated water.
  • The increased surface water contribution in 2021-22, compared to the last two years, meant less desalinated water was required to meet urban demand.
  • The supply strategy requires 'banking' of groundwater and desalinated water in the urban surface water storages during low demand periods to buffer peak period supply requirements.
  • For more information on the use of desalinated water for the Perth region, please visit Perth Water Corporation's Desalinated website.

 

Water restrictions

 

  • A permanent daytime sprinkler ban and 2-day a week sprinkler roster have been in place for urban water users since 2001 and 3-day a week sprinkler roster for domestic garden bores since 2007. A permanent winter sprinkler ban was introduced in 2010.
  • For more information, refer to the Bureau of Meteorology's Water restrictions website.