Perth: Supporting information

For the water account period 01 July 2022 - 30 June 2023

  • Rainfall during the 2022-23 year was below average for the fifth consecutive year, contributing to below-average runoff and storage inflows across the region.
  • Total storage volumes decreased by four percentage points during the 2022-23 year to finish at 51% full by 30 June 2023.
  • 60% of surface water allocations and 74% of groundwater allocations were taken in 2022-23, primarily for individual users.

Schematic representation of the Perth region. In 2022–23, runoff was 10% less than average. Storage volumes at 30 June 2023 were 51% full, marginally higher than the previous year. 84% of the total surface water accessible (208 GL) was taken. 83% of the total groundwater allocation (629 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 volumes in the Perth region at 30 June 2023 were 467 GL, around 94% of which was water held in surface water storages.
  • Around 6% of the water assets are part of the irrigation scheme's claims to surface water, while the remaining volume of water assets are held in rivers.

 

Surface water assets

  • Surface water assets were 440 GL at 30 June 2022, representing around 94% of the total water assets for the region.

 

Table S1 Accessible storage volume in the Perth region over the past six water accounting periods ending 30 June
  2023 2022 2021 2020 2019 2018
Canning 50,209 51,579 48,332 54,325 52,925 68,580
Churchman Brook 739 714 1,197 687 892 570
Drakes Brook 1,782 2,012 1,892 1,870 2,013 2,237
Harvey 32,331 32,331 15,362 12,087 22,051 19,167
Logue Brook 13,400 14,561 12,349 13,064 14,717 11,842
North Dandalup 40,096 42,405 35,380 35,765 38,275 28,282
Samon Brook 4,052 3,937 3,635 2,938 2,417 3,524
Serpentine 66,463 72,841 64,334 63,172 62,477 47,191
Serpentine Pipehead 1,453 1,525 1,533 1,687 1,665 1,555
South Dandalup 18,958 15,155 6,991 9,822 15,411 6,285
Stirling 26,883 36,588 22,203 20,142 24,673 24,914
Victoria 3,935 4,830 5,500 4,263 2,849 4,576
Waroona 7,464 7,577 6,995 7,875 10,663 10,909
Wellington 102,466 121,420 70,636 66,536 101,143 97,263
Wungong 44,673 39,188 42,767 38,246 35,909 37,560
Accessible total 414,904 446,663 339,106 332,479 388,080 364,455
Dead storage 23,098 23,098 23,098 23,098 23,098 23,098
Total storage 438,002 469,761 362,204 355,577 411,178 387,553
Total capacity 860,840 860,840 860,840 860,840 860,840 860,840
% full 50.9% 54.6% 42.1% 41.3% 47.8% 45.0%

 

  • Storage volumes decreased from 54.6% full at 30 June 2022 to 50.9% full at 30 June 2023 - a decrease of 3.7%.
  • Despite the decrease in storage volume, the region's total accessible storage volume was 36% above the long-term average. This is mainly attributed to wetter winters over the past few years, lowering diversions within the region, but also increasing the 'banking' of desalinated water in the region's storages. The Water Corporation's decision to reduce 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 2023 for each storage and total daily storage volume from 2009–2023 (inset)

  • Storage volumes steadily rose during the first few months of the 2022-23 year, following near-average rainfall during winter, with storages peaking around 65% full in September 2022. 
  • However, below-average rainfall from November 2022 to February 2023 resulted in a gradual decline in storage volumes, falling to 50% by autumn, and despite above-average rainfall throughout March 2023 and April 2023, storages reached as low as 48% during mid-May 2023.
  • By the end of June 2023, end-of-year storages were sitting at 50.9% on 30 June 2023.
  • 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 Perth region over the past six water accounting periods ending 30 June
Groundwater 2023 2022 2021 2020 2019 2018
Change in aquifer volume - 196,871 (70,695) (191,841) 50,556 206,060

 

  • Total annual change in aquifer volumes could not be calculated for the 2022-23 year due to a lack of necessary data. 

 

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 2022-23 year.

 

Table S3 Opening and closing balance of surface water allocations for individual users in the Perth region over the past six water accounting periods
Description 2023 2022 2021 2020 2019 2018
Opening balance at 01 July 10,009 8,522 8,522 8,522 8,522 8,522
add Allocation 44,325 45,580 45,173 43,998 43,599 38,455
less Allocated diversion 44,325 44,093 45,173 43,998 43,599 38,385
less Adjustment and forfeiture 0 0 0 0 0 70
Closing balance at 30 June 10,009 10,009 8,522 8,522 8,522 8,522

 

Table S4 Opening and closing balance of surface water allocations for the irrigation scheme in the Perth region over the past six water accounting periods
Description 2023 2022 2021 2020 2019 2018
Opening balance at 01 July 29,864 31,798 31,831 40,634 38,141 41,081
add Allocation 99,500 98,468 79,366 102,164 113,333 107,420
less Allocated diversion 65,991 66,112 49,701 73,827 74,809 72,969
less Adjustment and forfeiture 35,000 34,290 29,698 37,140 36,031 37,391
Closing balance at 30 June 28,373 29,864 31,798 31,831 40,634 38,141

 

Table S5 Opening and closing balance of groundwater allocations for individual users in the Perth region over the past six water accounting periods
Description 2023 2022 2021 2020 2019 2018
Opening balance at 01 July 102,352 102,376 102,377 102,377 102,377 102,376
add Allocation 304,530 303,993 300,494 301,028 310,525 308,161
less Allocation extraction 302,700 304,017 300,495 301,028 310,525 299,520
less Adjustment and forfeiture 0 0 0 0 0 8,640
Closing balance at 30 June 104,182 102,352 102,376 102,377 102,377 102,377

 

  • 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 3,811GL, 20% less than last year.
  • Surface water inflows contributed 1,893GL (49%) of total water inflows. Runoff contributed to 60% of the total surface water inflows.
  • Groundwater inflows contributed 1,352GL (36%) of total water inflows. Recharge from landscape contributed to 92% of the total groundwater inflows.
  • Urban water inflows contributed 499GL (13%) of total water inflows. Wastewater collected contributed to 29% of the total urban water inflows.
  • Irrigation scheme inflows contributed 67GL (2%) 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 3,948 GL, 14% less than last year.
  • Surface water outflows contributed 1,922GL (49%) of total water outflows. Outflow to sea contributed to 73% of the total surface water outflows.
  • Groundwater outflows contributed 1,477GL (37%) of total water outflows. Discharge to landscape contributed to 24% of the total groundwater outflows.
  • Urban water outflows contributed 484GL (12%) of total water outflows. Supply of drinking water to residential customers contributed to 38% of the total urban water outflows.
  • Irrigation scheme outflows contributed 66GL (2%) of total water outflows. Irrigation delivery contributed to 73% of the total irrigation scheme outflows.
  • A more detailed breakdown of inflows and outflows is given in the Statement of Changes in Water Assets and Water Liabilities or the Perth region.

 

Water availability

 

Table S6 Annual surface water available in the Perth region over the past six water accounting periods ending 30 June
Surface water 2023 2022 2021 2020 2019 2018
Water availability 2,016,585 2,588,051 1,236,124 1,126,134 1,775,330 1,868,117
Water accessible 208,289 201,255 141,696 163,580 230,946 144,588
Water taken 174,780 167,412 112,031 135,243 192,422 110,067
% water accessible taken 84% 83% 79% 83% 83% 76%

 

  • 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 availability in the Perth region in 2022-23 was above average for the second consecutive year, mainly due to the region's wetter winters over the past few years, increasing the physical surface water availability across the region.
  • Surface water accessible is calculated as the sum of surface water allocations and other statutory rights, plus carrover at the start of the year.
  • 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 accessible for take and water taken were both above average, reflecting the availability of surface water across the region.

 

Water use

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

 

Consumptive use

 

Table S7 Surface water taken for consumptive use in the Perth region over the past six water accounting periods ending 30 June
Surface water 2023 2022 2021 2020 2019 2018
Individual users 44,325 44,093 45,173 43,998 43,599 38,385
Urban system 64,464 57,207 17,157 17,418 74,014 (1,287)
Irrigation scheme 65,991 66,112 49,701 73,827 74,809 72,969
Total 174,780 167,412 112,031 135,243 192,422 110,067

 

Table S8 Groundwater taken for consumptive use in the Perth region over the past six water accounting periods ending 30 June
Groundwater 2023 2022 2021 2020 2019 2018
Individual users 302,700 304,017 300,495 301,028 310,525 299,520
Urban system 136,790 130,256 137,064 135,516 122,318 131,948
Total 439,490 434,273 437,559 436,544 432,843 431,468

 

  • Water taken from surface water and groundwater resources for consumptive use was 614,270ML, slightly more than the previous year.
  • Total surface water diverted in the region was 174,780ML, around 4% more than last year.
  • Around 37% of the total surface water diverted was to the irrigation scheme from storages in the Harvey and Collie river catchments, while roughly 37% of the diversions from surface water were to the urban system which included sub-surface water flows and desalinated water 'banked' in the storages.
  • The remaining 25% of the surface water diversions were for individual users (comprising allocated and non-allocated diversions).
  • Total groundwater extracted in the region was 439,490ML, slightly more than last year.
  • Individual users, including both allocated and non-allocated accounted for approximately 69% of the total groundwater extractions, while the remaining 31% of extractions was for the urban system.

 

Allocations and diversions

 

Table S9 Surface water allocations and diversions in the Perth region over the past six water accounting periods ending 30 June
Surface water 2023 2022 2021 2020 2019 2018
Individual users
Carryover 10,009 8,522 8,522 8,522 8,522 8,522
Allocated announcements 44,325 45,580 45,173 43,998 43,599 38,455
Allocated diversions 44,325 44,093 45,173 43,998 43,599 38,385
% used 82% 81% 84% 84% 84% 82%
Irrigation scheme
Carryover 29,864 31,798 31,831 40,634 38,141 41,081
Allocated announcements 99,500 98,468 79,366 102,164 113,333 107,420
Allocated diversions 65,991 66,112 49,701 73,827 74,809 72,969
% used 51% 51% 45% 52% 49% 49%
Total
Carryover 39,873 40,320 40,353 49,156 46,663 49,603
Allocated announcements 143,825 144,048 124,539 146,162 156,932 145,875
Allocated diversions 110,316 110,205 94,874 117,825 118,408 111,354
% sued 60% 60% 58% 60% 58% 57%

 

  • In 2022-23, total surface water allocated was 183,698ML (54,334ML for individual users and 129,364ML for the irrigation scheme).
  • Overall, roughly 60% of the allocated surface water was taken (82% of individual users allocations were used, while 51% of the irrigation scheme allocations were used).
  • Total allocations for both individual users and the irrigation scheme were similar to the previous year, reflecting the wetter winters over the past few years allowing allocations to be higher than usual.
  • Total diversions were similar to last year, much for the same reasons as total allocations. 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 S10 Groundwater allocations and diversions for individual users in the Perth region over the past six water accounting periods ending 30 June
Groundwater 2023 2022 2021 2020 2019 2018
Individual users
Carryover 102,352 102,376 102,377 102,377 102,377 102,376
Allocated announcements 304,530 303,993 300,494 301,028 310,525 308,161
Allocated extractions 302,700 304,017 300,495 301,028 310,525 299,520
% used 74% 75% 75% 75% 75% 73%

 

  • Total groundwater allocated in 2022-23, all for private and commercial use, was 406,882ML, similar to last year.
  • Roughly 74% of the allocated groundwater was taken during the 2022-23 year.
  • Total groundwater extractions have been consistent over the past few years as 'banking' of groundwater in the surface water storages was increased due to the low storage inflows.

 

Urban system supply

 

Table S11 Water sources used in Perth's urban supply system over the past six water accounting periods ending 30 June
 Water sources 2023 2022 2021 2020 2019 2018
Surface water 64,464 57,207 17,157 17,418 74,014 (1,287)
Groundwater 136,790 130,256 137,064 135,516 122,318 131,948
Desalinated water 94,474 116,198 143,641 140,047 89,295 148,904
Inter-region delivery 1,980 1,996 2,006 1,938 1,906 1,795
Total urban water supplied 297,708 305,657 299,868 294,919 287,533 281,360

 

  • Total inflow to the urban water supply system was 297,708ML, around 3% less than the previous year, but 3% above the long-term average.
  • Around 22% of the total urban supply was from surface water storages, while 46% was from groundwater extractions. 
  • Desalinated water made up roughly 32% of urban supply, with the remaining amount of water sourced in the urban supply system from inter-region delivery.
  • High storage inflows over the past few years has meant that Water Corporation could rely on surface water resources rather than desalination water. As a result, the increase in surface water contribution over the last two years has required less desalinated water to meet urban demand.
  • During low demand periods, the supply strategy requires 'banking' of groundwater and desalinated water in the urban surface water storages 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 Desalination 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.