National Water Account 2018

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Key findings

Climate and water

Water Accounting Statements

Supporting information

Region description

Reference information

Perth: Water access and use

Water rights and use

Surface water rights

Figure S14 Surface water allocation for each surface water management area in the region

• Surface water allocations in the Canning, Dandalup and Serpentine areas accounted for about half the allocation in the region and were mainly for urban purposes.
• Surface water allocations in the Harvey and Collie areas accounted for most of the other half of the total and included all the irrigation scheme allocations and about 30% of the urban system's allocations.

Figure S15 Allocated surface water diversions for each licence purpose

• 50% of the allocated surface water was used. Most of the surface water diverted in the region was for urban and agricultural purposes.
• The irrigation scheme accounted for most of the diversions for agriculture. Most of the diversions by individual users were for mining and industrial purposes, mainly for bauxite mining and alumina processing.

Figure S16 Surface water allocations and diversions in the Perth region for the years ending 30 June, from 2012–2018 

• Allocations for the irrigation scheme increased due to improved surface water availability.

• Diversions to the urban system were the lowest in six years as the Water Corporation reduced its reliance on surface water in favour of desalinated water and groundwater. A portion of these diversions is groundwater and desalinated water transferred to the reservoirs for storage (see Urban water system note).
• Allocations for individual users remained similar to the previous year.

Groundwater rights

Figure S17 Groundwater allocation for each groundwater management area in the region

• The Gnangara plan area had the highest groundwater allocations, about half for individual users and half for urban supply.
• The 'Other' category in Figure S17 includes 12 allocation areas in which 63% of the allocation was for individual users and 37% for urban supply.

Figure S19 Allocated groundwater extractions for each licence purpose

• 93% of the allocated groundwater was used. About one third of the region's allocated groundwater extraction was for urban purposes and about one third was for irrigated agriculture.  
• The remaining allocated extraction was mainly for watering of public parks and gardens, and for industrial and commercial purposes.

Figure S18 Groundwater allocations and extractions in the Perth region for the years ending 30 June, from 2012–2018

• Groundwater allocations for individual users were similar to the previous year.
• Groundwater extraction for urban supply was 5% lower than the previous year as improved surface water inflows led to reduced banking of groundwater in the surface water storages. 

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 restriction website.

Water market activity

• Most of the surface water transactions that occurred in the Perth region in 2017–18 were within the Harvey Water irrigation scheme, where 6% of the scheme's allocations changed hands in the year. 
• All groundwater transactions were entitlement trades, which represented about 1-2% of the total groundwater allocation. 
• Groundwater trading was most common in the superficial aquifer within the Gnangara plan area, which accounted for more than half the trades by both number and volume.
• More information on water trading in Western Australia is available from the Bureau's Water Market Dashboard and the Department of Water and Environmental Regulation website.

Cultural and environmental water

Environmental and cultural surface water provisions

• The main mechanisms for protecting ecological and cultural values of surface water systems in the region are regulated releases and annual allocation limits.
• Release requirements are defined in operating strategies negotiated between the Water Corporation and the Department of Water and Environmental Regulation, and in water allocation plans for the Middle Canning and Lower Collie rivers.
• The releases are made from water mains or the base of the dams, and are used to maintain baseflows, generate pulse flows important for ecological function, and meet cultural objectives.

Figure S20 Middle Canning River environmental release points

• The Middle Canning River allocation plan sets out requirements for releases from six locations along the Canning River to maintain downstream environmental and cultural river values.

Figure S21 Example water provisions for the Canning River; required baseflows and higher flow pulses are also shown 

• Environmental water releases to the Canning River are made during the drier months between November and May. The release schedule is based on rainfall and flow triggers.

Environmental and cultural surface water outcomes

Figure S22 Daily flow in the Canning River compared with the required flow regime during the 2017–18 year

• In 2017–18, releases to the Canning River began in early November based on the summer-flow release trigger of three consecutive days of flow below 9.3 ML/day.
• Flow remained above the target summer-flow release threshold for the entire release period. 
• A significant natural flushing event occurred in mid-January following the unseasonal rainfall associated with ex-tropical cyclone Joyce. 
• The releases finished in late May based on a rainfall trigger of 40 mm of rainfall recorded at Gosnells weather station. 

Environmental and cultural groundwater provisions

• Annual extraction limits in water allocation plans are the main instrument used to protect the environmental and cultural values of groundwater in the region (see Water management note).

 
Figure S23 Sites where Ministerial criteria have been set for groundwater levels

• In the Jandakot and Gnangara groundwater mounds, water level criteria for key sites have been set as Ministerial conditions under the Environmental Protection Act 1986 (see Ministerial Statements 688 and 819). 
• Over the past several years a number of the sites have been non-compliant with the Ministerial conditions due to a combination of factors including drying climate, groundwater extraction, and tree plantations limiting recharge (Department of Water 2017).
• In response the Department of Water and Environmental Regulation implements strategies to stabilise and restore groundwater levels. This includes reducing allocation limits, increasing recharge through land-use changes, improving water use efficiency, and investing in alternative water sources.
• For more information see the department's compliance reports for the Gnangara and Jandakot mounds

Environmental and cultural groundwater outcomes

Figure S24 Average groundwater levels in the Gnangara Mound from 1997 to 2018  

• Although groundwater levels remain relatively low, the improved rainfall conditions over the last two years have led to an increase in water levels compared to the previous five years. Water levels at 30 June 2018 were at their highest in eight years.
• Further information on the status of the Gnangara Mound is available from the Department of Water and Environmental Regulation's Gnangara groundwater microsite.