National Water Account 2017

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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 allocations

Surface water rights

 Figure S14 Surface water allocation by surface water allocation areas in the region, 2016–17

• Surface water allocations in the Canning River, Dandalup River System and Serpentine River Catchment allocation areas accounted for close to half of the surface water allocation in the region and were primarily for urban purposes.
• Surface water allocations in the Harvey and Collie allocations accounted for most of the other half of the total and included all the allocations for the irrigation scheme. The Harvey allocation area also included about 30% of the urban system's surface water allocations.

Figure S15 Surface water allocations and diversions in the Perth region for the years ending 30 June, from 2012–2017

• Allocations and diversions for irrigation scheme supply declined due to low surface water availability in the region and wetter than normal summer conditions.

• Diversions to the urban system decreased for the second successive year due to continued low surface water availability.
• A portion of the surface water diversion to the urban system is made up of groundwater and desalinated water transferred to the reservoirs for storage; in 2016–17 these transfers exceeded the volume of diversion to the urban system by around 8,500 ML (see Urban water system note).
• Allocations for individual users remained similar to the previous year.

Figure S16 Surface water allocation to individual users for each licence purpose

• Most of the surface water allocation for individual users is used for mining and industrial purposes, primarily for bauxite mining and alumina processing.

Groundwater rights

 Figure S17 Groundwater allocation by groundwater allocation areas in the region, 2016–17

• The Perth allocation area had the highest groundwater allocations, which comprised about 58% for individual users and 42% for urban supply.
• The 'Other' category in Figure S17 covers 12 allocation areas, mainly located on the coastal plain along the west of the region; about 63% of the allocation in these areas was for individual users and 37% for urban supply.

Figure S18 Groundwater allocations and extractions in the Perth region for the years ending 30 June, from 2012–2017

• Groundwater allocations for individual users decreased slightly from the previous year, likely due to a combination of the government policy of recouping unused entitlments to reduce future stress to the aquifers, and expiry of a number of licences related to dewatering and water supply for construction projects.
• Groundwater extractions for urban supply were similar to the previous year due to continued low surface water availability.

Figure S19 Groundwater allocation to individual users for each licence purpose

• Most of the groundwater allocation for individual users is sourced from the aquifers beneath the coastal plain in the west of the region for irrigated agriculture, and watering of public parks and gardens.

Water restrictions

• A permanent daytime sprinkler ban and 2-day a week sprinkler roster has 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

• All surface water transactions that occurred in the Perth region in 2016–17 were within the Harvey Water Irrigation Area. Trading is relatively established in the irrigation scheme, with about 17% of the overall allocation having changed hands during the 2016–17 year.

• Other than within the Harvey Water Irrigation Area, all other water trading in the region was for groundwater. The volume of groundwater allocation and entitlement traded represented about 1-2% of the total groundwater allocation.
• More information on water trading in Western Australia can be found on the Department of Water and Environmental Regulation website.

Water use

Economic and social benefit

• For a summary of the water used for various economic and social purposes within the Perth region, refer to Surface water rights and Groundwater rights above.

Environmental and cultural benefit

Environmental and cultural surface water provisions

• The two main mechanisms for protecting ecological and cultural values of surface water systems in the Perth region are regulated releases and annual allocation limits set by the Department of Water and Environmental Regulation.
• 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 used to maintain baseflows, generate pulse flows important for ecological function, and meet cultural objectives such as tourism amenity in the Harvey River. The releases are made from urban water mains or from the base of the dams.

Figure S20 Middle Canning River environmental release points

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

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 2016–17 year

• In 2016–17, 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 all days except two in early February. A significant flushing event occurred in mid-February following the record local rainfall.
• The releases finished in late May based on the rainfall trigger defined in the allocation plan 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 Perth region (see Water management note).

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

• In the environmentally sensitive 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). The Department of Water and Environmental Regulation is responsible for monitoring water levels at the sites and managing the resource within the conditions.
• 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 abstraction, and water use by tree plantations (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 annual environmental compliance reports.

Environmental and cultural groundwater outcomes

Figure S24 Average monthly change in water levels from July 2012 for 25 groundwater monitoring sites with Ministerial conditions on the Gnangara Mound

• The increased rainfall in 2016–17, including the record summer rainfall, contributed to reduced summer drawdowns and higher winter recoveries in groundwater levels across the Gnangara Mound compared with the previous 5 years (see Climate and water).
• These water level responses reflect the increased groundwater recharge that occurred during the 2016–17 year, as well as likely reduced summer groundwater extraction due to wet summer conditions.
• More hydrographs for key groundwater monitoring sites are available from Gnangara and Jandakot Mound data on the Department of Water and Environmental Regulation webpage.