Perth
Water access and use

This note provides information about the water access rights granted by jurisdictions to the users of the region's water resources and the associated allocation announcements, diversions, adjustments and forfeitures.

The 2012 Account acknowledges that the legislative water resource management frameworks relating to Australian water rights vary greatly across jurisdictions, sometimes making comparisons difficult. To facilitate meaningful comparisons between the water accounting reports included in the 2012 Account, the Bureau has developed and applied an accounting concept to classify and report water entitlements within a water asset/water liability framework.

According to that framework, water rights for the Perth region for the 2011–12 year have been classified as shown in Tables 1 and 2.

Table 1 summarises the surface water rights for the Perth region, including surface water allocations, abstractions, adjustments and forfeitures during the 2011–12 year.

Note that water allocations (line items 21.2 and 21.3), abstractions (line items 17.12 and 17.13) and adjustments and forfeitures (line items 13.2 and 13.3) shown in italics in Table 1 relate to surface water entitlements to the urban water system and irrigation schemes respectively. These line items appear in the Surface water section of the 'Water resources and systems' note; however, they do not appear in the water accounting statements because they are transactions that occurred within the region. These transactions did not impact the region's total water assets and water liabilities.

More information about the items presented in Table 1 is provided in the linked line item notes.

Table 2 summarises the groundwater rights for the Perth region, including groundwater allocations, abstractions, adjustments and forfeitures during the 2011–12 year.

The total water allocation announcement is assumed to equal 100% of the annual entitlement.

Note that water allocations (line items 22.2 and 22.3), abstractions (line items 18.12 and 18.13) and adjustments and forfeitures (line items 14.2 and 14.3) shown in italics in Table 2 relate to groundwater entitlements to the urban water system and irrigation schemes respectively. These line items appear in the Groundwater section of the 'Water resources and systems' note; however, they do not appear in the water accounting statements because they are transactions that occurred within the region. These transactions did not impact the region's total water assets and water liabilities.

More information about the items presented in Table 2 is provided in the linked line item notes.

During the 2011–12 year, urban-water users and garden-bore users were on a sprinkler roster.

Whilst on the sprinkler roster, urban-water users in the Perth region can use their sprinklers two days per week. The sprinkler days are determined by the last digit of the user's street number and sprinklers must be used before 9am and after 6pm.

The Harvey Water Irrigation Cooperative can trade water with the Water Corporation (see Water market rules: inter-valley and within-valley trading section in the 'Contextual information').

During the 2009–10 year, 1,500 ML of water from the Harvey Water Irrigation Area was transferred to surface water storages as a one-off external trade with the Water Corporation. However, no such trade occurred during the 2011–12 year (or the 2010–11 year).

Surface water and groundwater resources within the Perth region are used for public water supply, irrigation scheme supply, as well as private water supply for purposes such as agriculture, industry and mining. For a summary of the water volumes allocated for various economic purposes within the region, including the actual volumes abstracted, refer to line items 32.3 and 33.3.

Water is released from Harvey Reservoir during the irrigation season (generally November—May) to ensure that there is flow along Harvey River downstream of the reservoir. It is considered important that Harvey River has flow for aesthetic reasons, primarily because this region of the Harvey River is a tourist precinct.

Information on legislative, administrative and governing arrangements of environmental water in the region is available in the Environmental water management section in the 'Contextual information'.

Water for environmental benefit in the Perth region is provided according to three different environmental water management scenarios: planned, partly regulated surface water; planned groundwater; and held environmental water (groundwater).

For each scenario, the information, if available, is structured as follows:

• Environmental water determinations: the environmental objectives that define specific water levels and flow criteria at key representative sites that must be met.
• Environmental water commitments: the instruments in place to achieve the environmental water determination, e.g. environmental water storage release rules, water access rules to limit abstractions, rules on diversion to wetlands and annual environmental watering plans.
• Environmental water outcomes: the water levels and flow conditions that occurred during the year and the extent of the compliance with respect to the criteria set in the environmental water commitments.

The dominant feature of environmental water management in this scenario is the ability to control or influence flow by operational releases from storages. For the Perth region, these environmental water releases are referred to as riparian releases.

Environmental water determination

Downstream of storages that supply water to the urban water system

Environmental water provisions are currently only defined for the Canning River. These are outlined in the Lower Canning River Surface Water Allocation Plan.

The plan outlines a flow regime required to maintain current ecological conditions in the Lower Canning River. These ecological requirements for the Canning River were developed by Radin et al. (2010), and include the maintenance of:

• flow connectivity
• pool depth as refuge habitat
• a minimum flow over riffles for macro-invertebrates
• prevention of anoxic conditions in pools.

Downstream of storages that supply water to the irrigation scheme

There are environmental water provisions for river reaches downstream of the following storages that supply water to irrigation schemes within the Perth region:

• Drakes Brook
• Logue Brook
• Samson Brook
• Stirling
• Wokalup Pipehead.

These environmental water provisions are largely based on three flow components:

• continuous (ecological) flow provisions
• fish migration and reproduction
• maintenance of channel form and riparian vegetation.

However, no information on these environmental water provisions is available.

Environmental water commitment

Riparian releases are generally made seasonally from surface water storages and water mains within the Perth region. These releases are made from storages within the urban and irrigation water supply systems.

The timing, volume and point of release are determined through liaison between the Department of Water, Water Corporation and downstream water users.

Downstream of storages that supply water to the urban water system

Riparian releases from the surface water storages that supply water to the urban water system are made to meet the required water regime on the Canning River.

The Water Corporation operates the storages and manages the release of water from the environmental release points. The Department of Water monitors flows at each station to ensure these minimum flows are maintained.

Water release is only required during the drier months between November and May. The standard summer-flow schedule at each release point is given in Table 3. The summer-flow schedule commences when flow at a key downstream gauging station along the Canning River (Station 616027: Canning River – Seaforth) falls below 9.3 ML/day for three consecutive days in late spring.

There is also provision for up to three higher volume 'pulse' flows to aid upstream fish migration during summer. These pulse flows are scheduled to be released up to three times a year during the summer period. The pulse duration is five days, after which flows return to the above standard summer-flow schedule. Pulse flows may be cancelled if winter rainfall is low.

A more detailed description of these riparian release schedules are provided in Appendix B of the Lower Canning River Surface Water Allocation Plan.

Downstream of storages that supply water to the irrigation scheme

The Water Corporation is responsible for the release of water from irrigation supply storages to ensure that these environmental water provisions are met at specific compliance points downstream of the storages.

Environmental water outcomes

Downstream of storages that supply water to the urban water system

Table 4 shows the volume of riparian releases made during the 2011–12 year from the Lower Canning River. Almost the entire volume of water released occurred between November and May.

No information was available to evaluate the compliance of these releases with the statutory environmental water provisions (see 'Environmental water determination' in this section).

Other riparian releases were also made from other surface water sources within the Perth region (Table 5). However, there were no statutory requirements associated with these releases.

Downstream of storages that supply water to the irrigation scheme

No information available.

In the Perth region, limiting the groundwater extractions is the main instrument used to meet the requirements of the groundwater-dependent ecosystems. However, at the time of preparing this 2012 Account, no information was available on environmental water determination (target groundwater levels).

The Department of Water is currently working on a method to determine the water level surface in the unconfined aquifer necessary to maintain and protect groundwater-dependent ecosystems and the saltwater interface (the 'extractable limit' water level surface).

In the Perth region, managed aquifer recharge is used as an additional mechanism to supplement the requirements of groundwater-dependent ecosystems. Only limited information about the environmental water outcomes was available to be included in this report.

Environmental water outcomes

Two types of aquifer recharge occurred in the Perth region during the 2011–12 year, and these are described in the following line items:

• 10.9 Managed aquifer recharge – urban water system
• 10.10 Discharge from urban water system to groundwater.

The total volume of aquifer recharge was equivalent to approximately 2% of the total treated wastewater discharged from treatment plants within the region.