• Region overview
• Contextual information
  • Physical information
  • Administration
  • Water rights
  • Climate overview
  • Water overview
• Water Accounting Statements
  • Water Assets and Water Liabilities
  • Changes in Water Assets and Water Liabilities
  • Water Flows
• Notes
  • Accounting policies
  • Supporting information
  • Quantification approach
  • Reconciliations
  • Water resources & systems
  • Water access & use
  • Future outlook
  • References
• Accountability statement

Perth
Supporting information

Introduction

The following set of notes provides consolidated reports for each of the water stores and systems within the Perth region during the 2013–14 year. The water stores and systems included in the region are shown in Figure 1.

For more information about the region, please refer to the General description section of the 'Contextual information'.

Figure 1 Water stores and systems within the Perth region 

Information on all water flows to and from each water store and system are presented in the following set of notes, including between-store flows and transfers that are not presented in the water accounting statements. The between-store flows and transfers that occur in the region are presented in Figure 2.

Figure 2 Between-store flows that occur within the Perth region 

The between-store flows and transfers (Figure 2), which are eliminated from the region's water accounting statements, are shown in italics throughout the following set of notes. The allocation announcement, forfeiture, and allocation remaining line items associated with each between-store abstraction (brown arrows in Figure 2) are also shown in italics in the following notes. 

Surface water store

Surface water assets

The volume of the surface water assets represents water held in storages (204,898 ML). The volume of water in rivers, lakes and wetlands could not be quantified due to a lack of available data; however, the volume of water held in channels and lakes is considered to be relatively small compared to the volume held in storages.

The location of each storage within the Perth region and the volume of water in each storage (including dead storage) as a percentage of total storage capacity at the end of the 2013–14 year is shown in Figure 3.

Figure 3 Percentage-full volume on 30 June 2014 for each storage 

The overall storage volume within the Perth region increased during the 2013–14 year from 24% to 31% capacity. The water volume in almost all the storages increased during the year; however, with the exception of four storages (Drakes Brook, Harvey, Serpentine Pipehead and Stirling), storage volume was less than 50% capacity at 30 June 2014. The volume of the four largest storages (Canning, North Dandalup, Serpentine and South Dandalup) at 30 June 2014 was less than 30% capacity.

The increase in surface water storage during the 2013–14 year is primarily attributed to the increase in inflows into the storages compared to the 2012–13 year. According to the Water Corporation website, inflow into the storages during the year was approximately 80,000 ML, greater than the inflow recorded during the previous year of less than 30,000 ML. 

Storage volumes also include a portion of groundwater and desalinated water transferred from the urban water supply system. These transfers mainly occur in order to store winter production of desalinated water and groundwater and to prepare for summer peak demand (see Surface water inflows below).

Total volume of water within each storage at 30 June 2014, and at the end of the previous three years (2012, 2011 and 2010) is given in Figure 4.

Figure 4 Total volume of water in each storage at 30 June 2014, 2013, 2012 and 2011

Surface water liabilities

Surface water liabilities in the Perth region refer to the volume of surface water allocation remaining on licence entitlements at the end of the 2013–14 year for:

• individual users (12,587 ML)
• urban water system (0 ML)
• irrigation scheme (12,718 ML).

Most of the water supply licences for the region do not have a water management year that ends on 30 June. Therefore, the volume of allocation remaining at the end of the 2013–14 year for the Perth region is the unused component of the annual allocation for these licence entitlements.

The allocation remaining for each licence entitlement is provided in tables 1–3.

Surface water inflows and outflows

A schematic diagram representing all the inflows and outflows associated with the surface water store in the Perth region is provided in Figure 5.

Figure 5 Water inflows and outflows for Perth's surface water store during the 2013–14 year

Surface water inflows

The largest natural water inflow is runoff to surface water (787,143 ML). The volume of runoff during the 2013–14 year is more than double that during the previous year, which reflects the increase in rainfall experienced across the region during the year (see Climate overview).

The remaining two natural surface water inflows are precipitation on surface water (25,009 ML) and groundwater discharge (283,158 ML). The volume of precipitation represents rainfall that fell on the major storages within the region; the groundwater discharge volume represents the volume of water that discharged from Perth's superficial aquifers to rivers and drains.

The largest transfer of water to the surface water store is discharge from the urban water system (59,469 ML). This volume is comprised of two components:

• internal water transfers (56,916 ML): a combination of surface water, groundwater and desalinated water transferred from the urban water supply system in order to store winter production of desalination water and groundwater and to balance the storages to prevent overflow and enable summer peak supply capacity.
• riparian releases (2,553 ML): water discharged from water storages and water mains within Perth's urban water supply system into rivers for environmental benefit (see the Environmental benefit note).

The remaining two transfers of water to the surface water store are delivery of water from outside the region (2,539 ML), which represents the water transferred from the Collie River Irrigation District into the Harvey Reservoir, and point return from the irrigation scheme (– ML), which represents return flow from the Harvey Water Irrigation Area to rivers. This point return flow is not measured and cannot be quantified accurately.

Surface water outflows

The largest natural water outflow is the river outflow from the region (555,390 ML), which refers to the annual volume of flow to the sea from the Swan, Canning, Murray and Harvey rivers during the 2013–14 year. This outflow is more than double that during the previous year, which primarily reflects the improved flow conditions in these rivers compared to the very low flows experienced during the 2012–13 year (see Water overview).

Evaporation from surface water during the 2013–14 year was 33,600 ML, which represents evaporation from the major storages within the region. Total evaporation during the 2013–14 year is slightly higher than that during the previous year, which may be attributed to the increased rainfall (and hence water availability) that occurred during the year (see Climate overview).

The total annual leakage from surface water storages within the Perth region during the 2013–14 year was 196 ML.

Entitled water abstractions from the surface water store are described in Surface water allocation diversions below.

The volume of river and floodplain losses cannot be quantified accurately due to a lack of available data; however, these losses are considered to be relatively large and its omission may have a material impact on the water balance of the surface water store (see Balancing item).

Surface water allocation diversions

Entitled diversion of allocated surface water to the urban water system (105,998 ML) during the 2013–14 year accounts for more than 60% of the total allocation diversion in the Perth region. This volume represents the water diverted from storages to the Perth region's Integrated Water Supply System. The volume of water diverted from each storage to the urban water system is shown in Figure 6.

Figure 6 Surface water allocations and diversions for the urban water system during the 2013–14 year

Entitled diversion of allocated surface water for individual users during the 2013–14 year was 33,861 ML, which accounts for almost 20% of the total allocation diversion. Licences primarily relate to water use for the mining and industrial sectors (see Surface water allocation announcements below).

Entitled diversion of allocated surface water to the irrigation scheme (34,466 ML) during the 2013–14 year accounts for approximately 20% of the total allocation diversion. This volume represents the water diverted to the Harvey and Waroona irrigation districts within the Harvey Water Irrigation Area.

Surface water forfeitures

The portion of surface water allocation that has not been abstracted at the end of the water year is forfeited, that is, there is no carry-over of entitlements into the next water year. Water forfeitures in the Perth region during the 2013–14 year relate to licence entitlements for:

• individual users (5,219 ML)
• urban water system (142,071 ML)
• irrigation scheme (5,807 ML).

Surface water allocation announcements

Surface water allocation announcements in the Perth region during the 2013–14 year refer to surface water supply to:

• individual users (33,958 ML)
• urban water system (247,950 ML)
• irrigation scheme (46,481 ML).

There are approximately 200 individual users that primarily source water from rivers within the region for mining and industrial purposes. The water supply licences are divided into licence entitlement purposes. Figure 7 shows the annual allocation announcement to individual users for each licence purpose for the 2013–14 year.

Figure 7 Surface water allocation announcements to individual users for each licence purpose for the 2013–14 year

The surface water allocation announcements for the urban water system relate to licences to divert water from storages to the Perth region's Integrated Water Supply System. The annual allocation for each urban licence during the 2013–14 year is shown in Figure 6 above. The surface water allocation announcements for the irrigation scheme relate to licences to divert water from storages to the Harvey Water Irrigation Area. 

A more detailed description of surface water allocations and associated water rights in the Perth region is given in the Surface water rights note.

Surface water balancing item

The balancing item volume represents the difference between the measured opening and closing balances of the surface water store, after physical inflows and outflows have been applied (Table 4). This item is an indication of both the accuracy of the volumes reported and the degree to which the reported water flows represents a complete surface water store balance.

The calculation of the water balance on the surface water store yielded a balancing item of 348,401 ML. This is larger than the total surface water store volume at the end of the 2013–14 year and approximately 30% of the total surface water inflows during the year. The positive balancing item indicates that either the inflows are too high or the outflows are too low.

The balancing item is primarily attributed to the fact that river and floodplain losses cannot be quantified in the account. It is likely that these losses are a relatively large source of surface water decrease throughout the region. For example, the portion of total runoff to surface water (787,143 ML) that occurred upstream of Perth's storages is approximately 350,000 ML. According to the Water Corporation website, actual measured inflow into the storages during the year was approximately 80,000 ML, which represents a 270,000 ML unaccounted-for difference in the region (upstream of reservoirs) during the 2013–14 year. A portion of this difference can be attributed to river losses; the remainder is likely to be an overestimation of the runoff to surface water.

Runoff to surface water, which is a large source of surface water increase, is derived from a rainfall–runoff model and it is reasonable to expect a 10–20% uncertainty around the estimated runoff volume (+/– 155,000 ML).

The balancing item is also attributed to uncertainty associated with river outflow from the region (a large source of surface water decrease). The river outflow to sea is based on measured flow data collected at the most downstream station along a river. There is no adjustment made for the contributing area below the gauging station (see Quantification approaches). As such, outflow to sea is likely to be underestimated by 10–20% (110,000 ML).

Groundwater store

Groundwater assets

The aquifers in the Perth region are described in the Groundwater section of the 'Contextual information'. While good information exists on water movement to and from the aquifers (see Groundwater inflows and outflows below), no value is available for the volume of water stored in the aquifers.

The Gnangara groundwater system is the largest and most important groundwater resource in the region. 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).

Preliminary results have shown that there are some areas of the Gnangara system where the aquifer levels are above this extractable limit and other areas where the aquifer levels are below this limit. Water above the extractable limit is considered to be a water asset. In areas where the water table is below the extractable limit, the gap between the water table and the extractable limit is considered to be a water liability to the environment (i.e., water is owed back to the water table to raise it to the extractable limit).

The Department of Water is working on a similar method for the confined aquifers in the Gnangara groundwater system, but it will be some time before these methods can be applied to the other groundwater aquifers in the Perth region (including Stakehill and Rockingham water table aquifers).

It should be noted that groundwater levels in the Jandakot groundwater system have already been prescribed to maintain and protect groundwater-dependent ecosystems; however, at the time of preparing this water accounting report the Department of Water had not commenced work to determine the volumes of water asset and water liability in the Jandakot system.

Groundwater liabilities

Groundwater liabilities in the Perth region refer to the volume of groundwater allocation remaining on licence entitlements at the end of the 2013–14 year for:

• individual users (116,430 ML)
• urban water system (0 ML).

Most of the water supply licences for the region do not have a water management year that ends on 30 June. Therefore, the volume of allocation remaining at the end of the 2013–14 year for the Perth region is the unused component of the annual allocation for these licence entitlements.

The allocation remaining for each licence entitlement is provided in tables 5 and 6.

Groundwater inflows and outflows

A schematic diagram representing all the inflows and outflows associated with the groundwater store in the Perth region is provided in Figure 8.

Figure 8 Water inflows and outflows for Perth's groundwater store during the 2013–14 year 

Groundwater inflows

The largest water inflow is recharge from landscape (1,937,932 ML), which accounts for more than 95% of the groundwater inflows. The volume of recharge during the 2013–14 year is more than 60% greater than the previous year, which reflects the increase in rainfall experienced across the region during the year (see Climate overview). Total volume of rainfall over the entire landscape of the Perth region was 16,438,200 ML during the 2013–14 year (derived by multiplying the area-averaged rainfall of 777 mm [see Climate overview] by the area of the region [21,156 km²]), which means that approximately 12% of the total annual rainfall over the Perth region contributed to groundwater recharge.

Groundwater inflow from outside the region during the 2013–14 year was 52,788 ML, which is relatively similar to the previous year. Groundwater inflow from outside the region at the coast was 0 ML, which means there was no seawater intrusion into Perth's aquifers. It should be noted that the interface between the aquifer and the ocean moves throughout the year. During the summer months, when levels in the water table aquifers are relatively low, the saltwater interface moves towards the coastline; however, net flow occurs from the aquifers into the ocean.

Recharge from surface water (0 ML) during the 2013–14 year is consistent with previous years. This indicates that no groundwater recharge from rivers, drains and storages occurs within the region.

Managed aquifer recharge from the urban water system during the year was 614 ML and discharge from the urban water system to groundwater was 1,648 ML. Therefore, total aquifer recharge from the urban water system (2,262 ML) is approximately 2% of the total wastewater treated.

The volume of managed aquifer recharge represents recycled water recharged to the Leederville aquifer as part of the groundwater replenishment trial (see the Water Corporation website). The discharge from the urban water system to groundwater represents the volume of treated wastewater infiltrated to Perth's aquifers from the Kwinana Wastewater Treatment Plant. The infiltrated wastewater assists in maintaining environmental values at the Spectacles wetlands on the Swan Coastal Plain. The groundwater in this region is also extracted and recycled by Alcoa as part of the overall allocation of groundwater in the region.

Leakage from the urban water system (20,754 ML) during the 2013–14 year is relatively similar to the previous year. Leakage from the irrigation scheme (– ML) is not measured and cannot be quantified accurately.

Groundwater outflows

The largest water outflow from Perth's aquifers is discharge to landscape. During the 2013–14 year, 622,737 ML was discharged to the landscape, approximately 40% greater than the previous year. This increase reflects the increase in rainfall experienced across the region during the year (see Climate overview). 

Groundwater outflow to outside the region at the coast (433,999 ML) and discharge to surface water (283,158 ML) also increased by more than 40% from the previous year. Groundwater outflow to outside the region during the 2013–14 year was 30,164 ML, only marginally increased from the previous year. 

Entitled extraction of non-allocated groundwater to users during the 2013–14 year was 73,249 ML, which is similar to the previous year. This volume represents water extracted from domestic non-licensed bores within the Perth region.

Entitled water abstractions from the groundwater store are described in Groundwater allocation extractions below.

Groundwater allocation extractions

Most of the entitled extraction of allocated groundwater in the Perth region is for individual use. During the 2013–14 year, 281,518 ML of groundwater was taken by individual users, which accounts for almost 70% of the total allocated groundwater extraction. Licences primarily relate to water use for agricultural, local irrigation and industrial purposes (see Groundwater allocation announcements below).

Entitled extraction of allocated groundwater to the urban water system (124,851 ML) during the 2013–14 year accounts for approximately 30% of the total allocated groundwater extraction. The volume of water extracted from each bore field to the Perth region's Integrated Water Supply System is shown in Figure 9.

Figure 9 Groundwater allocations and abstractions for the urban water system during the 2013–14 year 

Groundwater forfeitures

The portion of groundwater allocation that has not been abstracted at the end of the water year is forfeited, that is, there is no carry-over of entitlements into the next water year. Water forfeitures in the Perth region during the 2013–14 year relate to licence entitlements for:

• individual users (14,172 ML)
• urban water system (7,203 ML).

Groundwater allocation announcements

Groundwater allocation announcements in the Perth region during the 2013–14 year refer to groundwater supply to:

• individual users (287,262 ML)
• urban water system (132,054 ML).

There are approximately 6,000 individual users that source water from aquifers within the region. The water supply licences are divided into licence entitlement purposes. Figure 10 shows the annual allocation announcement to individual users for each licence purpose for the 2013–14 year.

Figure 10 Groundwater allocation announcements to individual users for each licence purpose for the 2013–14 year

The groundwater allocation announcements for the urban water system relate to licences to extract water from bore fields to the Perth region's Integrated Water Supply System. The annual allocation for each urban licence during the 2013–14 year is shown in Figure 9 above.

A more detailed description of groundwater allocations and associated water rights in the Perth region is given in the Groundwater rights note.

Groundwater balancing item

The balancing item volume represents the difference between the measured opening and closing balances of the groundwater store, after physical inflows and outflows have been applied (Table 7).

The calculation of the water balance on the groundwater store yielded a balance of 164,060 ML, approximately 8% of the total groundwater inflows during the 2013–14 year. This volume actually represents the net change in groundwater store throughout the 2013–14 year.

During the 2013–14 year, total groundwater inflow was greater than in the 2012–13 year; in particular, recharge from landscape was approximately 744,000 ML greater than that reported during the previous year. This large increase in recharge reflects the increased rainfall conditions observed throughout the region during the 2013–14 year (see Climate overview) compared to the below average rainfall conditions experienced during the previous year.

Therefore, the net positive change in groundwater storage during the 2013–14 year (represented by the balancing item volume) is mainly due to a greater recharge from the landscape during the year.

Urban water system

Urban water assets

Perth’s urban water system comprises three subcomponents:

• urban water supply system (7,002 ML)
• wastewater system (– ML)
• recycled water system (– ML).

The volume of water in the urban water supply system changes little from year to year and comprises water in the distribution pipe network (5,542 ML) and service reservoirs (1,460 ML). The volume of water within the urban wastewater system and the recycled water system cannot be quantified due to a lack of available data; however, given that these systems are smaller than the urban water supply system, the volume of water within these systems is likely to be relatively small.

Urban water claims

There are two urban water claims in the Perth region:

• urban claim on surface water (0 ML)
• urban claim on groundwater (0 ML).

These claims are equivalent to the volume of surface water and groundwater allocation remaining for urban water supply licence entitlements at the end of the 2013–14 year. The allocation remaining for each licence entitlement is provided in tables 8 and 9.

Urban water system inflows and outflows

A schematic diagram representing all the inflows and outflows associated with the urban water system in the Perth region is provided in Figure 11.

Figure 11 Water inflows and outflows for Perth's urban water system during the 2013–14 year

Urban water supply system inflows

There are four sources of water for the urban water supply system:

• allocated surface water (105,998 ML)
• allocated groundwater (124,851 ML)
• desalinated water (113,060 ML)
• Inter-region import (2,121 ML).

Entitled diversion of allocated surface water to the urban water supply system (105,998 ML) is partially made up of groundwater and desalinated water transferred from the urban water supply system in order to store winter production of desalination water and groundwater and to enable summer peak supply capacity. Therefore, net surface water diversion to the urban water supply system (49,082 ML) is the difference between the total diversion and the volume of these internal transfers (56,916 ML) (see Urban water supply system outflows below).  Net surface water diversion contributed 17% of urban water supply; similar to the previous year (Figure 12).

Figure 12 Water sources used in Perth's urban water system and total volume for the years ending 30 June 2011, 2012, 2013 and 2014
 

Entitled extraction of allocated groundwater to the urban water supply system (124,851 ML) is the Perth region’s primary source of water for urban water supply; it made up 43% of the inflows to the system during the 2013–14 year (Figure 12).  Delivery of desalinated water contributed 39% of urban water supply this year, an increase of more than 17,000 ML from the previous year. In late 2013 the second stage of the Southern Seawater Desalination Plant was fully commissioned. More than 65,000 ML of desalinated water was produced for the Integrated Water Supply Scheme from the plant during the year.

Delivery of water from outside the region (2,121 ML) contributed less than 1% of urban water supply, which is similar to the previous few years. This delivery refers to surface water diversion from the Mundaring Reservoir, which is not considered a surface water asset in the Perth region as it primarily supplies water to the Goldfields and Agricultural region outside the Perth region boundary.

The volume of water abstracted from each surface water and groundwater resource to the urban water supply system during the 2013–14 year is given in Figure 6 and Figure 9 respectively. Desalinated water was supplied by the Perth Seawater (47,990 ML) and Southern Seawater (65,070 ML) desalination plants.

Wastewater system inflows

Total wastewater collected during the 2013–14 year was 141,024 ML, a marginal increase from the previous year. The volume of wastewater collected at each treatment plant is given in Figure 13.

Figure 13 Wastewater inflows and outflows at each wastewater treatment plant (source data)
 

Urban water supply system outflows

The largest water outflow from Perth's urban water system is the delivery of water to consumers. During the 2013–14 year, the total delivery of water to consumers 242,053 ML, of which 233,850 ML came from the urban water supply system (Figure 11). The remaining 8,203 ML came from the recycled water system (see Wastewater and recycled water system outflows).

The volume of discharge from the urban water supply system to surface water (59,469 ML) is comprised of two components:

• internal water transfers (56,916 ML): a combination of surface water, groundwater and desalinated water transferred from the urban water supply system in order to store winter production of desalination water and groundwater and to balance the storages to prevent overflow and enable summer peak supply capacity.
• riparian releases (2,553 ML): water discharged from water storages and water mains within Perth's urban water supply system into rivers for environmental benefit (see the Environmental benefit note).

During the 2013–14 year, 20,797 ML of water from Perth's urban water system was transferred outside the region. This volume comprises transfers to the Goldfields and Agricultural region (19,483 ML) and Western Australia's southwest region (1,314 ML).

Losses from the system included urban water system leakage to groundwater (20,754 ML), which was similar to the previous year. Other losses from the system (11,180 ML) include operational losses and all other non-revenue water from the urban water supply system, such as consumer meter inaccuracies and unauthorised consumption.

Wastewater and recycled water system outflows

The largest outflow from the wastewater system is wastewater that is treated and discharged into the sea (124,900 ML). Wastewater is also discharged to landscape (5,673 ML).

A portion of wastewater is further treated in the recycled water system (10,465 ML). The majority of the recycled water is supplied to users (8,203 ML), which includes onsite use (2,583 ML) and delivery for urban consumption (5,620 ML). Almost 6% of the total wastewater inflow to the system is recyled and delivered to users.

The remainder of the outflows from the recycled water system include managed aquifer recharge from the urban water system (614 ML) and discharge from the urban water system to groundwater (1,648 ML). Therefore, total aquifer recharge from the urban water system (2,262 ML) is approximately 2% of the total wastewater treated.

The volume of managed aquifer recharge represents recycled water recharged to the Leederville aquifer as part of the groundwater replenishment trial (see the Water Corporation website). The discharge from the urban water system to groundwater represents the volume of treated wastewater infiltrated to Perth's aquifers from the Kwinana Wastewater Treatment Plant. The infiltrated wastewater assists in maintaining environmental values at the Spectacles wetlands on the Swan Coastal Plain. The groundwater in this region is also extracted and recycled by Alcoa as part of the overall allocation of groundwater in the region.

Total wastewater outflows from Perth's wastewater and recycled water system is given in Figure 14. Outflows from each treatment plant are given in Figure 13.

Figure 14 Wastewater outflows from Perth's wastewater system during the 2013–14 year

There is likely to be some evaporation losses from the wastewater system but these cannot be quantified due to a lack of available data. These losses are considered to be relatively small and its omission will not have a material impact on the water balance of the urban water system.

Decrease of urban water claims

The portion of urban water claim that has not been abstracted at the end of the water year is forfeited, that is, there is no carry-over of entitlements into the next water year. Water forfeitures in the Perth region during the 2013–14 year relate to licence entitlements for:

• surface water supply (142,071 ML)
• groundwater supply (7,203 ML).

Increase of urban water claims

Increase of water claims for the urban water system refer to allocation announcements during the 2013–14 year for:

• surface water supply (247,950 ML)
• groundwater supply (132,054 ML).

Annual allocations for urban water supply from each storage and borefield for the year are given in Figure 6 and Figure 9 respectively.

Urban water system balancing item

The balancing item volume represents the difference between the measured opening and closing balances of the urban water system, after physical inflows and outflows have been applied (Table 10). This item is an indication of both the accuracy of the volumes reported and the degree to which the reported water flows represents a complete urban water system balance.

The calculation of the water balance on the urban water system yielded a balancing item of –277 ML. This is approximately 4% of the total urban water system store volume at the end of the 2013–14 year and less than 0.1% of the total urban water system inflows during the year.

Irrigation scheme

Irrigation scheme water assets

The Perth region's irrigation scheme represents the Harvey and Waroona irrigation districts within the Harvey Water Irrigation Area.

The volume of water in Harvey Water Irrigation Area's distribution pipe network at 30 June 2014 is 390 ML, which is the same as the previous year. Unless the pipe network is augmented or partly decommissioned, the volume of water in the irrigation supply system remains unchanged.

Irrigation scheme claims

In the Perth region there is an irrigation scheme claim on surface water (12,718 ML). This claim is equivalent to the volume of surface water allocation remaining for irrigation scheme licence entitlements at the end of the 2013–14 year. The irrigation scheme supply licences relate to surface water supply for the Harvey and Waroona irrigation districts within the Harvey Water Irrigation Area.

The allocation remaining for Harvey Water's water entitlement is provided in Table 11.

The licensed water management year for surface water supply to the Harvey Water Irrigation Area is 1 October–30 September. The above table indicates that there is 12,718 ML of water allocation remaining for the remainder of the 2013–14 irrigation season (which ends of 30 September 2014).

Irrigation scheme inflows and outflows

A schematic diagram representing all the inflows and outflows associated with the irrigation scheme in the Perth region is provided in Figure 15.

Figure 15 Water inflows and outflows for Perth's irrigation scheme during the 2013–14 year
 

Entitled diversion of allocated surface water to the irrigation scheme (34,466 ML) during the 2013–14 year is approximately 57% greater than the previous year. More detail on the irrigation scheme water abstraction and associated water rights is given in the Surface water rights note.

Total volume of water delivered to Harvey Water irrigation scheme users within the Perth region during the 2013–14 was 33,622 ML, approximately 49% greater than the previous year. A combination of increased allocations (see Surface water rights note) and a dry summer period during the 2013–14 year (see Figure C3 in the 'Climate overview') contributed to the increase in water delivery to irrigators compared to previous years.

The remaining two outflows of leakage to groundwater (– ML) and point return from the irrigation scheme (– ML), which represents return flow from the Harvey Water Irrigation Area to rivers, are not measured and cannot be quantified accurately.

Decrease of irrigation scheme claims

The portion of irrigation scheme claim that has not been abstracted at the end of the water year is forfeited, that is, there is no carry-over of entitlements into the next water year.

The adjustment and forfeiture of the irrigation scheme claim on surface water (5,807 ML) during the 2013–14 year occured on 30 September 2013 and represented the irrigation claim that was not abstracted at the end of Harvey Water's 2012–13 water year (1 October–30 September).

Increase of irrigation scheme claims

The increase of irrigation scheme claim on surface water (46,481 ML) refers to the allocation announcements during the 2013–14 year for surface water supply to the Harvey Water Irrigation Area. These allocations were made on 1 October 2013 at the start of the irrigation season (1 October–30 September). More detail on the irrigation scheme water allocation and associated water rights is given in the Surface water rights note.

Irrigation scheme balancing item

The balancing item volume represents the difference between the measured opening and closing balances of the irrigation scheme, after physical inflows and outflows have been applied (Table 12). This item is an indication of both the accuracy of the volumes reported and the degree to which the reported water flows represents a complete irrigation scheme store balance.

The calculation of the water balance on the irrigation scheme yielded a balancing item of 844 ML, which is approximately 2% of the total irrigation scheme inflows during the year.

Unaccounted-for difference

The volume recognised in the water accounting statements (513,028 ML) represents the total unaccounted-for difference for the Perth region for the 2013–14 year.

The unaccounted–for difference is the volume necessary to reconcile the opening water storage and closing water storage with the total water inflows and total water outflows reported in the water accounting statements (Table 13).

The unaccounted–for difference can also be calculated by summing the volumes necessary to reconcile (balance) the opening and closing storage with the water inflows and outflows of each of the separate water stores of the region, as shown in Table 14.

Table 14 shows that the unaccounted-for difference volume is primarily explained by the balancing item of the surface water and groundwater store. The surface water balancing item is attributed to uncertainty associated with runoff and river outflow, and the volume of river and floodplain losses not being able to be quantified (see Surface water note).

The groundwater assets of the Perth region could not be quantified (see Groundwater note). As a result, the calculation of the unaccounted-for difference in the first table above does not include opening or closing groundwater storage. Therefore, the groundwater balancing item volume of 164,060 ML represents the difference between known groundwater inflows and known groundwater outflows during the 2013–14 year (see Groundwater note), and any actual unaccounted-for differences when reconciling the terms.

National Water Account 2014

• National overview
• About the 2014 Account
• Quick Guide (2.2Mb)
• Glossary
• Copyright
• Partnerships
• Feedback

Related links

• About the National Water Account
• Frequently Asked Questions
• Information Sheet (211Kb)
• National Water Account Committee
• National Water Account history
• Water accounting standards
• Companion Guide (4.9Mb)

Water links

• Murray Darling Basin water information
• Water Act 2007
• Water Regulations 2008
• Water market information
• Water Dictionary
• Publications
• Contact Us