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Climate change, water demand and water availability scenarios to 2030 Perth-Peel regional water plan background paper

Looking after all our water needs

Department of Water

September 2009

Department of Water 168 St Georges Terrace Perth Western Australia 6000 Telephone +61 8 6364 7600 Facsimile +61 8 6364 7601 www.water.wa.gov.au

© Government of Western Australia 2009

September 2009

This work is copyright. You may download, display, print and reproduce this material in unaltered form only (retaining this notice) for your personal, non-commercial use or use within your organisation. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. Requests and inquiries concerning reproduction and rights should be addressed to the Department of Water.

978-1-921637-89-6 (online)

Department of Water iii

Contents Contents ..................................................................................................................... iii Summary .....................................................................................................................v

Climate and water resource availability ...................................................................................................v Public water demand and supply.............................................................................................................v Private demand and supply .................................................................................................................... vi

1 Introduction..............................................................................................................1 1.1 Purpose of the paper........................................................................................................1 1.2 Current demand ...............................................................................................................2

2 Climate change .......................................................................................................3 2.1 Recent rainfall trends .......................................................................................................3 2.2 Climate scenarios to 2030................................................................................................4 2.3 Natural variability of rainfall ..............................................................................................5

3 Water availability .....................................................................................................7 3.1 Groundwater availability...................................................................................................7 3.2 Surface-water availability ............................................................................................... 10

Surface-water availability for IWSS by 2030..........................................................................................11 4 Water demand scenarios ......................................................................................12

4.1 Population growth .......................................................................................................... 12 4.2 Demand scenarios for public water supply..................................................................... 12

Water-efficiency opportunities ...............................................................................................................13 4.3 Impact of backyard bores on public water supply demand............................................. 14 4.4 Self-supply demand ....................................................................................................... 15

5 Water demand and supply scenarios ....................................................................17 5.1 Gingin self-supply water demand and supply scenarios ................................................ 17 5.2 Gingin public water demand and supply scenarios ........................................................ 17 5.3 Peel self-supply water demand and supply scenarios.................................................... 18 5.4 Perth self-supply water demand and supply scenarios .................................................. 19 5.5 IWSS water demand and supply scenarios.................................................................... 20

6 Public water supply futures ...................................................................................22 6.1 Options........................................................................................................................... 22 6.2 Desalination ...................................................................................................................22 6.3 Possible groundwater sources for IWSS........................................................................ 23

Abstraction potential from the confined Gnangara aquifers ...................................................................23 6.4 Possible surface-water sources for IWSS...................................................................... 23 6.5 Alternative water supply sources.................................................................................... 24

Water recycling......................................................................................................................................24 7 Conclusions...........................................................................................................27

Climate 27 Groundwater availability ........................................................................................................................27 Surface-water availability.......................................................................................................................28 Water demand .......................................................................................................................................28 Water-use efficiency ..............................................................................................................................28

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iv Department of Water

Public demand and supply balance .......................................................................................................28 Self-supply demand and supply balance ...............................................................................................29 Competition between private and public supply.....................................................................................29 IWSS futures .........................................................................................................................................30 Self-supply futures .................................................................................................................................30 Water allocation and management priorities..........................................................................................31

Shortened forms ........................................................................................................33

References ................................................................................................................35

Department of Water v

Summary The Department of Water is responsible for the preparation and implementation of regional water plans to guide the sustainable management of Western Australia’s inland water resources. This includes the Perth-Peel regional water plan (PPRWP).

The PPRWP’s area extends from Moora in the north to Waroona in the south. It includes all of the Swan coastal plain and the Darling Range as far as Boddington. The three subregions are Gingin, Perth and Peel.

More than 75 per cent of Western Australia’s population lives in the region, which is also one of the fastest growing parts of Australia. Demand for water – from public water supply providers and self-suppliers – continues to increase with population growth. Significant reductions in water use have been achieved since 2001, and near-term targets have been set for further savings in the public supply and self-supply sectors.

Both water supply sectors have found it increasingly difficult to meet demand since the marked shift to a drier climate from the mid-1970s. Climate projections to 2030 indicate a continuing trend of less rainfall and higher evaporation – which will further decrease the availability of water resources.

This discussion paper addresses key climate, water demand and water availability issues for the PPRWP to 2030.

Climate and water resource availability

Climate projections to 2030 include a 50 per cent chance of an eight per cent reduction in average rainfall relative to the 1980–99 average rainfall (a ‘median’ scenario). In addition, there is a 10 per cent chance that average rainfall may decline by 15 per cent or more (a ‘dry’ scenario) and a 10 per cent chance that average rainfall will be the same or higher (a ‘wet’ scenario) relative to the 1980–99 average. Natural variability may add five to 10 per cent to the projected trends in average rainfall for timespans of several years to a decade.

Groundwater is the major water resource in the region with more than 830 GL/yr currently available for abstraction for consumptive use. With climate change, the groundwater available for consumptive use by 2030 may decrease to 700 and 580 GL/yr for the ‘median’ and ‘dry’ climate scenarios respectively. Allocation limits may be reduced as new information becomes available on the response of aquifers to adverse changes in climate and to abstraction.

Surface-water availability has decreased by about 50 per cent since the mid-1970s. Average flow for some streams since 2001 is less than one-third of previous flows. Streamflow (including Harvey basin sources) for the Integrated Water Supply Scheme (IWSS) has averaged about 105 GL/yr since 2001 and may reduce to 95 GL/y under the 'dry' climate scenario by 2030.

Public water demand and supply

Public water demand (IWSS) is projected to increase by between 20 and 95 GL/yr by 2030 relative to 2008. This will depend on population growth and water-efficiency programs. Achieving 80 kL/person/yr for the residential sector and 120 kL/person/yr for total scheme use will require substantial effort and financial resources to develop and implement water-efficiency programs. Many water-efficiency measures cost <$1/kL compared with future seawater desalination costs of $2–3/kL. A priority water planning challenge is to identify a more refined set of demand and supply options for evaluation.

The IWSS supply-demand balance by 2030 (with existing surface-water and groundwater sources and 95 GL/yr desalination) is likely to range between a surplus of 45 GL/yr for a

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vi Department of Water

‘median’ climate – with a 20 per cent efficiency saving across all use sectors – to a deficit of 85 GL/yr for the ‘dry’ climate scenario – with the achievement of the State water plan target of 100 kL/person/yr.

Further seawater desalination is a likely option to meet the supply shortfall by 2030. Indirect-potable re-use of wastewater through groundwater replenishment and recovery is also a major supply option. Reducing demand on the public supply system through wastewater re-use for industrial demands, such as those at Kwinana and Neerabup, is also important.

Future groundwater abstraction from existing sources is likely to include short-term emergency additional draw on confined aquifers, which will trigger development of a new supply source to replace and ‘repay’ the temporary overdraw.

Private demand and supply

Private or self-supply water demand is projected to increase by between 13 and 145 GL/yr by 2030 relative to 2008. This will depend on drivers for growth, water-use efficiency achievements and the availability of water. The State water plan aspirational target for agriculture and industry to improve efficiency by 20 per cent is believed to be achievable without loss of productive output. Yet achieving this target will require significant resources and commitment to develop and implement water-efficiency programs (with industry groups).

The groundwater resources of the Gingin and Peel subregions offer potential for private and public supply development. The most likely use is for agriculture and industry, given the growing demand for food and sufficient land to produce it in the Gingin area in particular. However, the location of demand in relation to supply and the impact of abstraction on local ecological values will be issues to consider.

In the Perth subregion, significant reductions in water use are likely as a result of climate change – even with no growth in horticulture. There is unlikely to be sufficient groundwater to meet the projected large increase in public open space watering (60 per cent) by 2030. Under the 'dry' scenario, private water use would need to be reduced by about 35 per cent to match reduced availability, but this may be offset to some extent by increased recharge associated with urban expansion. Other sources may need to be developed, such as drainage or wastewater, to supply some of this demand.

More detailed evaluation is required of the potential for domestic groundwater use (‘backyard’ bores) in new urban and urban-infill areas.

Use of the estimated 180 GL/yr of climate-independent water available from wastewater treatment plants is likely to significantly increase by 2030. Priority opportunities will be for industry at Kwinana and Neerabup, the Water Corporation’s indirect-potable IWSS scheme at Gnangara and for smaller schemes by local councils. Significant horticulture growth in the Perth region will require a source such as re-used wastewater.

More detailed planning, including better integration of land and water planning at the water allocation planning level, is needed.

The views of stakeholders (general community, regulators and customers) are important in shaping these options to meet the region’s future water needs.

Department of Water 1

1 Introduction

1.1 Purpose of the paper

The Perth-Peel regional water plan (PPRWP) will provide strategic directions for sustainable water management in the region to the year 20301. Figure 1 displays the Perth-Peel region’s boundaries including its three subregions: Gingin, Perth and Peel.

Figure 1 Perth-Peel regional water plan boundary

1 Water resources in this context do not include marine waters.

2 Department of Water

This background paper examines the impact of climate change, demand for water for consumptive purposes and the likely range of surface-water and groundwater available in the region to 2030. It is one of four background papers prepared in support of the Perth-Peel strategic directions discussion paper.

The four Department of Water background papers are:

1 Water efficiency, recycling and alternative water supplies 2 Waterways and wetlands 3 Climate change, water demand and water availability scenarios to 2030 4 Land and water planning

1.2 Current demand The region’s estimated demand for water in 2008 is summarised in Table 1 by sector of use and by supply from scheme (e.g. IWSS for public supply) or self-supply (private supply). Total water use in 2008 was estimated to be ~770 GL, of which 70 per cent was attributed to the Perth subregion.

Self-supply accounted for two-thirds (~516 GL) of total water use in the region in 2008, while scheme supply (IWSS and standalone schemes2) accounted for one-third (254 GL) of the total. Households consumed 22 per cent of all water used, which when combined with the estimate for unlicensed private use (‘backyard’ bores) accounted for 37 per cent of all use. Agriculture used 28 per cent of the water resource, almost all self-supply from groundwater. Industry (manufacturing and processing) accounted for ~10 per cent of water use in 2008.

Table 1 Estimated 2008 water demand (GL/yr)

Perth Peel Gingin Total Water-use sector Sc Ss T Sc Ss T Sc Ss T Sc Ss T Agriculture 78 78 17 17 123 123 218 218 Fishing and forestry 2.5 2.5 0.5 0.5 0.2 0.2 3.2 3.2 Mining 4.8 4.8 9.9 9.9 12 12 26 26 Manufacturing and processing 27 28 56 2.0 18 20 0.3 1.5 1.8 30 48 77 Service industries 52 5.4 57 2.5 6.2 8.7 0.6 0.3 0.9 55 12 67 Households (scheme supply) 157 157 11 11 0.7 0.7 169 169 Parks, gardens, sport etc. 1.2 57 58 0.1 3.0 3.1 0.5 0.5 1.3 60 61 Licensed domestic and stock 21 21 4.2 4.2 7.4 7.4 32 32 Unlicensed (e.g. household bores) 113 113 4.0 4.0 0.4 0.4 117 117 Total 238 309 546 15 62 77 1.6 145 147 254 516 771

Source: Adapted from Resource Economics Unit, 2008.

Sc = scheme or public demand (e.g. IWSS)

Ss = self-supply (private) demand

T = total = scheme + self-supply demand

2 A standalone scheme is one not connected with the IWSS (e.g. Guilderton).


2 Climate change

2.1 Recent rainfall trends

The Perth-Peel region has a seasonal climate of hot, dry summers and mild, wet winters. Approximately 80 per cent of the rainfall and most of the streamflow and recharge to groundwater occur in the ‘wet’ season between May and October.

Climate is known to vary naturally on timescales from decades to millennia. In addition to natural climate variability, human activities such as fossil fuel use, broadscale deforestation and land-use changes have increased atmospheric concentrations of carbon dioxide, methane, nitrous oxides and other greenhouse gases. The increasing concentration of greenhouse gases is changing the climate. The effects of climate change are already noticeable in the region.

Since the mid-1970s, the South West has experienced a significant decline in rainfall. Figure 2 displays the May to October average rainfall sequence for the area of the state south of a line between Geraldton and Albany. The overall trend is of decreasing rainfall with significant variation over periods of years with ‘runs’ of wetter and drier years, which is shown as the 11-year-average rainfall (red line) in Figure 2.

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Figure 2 Long-term trends in May to October rainfall for South West Western Australia

(Source: Bureau of Meteorology)

A feature of the decrease in rainfall is its reduction in late autumn and winter. The more than 10 per cent decline in average ‘wet season’ rainfall since the mid-1970s has resulted in a 50 per cent reduction in streamflow (IOCI 2005). This has resulted in a dramatic decrease in the inflows to reservoirs that provide public drinking water to the greater Perth metropolitan area.


Rainfall and hence streamflow (May to October) was particularly low from 2001 to 2007 (Figure 3). These large variations of streamflow pose a significant risk to the security of water supply to IWSS customers, as well as to those who self-supply through dams or stream pumping on private property. Reduced rainfall has also resulted in falling groundwater levels across much of the region and increasing pressure on groundwater-dependent ecosystems.

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Figure 3 May to October streamflow into IWSS major surface-water storages (GL)

2.2 Climate scenarios to 2030

Projections of future climate are needed to estimate water demand and in particular water availability (surface water and groundwater) for the region. The Australian Government’s Climate change in Australia (2007) has developed temperature, precipitation and evaporation projections to 2070 relative to a 1980–99 climate baseline for all of Australia. These have been used with regional climate projections by Sadler (2007) to estimate average rainfall scenarios by 2030 (relative to the average rainfall between 1980–99 as a baseline), as shown in Table 2.

Table 2 Perth-Peel region average ‘wet season’ rainfall scenarios

Change in average ‘wet season’ rainfall relative to the 1980–99 average Change by 20301 Minimum average rainfall change (‘wet’ climate scenario) 0% 2 Most likely average rainfall change (‘median’ climate scenario) -8% 3 Maximum average rainfall change (‘dry’ climate scenario) -15%

Evaporation is also likely to increase in the region because of climate change. The average temperature may increase by 0.8oC by 2030 (Sadler 2007) and the best estimate is an increase of five per cent in potential evapotranspiration by 2030 for the winter season, with


an annual increase of two per cent. Increased evaporation in combination with declining rainfall will further decrease the region’s available water resources by 2030.

2.3 Natural variability of rainfall

Since 2001 the average rainfall recorded for the IWSS’s surface-water catchments has been ~10 per cent less than the 1980–99 average. This reduction is much larger than the rainfall change expected before 2010, as shown in Table 2. This large decrease perhaps indicates that climate change is occurring faster than that projected by Climate change in Australia and/or the period since 2001 represents a severe extended drought superimposed on a trend of declining rainfall. Extended periods of wetter and drier weather, usually termed as natural variability, have been recorded during the past 100 years, some lasting many years. It is reasonable to assume that natural variability, including extended droughts, will occur in addition to declining average rainfall driven by climate change to 2030. Adding natural variability to the projected climate-forced reduction in rainfall is very important for the security of large public water supply systems such as the IWSS.

For example, analysis of the region’s rainfall records indicates a 10 per cent chance that the natural variability of average rainfall over a five-year ‘run’ of drier years could be ~10 per cent less than the average rainfall. Adding this natural variability to the ‘median’ and ‘dry’ average rainfall scenarios in Table 2 results in a range of rainfall from +2 to -18 per cent and -5 to -25 per cent respectively (relative to the 1980–99 average). A five-year duration rainfall decrease of -18 to -25 per cent would have significant impacts on the security of water supply systems, private water users and the ecological values that depend on the region’s water resources.

An example of the application of the average rainfall scenarios (based on Table 2 with natural variability) is shown in Figure 4 (below) for Perth’s May to October rainfall. The graph shows a five-year duration moving average rainfall to 2007, and the average rainfall for 1980–99 (691 mm) and for the seven-year drought of 2001–07 (604 mm). The average rainfall projections are from 1990 (the mid-point of the 1980–99 period) using the 1980–99 average for the ‘median’ change estimate (blue line), minimum change (green line) and maximum change (red line) to 2050. Natural variability is illustrated (dashed black lines) for five-year duration averages above and below the ‘median’ change estimate rainfall scenario. The variability represents +/-10 per cent for the wetter and drier five-year ‘runs’.


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Figure 4 May to October rainfall for Perth, 1950 to 2050

Projections of climate by 2030 and of rainfall in particular, are uncertain. Climate research, notably by the CSIRO and Bureau of Meteorology, will continue to improve the projections of rainfall and temperature for the next few decades. It is important the results of this research are monitored and the implications of climate change projections and natural variability are included in the region’s water resource planning.


3 Water availability

3.1 Groundwater availability

The largest sustainable water resource in the region is groundwater. The groundwater resources of the Swan coastal plain and Dandaragan Plateau are extensive, mainly in the unconfined Superficial and the deep confined Leederville and Yarragadee aquifers. Table 3 provides a summary of the main features of these aquifers.

Table 3 Major aquifers in the Perth region

Aquifer Areal extent Maximum thickness (m) Salinity (mg/L TDS) Storage (GL)Superficial Widespread 70 (50 north, 20 south) ~250 60 000 Mirrabooka Localised 140 ~350 12 100 Leederville Widespread 600 <500 to >3000 280 000 Yarragadee Widespread >2000 <500 to >3000 950 000

Source: Davidson and Yu, 2006

While the storage in the aquifers is very large, the amount available for sustainable abstraction is only a small proportion.

As shown in Table 4, the total groundwater allocation limit3 is 863 GL/yr, of which 60 per cent (519 GL/yr) is currently licensed. The estimated actual use of groundwater is ~600 GL/yr. In the Perth subregion an estimated 160 000 private unlicensed backyard bores are abstracting about 113 GL/yr and this is not part of the allocation limit in Table 4. This is why the 442 GL/yr of estimated actual total use of groundwater for the Perth subregion in 2008 is larger than the allocation limit. The Department of Water makes an allowance for unlicensed water use when setting the allocation limit to protect the overall resource.

Table 4 Estimated use of groundwater resources (GL/yr)

Subregion Allocation limit

Licensed public

(scheme)

Licensed private (self-

supply)

Licensed total

Estimated unlicensed

Estimated use 2007–08

Gingin 326 2 139 141 3 132 Perth 410 145 200 345 113 442 Peel 127 1.3 32 33 NA 30 Totals 863 148 371 519 NA 604 Note: On average ~92 per cent of all self-supply licensed water is actually used.

There is clear evidence that reduced rainfall since the mid-1970s has affected water levels in the region’s aquifers. Figure 5 gives an example – the water-level decline in a Superficial aquifer bore in an area of undisturbed woodland on Gnangara Mound (Yesertener 2007).

3 Allocation limit is the amount of water set aside for annual licensed use.


This shows that the water level has fallen by several metres as a result of lower rainfall. Water-level changes in other bores across Gnangara range from increases (e.g. in areas being urbanised) to falls of many metres.

Figure 5 Measured water level (red, left axis) compared with the cumulative departures of

rainfall from the long-term mean (blue, right axis) for bore PM3 on Gnangara

Table 5 shows the effect of the ‘wet’, ‘median’ and ‘dry’ rainfall scenarios (described in Table 2) on the availability of water from all the region’s aquifers. Using these scenarios, a net-groundwater-recharge-change to rainfall-change multiplier of two was used to project the groundwater allocation potentially available at 2030.

Table 5 Scenarios of average groundwater availability to 2030 (GL/yr)

Sub Allocation Licensed + Balance PWS Balance available by 2030 region limit approved available future Wet Median Dry Gingin 326 153 173 72 173 121 75 Perth 380 345 35 23 35 -28 -91 Peel 127 33 94 0 94 74 56 833 531 302 95 302 167 40

Table 5 includes the current (2008) estimate of the allocation limit as the baseline groundwater available in the region. Also included is ‘licensed + approved’, which is the total of what is licensed and conditionally approved for licensing. The ‘balance available’ column is the difference between the ‘allocation limit’ and ‘licensed + approved’ for 2008. The future allocation for public water supply (PWS) is included to illustrate the amounts set aside for possible future public supply development. The last three columns are the difference between the projected allocation limit as impacted by climate change at 2030 and the current ‘licensed + approved’ column. A negative value means that by 2030 the groundwater available for abstraction may be less than what is currently licensed and approved for


licensing. Note that the ~30 GL/yr allocated to the IWSS in the Perth subregion (until the second seawater desalination plant is commissioned in ~2012), which is shown in Table 4, has been subtracted in Table 5 to estimate the groundwater available by 2030.

In the Gingin subregion, 46 per cent of the current allocation is licensed or approved for licensing. Under the ‘median’ climate scenario, the net water available for further licensing may be ~120 GL/yr and still a significant 75 GL/yr under the ‘dry’ climate scenario. There may also be substantial groundwater available for future licensing in the Peel subregion (56 to 74 GL/yr) by 2030. In both Peel and Gingin, however, the location of remaining available groundwater at 2030 in relation to water demand will be important. More detailed investigation of these opportunities will be required.

The current provision of 72 GL/yr for Gingin’s future public water supply is a significant proportion of the balance available by 2030 after the impacts of climate change (Table 5). The Department of Water will re-examine these provisions when it reviews the Gingin subregion’s allocation limits. The available groundwater resources are likely to be less than those projected in Table 5. This is because of the drier climate, the difficulty in accessing some resources in areas of high conservation value (e.g. national parks and military reservations) and possibly because of water quality constraints (e.g. salinity).

For the Perth subregion, the current balance available is ~35 GL/yr (Table 5). With climate change the balance available for licensing by 2030 could decrease to -28 GL/yr and -91 GL/yr for the ‘median’ and ‘dry’ climate scenarios respectively.

Nearly 75 per cent of the Perth subregion’s allocated groundwater occurs in the important Gnangara groundwater system. This is an area of ~2200 km2 located between the Swan River, the coast, Gingin Brook and the Darling Scarp. In 2008 the Department of Water reduced the allocation limits for the Gnangara system to reflect the impacts of declining rainfall and land use on the resource. This includes a reduction in the allocation to the IWSS from 175 GL/yr to 145 GL/yr for the next few years until the second seawater desalination plant is commissioned (~2012), with the intention of a further reduction to 120 GL/yr thereafter (DoW 2008).

The Department of Water may reduce the allocation limits as a result of projections of less rainfall.

The multi-agency Gnangara Sustainability Strategy (GSS), which is being led by the Department of Water and due for completion this year, is considering the impacts of changes in climate and land use (e.g. pines removal) on the Gnangara groundwater system. Preliminary groundwater modelling results from the GSS project indicate that by 2030 – under a similar ‘dry’ climate scenario and current levels of water use – the Superficial aquifer may still be declining by about 60 to 70 GL/yr even with the removal of ~20,000 ha of pines. Further work by as part of the GSS (including climate scenarios), combined with the CSIRO-led South West Sustainable Yields (SWSY) project, will help to determine more accurate estimates of likely groundwater available for the region by 2030.

In summary, while potential exists for increased use of groundwater in the region, this should be viewed with caution until the Department of Water reviews all the relevant groundwater allocation plans (the Gnangara Mound, Rockingham and Cockburn reviews are complete). In broad terms the net available groundwater by 2030 may range between ~40 and ~167 GL/yr (Table 5) depending on climate change (‘dry’ and ‘median’ cases) relative to current licensed and other commitments. However, the opportunity for increased use of groundwater in the Perth subregion is limited. Provisional allocations for future public water supply are likely to reduce under most climate scenarios.


3.2 Surface-water availability

The region’s surface-water resources (streamflow) have been a major source of water for public water supply and a minor source for industry and agriculture. The three major river basins are the Moore (part of the Moore-Hill system), the Swan coastal and the Murray.

The region’s freshwater resource is small relative to the total streamflow volume. Most of the quality freshwater resources are in the western, mostly forested and higher-rainfall parts of the Darling Range. Hence the region’s dominant surface-water use is public water supply from dams on streams in the west of the Darling Range. Small quantities (~20 GL/yr) are licensed for use by industry (e.g. mining and mineral refining) in the Murray basin and by agriculture (~5 GL/yr) in the Moore basin (e.g. irrigation from Gingin Brook). An unknown amount, perhaps 10 per cent of the mean annual flow, is being used from small streams in areas such as Gidgegannup and Chittering.

Streamflow is typically a small proportion of rainfall (5–10 per cent) so relatively small decreases in rainfall result in large decreases in streamflow. The major issue for future surface-water availability is the impact of climate change on the sustainable yields of the region’s freshwater sources.

Table 6 displays the estimated mean annual streamflows by 2030 using the climate change scenarios in Table 2 and a streamflow-change to rainfall-change multiplier of three to one. Note that because most of the streamflow in the Moore River basin is brackish to saline, this resource is not considered further. By 2030 the mean annual streamflow may decrease by nearly 30 per cent relative to 1980–99 for the ‘median’ climate scenario and by nearly 50 per cent for the ‘dry’ scenario. These reductions have significant implications for the security of the public water supply system, for local users and for ecosystems that depend on streamflow (e.g. wetlands and estuaries on the coastal plain).

Table 6 Projections of mean annual streamflow by 2030 (GL/yr)

Basin Scenarios of mean annual streamflow by 2030 (GL/yr) Wet Median Dry

Murray River 370 268 201 Swan coastal 280 202 152 Perth-Peel totals 650 470 354 % of 1980–99 baseline 100% 72% 54%

However, the amount of surface water available for consumptive use is much less than the estimates in Table 6 because:

• most of the readily available high-quality resource has already been developed for the IWSS (e.g. Helena, Canning, Dandalup and Serpentine river systems)

• much of the remaining resource is unavailable because of ecological constraints, such as potential dam sites being located in parks or nature reserves (e.g. Lane-Poole Reserve on Murray River)

• allocation of streamflow to sustain ecological values (i.e. environmental water provisions)

• water quality issues, particularly salinity (e.g. Murray and Swan-Avon systems)


• limited capacity for private users to access the remaining resources (i.e. need to be close to streamlines such as along Gingin Brook and Lennard Brook).

Therefore the availability of surface water for consumptive purposes in the region is mainly limited to existing developments for the IWSS, and these have declined significantly over recent decades (as discussed below).

Surface-water availability for IWSS by 2030

Table 7 shows how climate change will potentially affect the contribution of surface water to the IWSS by 2030. These are estimates of streamflow from within the region, plus streamflow from the Harvey basin, and include an allowance for loss of water owing to evaporation from storage reservoirs. By 2030 the contribution of surface water to the IWSS could decline from 220 GL/yr to 130 GL/yr under the ‘median’ climate scenario and to 95 GL/yr under the ‘dry’ climate scenario.

Year Wet climate Median climate Dry climate 2001–06 conditions continue 2030 220 130 95 105

Table 7 Scenarios of average surface-water contribution to IWSS by 2030 (GL/yr)

Since 2001 the streamflow into IWSS storages has declined by ~50 per cent (relative to the 1980–99 average) to ~105 GL/yr. For the observed decline in rainfall, this decline was more than expected. It indicates that the catchments are now less efficient, by about ~35 GL/yr, in producing streamflow for a given amount of rainfall. The likely causes are decreasing groundwater levels in catchments and increases in vegetation water use because of increased vegetation density.

The ‘dry’ climate scenario produces a significantly worse outcome if the low rainfall experienced in the period since 2001 continues. However, it is possible that the current ~105 GL/yr will continue from now with further reductions to the ‘dry’ climate scenario ~95 GL/yr by 2030. This would have serious implications for the security of the IWSS in the next few years and illustrates the need for a major new source – as is planned for the seawater desalination plant at Binningup by ~2012.

These estimates are approximate only; the completion of the South West Sustainable Yields project by the end of 2009 by CSIRO and the Department of Water may provide refined estimates of the likely availability of surface-water resources in the region by 2030.


4 Water demand scenarios This section examines the effects of population growth and water-use factors on the demand for water supply.

4.1 Population growth

In August 2008 the Department for Planning and Infrastructure released updated population projections to 2031. The projected population for 2030 includes an additional 160 000 people in the metropolitan area compared with the Western Australian Planning Commission’s projection for the same period (WAPC 2005).

The estimated population in 2008 and the projection for 2030 are summarised in Table 8 below. For the Perth metropolitan area this represents an additional 590 000 people and nearly a doubling of the Peel subregion’s population by 2030. Population growth in the Gingin subregion may increase by 50 per cent to ~15 000.

Table 8 Approximate population projections

Subregion 2008 2030 Additional 2008 to 2030 Perth (metropolitan) 1 556 000 2 146 000 590 000 Peel4 102 000 193 000 91 300 Gingin5 10 000 15 000 5000

4.2 Demand scenarios for public water supply

Table 9 summarises scenarios for public supply demand to 2030 using per capita rates of water use and assumptions about water-efficiency achievements. Note that water supply to the Goldfields and Agricultural Scheme (GAWS) is included on the assumption that the Perth-Peel region will continue to meet the needs of this scheme.

Table 9 Public water supply demand scenarios by 2030 (GL/yr)

Demand scenario

Gingin

Perth Peel GAWS Total Additional 2030–2008

Current demand (2008) 2 238 15 27 282 1. Business as usual (2002–07 per capita) 3 328 28 35 394 112 2. Baseline: SWP 100 per capita by 2012 3 311 28 35 377 95 3. Baseline with 10% efficiency all sectors 2.7 280 26 32 340 58 4. Baseline with 20% efficiency all sectors 2.4 249 23 28 302 20

4 The Peel subregion consists of Mandurah, the shires of Murray, Serpentine-Jarrahdale and Boddington and 50

per cent of the Shire of Waroona. 5 The Gingin subregion includes the Shire of Gingin, the western part of the Shire of Chittering and the town area

and some rural areas of the Shire of Moora.


The ‘business as usual’ scenario assumes a continuation of average 2002–07 rates of water use and would result in the need for an additional 112 GL/yr by 2030. The baseline scenario assumes the achievement of the State water plan (DPC 2008) 100 kL/person/yr residential water-use target for Perth by 2012 and 45 kL/person/yr target for the balance of water use (i.e. the non-residential sector such as industry and commerce and non-revenue water such as meter errors, leakage, bursts, theft and fire-fighting) and a continuation of this to 2030. This would result in an additional 95 GL/yr.

Scenario 3 shows a 10 per cent efficiency improvement across all sectors. This would reduce the additional water required by 2030 to ~60 GL/yr. A 20 per cent efficiency saving would reduce the additional public water supply demand to ~20 GL/yr.

The achievement of the 100 kL/person/yr target for residential water use in the Perth subregion will require investment in water-use efficiency programs. The achievement of significantly better than the 100 per capita target is likely to require significant changes to the form of urban areas (including density of dwellings and landscaping of public open space) and water-use practices (e.g. outside watering regimes). Achieving 20 per cent efficiency is a major challenge and will require more detailed investigation of opportunities and constraints than is possible for this strategy.

The most likely range of additional public water supply demand to 2030 is ~60 to 95 GL/yr for a total IWSS demand of ~340 to 377 GL/yr (Table 9).

The Department of Water requires the Water Corporation to develop and implement a water-efficiency program for the IWSS as part of its license to abstract groundwater and surface water to supply the system. Through the Water Forever program, the Water Corporation (2008a) is developing a long-term water supply plan for the IWSS that is expected to include an enhanced water-efficiency program in addition to proposed new sources of supply.

Water-efficiency opportunities

The Water Corporation (2008b) has estimated the potential water savings if a range of additional water-efficiency measures were adopted (Table 10). These total more than 20 GL/yr, of which ~15 GL/yr would involve ‘structural’ measures such as replacement of lawns, Waterwise gardens and the retrofitting of more efficient appliances (e.g. showerheads).

The indicative costs of most of these options are <$1/kL, which is much less than the cost of future seawater desalination plants. The Water Corporation (2009) indicates that a 15 per cent improvement in water-use efficiency by 2030 would result in a saving of 50 GL/yr. The breakdown of projected water savings are 30 GL/yr from homes and gardens; 15 GL/yr from increased urban density; and 5 GL/yr from industry and commerce. A detailed examination of the opportunities and constraints for a program to implement these measures should be undertaken.


Table 10 Water Corporation estimates of water-efficiency opportunities (GL/yr)

Program Assumptions Yield (GL/yr)

Indicative cost ($/kL)

Retrofit – replacing inefficient showerheads, installing tap flow-control devices, and fixing visible leaks

100 000 households save 15 kL/yr

1.5

<1 Retrofit – replacing inefficient toilet suites


2.0 <1

Building Code of Australia 5 Star Plus – Phase 3


2.0 <1

Lawn replacement program – paving or synthetic turf

50 000 households replace 100 m2 save 100 kL/yr

5.0 <1

Lawn replacement – Waterwise garden 50 000 households replace 100 m2 save 50 kL/yr

2.5 <1

Quarterly billing 2.5 ? Leakage detection and repair 2.5 1-2 The Biggest Reducer 1 <1 Sprinkler ban 1 (winter time) 1 to 3 <1 Total 22 Source: Water Corporation 2008b, Water efficiency information sheet, April 2008.

4.3 Impact of backyard bores on public water supply demand

The Perth region has an estimated ~160,000 private ‘backyard’ bores, which translates to ~25 per cent of dwellings having access to the shallow groundwater. The estimated groundwater consumption is ~113 GL/yr, which effectively reduces the demand from the public water supply system by an estimated 30 GL/yr.

The projected population increase represents an additional ~240 000 dwellings by 2030. The baseline demand projection (Table 9) assumes that 25 per cent of dwellings (old and new) will continue to have ‘backyard’ bores as a baseline scenario. However, the opportunity for new ‘backyard’ bores is likely to be low in the eastern and south-eastern WAPC planning sectors, which may accommodate ~30 per cent of all new dwellings. The opportunity for access to groundwater in most of the northern and south-western parts of the metropolitan area is likely to be good (>50 per cent). However, the depth to groundwater, and hence the expense of drilling and pumping equipment, may reduce the ability of individual households to use this resource.

Therefore it may be difficult to maintain 25 per cent of all dwellings with access to local groundwater by 2030 and this would result in more demand from the IWSS than has been projected. A more detailed assessment of the opportunities and constraints related to bore uptake is needed, particularly in the important north-west urban corridor. The benefits and costs of community-based schemes to access the resource (e.g. the Brighton Stage 4 development) versus the traditional individual-access approach will also need to be assessed.

The requirement for local governments to develop and implement water-efficiency programs as part of the conditions for groundwater licensing is a major advance. This will result in improved management of this critical resource in existing and future urban areas.


Increased monitoring of the Superficial groundwater system may be required in some parts of the metropolitan area because of localised impacts of abstraction on groundwater-dependent ecosystems.

4.4 Self-supply demand

Scenarios for self-supply (private) demand to 2030 are summarised in Table 11. This includes household water use from ‘backyard’ bores. The additional projected demand relative to the current (2008) demand is in the right-hand column of the table.

Table 11 Perth-Peel self-supply demand scenarios to 2030 (GL/yr)

Scenario Gingin Perth Peel Total Additional 2030-2008

Current 2008 145 309 62 516 1. Business as usual 185 445 86 716 200 2. Baseline; no growth for agriculture in Perth and Peel 185 396 79 661 145 3. Baseline with 10% efficiency for all self-supply 167 357 71 595 79 4. Baseline with 20% efficiency for all self-supply 148 317 63 529 13

Source: Baseline adapted from Resource Economics Unit, 2008.

Total self-supply demand in the region in 2008 is estimated to be 516 GL/yr, of which 60 per cent is in the Perth subregion.

The ‘business as usual’ scenario, which assumes no constraints on water or land resources, suggests that total demand would increase by 200 GL/yr by 2030. However, this is unlikely because of the pressure of urbanisation on rural land in the Perth subregion and parts of the Peel, and the lack of access to groundwater in the Perth subregion.

Therefore, the baseline scenario represents no growth in demand from agriculture or other rural (domestic and stock) land uses in the Perth and Peel subregions and produces a total self-supply demand increase of 145 GL/yr by 2030. Of this increase, 88 GL/yr may occur in the Perth subregion, 17 GL in Peel and 40 GL in Gingin.

For the Perth subregion, 70 GL of the increase may result from urban use (e.g. unlicensed household bores and licensed water use for parks and gardens by local authorities) as shown in Table 12. The balance is for industry such as manufacturing, processing and services not otherwise supplied by the IWSS.

For the Peel subregion the additional demand is evenly split in thirds between urban use (household bores), parks and gardens and rural-based activities such as agriculture and mining. Agriculture and mining account for most of the increased self-supply demand for the Gingin subregion.


Table 12 Additional self-supply demand by sector for baseline scenario by 2030 (GL/yr)

Sector Gingin Perth Peel Total Rural: agriculture, forestry, fishing and mining 35 8 5 48 Manufacturing, processing and services 2 10 6 18 Urban: local authorities and residential 3 70 6 79 Total 40 88 17 145

The State water plan (DPC 2007) set an aspirational target of 20 per cent improvement in water-use efficiency for the agricultural and mining sectors by 2012 through application of best-management practices. Scenarios 3 and 4 in Table 11 show the impact of a 10 and 20 per cent efficiency saving for all self-supply sectors relative to the baseline scenario by 2030. The increase in self-supply demand ranges from ~80 GL/yr for a 10 per cent efficiency to ~13 GL/yr for a 20 per cent efficiency achievement.


5 Water demand and supply scenarios

5.1 Gingin self-supply water demand and supply scenarios

Estimates of the demand for licensed self-supply water in the Gingin groundwater area indicate growth from 145 GL/yr at present to 185 GL/yr by 2030 – an additional 40 GL/yr (Table 13). Note that this analysis does not include projected unlicensed demand (e.g. from ‘backyard’ bores).

Table 13 Gingin self-supply supply-demand balance scenarios by 2030 (GL/yr)

Supply-demand balance Wet Median Dry Gingin demand scenario Demand 326 274 228 Current 2008 145 181 129 84 1. Business as usual 185 141 89 44 2. Baseline; no growth for agriculture in Perth and Peel 185 141 89 44 3. Baseline with 10% efficiency for all self-supply 166 160 108 62 4. Baseline with 20% efficiency for all self-supply 148 178 126 80

The self-supply supply-demand balances at 2030 shown in Table 13 are for the available groundwater of 326, 274 and 228 GL/yr for the ‘wet’, ‘median’ and ‘dry’ climate scenarios respectively. With all balances larger than 44 GL/yr there are likely to be sufficient groundwater resources in the Gingin area to meet the projected increase in demand. However, the location of the demand in relation to available groundwater is likely to be an issue: there is evidence of falling water levels in some areas, which indicates less recharge because of lower rainfall and high levels of abstraction. In addition, much of the available water is in the subregion’s north-west and this may be constrained by land inaccessibility (e.g. military land) and/or poor water quality (i.e. salinity).

If all self-supply sectors achieved 10 per cent improvement in water-use efficiency, the additional self-supply licensed demand by 2030 could be reduced to 19 GL/yr. Most of the additional demand is for agriculture and mining (Table 12).

The Department of Water will review groundwater and surface-water allocation plans for the Gingin subregion over the next few years.

The Department of Agriculture and Food WA is leading an investigation into establishing an agricultural precinct in Gingin. Land and water planning for intensive agriculture, and horticulture in particular, will be reviewed.

5.2 Gingin public water demand and supply scenarios

Public water supply demand in the Gingin groundwater area is projected to increase from ~2 GL/yr to 3 GL/yr by 2030. This is a relatively small increase which, given water-efficiency measures and the area’s large readily available groundwater resources, should be supplied with few challenges, particularly in coastal areas of the Gingin Shire.


The supply of potable water for growth pressure areas in the Shire of Chittering is an issue. Groundwater is not available because the groundwater system is fully allocated. Supply needs are currently being met through water licence trading, principally from horticultural uses to potable water supply. Land-use planning in this area needs to recognise these constraints to development.

5.3 Peel self-supply water demand and supply scenarios

The Peel subregion self-supply supply-demand balances at 2030 are shown in Table 14 for the available groundwater of 127, 107 and 89 GL/yr for the ‘wet’, ‘median’ and ‘dry’ climate scenarios respectively. The supply-demand balances range from 55 to 97 GL/yr and show that groundwater resources will be adequate to meet expected demand by 2030.

As with Gingin, the location of future demand in relation to groundwater available for licensing will be crucial to demand being met. The quality of much of this resource may also constrain development. The allocation limits for the Serpentine and Murray groundwater management areas will be reviewed in the next few years.

Table 14 Peel self-supply supply-demand balance scenarios by 2030 (GL/yr)

Supply-demand balance Wet Median Dry Peel demand scenario Demand 127 107 89 Current 2008 33 94 73 56 1. Business as usual 44 83 63 45 2. Baseline; no growth for agriculture in Perth and Peel 37 90 69 52 3. Baseline with 10% efficiency for all self-supply 34 93 73 55 4. Baseline with 20% efficiency for all self-supply 30 97 77 59

Note that the demands in Table 14 use groundwater, not surface water. Currently ~25 GL is licensed from surface-water sources in Peel. The gold mining operation at Boddington and the alumina refining operation at Pinjarra account for ~20 GL/yr of the current surface-water licences in the region. It is not clear how climate change will affect self-supply users of surface water from the Murray basin, although projections indicate that streamflow for the sources used by these industries could decrease by ~50 per cent by 2030.

A 20 per cent improvement in water efficiency in the agriculture sector would significantly reduce the projected demand for water in line with the aspirational target set by the State water plan (DPC 2007). However, achieving 20 per cent efficiency is likely to be a challenge: the lack of full metering of self-supply use and the absence of financial incentives to improve water-use efficiency are among some of the issues. A key initial step is for state agencies to allocate resources to develop and implement water-efficiency programs for the region (with industry groups).

Additional private demand in the Peel subregion may be met, at least in part, through alternative sources such as re-use.


5.4 Perth self-supply water demand and supply scenarios

The Perth subregion self-supply supply-demand balances at 2030 are shown in Table 15 for the available groundwater of 212, 175 and 142 GL/yr for the ‘wet’, ‘median’ and ‘dry’ climate scenarios respectively. The available groundwater for the scenarios have had 145, 120 and 100 GL/yr subtracted to account for the allocation for public water supply (IWSS) for each climate scenario. The Department of Water has a provisional allocation for additional public water supply of 23 GL/yr (see Table 5). This has been subtracted from the groundwater available in Table 5 to produce the resource potentially available for self-supply in Table 15.

The demands are licensed demands and do not include the large (>100 GL/yr) unlicensed (‘backyard’ bore) water-use sector. This is because the available groundwater resource (e.g. 212 GL/yr for the ‘wet’ climate scenario) does not include an explicit allowance for unlicensed groundwater use.

While agriculture is currently a significant water user in the Perth subregion, the pressure of urbanisation and reducing availability of groundwater is likely to result in a decline in the number of hectares in agricultural production by 2030. Some agricultural activities may move into the Gingin area or south of Waroona. Hence the ‘baseline’ scenario assumes zero increase in demand from agriculture in the Perth subregion.

The supply-demand deficits in Table 15 show the limited prospects for increases in groundwater abstraction for self-supply in the Perth subregion (see also Table 5). Only the scenario of a 20 per cent improvement in water efficiency in all self-supply sectors and a ‘wet’ climate would result in a small surplus of 13 GL/yr by 2030. The other demand and supply scenarios show there is barely enough water to meet existing (2008) demand.

Table 15 Perth self-supply supply-demand balance scenarios by 2030 (GL/yr)

Supply-demand balance Wet Median Dry Perth demand scenario Demand 212 175 142 Current 2008 196 16 -21 -54 1. Business as usual 297 -85 -122 -155 2. Baseline; no growth for agriculture in Perth and Peel 249 -37 -74 -107 3. Baseline with 10% efficiency for all self-supply 224 -12 -49 -82 4. Baseline with 20% efficiency for all self-supply 199 13 -24 -57

A possible increase in urban water use of ~70 GL/yr (Table 12) is the largest part of the baseline demand increase by 2030, with 50 per cent each to local authorities and to residences (i.e. unlicensed and not shown in Table 15). Urbanisation usually results in increased groundwater recharge because of the removal of native vegetation and the large areas of runoff from roads and buildings. This increased recharge may provide some of the increased demand generated by these sectors, particularly if it is combined with a 20 per cent water-use efficiency improvement for this sector. However, the sustainability of maintaining ~25 per cent of future dwellings with access to low-cost self-supply groundwater by 2030 will need investigating and monitoring.

Some of the additional self-supply demands from the industrial and commercial water-use sectors may be met from increased groundwater recharge resulting from development (i.e.


roads and roof-area runoff). However, the IWSS or alternative sources (such as wastewater re-use) may need to meet some of the demand. The State water recycling strategy proposes that water from the new Alkimos Wastewater Treatment Plant has some potential for future use in horticulture; and may be reserved for this purpose. The State water recycling strategy supports the ‘expansion of the existing KWRP [Kwinana Water Reclamation Plant] to 9.6 GL/yr by 2010‘ (DoW & DPC 2008).

Current self-supply use of surface water is small relative to use for public water supply, but accurate information on use is poor. It is likely that pressure on current levels of use will occur in areas in the foothills, such as along streamlines (e.g. Piesse Brook).

5.5 IWSS water demand and supply scenarios

Scenarios of additional demand for the IWSS range from ~20 to 95 GL/yr by 2030 relative to 2008 (see Table 9) for a total system demand of between 300 and ~380 GL/yr. Achievement of water-efficiency targets will have a significant impact on the additional amount of source development required for public water supply, as shown in Table 9. Note that the IWSS does not supply the small towns in the Gingin subregion.

Three demand scenarios, excluding the Gingin subregion public water supply demand, are shown in Table 16. The first demand (280 GL/yr) is current (2008) demand; the second (375 GL/yr) assumes achievement of the State water plan (SWP) target of 100 kL/person/yr for the residential sector in Perth; and the third (300 GL/yr) assumes achievement of 20 per cent improvement in water use across all sectors.

Table 16 IWSS demand and supply balance scenarios by 2030 (GL/yr)

Demand scenarios

Available for supply by 2030 280 (current)

375 (SWP)

300 (20%)

Climate scenarios Surface water

Groundwater

Seawater desalination

Total supply

Balance = supply-demand

Wet climate 220 145 95 460 180 85 160 Median climate 130 120 95 345 65 -30 45 Dry climate 95 100 95 290 10 -85 -10 2001–06 continues 105 120 95 320 40 -55 20

Table 16 includes a range of surface-water contributions by 2030: from 220 GL/yr for the ‘wet’ climate change scenario to 95 GL/yr for a ‘dry’ climate change scenario. Groundwater (mostly from Gnangara) is assumed to range from 145 to 100 GL/yr to reflect climate change impacts. Seawater desalination (SWRO) consists of the existing 45 GL/yr plant at Kwinana and 50 GL/yr from the first stage of the planned Binningup plant by 2012.

The current (2008) supply-demand balance with a continuation of the climate since 2001 is a surplus of 40 GL/yr. No new sources would be needed if the ‘wet’ climate scenario occurred.

The impact of water-use efficiency is apparent for the ‘median’ climate scenario, where the supply-demand balance would be -30 GL/yr for the achievement of the State water plan target of 100 kL/person/yr to a surplus of 45 GL/yr if a 20 per cent efficiency was achieved for all sectors. For the ‘dry’ climate scenario, the balance is -85 GL/yr and -10 GL/yr respectively (the bold numbers in Table 16).


The demand and supply balance scenarios in Table 16 are based on average streamflow and groundwater contributions to the IWSS. As noted in the climate change discussion above, natural variability of rainfall over several years has a major impact on the security of water supply systems such as the IWSS. For example, a ‘run’ of well-below-average rainfall years, as experienced since 2001, results in depleted surface-water reservoirs, falling groundwater levels at Gnangara and the need to implement water restrictions and commission new sources of supply.

As part of the Water Corporation’s licence to abstract groundwater and surface water, the Department of Water requires the development of contingency plans for drought situations. The department expects the current yearly rules for groundwater abstraction from Gnangara for the IWSS to be changed when the first stage of the Binningup seawater desalination plant is commissioned.


6 Public water supply futures

6.1 Options

The large (up to 85 GL/yr) public water supply-demand deficits by 2030 identified in Table 16 might be closed in a variety of ways. The Water Corporation (2008a) is considering a range of options through the Water Forever project, as summarised in Table 17. The risk of climate change influencing further declines in source yields is a major factor in addition to the cost of developing these options.

Option GL/yr Option GL/yr

NW corridor groundwater 15-25 Seawater desalination – others 100 Jandakot South groundwater 3 Industrial recycling 30 Gingin-Jurien groundwater 20-50 Groundwater replenishment 25-50 Catchment management 25 Rainwater tanks 10 Harvey water trade 7 Garden bores 15 Wellington dam 14 Greywater systems 6 Wellington water trade 12 Community bore systems 10 Brunswick dam 20 Sewer mining 10 Esperance SWRO and pipe 20 Community third-pipe systems 10 Seawater desalination (Binningup) 50 Water-use efficiency 12

Table 17 Water Corporation additional demand and supply options

Source: Water Corporation, 2008a and 2009

6.2 Desalination

In November 2006 the Water Corporation commissioned Australia’s largest seawater desalination plant at Kwinana to supply ~17 per cent of the public water supply needs for the IWSS. Another ~50 GL/yr plant is planned for Binningup (north of Bunbury) for 2012, which has the capacity to expand to 100 GL/yr with further investment.

With improvements in technology, particularly reductions in energy use and/or the sourcing of renewable energy to operate the plants, it is likely that much of the future demand of major urban centres will be provided by desalination. A major incentive for use of this technology is the likely continued trend of decreased rainfall and higher evaporation owing to climate change and the reduced availability of ‘traditional’ surface water and groundwater resources. At a cost of $2–3/kL this supply option is the benchmark for comparing alternative demand and supply options (e.g. water-efficiency programs, rainwater tanks and groundwater schemes).

The potable water needs of the Goldfields area is projected to increase by ~8 GL/yr by 2030 (Table 9). A private proposal to develop a seawater desalination plant and pipe water from Esperance to Kalgoorlie is one option to ensure the Perth-Peel region continues to meet the potable water needs of the Goldfields region by 2030.


6.3 Possible groundwater sources for IWSS

Possible additional groundwater options to meet growth in demand for the public water supply system by 2030 are discussed below, with associated issues that could constrain or prevent their development:

• The north-west coastal groundwater resources (Quinns, Eglinton and Yanchep-Two Rocks schemes) could contribute 15–25 GL/yr. However, there are development risks associated with declining rainfall, water quality (e.g. contamination from ‘upstream’ agriculture, particularly if a horticulture precinct is established) and the ocean/groundwater interface.

• Additional development of the wellfield at South Jandakot could contribute ~3 GL/yr. The impact of urbanisation and risks to water quality, as well as competition for the resource with local users, are important issues for this proposal.

• Gingin-Jurien groundwater could contribute 20–50 GL/yr. Note that the Jurien groundwater management area is not part of the Perth-Peel area. Development risks include large distances between the various possible wellfields, variable water quality (salinity), the impact of abstraction on local users and the environment, and competition from horticultural development. The Department of Water is planning to review the allocation in the Gingin groundwater area in the next few years. It is expected the allocation for future public water supply may be decreased and a priority placed on meeting the demands of growing local urban communities.

Abstraction potential from the confined Gnangara aquifers

Very large quantities of water stored in the Leederville and Yarragadee aquifers are readily accessible for the IWSS. It is estimated that there is ~25 000 GL of freshwater in the confined aquifers off the coastline, some of which is only recoverable by maintaining pressures in the confined aquifers at less than sea level (0 m AHD). It may take centuries for seawater intrusion to become an issue and this is best addressed by a network of monitoring bores.

These large confined groundwater resources provide a strategic opportunity to maintain high rates of abstraction for a few years, particularly under drought conditions, with relatively little impact on groundwater-dependent ecosystems. These aquifers also provide the opportunity for combined (conjunctive) use with the Superficial aquifer, particularly as the prospects for managed aquifer recharge (replenishment) of highly-treated water.

6.4 Possible surface-water sources for IWSS

Increasing streamflow from forested catchments of existing dams may be the only surface-water source option for possible development in the region. The Water Corporation’s Wungong catchment trial is determining the extent to which alternative forest-thinning treatments can increase streamflow, the costs, and ecological impacts. If extended to other IWSS catchments, it is estimated these treatments could produce an additional 25 GL/yr by 2030. However, further reductions in rainfall as a result of climate change could significantly decrease these projected savings.

Other surface-water options outside of the region that may be considered for the IWSS include:

• Additional surface water from water trades in the Harvey River basin (~7 GL/yr) and investment in rehabilitating the Collie River basin (~10–16 GL/yr). As with catchment


management, there is a risk of reduced contribution by 2030 because of climate change. There is also the challenge of managing water quality and sharing of the resource with local users.

• Wellington Dam could supply up to 16 GL/yr by 2030 by trading water with irrigators and resolving water quality issues associated with recreation activities on the reservoir. Thirty to 45 GL/yr could possibly be available if reverse-osmosis treatment were used to recover poor-quality water from the system – alongside resolution of water trading and potential impacts on the very high conservation values of the lower Collie River.

• Construction of a dam on the Brunswick River offers a potential contribution of ~20 GL/yr by 2030. However, climate change may not allow this volume of water to be sustainably withdrawn for public supply. In addition, there are likely to be ecological issues with the diversion of streamflow from the Brunswick, which discharges into Leschenault Inlet near Bunbury.

6.5 Alternative water supply sources

Local user-controlled options such as greywater systems, rainwater tanks, garden bores and water-use efficiency are intended to reduce the demand on the public water supply system for high-quality and increasingly expensive drinking water. The installation of these options poses several challenges. An initial challenge is acceptability to the users, including cost and convenience (e.g. large rainwater tanks pose problems for location around dwellings and greywater systems require monitoring and maintenance). Some water-use efficiency measures are subject to continued behavioural change. The benefits of these measures may not be achieved initially or may reduce over time due to lack of maintenance or changes in behaviour (e.g. change in ownership of the property). An implication of this is that additional demand may be placed on the public water supply system, other than what was expected.

When these options form a relatively small component of the supply-demand equation, there is a small risk of IWSS security being compromised. However, if these options form a substantial part of closing a demand-supply deficit, there is a risk that the demand or supply benefit will not be achieved.

Water recycling

The Water Corporation’s Water Forever project outlines some possible recycling opportunities for the major wastewater treatment plants (summarised in Table 18). Annual wastewater flows for the Perth-Peel region are projected to be 192 GL/yr by 2030 or 167 GL/yr with 15 per cent water-use efficiency (Water Corporation 2009).

Table 18 Water Corporation wastewater recycling opportunities by 2030 (GL/yr)

Treatment plant Available Recycled Use opportunity Alkimos 11 4.4 Horticulture; industry Beenyup 50 35 Groundwater replenishment for indirect potable

recycling Subiaco 35 3.5 Public open space; groundwater replenishment by

2030 Woodman Point 74 14.8 Industry; groundwater replenishment by 2030


Treatment plant Available Recycled Use opportunity East Rockingham 8 1.6 Industry; groundwater replenishment Kwinana 3 Mandurah (combined)

10 1.2 Industry; public open space

Mundaring, Bullsbrook

0.7

Total (GL/yr) 191.7 60.6 % recycled 32% Source: Water Corporation, 2009

These drought-independent resources could potentially meet a large proportion of the region’s expected increase in demand. This would be subject to fit-for-purpose use, regulatory approval (e.g. health and environment), public acceptance and cost competitiveness.

The Kwinana Water Reclamation Plant (KWRP) provides up to 6 GL/yr of high-quality industrial-grade water to customers (e.g. BP, Hismelt, CSBP and Tiwest) in the Kwinana Industrial Area south of Perth. The KWRP uses treated wastewater from the Woodman Point treatment plant. The industries return their effluent to the Sepia Depression Ocean Outfall Line (SDOOL) for discharge 4 km offshore.

The Kwinana Industry Council (KIC 2006) projects a total water demand of ~70 GL/yr by 2021 and proposes a range of options to meet this demand. Much of the future supply is expected to come from recycling of secondary treated wastewater and an expanded capability for reverse-osmosis treated wastewater. The recently released State water recycling strategy supports the ‘expansion of the existing KWRP to 9.6 GL/yr by 2010’ (DoW & DPC 2008). Funding and pricing appear to be issues for increased use of this resource, as are the impacts of marine disposal of the SDOOL concentrated effluent.

Growing demand for water in the Neerabup industrial area is also constrained by supply and opportunities for re-use of treated wastewater have been considered.

Major schemes for indirect-potable re-use (e.g. injection of reverse-osmosis treated water from Beenyup and Subiaco) may be developed from ~2015 onwards and may contribute >30 GL/yr by 2030. Costs are likely to be similar to or less than seawater desalination. An added benefit of these schemes is the ecological support provided in some areas by the injection of highly treated wastewater. Public acceptance and regulatory approval are required for this proposal. As such, the Water Corporation is investing ~$40 million in a trial at the Beenyup wastewater treatment plant as a demonstration of the technology. The full-scale development proposed is the injection of 25–30 GL/yr of reverse-osmosis treated water from Beenyup into the Leederville aquifer on Gnangara Mound (after ~2015) to enable abstraction of a similar amount of groundwater to supply the IWSS.

If this is successful, by 2030 additional indirect-potable schemes may be feasible using the large water resources from the Subiaco and Woodman Point treatment plants for injection into local aquifers, while abstracting comparable amounts of groundwater. These schemes alone could meet most of the projected increase in demand for the metropolitan area by 2030.

The potential contribution of other non-traditional options (e.g. rainwater tanks, greywater re-use, stormwater harvesting and sewer mining) is difficult to estimate because there is insufficient information from real cases to demonstrate their effectiveness. Table 19 provides a broad estimate of the potential contribution of such options by 2030.


Table 19 Estimated potential contribution of alternative supplies by 2030 (GL/yr)

Option 2030 Community bores accessing non-potable groundwater 10 Rainwater tanks 9 Greywater re-use systems 2 Sewer mining 3 Recycled wastewater for open space, industry and groundwater replenishment 60 Harvesting of stormwater (e.g. community bores for non-potable use) 5 Total 104


7 Conclusions This paper has examined climate, water demand and water availability scenarios to 2030 for the rapidly growing Perth-Peel region, which contains ~75 per cent of the state’s population. Key conclusions for strategic water demand and supply planning for the region to 2030 are summarised below.

Climate

• The ‘median’ and ‘dry’ climate-scenario projections are for 8 and 15 per cent declines in average annual rainfall by 2030 respectively, relative to the 1980–99 average (Table 2). (Note that the Perth-Peel 15 per cent decline scenario is equivalent to the Gnangara Sustainability Strategy 'dry' climate scenario of an 11 per cent decrease in the 1976–2006 rainfall, since the 30-year-rainfall average is 4 per cent drier than the 20-year-rainfall average).

• Natural variability may add 5–10 per cent to the trend in average rainfall for durations of 5–10 years (‘runs' of wetter and drier years). For example:

− ‘median’ scenario with five-year dry run might result in 18 per cent rainfall reduction

− ‘dry’ scenario with a five-year dry run might result in 25 per cent rainfall reduction.

Groundwater availability

• Groundwater modelling in the region indicates that a 10 per cent reduction in rainfall results in about a 20 per cent reduction in groundwater recharge. Hence the 'median' and 'dry' climate scenarios would result in 16 and 30 per cent less groundwater available respectively in 2030.

• Based on current allocation limits, sizeable amounts of groundwater are potentially available for additional licensed use in the Gingin and Peel subregions. By 2030 under 'median' or 'dry' climate scenarios, approximately 75–121 GL/yr would be available for additional use in the Gingin subregion and 56–74 GL/yr in the Peel subregion (Table 5).

• However, groundwater levels in the Perth subregion have been reducing since the mid-1970s under the influence of a drier climate and increasing water use. In particular, groundwater storage on the Gnangara Mound has been declining by about 45 GL/y since the mid-1990s.

• In response, the Department of Water has made an initial reduction in allocation limits for the Gnangara Mound and other groundwater management areas. The department expects that allocation limits may need to be reduced further as new information becomes available on the response of aquifers to abstraction and adverse changes in climate.

• For the Perth subregion the current balance of water available for future public and private use – 35 GL/y – reduces to about -28 GL/y for the 'median' scenario and 91 GL/y for the 'dry' scenario (Table 5). This is effectively a reduction in current water availability of between 65 GL/y under the 'median' scenario and 120 GL/y under the 'dry' scenario by 2030.

• The Gnangara Mound groundwater is critical to the security of the IWSS and for self-supply users. With abstraction from Jandakot Mound, the total groundwater available


for the IWSS may range between 100 and 145 GL/yr by 2030, depending on climate conditions. Using the Gnangara Mound’s confined aquifers is important for the security of the IWSS and as a strategic opportunity for large-scale managed aquifer recharge (aquifer replenishment).

Surface-water availability

• Surface-water availability has decreased by about 50 per cent since the mid-1970s. Average flow for some streams since 2001 is less than one-third of previous flows. This indicates that in the Perth-Peel region, a 10 per cent reduction in rainfall results in about a 30 per cent reduction in streamflows.

• Drinking-water-quality surface-water resources are already largely developed. The remaining resources (e.g. tributaries of the Avon River and Murray River) have limited prospects for significant public or private water supply development because of constraints associated with ecological flows, water quality and the likelihood of a drier climate.

• Streamflow (including Harvey basin sources) for the IWSS has averaged about 105 GL/yr since 2001 and may reduce to about 95 GL/y under the 'dry' climate scenario by 2030 (Table 7).

• Additional releases of about 5–10 GL/yr from the IWSS dams for environmental water purposes will further reduce the surface water available to the IWSS.

Water demand

• Public (IWSS) water demand is projected to increase by between 20 and 95 GL/yr by 2030 relative to 2008. This will depend on population growth and water-efficiency programs (Table 9).

• Self-supply water demand is projected to increase by between 13 and 145 GL/yr by 2030 relative to 2008 (Table 11). This will depend on drivers for growth, water-use efficiency achievements and the availability of water for self-supply.

• A key assumption is that demand from the agricultural sector, and to some extent from the rural ‘domestic and stock’ category, is likely to reduce because of urbanisation pressure (and subsequent displacement of these land uses) – particularly in the Perth subregion.

Water-use efficiency

• The State water plan has set a target of 20 per cent improvement in water-use efficiency for agriculture and industry generally. This is believed to be achievable without loss of productive output. A 20 per cent efficiency improvement would significantly reduce self-supply water use in the region.

• Improved water efficiency is also likely to significantly reduce demand from the IWSS. Achieving a target of 80 kL/person/yr for the residential sector and 120 kL/person/yr for total scheme use will require substantial effort and financial resources in developing and implementing a water-efficiency program for the Perth metropolitan area.

Public demand and supply balance

• The IWSS supply-demand balance by 2030 (with existing surface-water and groundwater sources and 95 GL/yr desalination) is likely to range between a surplus


of 45 GL/yr for a ‘median’ climate – with a 20 per cent efficiency saving across all use sectors – to a deficit of 85 GL/yr for the ‘dry’ climate scenario – with the achievement of the State water plan target of 100 kL/person/yr (Table 16).

Self-supply demand and supply balance

• The groundwater resources of the Gingin subregion offer significant potential for private and public supply development. The most likely use is for agriculture, given the growing demand for food and sufficient land to produce it in the Gingin area. The impact of abstraction on groundwater-dependent ecosystems may be an important constraint.

• Achieving the State water plan aspirational target of 20 per cent water-use efficiency in the important agriculture water-use sector will require resources for state agencies to develop and implement water-efficiency programs (with industry groups).

• In the Perth subregion, significant reductions in water use will be required to match reduced water availability as a result of climate change – even with no growth in horticulture (Table 15). There is unlikely to be sufficient groundwater to meet the projected large increase (60 per cent) in public open space watering by 2030. The increase would need to be half this rate and accompanied by strong water-efficiency gains. Under the 'median' climate scenario, private water use would need to be reduced by about 20 per cent to match the reduced water available. Under the 'dry' scenario, private water use would need to be reduced by about 35 per cent to match reduced availability, but this may be offset to some extent by increased recharge as a result of urban expansion. Alternatively, additional water could be provided through groundwater replenishment from drainage or wastewater.

• The projected domestic-bore growth rate may be possible in new urban areas and is likely to require significant efficiency gains. Increased density of dwellings, as projected under Network City (WAPC & DPI 2004), may partly offset the need for more new bores. This issue requires more detailed evaluation.

Competition between private and public supply

• There is generally little competition between private and public water needs in the Gingin and Peel subregions. Competition is occurring in the Chittering area and water is being traded to provide potable drinking water for urban development. The nominal reserve of 72 GL/y for public supply in the Gingin subregion will need to be reviewed.

• There is direct competition for the Perth subregion’s groundwater on the Gnangara Mound. The Department of Water has provisionally allocated ~17 GL/yr to future public water supply in the newly urbanising north-west corridor. There may be competition for this resource from private developers (e.g. in the style of the ‘The Green’ development at Brighton).

• By 2030 the Water Corporation predicts that ~180 GL/yr of climate-independent water may be available from wastewater treatment plants. Recycling of the resource is occurring in the Kwinana Industrial Area with plans for expansion. Recycled wastewater has been considered for the Neerabup industrial area and is being considered for agricultural use in the Carabooda area as part of the Gnangara Sustainability Strategy. The corporation is proposing a ~25 GL/yr indirect-potable supply to the IWSS using the resource from the Beenyup plant. Smaller schemes have been proposed for groundwater replenishment to sustain abstraction by local councils and households and for maintaining the salt-water interface along the coastline.


IWSS futures

• The Water Corporation has invested more than $1 billion since the mid-1990s on securing the IWSS, which supplies ~98 per cent of the Perth-Peel population.

• An additional ~$1 billion is planned for 50 GL/yr of seawater desalination at Binningup by 2012 (with a capability to expand to 100 GL/yr).

• Future options include water-efficiency measures, many of which cost <$1/kL compared with future seawater desalination of $2–3/kL.

• A priority water planning challenge is to identify a more refined set of demand and supply options for evaluation.

• Wastewater re-use through groundwater replenishment and recovery of ~35 GL/y is a major supply option and, if successful, larger schemes could meet much of the projected increase in demand.

• Reducing demand on the public supply system through wastewater re-use for industrial demands such as those at Kwinana and Neerabup is also important.

• The current annual groundwater abstraction rule linked to surface-water availability will need to be replaced when the Binningup seawater desalination plant comes into production in 2012. Groundwater abstraction should be linked to groundwater availability under a drying climate. Possible new arrangements could include short-term emergency additional draw on confined aquifers, which will trigger development of a new supply source to replace and ‘repay’ the temporary overdraw.

• Some additional surface-water flows will need to be provided to meet environmental water requirements in the Canning-Wungong, Serpentine and Dandalup river systems. This is expected to be ~5 to 10 GL/y additional to current riparian releases.

Self-supply futures

• Most new supply to the private-use sector will be from groundwater – with large increases in use possible in the Gingin and Peel subregions. However, the issues will be location of demand in relation to supply and the impact of abstraction on local ecological values.

• In the Perth subregion the most likely prospect is a substantial decrease in self-supply from groundwater by 2030. The Department of Water is likely to progressively decrease allocation limits in response to a drier climate. This is likely to increase the need for improvements in water-use efficiency with the possibility of increased water trading.

• Substantial water-efficiency reductions in private water use from all sectors will be required by 2030 as well as increased monitoring and management of water in urban areas.

• Any horticulture growth in the Perth region would require an alternative source of supply such as wastewater re-use. Without this, the additional demand would have to be moved to another location such as Gingin.

• There are opportunities for groundwater replenishment by re-use of wastewater and drainage water in coastal and urban areas to alleviate declining water levels and potential salt-water intrusion under a drying climate.


Water allocation and management priorities

• More detailed planning, including better integration of land and water planning at the water allocation planning level, is needed.

• The views of stakeholders (general community, regulators and customers) are important in shaping these options to meet the region’s future water needs.


Shortened forms BMP best-management practice

CCI Coastal Catchment Initiative

CALM former (department of) Conservation and Land Management

CSIRO Commonwealth Scientific and Industrial Research Organisation

CAMBA China Australia Migratory Bird Agreement

DEC Department of Environment and Conservation

DAFWA Department of Agriculture and Food WA

DPUD former Department of Planning and Urban Development

DoE former Department of Environment

DoH Department of Health

DoW Department of Water

DPC Department of Premier and Cabinet

DPI Department for Planning and Infrastructure

EPA Environmental Protection Authority

FPC Forest Products Commission

GAWS Goldfields and Agricultural Scheme

GSS Gnangara Sustainability Strategy

GW groundwater area

ICLEI International Council for Local Environmental Initiatives

ILWMP integrated land and water management plan

IOCI Indian Ocean Climate Initiative

IWSS Integrated Water Supply Scheme

JAMBA Japan Australia Migratory Bird Agreement

KIA Kwinana Industrial Area

KIC Kwinana Industries Council

KWRP Kwinana Water Reclamation Plant

LGA local government area

MAR managed aquifer recharge

MRPA former Metropolitan Region Planning Authority

MRS Metropolitan Region Scheme (MRS)

NACC Northern Agricultural Catchments Council

NRM natural resource management

NWI National Water Initiative

PDWSAs public drinking water source areas

PHCC Peel-Harvey Catchment Council


PDC Peel Development Commission

POS public open space

PPRWP Perth-Peel regional water plan

PWS public water supply

SCC Swan Catchment Council

SDOOL Sepia Depression Ocean Outfall Line

SME small- to medium-size enterprise

SPP State planning policy

SRT Swan River Trust

SWCC South West Catchments Council

UWPCAs underground water pollution control areas

WALGA Western Australian Local Government Association

WAPC Western Australian Planning Commission

WCP water conservation plan

WELS Water Efficiency Labelling and Standards Scheme

WRC Water and Rivers Commission (now Department of Water)

WRMS water resource management strategy

WRRC water resource recovery catchment

WSUD water sensitive urban design

WWF World Wildlife Fund – Australia

WWTP wastewater treatment plant


References ABS 2008, Population projections Australia 2006 to 2101, Reference 3222, September 2008.

Climate Change in Australia (CCA) 2007, www.climatechangeinaustralia.gov.au/resources.php

CSIRO 2008, South West Sustainable Yields project, www.csiro.au/partnerships/SWSY.html

Davidson, WA & Yu, X 2006, Perth regional aquifer modelling system (PRAMS) model development: Hydrogeology and groundwater modelling, Department of Water, Western Australia, Hydrogeological record series no. HG 20.

Department for Planning and Infrastructure 2008, Population forecast initial update: Seeing the long-term future in the midst of a boom, August 2008.

Department of Premier and Cabinet 2007, State water plan, Perth, Western Australia.

Department of Water 2008, Gnangara groundwater areas water management plan: Draft for public comment, March 2008.

Department of Water & Department of Premier and Cabinet 2008, State water recycling strategy, June 2008.

DoW – see Department of Water

DPC – see Department of the Premier and Cabinet

DPI – see Department for Planning and Infrastructure

Indian Ocean Climate Initiative 2005, How our river flows have changed, Climate note 7/05, Indian Ocean Climate Initiative.

IOCI – Indian Ocean Climate Initiative

KIC – see Kwinana Industries Council

Kwinana Industries Council 2006, Kwinana Industrial Area water planning study.

McFarlane, DJ, Inman, M, Loh, M, Scott, I, Turner, A and Brennan, D 2006, An integrated supply demand planning model for Perth, Client report to WA government, CSIRO: Water for a Healthy Country National Research Flagship, Canberra.

Resource Economics Unit 2008, Water futures for Western Australia: A demand scenario modelling tool, Department of Water, Perth, June 2008

Sadler, B (ed.) 2007, Climate change scenarios affecting the water supply/demand balance in Western Australia (draft), Part 2 – regional scenarios. Climate scenario development for Western Australian water regions, Department of Water, Western Australia.

Water Corporation 2008a, Water Forever: Options for our water future, April 2008.

— 2008b, Water Forever: Water efficiency information sheet, April 2008.

— 2009, Water Forever: Directions for our water future, February 2009.

WAPC – see Western Australian Planning Commission

Western Australian Planning Commission 2005, Western Australia tomorrow: Population projections for planning regions 2004 to 2031 and local government areas 2004 to 2021. Population report 6, November 2005.

Western Australian Planning Commission & DPI 2004, Network City: Community planning strategy for Perth and Peel, Government of Western Australia, Perth, WA.


Yesertener, C 2007, Assessment of the declining groundwater levels in the Gnangara Groundwater Mound, Western Australia, Department of Water, Hydrogeological record series no. HG14.

Looking after all our water needs

Department of Water168 St Georges Terrace, Perth, Western Australia

PO Box K822 Perth Western Australia 6842Phone: (08) 6364 7600

Fax: (08) 6364 7601www.water.wa.gov.au

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