South-West Western Australia Sustainable Yields …Perth and Collie basins, plus the western Bremer...

South-West Western Australia Sustainable Yields Project

Don McFarlaneProject Leader

CSIRO South-West Western Australia Sustainable Yields Project – Overview

Acknowledgements

• DEWHA – funding and policy guidance• Department of Water – data, models, researchers, report review• Water Corporation – data, report review• Department of Agriculture and Food WA – soils data • Bureau of Meteorology – climate data, surface water modelling• Queensland Department of Environment and Resource Management – SILO

data• Contracts and consultancies

• URS – Peel Harvey groundwater model• CyMod Systems Pty Ltd – groundwater model calibration• Resource Economics Unit – demand estimation• Geographic Information Analysis – model data preparation• Jim Davies and Associates – yield and demand analyses

• External reviewers: Peter Davies (University of Tasmania); Andy Pitman (University of New South Wales); Tony Jakeman (Australian National University): Don Armstrong (Lisdon Associates) and Murray Peel (University of Melbourne)

Presenter

Presentation Notes

It is important to acknowledge the very substantial contributions made by people and groups outside CSIRO DEWHA provided funding and policy guidance; the DoW provided significant assistance from the provision of data and models to being partners in the research and review – about 25 DoW people had some input. Water Corp, DAFWA and the Bureau of Met provided data and technical assistance; SILO data were used in the modelling. Five consulting groups were used to provide important technical input as shown in the slide. Finally the results and reports underwent extensive review – internally, with the DoW and Water Corporation; then through a national Technical Reference Panel and also an external group of reviewers as shown on the slide. As a result, hundreds of suggestions were incorporated into each of the three main reports.


Broad terms of reference

• Estimate the current and 2030 yield of water for catchments and aquifers in the south-west of WA considering climate change and development (plantations, farm dams, groundwater abstraction)

• Compare the estimated current and future water yields to those needed to meet the current levels of extractive use, future demands and environmental needs


Publications

Main reports Executive summaries

FactsheetsWeb: www.csiro.au/partnerships/SWSY.html

Presenter

Presentation Notes

The results are contained in three main reports of 170 to 330 pages in length – one on surface water; one on groundwater and one on water yields and demands. There are also three executive summary reports of 12 to 16 pages in length. The third one of these contains results from all three areas Finally there are four 4-page Factsheets with the Key Findings summarised for each area of work.


Project context

• The project does not attempt to set new allocation limits

• The project is regional and doesn’t address local issues

• The results are scenarios based on assumptions about the future climate, landuses, abstraction levels and demands

Water resource planning, management and investment

This Project

Assessments of current and future water yields and demands

Environmental impacts of alternate allocation regimes

Socio-economic impacts of alternate allocation regimes

Stakeholder and community consultation

Presenter

Presentation Notes

This slide shows what the project is about, and more importantly what it isn’t. The work is confined to the green box – the assessment of current and future water yields and demands under climate and development scenarios. It is a regional study and doesn’t look at environmental, socio-economic or community consultation issues required to set sustainable limits on extraction of water. This is the role of the Department of Water. Wherever possible we have used realistic assumptions in our estimations. They were chosen after much consultation with water managers. The results as will be seen soon are in the form of scenarios – some conservative and others less so to get an appreciation for how sensitive water resources are to changed environment and development.


Sustainable Yields Projects – 2007 to 2009

Murray-Darling BasinNorthern AustraliaSouth-West Western AustraliaTasmania

Presenter

Presentation Notes

This is one of four Sustainable Yield projects carried out by CSIRO around Australia. The Murray Darling Basin project was completed in 2008, the Northern Australia project was launched at the River Symposium in 2009, and the Tasmanian and SWWA projects in early 2010. By using a consistent methodology we are now able for the first time to say what impacts climate change and development may have on water resources for all of the main water regions of Australia. The rest of this talk will focus on the blue area shown on the map.


Location of the project area

• All fresh, marginal and brackish surface water catchments between Gingin Brook and the Hay River

• All aquifers within the Perth and Collie basins, plus the western Bremer Basin

• Area = 62,500 km2

Presenter

Presentation Notes

The project area includes all of the fresh, marginal and brackish water resources in SWWA The surface water basins are shown in blue and extend from Gingin Brook to the Denmark and Hay catchments. The saline Avon, Murray, Blackwood and Frankland Rivers were not modelled The groundwater resources are shown in red and include the Perth Basin west of the Darling Fault, the Collie Basin and the western part of the Bremer Basin near Albany.


Project area topography

• Short streams that arise in the Darling Ranges are fresh

• Darling Fault separates Perth Basin from Darling Plateau

• Coastal plains are flat and low lying – Swan Coastal Plain; Scott Costal Plain; South Coast

• Perth Basin Plateaux are higher in elevation

Presenter

Presentation Notes

The yellow line shows the project boundary. The blue (cooler) colours are areas with a low elevation and the hotter colours are high. Only short streams that arise in the Darling Ranges are fresh and were modelled. Not all of the Perth Basin has a low elevation. The Swan Coastal Plain is very low and flat as a result of ocean inundation in the Pleistocene but the northern plateaux, and to a lesser extent the Blackwood Plateau, are moderately elevated.


Land cover

• Surface water catchments are mainly forested

• About 60% of the Perth Basin is cleared about 56% of this being under dryland agriculture

• The uncleared areas include coastal areas north of Perth, the Gnangara Mound and the Blackwood Plateau

Gnangara Mound

Blackwood Plateau

Presenter

Presentation Notes

Surface water catchments are mainly forested whereas most of the Swan Coastal Plain has been cleared. Areas on the Perth Basin that remain under perennial vegetation are the coastal strip north of Jurien Bay, the Gnangara Mound and the Blackwood Plateau. The Collie and Albany groundwater areas are also mainly vegetated.


Climate – annual averages, 1975 to 2007

Potential evapotranspiration

Rainfall - APET

Presenter

Presentation Notes

Annual rainfall is highest in the south west and along the Darling Range. It ranges from less than 400 mm in the NE to more than 1300 mm on the south coast. Aerial Potential Evapotranspiration or APET, a measure of potential evaporation (e.g. water exposed to sunlight and the wind), is highest in the north and lowest in the south. If you take APET from rainfall, then almost all of the project area has a ‘rainfall deficit’ in that only one small area has a rainfall greater that APET. In the north, potential evaporation exceeds rainfall by more than a metre.


South-west WA has had reduced rainfall since 1975

0

100

200

300

400

500

600

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Tota

l rai

nfal

l (m

m)

May – JulyAugust October–

The 1975 to 2007 period is the baseline for all subsequent comparisons

-18%

-8%

Presenter

Presentation Notes

It is generally accepted that the south west of WA experienced a climate shift in about 1975 when rainfall decreased. The average decrease for May to July rainfall was about 18% with a lesser decrease between August and October. All future projections of changes in rainfall, runoff and groundwater replenishment use the post 1975 period as a baseline. i.e. we are ‘factoring in’ this decrease and comparing all future estimates with this already dry period. This is unlike all other Sustainable Yield projects where a similar climate shift is not apparent in their record. They used long term climate records that include wetter periods in the past.


Scenarios

• The ‘historical climate’ assumed that the climate of the last 33 years (1975 to 2007) would continue. This was used as a base case for comparison of other climate scenarios

• The ‘recent climate’ assumed that the climate of the last 11 years (1997 to 2007) would continue

• The ‘future climate’ used 15 GCMs with 3 GHG emission levels which would result in 0.7, 1.0 and 1.3oC of warming by 2030 = 45 possible climates. They are reported as

• wet future climate• median future climate, and • dry future climate

• Current levels of abstraction and land use were assumed to continue for all scenarios above

• The ‘future climate and development’ assumed a median future climate and full groundwater abstraction, new plantations and farm dams (where important)


Annual rainfall and inflow into Perth dams Runoff is affected by climate and other factors

Yearly rainfall at Jarrahdale

0

500

1000

1500

2000

2500

1911

1914

1917

1920

1923

1926

1929

1932

1935

1938

1941

1944

1947

1950

1953

1956

1959

1962

1965

1968

1971

1974

1977

1980

1983

1986

1989

1992

1995

1998

2001

2004

2007A

nnua

l Rai

nfal

l at J

arra

hdal

e (m

m)

Annual Total1911 to 1974 (1251mm)1975 to 2009 (1047mm)1997 to 2009 (1003mm)

Yearly streamflow for major surface water sources - IWSS

0

100

200

300

400

500

600

700

800

900

1000

1911

1914

1917

1920

1923

1926

1929

1932

1935

1938

1941

1944

1947

1950

1953

1956

1959

1962

1965

1968

1971

1974

1977

1980

1983

1986

1989

1992

1995

1998

2001

2004

2007Ann

ual I

nflo

w to

Per

th D

ams

(GL)

Annual Total

1911 to 1974 (338GL)

1975 to 2009 (151GL)

1997 to 2009 (107GL)

Note: A year is taken as May to April (Data courtesy of the Water Corporation)

16% reduction

55% reduction

Historical

Recent

Presenter

Presentation Notes

The northern catchments in the project area flow into Perth metropolitan dams. A 16% reduction in annual rainfall after 1975, as evidenced by the Jarrahdale station, has been accompanied by runoff reducing by more than 50%. The blue line shows the Historical Climate period and the yellow line the Recent Climate period. Not all of the change in runoff may be due to the decrease in rainfall – other factors affect runoff in these catchments such as fire, logging, mining and dieback.


Annual rainfalls have been even drier since 1997

1997 to 2007 rainfall compared with

1975 to 1996 rainfall

Presenter

Presentation Notes

Comparing the rainfall of the last 11 years, the Recent Climate, with the previous 22 years between 1975 and 1996 shows that the south coast has been less affected than the central and northern parts of the project area. The left hand map shows the difference in percent and the right hand in mm per year. Some areas in the Peel – Harvey area have had annual rainfalls more than 100 mm less than in earlier years.


14 of 15 GCMs project it will get drier

Mid warming

Low warmingHigh warming

• Median future climate -7%

• Wet extreme future -1% climate (90 percentile)

• Dry extreme future -14% climate (10 percentile)

Change in annual rainfall

Presenter

Presentation Notes

This graph shows what 15 global climate models project for 2030 rainfall in the project area. The models are ranked on the vertical axis and the estimated change in annual rainfall is shown on the lower axis. Three global warming scenario are also shown – high warming or 1.3o C which would be expected if GHG emissions are high, mid warming or 1.0o C which equates to median emissions and low warming or 0.7o C which assumes that GHG emissions will be lower. Almost all models projects a drier climate with the median being a reduction of about 7% compared with the Historical Climate and with a range of 1 to 14 percent reduction. It must be remembered that the baseline already includes a reduction in rainfall and this projection is in addition to that which has been recorded since 1975. For comparison the median projected reductions in the Murray Darling Basin and Tasmania are about 3 percent with no net reduction being estimated for northern Australia.


Subsequent talks

• Surface water Richie Silberstein

• Groundwater Riasat Ali

• Environment Olga Barron

• Water yields and demands Don McFarlane

Short period for questions after each talk

• Meet the Team – informal session over afternoon tea

Presenter

Presentation Notes

The results from each part of the project will be covered by the respective Team Leaders, after which there will be a period of general questions and an opportunity to talk to all Team Leaders informally.

Rainfall and runoff in south-west Western Australia

Richard Silberstein Surface Water Team Leader

CSIRO South-West Western Australia Sustainable Yields Project – Surface Water

Objectives – Surface Water

• Project future quantity, duration and seasonal distribution of runoff (mm) and streamflow (ML) for conditions in 2030

• under specified climate scenarios, and • with future plantations and farm dams

• These results were used in estimating divertible yields and impacts on ecosystems

Presenter

Presentation Notes

Runoff is streamflow volume expressed as depth equivalent over an area 1 megalitre (ML) = 1 mm over 1 km2 As described in the earlier talk, four climate scenarios were considered.


Geographic scope

• 13 surface water basins covering 39,000 km2

Presenter

Presentation Notes

The map shows location of 13 surface water basins in different group colours indicating three different regions. Rivers with highly saline flow were not included as shown by the gaps between the some of the basins. These were: the Avon, Murray River, Blackwood, and Frankland, although fresh tributaries of these were included. For Busselton Coast basin, a number of small streams discharging directly to the Southern Ocean or the Geographe Bay were modelled.


Rainfall runoff modelling

• Runoff simulated using five simple conceptual models • Sacramento• IHACRES• SIMHYD• AWBM• SMARG

• One catchment model • LUCICAT (in about half the catchments)

• The calibrated model output was compared with observed data and an average of runoff from Sacramento and IHACRES was the best

Presenter

Presentation Notes

Five simple conceptual rainfall–runoff models, and LUCICAT, which is used in many WA catchments, were used. LUCICAT is a more complicated conceptual model, only used where pre-existing calibrations were available.


Catchment representation

Collie Basin

• 0.05o x 0.05o grid (~ 5 x 5 km)• Each cell mapped into a catchment• Flow accumulated for 204 defined streamflow reporting nodes

Presenter

Presentation Notes

The figures shows an example of the ~ 5 x 5 km grid over the Collie basin. A similar grid was laid out over the whole of the surface water modelling area. Input climate data were extracted for each of these cells from the SILO Data Drill data set. The five conceptual models were applied to each of these cells and the output (runoff) summed for each catchment shown here in different colours. Runoff from each catchment was then accumulated for catchments downstream (if any). Average runoff from each cell within a catchment gives runoff at the catchment outlet.


106 Calibration catchments

Criteria for use in calibration:

• Catchments larger than 10 km2

• At least 10 years of available streamflow data between 1975 and 2007 (average record length 27 years)

Presenter

Presentation Notes

We’ll first review the calibration results. The map shows outlets of 106 calibration catchments distributed across the project area Runoff calculated at each of the 106 catchments were compared to determine the model performance. Nash Sutcliffe efficiency (NSE) values of daily, monthly and yearly flow were used as the indicator of model performance. Sacramento and IHACRES were found to perform better than other conceptual models used. Adopted model was average of the daily runoff from Sacramento and IHACRES


0

100

200

300

400

500

Mod

elle

d a

nnua

l run

off (

mm

)

NSE = 0.82

Calibration results – examples

0

100

200

300

400

1975 1985 1995 2005

Ann

ual r

unof

f (m

m)

.

Scott River - Brennan's Ford Observed

Modelled

0

100

200

300

400

500A

nnua

l run

off (

mm

)

.Harvey River - Dingo Road Observed

Modelled

0

100

200

300

400

0 100 200 300 400

Mod

elle

d a

nnua

l run

off (

mm

)

Observed annual runoff (mm)

NSE = 0.87

Average model efficiency = 0.84, >0.8 in 80% of catchments

Presenter

Presentation Notes

Annual hydrograph of observed and modelled flows and their scatter plots are shown. Calibration runs illustrate excellent fit to observed data in most cases. The points on the scatter plot lie around 1:1 line. In both of these cases the modelled runoff is slightly higher than the observed runoff in the last 5 to 6 years.


Calibration results

• In about half of catchments, runoff coefficients have reduced over the recent past (1995 to 2007) – i.e. the same amount of rainfall produces less runoff

• Our rainfall-runoff models are over predicting runoff during the recent period

Annual runoff vs rainfall Model – observed runoff

0

150

300

450

600

600 800 1000 1200 1400 1600

Rainfall (mm)

Run

off (

mm

)

1975-19941995-2007

Bancell Brook – Waterous

-100

-50

0

50

100

1970 1980 1990 2000 2010

Mod

elle

d – o

bser

ved

(mm

)

Bancell Brook – Waterous

Year

Presenter

Presentation Notes

The left graph shows the runoff for a given rainfall through the record, data from 1975-1994 are blue, and from 1995-2007 are red, runoff coefficient was less during the latter period. There are a number of possible reasons for this, some of which are described in the surface water report. The right-hand plot shows the difference in modelled and observed runoff depicting that the models are over predicting runoff during the recent period


Rainfall, runoff and runoff coefficient under historical climate

Presenter

Presentation Notes

Under the Historical Climate: The highest rainfall is in the southern basins and along Darling Scarp The highest runoff is in in Harvey Basin and some basins in south west and south Note that the higher rainfalls along the northern parts of the Darling Scarp do not produce high runoff as in the southern basin. The highest runoff coefficients are in the Harvey Basin and some areas around Margaret River. Northern and inland areas have low runoff coefficients due to their lower rainfalls and high evaporative demands


-50 -40 -30 -20 -10 0

inmcmncar_pcm

iapcccma_t63

ipslmiroccnrm

cccma_t47ncar_ccsm

mrimpigfdl

csirogiss_aom

miub

Change in runoff from historical (%)

Glo

bal c

limat

e m

odel

s

Averaged across the surface water basins 15 global climate models project less runoff

Mid warming

Low warmingHigh warming

Wet future climate -10%

Median future climate -25%

Dry future climate -42%

Runoff change across all basins

Presenter

Presentation Notes

We are now presenting scenario modelling results This plot shows projections of change in runoff for 2030 rainfall for 15 global climate models. The vertical axis shows the names of the climate models. The models are ranked on the vertical axis in order of magnitude of change and the estimated change in annual runoff is shown on the horizontal axis. The leftmost end of the orange bar shows the percent change in runoff due to the high warming climate scenario. The right end of the green bar shows the same for the low warming scenario. The middle point, where the orange and green bars join, shows the change in runoff due to mid warming climate scenario. All models project less runoff with the median being a reduction of about 25% below that under the Historical Climate and with a range of 5 to 49 percent reduction. The symbols on the plot show runoff change for the wet and dry extremes and median future climates given by 5th wettest, 5th driest and median, being 10th, 90th and 50th percentile runoff.


Projected change in mean annual rainfall relative to the historical climate

• Rainfall declines by 8% under median future climate and 14% under dry climate• Proportion of area receiving over 900 mm is: 37% under historical climate, 34% under

recent and wet future, 22% under median future, and 16% under dry future climate

Presenter

Presentation Notes

Our results are means for 33 yr scenarios, they are not forecasts for a particular year at 2030. Recent Climate shows a major decline in rainfall in north and central region, very little change in south. Recent Climate is somewhat similar to wet future climate, however there are some areas in southern basins with higher rainfall under recent climate than under Historical Climate. Locations in Murray and Harvey basins have undergone more changes under Recent Climate (relative to under Historical Climate) than projected under Wet Extreme Climate. Projections under the Median and Dry Future Climate are for a major impact along the Darling Scarp and in the southern region.


Projected change in mean annual runoff relative to the historical climate

• Runoff declines by 25% under median future climate and 42% under dry climate• Proportion of area generating 110 mm runoff is: 37% under historical climate, 34% under

recent and wet future, 22% under median future, and 16% under dry future climate

Presenter

Presentation Notes

The four maps show that as the climate dries up the runoff is also decreased. Interesting to note that areas in the Darling Scarp and Southern basins are affected more (in absolute terms) than inland areas. These changes may not show the same pattern for the percentage change. Under the Median Future Climate, rainfall is projected to decline by an average of 8% and runoff by 25% The proportion of the area receiving more than 900 mm rainfall and (on the average) producing high levels of runoff is (110 mm): 37% under the Historical Climate 22% under Median Future Climate 16% under the Dry Extreme Future Climate


Projected changes in rainfall and runoff

Historical Percent change relative to historical climate

Surface water modelling area mm Recent Wet Median Dry

Mean annual rainfall 837 -2% -2% -8% -14%

Mean annual runoff 98 -7% -10% -25% -42%

Frequency of rainfall exceeding 900 mm generating more than 130 mm runoff

1 in 5 years

1 in 9years

1 in 8years

1 in 14years

<1 in 33years

Presenter

Presentation Notes

Future Climate has the same distribution as Historical because of the scaling A relatively small reduction in rainfall results in a larger proportional decrease in runoff. A rough ‘rule of thumb’ is that a 1% reduction in rainfall results in a 3% reduction in runoff


Percent decline in runoff in all basins

• Decline under recent climate is greatest from Gingin to Collie• Decline under median future climate more uniform across the area

-40

-30

-20

-10

0 Gingin

Swan C

oasta

lMurr

ayHarv

eyColl

ie

Preston

Busse

lton C

oast

Lower

Blackw

ood

Donne

llyWarr

enSha

nnon

Kent

Denmark

Cha

nge

in m

ean

annu

al ru

noff

(%)

Recent climate

Median future climate

Northern region Central region Southern region

Presenter

Presentation Notes

This shows change in mean annual runoff in the 13 surface water basins under Recent and Median Future Climates from that under Historical Climate. The greatest difference between the Recent and Median Future Climate is mainly in the southern basins. The drier last 11 years is not yet apparent in the south of the project area


Key Findings – Surface water

Relative to the historical climate, under the median future climate:

• Rainfall declines by an average of 8% and runoff by 25%

• Mean annual runoff declines by 24 mm and streamflow declines by 800 GL in addition to the decline since the mid-1970s

• Declines in runoff are proportionally greater in the northern surface water region but greater volumetrically in the central and southern regions

• Climate impact on projected streamflows is much greater than that of projected increase in plantations and farm dams after 2007

Presenter

Presentation Notes

The declines in rainfall and runoff are by 8 and 25% under the Median Future Climate and by 14% and 49% under the Dry Future Climate About half the catchments appear to have a reduction in runoff coefficient in recent years which indicates that the projected changes may be optimistic (i.e. underestimates) i.e. in future less runoff may result from the same rainfall amount


Questions?

Groundwater in south-west Western Australia

Riasat AliGroundwater Team Leader

CSIRO South-West Western Australia Sustainable Yields Project – Groundwater

Landforms

Geomorphic landforms affect groundwater response to climate change

Presenter

Presentation Notes

This map shows important features of the Perth Basin which lies to the west of the Darling Scarp and considered for groundwater modelling and assessment. As was shown earlier, the blue Swan Coastal Plain is flat, sandy and a large part of it has been cleared for dryland agriculture. The orange area is the Gnangara Mound which has Banksia Woodland and pine plantations as important land uses, and there are high levels of abstraction from this area. The northern plateaux of Dandaragan, Arrowsmith and Yarra Yarra are elevated and contain soils which are gravelly and less sandy than the coastal plain. The Blackwood Plateau is slightly elevated and contains more clayey soils. The Scott Coastal Plain is sandy, flat and waterlogged. Some of it has been cleared, especially in the west.


Groundwater areas

• All together 24 GWAs considered for groundwater modelling and/or assessment

• Recharge modelling in GWAs of the Northern Perth Basin and Albany area

• Recharge and groundwater modelling for all remaining GWAs

Presenter

Presentation Notes

The groundwater areas are shown for the entire project area. Many of the later slides relate to the southern half of the Perth Basin – south of Moora; and the Collie Basin for which we have groundwater model data


Groundwater models

• The PRAMS model as used in the Gnangara Sustainability Strategy was used

• A new model (PHRAMS) was developed for the Peel Harvey area

• The SWAMS model was linked to a recharge model and recalibrated

• The Collie model was linked to a recharge model and recalibrated

Perth Regional Aquifer Modeling System

(PRAMS)

Peel Harvey Regional Aquifer Modeling

System (PHRAMS)

South West Aquifer Modeling System

(SWAMS)

Collie model

Presenter

Presentation Notes

Four groundwater models were used to estimate groundwater levels in 2030 under climate and development scenarios; Perth Regional Aquifer Modelling System or PRAMS as used in the Gnangara Sustainability Strategy but over the whole domain and with more climate scenarios A new model was developed by URS under guidance from CSIRO and DoW for the area between Mandurah and Bunbury – PHRAMS The South West Aquifer Modelling System (or SWAMS) was updated and upgraded by linking a vertical flux model to the groundwater system Likewise the Collie groundwater model was updated and upgraded. Neil Milligan from Cymod Systems helped re-calibrate the SWAMS and Collie models.


Objectives – Groundwater

• Project groundwater levels in 2030 under future climate and development scenarios

• Understand why some areas and aquifers may be less sensitive to climate change than others

• The groundwater results are later used to:• assess the impacts of levels on groundwater

dependent ecosystems (GDEs); and• estimate future groundwater yields

Presenter

Presentation Notes

The main aim was to project groundwater levels under a range of historical, recent past and future climate scenarios and current and future landuses. The rate of abstraction was kept constant in all scenarios except the development scenario where it was increased to full allocation levels. Groundwater yields are an estimate of how much water can be safely abstracted from an aquifer


Recharge estimation

• The project developed an estimate of net recharge / discharge for combinations of:

• Climate• Soil types• Land cover • Depth of the watertable

• These estimates were linked to the groundwater models

Presenter

Presentation Notes

The project area was subdivided into various climate, soil and land cover zones. The recharge rates or deep drainage from the unsaturated zone into the saturated zone were estimated by using vertical flux models at each stress period and supplied to the saturated or groundwater models internally. The groundwater models then distributed this water in various unconfined and confined aquifer systems through physical processes. Temporal variations in depth to the watertable are considered through dynamic link between VFM and groundwater flow model.


Climate zones

• 15 climate zones in the groundwater assessment area

• Representative stations in each zone were used

Presenter

Presentation Notes

This map shows the 15 climate zones that were used to estimate recharge. Data from one climate station in each zone was chosen as being representative to reduce the amount of computations required to provide input to the models. Future climate data were scaled using the historical record. As a result the estimates are somewhat coarse or ‘lumpy’ – a limitation of the method that we used.


Soil types used in models likely to affect recharge

• Coastal plain soils are sandy except Guildford which is clayey

• Plateau soils are mainly gravelly (north) or clayey (Blackwood Plateau)

Presenter

Presentation Notes

Soil types with similar hydraulic properties were also grouped into 14 classes to estimate recharge and discharge rates The Swan Coastal Plain has sandy soils associated with dunes in the west – Quindalup, Spearwood and Bassendean – and clayey soils in the east – Guildford. The Mowen soils on the Blackwood Plateau are also clayey and reduce the amount of recharge that would otherwise occur.


Land cover likely to affect recharge / discharge

Groundwater assessment areas

• 56% dryland agriculture

• 38% native vegetation

• 6% plantations, urban, irrigated, open water

Presenter

Presentation Notes

This map shows the main landuses over the whole project area Perennial vegetation is shown in green and cleared dryland agricultural land in bronze. The areas of pines on the Gnangara Mound, Myalup and Donnybrook Sunkland areas are shown in purple. For the Perth Basin, dryland agriculture occupies 56% and about 38% is under native vegetation. About 60% is cleared and 40% vegetated to some extent.


Maximum depth of the watertable in the southern half of the Perth Basin in 2007

• Coloured areas are potential GDEs if not cleared

• Coastal plain soils have very shallow watertables except Gnangara and Spearwood Dunes

• Plateaux areas mainly have deep watertables

22%14%10%46%

Presenter

Presentation Notes

This map shows areas in the modelled domain with a shallow watertable – green is within 3 m, yellow 3 to 6 m and pink, 6 to 10 m. Almost half of this area has the potential to contain groundwater dependent ecosystems if they are not cleared. The Swan and Scott Coastal Plains have especially shallow watertables whereas the plateau areas (Dandaragan, Blackwood) usually have deep watertables.


Current abstraction by groundwater areas

Most groundwater abstraction currently occurs close to Perth because of high demand and water availability

Presenter

Presentation Notes

These maps show where groundwater is currently being abstracted from groundwater areas. The hot colours are areas of high abstraction. The units are ML per square kilometre per year or mm (the same as rainfall is measured) The very high levels of abstraction around Perth – over 100 and up to 500 mm per annum, reflects the presence of very high yielding aquifers – the Superficial, Leederville and Yarragadee especially – and the high demand for water for public and private users. Currently abstraction is modest away from Perth – often 50 mm or less per year


Change in groundwater levels between 2008 and 2030 under climate and development scenarios

Presenter

Presentation Notes

These maps are the main groundwater findings from the project They show the change in groundwater levels between 2008 and 2030 under four climate scenarios – the Historical Climate (1975 to 2007), the Recent Climate (1997 to 2007), and the Median and Dry Extreme future climates. If the climate of the past 33 years were to continue until 2030 groundwater levels are projected to rise under the Dandaragan Plateau, the Swan Coastal Plain near Lancelin and where the pines are removed at Gnangara and on the Swan and Scott Coastal Plains in the south. Areas under the Blackwood Plateau and the crest of the Gnangara Mound however would continue to fall. If the climate of the past 11 years were to continue until 2030 more areas would record a fall in levels but the pattern remains very similar. Under the future climate scenarios this trend continues such that under the dry extreme future climate, even removing the pines on Gnangara will not be enough to prevent groundwater levels from falling. Interestingly, groundwater levels are projected to rise under the Dandaragan Plateau even under a Dry Extreme Future Climate. This area has a relatively poorly calibrated model so this may be optimistic. However it is an area under dryland agriculture and sandy soils with modest levels of abstraction and we know that similar areas in the wheatbelt would be recording rises in groundwater levels under a annual rainfall of about 500 mm or we would not have a dryland salinity problem in the state. The Swan Coastal Plain between Perth and Bunbury changes relatively little compared with many areas. You will recall that these areas had groundwater levels within about 3 metres of the soil surface indicating that the aquifers were relatively full. It is believed that these areas are comparatively resistant to a drier climate because drainage and evaporation losses decrease as watertables fall. The lower watertables also enable more recharge to enter the aquifers. This reduction in evaporation losses will be accompanied by a loss of wetlands so there is a price to be paid for in having ‘climate resilience’. Like the Gnangara Mound, groundwater levels under the Blackwood Plateau have been falling for the last 40 or so years and this trend is projected to continue even under an historical climate. Both areas are under perennial, native vegetation and in the case of the Blackwood Plateau, the soils are clayey.


The additional impact on 2030 groundwater levels of allowing full abstraction under a median future climate

• There are a few areas where additional abstraction will cause a decline in levels

• This may not be a problem where groundwater levels are projected to rise

• There are many areas already fully allocated

Presenter

Presentation Notes

The map on the right is the change in groundwater levels by 2030 under a Median Future Climate as you saw on the previous slide. The map on the left is the additional reduction in levels if all remaining unlicensed water is allowed to be abstracted between 2008 and 2030. Most areas have reductions of less than 0.5 m over a 22 year period. This would be expected where abstraction is already at the Allocation Limit for the groundwater area. The main area where additional abstraction is projected to reduce levels is on the Swan Coastal Plain north of Lancelin where groundwater levels are projected to rise by a similar amount. The other area is the Swan Coastal Plain South of Perth where large areas are cleared of native vegetation. These are regional projections and there has been no attempts to compare changes in levels with groundwater dependent ecosystems.


Collie groundwater basin level changes between 2008 and 2030

Groundwater levels are less affected near rivers

Presenter

Presentation Notes

Projecting future groundwater levels in the Collie Basin is difficult because there is a complex aquifer system within the sedimentary basin, heavy abstraction occurs around mine voids and for power production, groundwater inflow to voids after mining ceases and interactions between groundwater and the tributaries of the Collie River. Groundwater levels are projected to decline in the Premier Sub-basin under the Historical Climate and under almost the whole basin under the future climates. The reductions are lower near the rivers, possibly because river flows may recharge the aquifer whereas at present the rivers receive groundwater. This projection is not considered to be accurate and the new finite difference groundwater model being prepared by the Department of Water will be a better estimate of future levels.


Northern Perth Basin bore hydrographs

Slight fall in groundwater levels under native vegetation

Rising levels under dryland agriculturesince 1978

GS1B

-25

-20

-15

-10

1995 2000 2005 2010 2015 2020 2025 2030

OB1-75

-60

-55

-50

-45

-40

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

Historical climateRecent climateMedian future climateObserved level

Fitted 1975-2007 Range between wet anddry extreme future climate

-30

Gro

undw

ater

leve

l (m

)G

roun

dwat

er le

vel (

m)

Presenter

Presentation Notes

We didn’t have groundwater models for the Northern Perth Basin. We developed relationships between rainfall and groundwater levels for some bores and used the projected future climate data to estimate where levels may be by 2030. Three examples are shown here. Under areas where there is native vegetation the future level were expected to decline because of reduced rainfall Areas under dryland agriculture were projected to rise as shown in the lower hydrograph. In this case groundwater levels shown in pink have risen since the late 1970s although they are starting to level off in recent years. This is similar to coastal plain areas where levels may rise under annual crops and pastures provided the soil are sandy and abstraction is low.


Albany Area bore hydrographs

Groundwater levels are projected to decline under all future climates

CST-99-78

-45

-40

-35

-30

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

CST-W78

-15

-10

-5

0

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

Gro

undw

ater

leve

l (m

)G

roun

dwat

er le

vel (

m)

Observed levelFitted 1975-2007

Historical climateRecent climateMedian future climateRange between wet anddry extreme future climate

Presenter

Presentation Notes

In the Albany area, where a suitable groundwater model was also not available, levels are projected to decline under all except a continuation of the historical climate. The area where these bores are located is vegetated. It appears likely that under a drier climate the proportion of rainfall intercepted by the vegetation increases and the amount of recharge decreases. The Albany wellfield area is already fully allocated so any future decrease in recharge may require reductions in abstraction if groundwater levels are to be maintained. A new groundwater model is being developed which will enable this rough projection to be properly tested.


Level of confidence in the 2030 projections of groundwater levels

• Central and Southern Perth Basin groundwater models are generally better than others

• Northern Perth Basin and Albany Area require models

Presenter

Presentation Notes

This maps shows how confident we are in our projections of 2030 groundwater levels. Cool colours such as dark blue show we have relatively high levels of confidence compared with the hot red colours The blue areas are mainly around Perth and the South West although the projections for the Dandaragan Plateau are low because there are few calibration bores for the PRAMS model in this area. The Peel Harvey areas has a medium to low level of confidence because the models for this area was only just constructed for the project. The model was also poorly calibrated in the Serpentine area which is shown in red. The lowest levels of confidence are for the Northern Perth Basin and Albany Areas where we don’t have any groundwater models to do the projections.


Key findings – Groundwater

• A future drier and hotter climate is likely to lower groundwater levels, especially where there is perennial vegetation

• Groundwater levels under cleared, sandy coastal plains are expected to be less sensitive to climate change except under the dry future climate and high abstraction

• As groundwater levels fall in these areas, evapotranspiration and drainage losses decrease and there is room in the aquifer to accept recharge


Key findings – Groundwater (cont.)

• Interactions between surface water and groundwater may change in both volume and direction as a result of lower water levels in rivers and surrounding aquifers

• Groundwater models are needed to estimate the impact of climate change and development for the Northern Perth Basin and Albany Area to extend the results of this project

• Confidence in model predictions varies depending on calibration error, hydrogeology, data quality, model maturity and other factors


Questions?

Water Dependent Ecosystems

Olga BarronEnvironment Team Leader

Presenter

Presentation Notes

Variations in surface water and groundwater regimes under future climate and development scenarios may affect some functions of ecological system dependent on these water resources. This part of the SWWASY project assessed how the scenarios may affect water dependent ecosystems

CSIRO South-West Western Australia Sustainable Yields Project – Water Dependent Ecosystems

Objective

• Assess the impact of climate change on hydrologic regimes likely to affect water dependent ecosystems

This was applied to: • Surface water dependent ecosystems (SDEs)

• 33 rivers• Groundwater dependent ecosystems (GDEs)

• Four types of ecosystems assessed – wetlands and vegetation with various depths to the watertable

• Only future risks were assessed

Presenter

Presentation Notes

Only future risks (post 2008) were considered. The effect of the recent drier climate on surface water and groundwater dependent ecosystems is outside the project’s scope


Environmental assets in the project area

• Ramsar listed wetlands

• Wetlands of national significance

• Conservation category wetlands

• Wild rivers

• Caves

Presenter

Presentation Notes

The SWWA region has a large numbers of SDEs and GDEs including Ramsar sites, wetlands of national significance, conservation category wetlands, wild rivers and caves


Surface Water Ecosystems


Assessing the effects on ecologically significant surface water flows

1. Rivers where Ecological Water Requirements were available (9 rivers shown in blue)

2. Rivers where Ecological Water Requirements were not available (shown in red)

3. Duration of “no-flow” periods under future climate scenarios

Presenter

Presentation Notes

The analysis was tailored to the constraints of current knowledge of the ecological river functions and their dependence of river flow regimes Three type of analysis were undertaken for rivers where Ecological Water Requirements were available; rivers where Ecological Water Requirements were not available; and spatial analysis of “no-flow” duration under future climate scenarios. The figure shows the locations of the stations for which the EWRs were available (blue triangles) and locations where the river discharges were modelled in the project (red triangles)


1. Frequencies of daily river flow under the historical climate: fhist

Ecological significance

Maintain pool habitat in summer

Minimum flow to maintain pool quality

Upstream migration of small native fish

Summer habitat for invertebrates

Winter habitat for invertebrates

Inundate trailing vegetation

Inundate low elevation benches

Inundate high elevation benches

Ecological function flow threshold (ML/day)

1

6

10

16

60

120

320

1080

Based on data from DoW

Lefroy Brook

Flow threshold exceeded (%)

0 20 40 60 80 100

Presenter

Presentation Notes

Various flow rates support different ecological functions such as those listed here. For individual rivers, the identification of the flow rates required to maintain the specific ecological function requires site-specific field investigations. For example, for Lefroy Brook, the minimum daily flow rates to support each function was determined by the DoW. For historical data the frequency that these flows equalled or exceeded the thresholds was estimated based on surface water modelling. For instance, the flow supporting upstream migration of small native fish or greater occurs on about 85% of days Overall, ecological systems are more sensitive to variation during low flow periods












1

6

10

16

60

120

320

1080

Change in the frequencies of daily river flow under future climate scenarios: (fhist - fscenario )

RecentclimateWet extremefuture climateMedian futureclimateDry extremefuture climate

-16 -12 -8 -4 0 4

Difference (%)

Lefroy Brook

Presenter

Presentation Notes

Future climate scenarios change the daily flow frequencies and therefore the flows required for a specified ecological function may occur less or more often. For example, the frequency of the daily flow rate required to support upstream migration of small native fish is projected to reduce by 3, 7 and 13% under the Wet Extreme, Median and Dry Extreme future climates respectively. This means that under the Dry Extreme Future Climate this river function may be supported during only 72% of days instead of during 85% of days under a continuation of the Historical Climate.












1

6

10

16

60

120

320

1080

Relative frequency difference under dry extreme future climate (relative to historical climate): (fhist - fscenario )/fhist

-100 -80 -60 -40 -20 0

Relative difference

Lefroy Brook

Presenter

Presentation Notes

In addition to absolute values, a relative difference in exceedence frequency was estimated. This is the proportion of the absolute difference in frequency relevant to the Historical Climate frequency of the specified daily flow rates exceedance. The graph shows that larger differences occur during low frequency, high flow events such as those needed to inundate high elevation benches. That is there is projected to be few floods under a Dry Extreme Future Climate


2. Variation in runoff during high runoff and low runoff periods under future climate

• More than 80% percent of annual runoff is generated during the high runoff period • Runoff during this period decreases under future climates relative to historical data

Lefroy Brook

Runoff decreasefor all rivers

5–20%

20–30%

40–50%High runoff periodLow runoff period

Historical climate

Recent climate

Wet extreme future climate


Dry extreme future climate

0 10 20 30 40 50 60 70Streamflow (GL/y)

Presenter

Presentation Notes

In the rivers where EWRs were not available, variations in total runoff during the low and high runoff periods were considered. The time for those period separations was 15th June and 15th October. It was assumed that river ecological functions are likely to be more sensitive to the variation in rivers runoff during the low runoff period between October and June Similar changes are projected for runoff during both seasons, and when all 33 rivers were considered the reduction in river runoff is 5 to 20, 20 to 30 and 40 to 50% under the Wet Extreme, Median and Dry Extreme future climates respectively


Change in runoff under the median future climate (relative to historical climate)

• Climate impacts on runoff are greater in southern (Kent and Denmark) and northern rivers (Gingin)

• There is a slightly greater percentage decrease in summer runoff compared to winter

-70

-60

-50

-40

-30

-20

-10

0

Den

mar

kK

ent 5

Ken

t 4K

ent 3

Ken

t 2K

ent 1

Lake

Mui

rS

hann

on

Dee

pLe

froy

War

ren

Don

nelly

Cha

pman

2C

hapm

an 1

Mar

gare

t 4C

owar

amup

Wily

abru

p 2

Wily

abru

p 1

Mar

gare

t 3M

arga

ret 2

Mar

gare

t 1Th

omso

n

Ferg

uson

Pre

ston

Col

lieB

runs

wic

k 2

Bru

nsw

ick

1B

ance

ll

Har

vey

Ser

pent

ine

Can

ning

Gin

gin

2G

ingi

n 1

Cha

nge

in fl

ow (%

)

High runoff periodLow runoff period

Presenter

Presentation Notes

This slide illustrates the effect of future climates on various rivers within the entire study region. The plot shows % changes in the river flow under the Median Future Climate scenario relative to a continuation of the Historical Climate. It is projected that the largest changes in river flows may occur in the most northern and southern rivers. It also shows that the changes in summer runoff are slightly greater, which is true for all climate scenarios.


3. Change in “no-flow” days

Perennialrivers

No-Flow days Change in number of no-flow days

Presenter

Presentation Notes

Based on the surface water modelling, the distribution of “no-flow” days under a continuation of the Historical climate was estimated. Under this climate runoff does not occur for most of the year in the areas shown in red, while in the blue areas runoff is continuous throughout the year; that is, they are perennial. The variation in number of no-flow days under Future Climate scenarios relative to Historical Climate was also mapped for the Wet Extreme, Median and Dry Extreme future climates. Under the Recent Climate there is an increase in annual river flows in some regions with overall small changes in flow duration in the region. Particularly significant reductions in flow duration are projected under the Dry Extreme Future Climate, when the number of days with no-flow increase by more than 120 days Perennial rivers are projected to remain perennial under all future climate scenarios even though their flows may reduce in volume


Groundwater Dependent Ecosystems


Areas of potential GDEs

• Only regional risk assessments were undertaken

• The analyses were carried out where groundwater models were available and where potential GDEs may occur (coloured areas)

Presenter

Presentation Notes

Groundwater modelling results were used to estimate the potential risk to GDEs. No individual GDEs were assessed in the project. Four types of groundwater dependency were considered Wetlands where groundwater depths was less than 3 m GDEs in areas where the groundwater depth was less than 3 m GDEs in areas where the groundwater depth was between 3 and 6 m GDEs in areas where the groundwater depth was between 6 and 10 m The map shows the areas where those types may potentially occur based on depth of the watertable. Many of these areas have been cleared of native vegetation and have lost their ecological values.


GDEs ecological risk assessment

*Depth to watertable

(Froend and Loomes, 2004)

0

0.2

0.4

0.6

0

0.2

0.4

0.6

0 1 2 3

Rat

e of

dec

line

(m/y

)

0 1 2 3

Magnitude of groundwater decline (m)

Severe riskHigh riskModerate riskLow risk

Wetland Vegetation (0–3 m*)

Vegetation (3–6 m*) Vegetation (6–10 m*)

0 0.4 0.6 1 0 1 2 30.2 0.8

Presenter

Presentation Notes

The groundwater model estimates were analysed within a framework developed by Froend and Loomes for GDEs risk analysis for the Gnangara region. The severity of the risk to GDEs types was defined based on both the absolute changes in the groundwater levels and the rate of change in levels. For example, 0.3 m changes in water level in the vicinity of wetlands may cause severe risk, if the rate of water level reduction is greater than 0.2 m/y, but the risk is classed as moderate if the water level reduction was less than 0.1 m/y The graph colours used to depict levels of risk (blue = low to red = severe) is used in the next slides


Risks to GDEs in the Central Perth Basin under a Median Future climate (in addition to current conditions)

Presenter

Presentation Notes

The analysis was undertaken for the southern half of the Perth Basin. This slide shows the risks in the Central Perth Basin (PRAMS model) under a Medium Future climate scenario for the four GDE types. The analysis indicated that over the majority of the area where GDEs may occur, there is a low or no risk of GDE degradation. This assessment does not measure past degradation The area with potentially high or severe risk is greatest for vegetation dependent on deeper groundwater levels, that is 6 to 10 m This probably reflects the buffering of water levels where they are close to the surface – as mentioned before – and the rapid fall in levels where this buffering no longer exists


Projected risk to wetlands

Historical climate



Full abstraction under a median future climate

Presenter

Presentation Notes

This slide shows the wetlands risk for the region under of Future climate scenarios. Under Historical and Median Future climate scenarios some GDEs risk (low category) are projected for the Peel-Harvey area. Under a Dry Extreme Future Climate and full groundwater development under with a Median Future Climate, wetlands may experience high and severe risks in the Gnangara, Peel-Harvey and Scott Coastal Plain areas These are regional assessments and individual GDE assessments would be required to properly assess the risks


High and severe ecological risk to GDEs in the southern half of the Perth Basin

• Dry future climate scenario results in significant increase in risk to GDEs• There appears to be a threshold between median and dry future climates

0

10

20

30

40

Per

cent

are

a gr

eate

r tha

n hi

gh ri

sk

Central Perth BasinPeel Harvey AreaSouthern Perth Basin

0

10

20

30

40

Historical climate

Recent climate




Future climate and

future development

Historical climate

Recent climate




Future climate and

future development

Wetland Vegetation (0–3 m)

Vegetation (3–6 m) Vegetation (6–10 m)

Presenter

Presentation Notes

A summary of the results are presented here in terms of the % area where potential GDEs risk is high or severe in the southern half of the Perth Basin. For all GDEs types, high and severe risk may occur in a limited area under most of the climate scenarios. The Dry Extreme and Development scenarios results in significant increases in the area where the risk to GDEs is high or severe.


Key findings – water dependent ecosystems

• For surface water dependent ecosystems• Runoff during both the wet and dry seasons is expected to

decrease by 20 to 30 percent under a median future climate• The impact of a drier climate is greater for low frequency-

high flow events, but ecosystems are less sensitive to such conditions

• For groundwater dependent ecosystems• About 40% of potential GDEs may be affected to some

degree under a median future climate • There are some localised high risk areas under the dry

future climate and development scenarios

Presenter

Presentation Notes

Overall the results indicates that there is some risk which future climate and development scenarios may pose to surface water and groundwater dependent ecosystems.


Questions?

Water yields and demands

Don McFarlaneProject Leader

CSIRO South-West Western Australia Sustainable Yields Project – Water Yields and Demands

Some terminology clarification

• Runoff = amount of surface water expressed as a depth (mm)

• Streamflow = amount of surface water expressed as a volume (runoff x area)

• Surface water yield = streamflow that can be diverted for use. Takes account of water for the environment and the location of nature reserves, national parks, irrigable land etc.

• Use = water that is currently being used (metered, estimated)

• Yield = the amount of surface water and groundwater that is available for use – either under license and as unlicensed ‘stock and domestic’

• Demand – as estimate of the future requirement for water as a result of economic, demographic and industrial growth. Unmet demand may result in higher water prices, reuse, water conservation, trading, desalination, etc. as well as a curtailment in growth


Water use in the project area

• Total use is about 1200 GL/y of which 71% is self supplied (on-site bores and farm dams) and three quarters is groundwater

• About 35% is used for irrigated agriculture – elsewhere in Australia it is 66 to 75%

• Can be competition for water between water sectors – residential, industry, mining and agriculture

• Most irrigation water in south-west is used for high value products

• This, in addition to it being self supply and mostly groundwater, makes transfers and trading less feasible

Presenter

Presentation Notes

First some interesting facts about current water use in the project area


Water demand was assumed to grow because of:

• population growth;• economic growth; and• industry growth – some industries have high water use coefficients

1.0

1.5

2.0

2.5

3.0

3.5

2006 2010 2014 2018 2022 2026 2030

High growthMedium growthLow growth

Population(Million)

Year

Presenter

Presentation Notes

Three factors were assessed in estimating future water demands Population growth which affects domestic water consumption especially Economic growth, and How the growth of different industries will affect water demands – e.g. horticultural growth may affect water demands more than growth in the service sector of the economy. An example of high, medium and low population growth estimates for the project area is shown. Along with per capita consumption, this provides an estimate of water demand for residential water. The project aligned its estimates with those made by the Water Corporation’s Water Forever plan.


Yield and demand areas

• 21 surface water management areas

• 23 groundwater areas

• 8 demand regions

Perth Demand Region

Presenter

Presentation Notes

Future yields and demands were separately estimated for 21 surface water areas shown in blue, for 23 groundwater areas shown in red and for 8 demand regions shown in green. The demand regions combined surface water and groundwater yields and demands The Perth Demand Region has been highlighted as this will be shown later in the talk


Surface water use is highest in central catchments and demand will grow in future

Current use = 299 GL/y Growth in demand

Metro basins are fully used and growth in demand was assumed to be zero

Presenter

Presentation Notes

Current surface water use is shown on the left hand map with areas of high use in the hotter colours. The units are ML per square kilometre per year, or mm – as has been used in previous maps to take account of the different sizes in the areas shown. Interestingly, the highest use per unit of catchment area is in the central basins around Dandalup, Harvey and Collie. Growth in demand for surface water is shown in the other two maps. Under both the medium and high growth in demand scenarios, the estimated demand pressures are highest in the central basins as well as the Warren. These are all horticultural areas and the growth in demand estimates result from assumed increases in demand for surface water to help meet the demands fro horticultural products by a growing population and economy.


Current surface water yields

Volumetric yield Yield per unit area Total yield = 425 GL/y

Licensed allocations

• Public Water Supply 24%

• Irrigation schemes 27%

• Self supply 49%

• Harvey and Collie contribute 43% of total yield

Presenter

Presentation Notes

These maps show surface water yields – or the amount of water than can be safely diverted for use – in two ways The left map shows yields in volumes per year from each of the 13 basins while the right map show them in ML per square kilometer per year (or mm per year) The highest yielding basins are in the centre with those to the north and south with low yields, either because there is little streamflow (north) or because the streamflow may be within areas that contain nature reserves or national parks (south) as well as having lower streamflows per area. The total yield of all basins is about 425 GL/yr with about 43% of this coming from the central Harvey and Collie Basins. Currently surface water is used by self-supply irrigators with dams on streams within their property (about half), and by irrigation schemes (mainly Harvey Water) and public water supply dams which each use about a quarter.


Surface water yields are projected to change by -24% under a median future climate. Range of -4 to -49%

IWSS yields reduced by 18% to 77 GL/y under a median future climate

Presenter

Presentation Notes

These three maps show the projected percentage change in surface water yields under three climate scenarios – a continuation of the Recent Climate, the Median Future Climate and the Dry Extreme Future Climate Under the Median Future Climate, surface water yields are estimated to decrease by about 24% compared with the Historical Climate with the range being between 4% (under the Wet Extreme Future Climate) and 49% decrease (under the Dry Extreme Future Climate). The projected future reductions in yields are not uniform across all basins. Interestingly the high yielding Harvey and Collie Basins also appear to have lower reductions compared with basins to both the north and south. The Gingin, Donnelly, Warren and Denmark catchments appear to be most affected. The estimated reduction in 2030 yield to the metropolitan dam catchments which supply water to the Integrated Water Supply Scheme is 18% or 77 GL/y. These estimates are very similar to those in Water Corporation’s Water Forever plan


Gaps in surface water yields and demands in areas where irrigation is important

DeficitSurplus

Presenter

Presentation Notes

Having estimated future demands and yields it is possible to map gaps between them. A positive gap represents a surplus of water – shown here in cool colours, and a negative gap is a potential deficit of water – shown here in hot colours. Under the Median and Dry Extreme Future Climates, surface water deficits are evident in the Harvey and Dandalup Basins. Deficits are apparent wherever horticultural demand is expected to grow by 2030 and yields are projected to decline.


Current groundwater yields as estimated by adding the 2009 Allocation Limits

Volumetric yield Yield per unit area Total yield = 1556 GL/y(3.6 x surface water yield)

Main aquifers:

• Superficial 58%

• Leederville 12%

• Yarragadee 26%

Presenter

Presentation Notes

To estimate current groundwater yields we added all of the allocation limits for all aquifers in each groundwater area. The total yield of these aquifers was 1,556 GL per year with 58% contained in the Superficial Aquifer,12% in the Leederville and 26% in the Yarragadee The left map shows the yields in GL per groundwater area and the right map in ML per square kilometer per year or mm per annum. The highest yielding areas shown in blue on the right map are located around Perth and in the SW Coastal area around Preston. These areas have multiple aquifers which are high yielding – over 200 mm per annum being able to be abstracted. In comparison the aquifers in the northern and southern Perth Basins, and near Albany, are much lower yielding as defined by this method. Perth is very fortunate to have been located in a water-rich area. Its is also possible that the resources in this area of high demand have been more fully investigated and exploited and therefore they appear relatively high.


Groundwater use and future demand is highest near Perth and Bunbury

Current use = 808 GL/y (2.2 x surface water use)

Perth – Peelarea

Bunbury

Additional

Growth in demand

Presenter

Presentation Notes

The map on the left shows current groundwater use reflects the current water yield map that was just shown with high concentrations near Perth and around Bunbury and Collie. Everything ‘hotter’ than yellow has an annual use of more than 50 mm per annum. The other two maps show the expected growths in demand for groundwater under medium and high demand scenarios. Future growth in demand for groundwater is expected to be substantial near Perth and Bunbury with demand growing by 25 to 50 % of current use in these areas. This does not mean that all of this demand will be met but it does show that there may be requirements for increased efficiencies of use, other water sources may need to be developed or imported and there may be significant unmet demand.


Future groundwater yield method

• Almost all groundwater areas are proclaimed and have an annual allocation limit set under an allocation plan

• This limit was assumed to be the best estimate of the aquifer’s current yield

• The limit was assumed to be related to the historical climate and 2008 aquifer storage volumes (groundwater levels)


Groundwater yields are projected to change by -2% under a median future climate. Range = +2 to -7%

Yield reductions are low because1. Drain and ET losses reduce as watertables fall 2. Areas under dryland agriculture (56% of Perth Basin) have rising levels3. Allocation Limits account for a future drier climate

Recentclimate


Dryfuture climate

Presenter

Presentation Notes

Using this method it was estimated that future groundwater yields would decrease by about 2% under the Median Future Climate with a range of +2% under a Wet Extreme Future Climate to a decrease of about 7% under a Dry Extreme Future Climate. Areas with the greatest decreases in yield were Gnangara, the Blackwood, Collie groundwater basin and the Albany Area All of these areas are overlain by perennial vegetation which reduces recharge compared with cleared dryland agricultural land, the areas where yields were less affected. While the average reduction in groundwater yields is relatively small, some resources have substantial projected decreases under the Dry Extreme Future Climate – e.g. by between a quarter and a half for the four areas just mentioned


Groundwater deficits may develop near Perth, Collie and Albany

Recent climate 2030 gap

Median future climate2030 gap

Dry future climate2030 gap

Surplus

Deficit

Presenter

Presentation Notes

This slide shows surpluses in blue and deficits in ‘hot colours’ under three scenarios – Recent Climate, Median Future Climate and Dry Extreme Future Climate The main groundwater deficits are expected to develop near Perth, Collie and Albany A limitation of the method used to estimate future water demands is that new industries are not included in the estimates of growth, e.g. a paper pulp mill or a new mine. It is therefore feasible that the apparent surplus of water in the Northern Perth Basin may be used if demands by mid-west iron ore companies eventuate. These demands can be incorporated into the method that was developed by this project if the demands are known, but they were not included in this analysis.


Current yield

HistoricalRecent

Wet extremeMedian

Dry extreme

Avai

labl

e S

W/G

W y

ield

(GL/

y)

2005 2010 2015 2020 2025 2030 2035

2030 Low demand Recent

2030 Medium demand Wet extreme

2030 High demand Median

Historical Dry extreme

Tota

l dem

and

v To

tal a

vaila

ble

yiel

d (G

L/y)

Yarragadee

Mirrabooka

Leederville

Superficial

Other aquifer

Self-supply dams

Scheme dams

Fractured rock

400

500

600

700

800

0

100

200

300

400

500

600

700

Combined yield and demand for the Perth Demand Region

Potential gap under median future climate and medium demand within 15 years

Median demand =median future

climate yield

Presenter

Presentation Notes

The left graph shows what may happen to surface water and groundwater yields in the Perth demand Region by 2030 for each climate scenario. Surface water scheme dams and Superficial Aquifer yields are projected to decline, especially under the Dry Extreme Future Climate. Confined aquifers such as the Leederville and Yarragadee appear more stable however. Water from the two desalination plants at Kwinana are not included in this assessment but they add an additional 50 GL/year at present. The right hand graph shows that the growth in demand for water (blue lines) is expected to be very substantial which mainly reflects the grown in residential, peri-urban agriculture, council and industrial water demands. Under the Median Future Climate and Median Demand a deficit for the region is expected by 2025. This may seem optimistic but it is important to remember that the Perth Demand Region includes provision for increased recharge after the pines are removed from Gnangara and includes water which is currently reserved for future drinking water supplies. It is expected that there will be increased competition between public and private water supplies in future. A high rate of growth in water demand and a Dry Extreme Future Climate would result in this cross-over occurring about eight years earlier


0

500

1000

1500

2000

2500

Current yield

HistoricalRecent

Wet extremeMedian

Dry extreme

Avai

labl

e S

W/G

W y

ield

(GL/

y)

0

500

1000

1500

2000

2500

2005 2010 2015 2020 2025 2030 2035

2030 Low demand Recent

2030 Medium demand Wet extreme

2030 High demand Median

Historical Dry extreme

Tota

l dem

and

v To

tal a

vaila

ble

yiel

d (G

L/y)

Yarragadee

Mirrabooka

Leederville

Superficial

Other aquifer

Self-supply dams

Scheme dams

Fractured rock

The project area can meet all except high demands until 2030 under a median future climate

A 250 GL/y deficit may develop under a dry future climate and high demand

250 GL

Presenter

Presentation Notes

These graphs show the yield and demand gaps for the entire project area. The decrease in surface water yields is very apparent in the left graph, along with a substantial decrease in yields in the Superficial Aquifer. Groundwater, which currently supplies about three quarters of all water needs, may become even more important in future, along with other water sources such as desalination and water reuse. The right graph shows how both demand and yields are projected to change between 2008 and 2030. If there is median grown in demand and a Median Future Climate, there is enough water to meet all growth in existing industries until 2030. This assumes that water quality is adequate and transportations cost are not prohibitive. This situation is possible largely because of the large groundwater reserves that are contained within the Perth Basin. In reality there will be local deficits and alternative sources will be developed, as is occurring already through desalination, and there will be an increasing need for increased water efficiencies, reuse and trading. If we experience a Dry Extreme Future Climate and demand growth is high there could be a 250 GL per year deficit by 2030. Obviously these estimates are approximate only and are based on a set of assumptions which affects estimates of both future yields and demands. This project has developed some tools that could be adapted and used over time as both data and assumptions are improved.


Key findings

1. South-west Western Australia has experienced a significant climate shift since 1975 which is thought to include a component of climate change. Climate models project that rainfall could decline further by about 7% by 2030 (up to 14%)

2. Surface water yields are projected to decrease by about 24% (up to 49%) • The yields have already decreased in northern catchments

and may decrease further by 2030• Central catchments are higher yielding and the decrease

could be less• Streamflows are projected to decrease the most in the

Southern catchments


Key findings (cont.)

3. Groundwater levels are projected to fall most under areas of perennial vegetation, e.g. Gnangara, Blackwood Plateau, Collie and Albany.

Levels are least affected in areas with high watertables such as coastal areas under dryland agriculture, e.g. Swan and Scott Coastal Plains; Dandaragan Plateau

As watertables fall, drainage and evaporation from GDEs decrease and this slows the rate of fall

4. Water dependent ecosystems have already been impacted and these impacts are projected to worsen, especially for high streamflows and GDEs with a watertable depth of 6 to 10 m


Key findings (cont.)

5. Water deficits between yields and demands are likely in:• Surface water irrigation catchments• Aquifers near Perth, Collie and Albany

6. Overall there is enough water to meet all except high demands under a median future climate. However if there is a dry extreme climate and a high demand the deficit may be as much as 250 GL/y


Contributors

Project Director Tom HattonSustainable Yields Coord. Mac KirbyProject Leader Don McFarlaneProject Support Frances Parsons, Therese McGillion, Paul Jupp, Josie GraysonData Management Geoff Hodgson, Jeannette Crute, Christina Gabrovsek, Mick Hartcher, Malcolm Hodgen

DOW – Aidan BelouardiDAFWA – Damien Shepherd, Dennis van Gool, Noel Schoknecht

Climate Stephen Charles, Francis Chiew, Randall Donohue, Guobin Fu, Ling Tao Li, Steve Marvanek, Tim McVicar, Ian Smith, Tom Van NielNSW Dept of Water and Energy – Jin Teng

Surface Water Richard Silberstein, Santosh Aryal, Neil Viney, Ang YangDOW – Mark Pearcey, Jacqui Durrant, Michael Braccia, Kathryn Smith, Lidia Boniecka, Simone McCallumBOM – Mohammad BariGeographic Information Analysis – Geoff Mauger

Groundwater Riasat Ali, Warrick Dawes, Sunil Varma, Irina Emelyanova, Jeff Turner, Glen Walker, John Byrne, Phil Davies, Steve Gorelick, Mahtab AliDOW – Chris O’Boy, Binh Anson, Phillip Commander, Cahit Yesertener, Jayath de Silva, Jasmine Rutherford Water Corporation – Mike Canci, Chengchao XuCymod Systems – Neil MilliganURS Australia – Wen Yu, Andrew Brooker, Amandine Bou, Andrew McTaggart

Water Yields and Demands Olga Barron, Natalie Smart, Michael DonnDOW – Roy Stone, Phillip Kalaitzis, Rob Donohue, Fiona Lynn, Adrian Goodreid, Andrew Paton, Susan Worley, Kylie La SpinaResource Economics Unit – Jonathan ThomasJim Davies and Associates – Sasha Martens, Kate Smith

Reporting Viv Baker, Becky Schmidt, Susan Cuddy, Simon Gallant, Heinz Buettikofer, Elissa Churchward, Chris Maguire, Linda Merrin

Communications Anne McKenzie, Helen Beringen, Mary Mulcahy


Questions?

Date post:	02-Jun-2020
Category:	Documents
Upload:	others
View:	0 times
Download:	0 times

South-West Western Australia Sustainable Yields …Perth and Collie basins, plus the western Bremer...

Documents