Surface and Groundwater Management, Availability, Allocation and Efficiency of Use
Western Australian Technical Report
Australian Water Resource Council (AWRC) river basins were used to define 44 surface water management areas (SWMAs), with priorities for data collation (Priorities 1, 2, 3, & 4) defined by Water & Rivers Commission (WRC).
SWMA areas were extracted from digitised boundaries provided by WRC. It should be noted that in some SWMA, the area which contributes to catchment runoff is smaller than the total SWMA area.
Catchment descriptions were obtained from Streamflow Records of Western Australia to 1982 (Public Works Department, 1984) and more recent WRC publications such as State of the Northern Rivers (WRC, 1997).
Sub areas within each SWMA were defined for estimation of sustainable yields and resource categorisations. SWMA sub areas were defined using catchment boundaries delineated by existing and/or potential dam sites and current self supply management areas defined by WRC.
WRC identified key gauging stations and water quality monitoring sites for each SWMA. For Priority 1 basins, an average of 4 gauging stations and 6 water quality monitoring stations per basin were identified. For Priority 2, 3, and 4 basins a single gauging station and water quality station was used in most instances.WRC extracted, collated and estimated relevant statistics for key streamflow and salinity station within each SWMA. Statistics for individual streams were then accumulated to determine SWMA totals. Extrapolation was required for the majority of SWMA, as few SWMAs have complete gauging to the basin outlet.Total basin outflow statistics are reported to the Audit via the SWMA number prefix with suffix '000 (eg 616000, 801000). Statistics reported include:
Present (regulated) and natural monthly streamflows, including standard HYDSYS quality codes for the monthly streamflow data
Mean, maximum and minimum annual rainfall & annual runoff
Contributing catchment area
Median, maximum and minimum flow-weighted annual salinity
Latitude & Longitude for each station.
Various methods were used to estimate monthly flows and salinities. Linear and non-linear regression methods were used to extend data for existing sites using data from catchments of similar size and characteristics. Regression constants (R2) were typically above 0.80.For monthly streamflow, catchment area proportions were used to estimate the flow at the catchment outlet for each major stream/river, which were then accumulated to provide a total basin outflow. For salinity, annual salt loads were estimated for each stream and the basin total divided by the basin total streamflow, to give an average flow-weighted salinity for the basin.Calculated statistics were reviewed in comparison to published data from recent WRC reports, including the Water Resource and Allocation Planning Series (WRAPS), and Review '85 results. Streamflow and salinity reliability classes were determined based on the 4 classes (A, B, C, & D) required by the Audit, with comparisons conducted against Review '85 data.
Key infrastructure and major diversions were identified using WRC's Water Resource Allocation and Planning Series reports (WRAPS), Water Resource Licencing (WRL) database, and DWAID water resources database.
Key infrastructure consisted of existing dams, pipeheads or pumpbacks, and diversion weirs. The infrastructure capacity was obtained from WRAPS report or DWAID, with third party verification via WRC or Water Corporation where required. Capacity data was collected for major infrastructure only, with capacities included for minor infrastructure (eg minor town water supply dams) where readily available in DWAID.
The Water Corporation provided asset numbers for the majority of infrastructure, with the remaining private and local authority infrastructure assigned asset numbers for the purposes of the Audit. Location information for infrastructure was obtained from DWAID and verified by GIS.
Major diversions were reported as the total amount of water diverted for use in Level 1 Use categories (Urban/Industrial, Rural, Irrigation, In-situ, and Inter-Basin Transfer). Diversions were reported for each existing key infrastructure item.
Self-supply minor sources (irrigation, livestock use) are not reported as major diversions.
Sub areas within each SWMA were defined for estimation of sustainable yields and resource categorisations. SWMA sub areas were defined using catchment boundaries delineated by existing and/or potential dam sites and current WRC self supply management areas.
Sub areas were also defined for key National Parks.
Approximately 400 sub areas were defined for use in sustainable yield calculations.
Divertible yields were determined for sub areas based on published estimates in WRC reports and databases including Water Resource Allocation and Planning Series (WRAPS) reports, Surface Water Hydrology Report Series (SWHS) reports, DWAID database, and Review '85.
For self supply areas the divertible yield was estimated based on adopting 50% of the 10th percentile flow of the sub area, or alternatively as 25% of the mean annual flow where more detailed information was not available. This method provided good agreement to surface water licenced allocations in self supply areas known to be near the limit of sustainable yields.
For the South West Division, the period of record used to estimate divertible yield was typically 1964-1995, while for the Indian Ocean Division the period use for yield calculation was 1972-1995. For the Timor Sea the period 1968-1995 was adopted. These periods were adopted on the basis of consistency with published WRAPS reports, and for divertible yield estimates to include the effects of climate perturbation in the South West of Western Australia, which has occurred over the last 25 years.
Divertible yields for the Western Plateau SWMA are considered nominal only and no detailed calculation of these figures has been undertaken.
In accumulating sub area data to the SWMA scale, the sites adopted assumed a development scenario which would maximise yield. As divertible yields for different sites obtained via publications were independent yields, yields were adjusted to reflect the interaction of sites in the assumed development scenario.
For each sub area, a management objective was defined. These objectives were used for the determination of sustainable yield from divertible yield where more detailed environmental flow requirements had yet to be determined. Four broad classifications were adopted:
M1 : Environment pre-eminent - development highly restricted
M2 : Water development sensitive to defined environmental values
M3 : Water development pre-eminent - low environmental values
M4 : Little development potential or recognised environmental ranking
These broad classifications were used to determine appropriate environmental provision factors for application to divertible yield estimates to calculate sustainable yield. Factors were adopted where formal environmental provisions were not determined and were set at precautionary levels on the basis of the type of development. Factors adopted ranged from 0 for proposed sites located in M1 areas to 1 for existing sources and self supply areas.
Factors for dam sites and pipeheads were typically 0.8 and 0.6 respectively in M2 areas, increasing to 0.9 and 0.7 respectively for M3 areas.
Estimation of sustainable yields was undertaken as a two-stage process.
The first stage, or first cut, involved accumulating sub area data to the SWMA scale, for the likely development scenario. This development scenario included applying all constraints explicit or strongly implicit in established regional allocation plans, policy or regulations, in the selection of preferred sites.
Similarly for divertible yield calculations, individual sub area yields were adjusted to reflect the interaction of sites in the adopted development scenario.
First cut sustainable yields were then estimated based on applying management objective factors.
The second cut involved refinement of selected sites for the likely development scenario established in the first cut, and further adjustment of management objective factors (environmental water provisions) for individual sites.
This second cut refinement aimed to provide allowances for regional reservations yet to be established. While the second cut involved subjectivity, the refinements made were based on accumulated regional planning experience, and are believed to reflect realistic outcomes at SWMA levels.
The calculated second cut sustainable yields at SWMA level represent the surface water sustainable yields reported by Western Australia for the purposes of the Audit.
Sustainable yield estimates for the Audit at SWMA level should be interpreted as indicative of the broad outcomes of a planning process which has approached sustainability through application of precautionary principles for determination of environmental reservations and environmental flow provisions.
Although calculated at the sub area level, sustainable yield estimates at the sub area level do not have sufficient specific information to be regarded as prescriptive, except where environmental water provisions have been formally established. It is considered invalid to interpret these sub area assessments as definitive in a planning sense.
Urban and industrial water use statistics were obtained for 1996/97 for relevant public supply and private schemes. Public supply schemes included town water supplies, with private schemes predominately developed for industrial purposes.
Public supply schemes are generally operated by Water Corporation and information was principally obtained from annual reticulated town water supply scheme reports, the Corporation's Towns database, and Revenue Billing System (RBS) statistics. Data on both major public supply schemes and minor schemes (standalone country town water supply schemes) were collated. Major schemes included:
- The Perth Metropolitan Water Supply Scheme
- The Goldfields and Agricultural Water Supply Scheme (G&AWS)
- The Great Southern (and Lower Great Southern) Towns Water Supply Scheme (GSTWS, LGSTWS)
Private supply scheme use was collated from WRC and private users. Private supply schemes included:
- Opthalmia Dam (BHP Iron Ore)
- Alcoa Pinjarra Refinery Dams
- Alcoa Wagerup Refinery Dams
- Boddington Gold Mine Dam
- Hedges Gold Mine Dam (de-commissioned since 1996/97)
- Rottnest Island Authority Dams
All water use figures adopted included system and distribution losses and represent the total water diverted for use from existing infrastructure.
1996/97 water use data for major public irrigation schemes was collated from WRC, Water Corporation, and irrigation scheme operators such as South West Irrigation and Preston Irrigation Co-Operative.
Major irrigation schemes included:
- The Waroona Irrigation District
- The Harvey Irrigation District
- The Collie Irrigation District
- The Preston Valley Irrigation District
- The Ord Irrigation District
Irrigated areas not located within an irrigation district were assumed to obtain water from self supply schemes. Water use for these areas was calculated by converting known irrigation areas to water use by applying estimated annual crop water requirements. Irrigated areas were obtained from Agriculture Western Australia and checked with data from the Australian Bureau of Statistics. Areas were provided on a shire basis and aggregated to 19 statistical divisions.
Statistical divisions were different to SMWA boundaries and distribution of areas to SWMA boundaries was required. This was undertaken subjectively on the basis of accumulated regional planning experience, and more detailed water use data collated for Review '85.
Irrigation use was determined by applying different water requirements to various crop types within each SWMA. Seven broad crop types were adopted - pasture, cereal, vegetables, fruit (including nuts), grapes, sugarcane, and other crops. The values adopted for crop water requirements were provided by WRC as ML/ha/yr, and represented values used in determining licensing allocations
The majority of rural water use is via self supply, with some rural use supplied with reticulated water from major public water supply schemes (G&AWS, GSTWS, LGSTWS).
For major public supply schemes, reticulated supply data for 1996/97 was obtained from Water Corporation.
For self supply schemes, it was assumed that rural domestic water use was negligible in comparison to livestock use. Water use by livestock was determined by obtaining numbers of sheep and cattle from Agriculture Western Australia. Similar to irrigated areas, livestock numbers were provided on a shire basis and aggregated to statistical divisions.
Statistical divisions were different to SMWA boundaries and distribution of areas to SWMA boundaries was required. This was undertaken on the basis of two methods for different regions of WA:
South West Drainage Division
Livestock use was evenly distributed over the total cleared area minus any National Parks, State Forest, Reserves etc, as identified in Department of Conservation and Land Management mapping.
Remainder of the State
Livestock water use was evenly distributed over areas identified as Pastoral Leases from Water & Rivers Commission's "State of the Northern Rivers" report (WRC, 1997).
The average water use by livestock was determined by the volume of water required by a sheep under normal conditions, referred to as a "Dry Sheep Equivalent" (DSE). DSE water use is measured in m3/head/yr, and values adopted for the Audit were consistent with values used in Review '85.
To determine the percentage of self supply livestock water use from surface water as opposed to groundwater, Review '85 proportions were adopted, with some modifications on the basis of more recent regional planning experience.
Groundwater provinces are based on major geological subdivisions recognised in Western Australia. The provinces comprise rocks of different ages, rock types, geological structure and topographic expression, in which the location, depth, yield, salinity and quality of groundwater may vary substantially, in particular between sedimentary basins (Phanerozoic age) and fracture rock provinces (Archaean - Proterozoic age).
The definition of the groundwater provinces are based on tectonic subdivisions recognised on the 1998 Western Australia Geological Survey 1:2.5M Geological Map of Western Australia.
For practical purposes some modifications were necessary:
- Bremer Basin: subdivided into Bremer East and Bremer West.
- Albany - Fraser Province: subdivided into Albany-Fraser East, and Albany-Fraser West.
- Officer Basin: the western boundary was drawn to conform to the 1998 Western Australia Geological Survey 1:2.5M Hydrogeological map of Western Australia, showing the inferred extent of saturated sedimentary rocks.
- Eucla Basin: the northern boundary was drawn to conform to the State Hydrogeological map for the same reasons as the Officer Basin.
Some provinces recognised in the 1985 Review of Australia's Water Resources and Water Use (1985 Review) were redefined, subdivided, or renamed as a result of new data and understanding of the hydrogeology as follows:
- Yilgarn - Murchison: boundaries have been redefined to correspond with regional Yilgarn - South-west drainage divisions
- Yilgarn - Goldfields:
- Capricorn Province: has been subdivided into the Ashburton, Capricorn, Glengarry and Nabberu Provinces.
- Calyie-McFadden Province: renamed Savory Province
- Bangemall Province: eastern area has been included in Savory Province
The names of some of the provinces do not conform to the major geological subdivisions now recognised on the State geological map. The names adopted for the Audit with the name of the corresponding geological units are given below:
- Halls Creek Province: Halls Creek Oregon and King Leopold Oregon
- Savory Province: Centralian Superbasin (Part)
- Glengarry Province: Yerrida Basin
- Paterson Province: Lamil Group and Rudall Complex
Thirty four groundwater provinces are recognised for the purpose of the Audit. These comprise nine sedimentary basins and twenty five fractured rock units. Nine of the groundwater provinces extend into adjoining states: three into South Australia and six into the Northern Territory.
The groundwater provinces were outlined on a master copy of the State geological map and the boundaries imported from digital data supplied by the Department of Minerals and Energy. The province boundaries were modified as noted, and areas calculated by computer.
The groundwater provinces were aggregated into seven Groundwater Divisions, reflecting the major basins and basic groupings of the provinces comprising fractured rocks, for convenience of description of the groundwater resources.
Groundwater Management Areas
Groundwater management areas (GMAs) have been defined by the Water and Rivers Commission and preceding organisations (Public Works Department, Metropolitan Water Authority and Water Corporation) which have had responsibility for groundwater regulation. They are statutory areas declared under the Metropolitan Water Supply Sewerage and Drainage Act and the Rights in Water Irrigation Act.
The boundaries to the GMAs follow cadastral boundaries or boundaries defined by latitude and longitude, which cover all of the State except the area bordering the southern coast, and in the south western part of the State. The GMAs have been erected for various reasons such as protection of town water supplies and to enable legislative control of groundwater in response to various development pressures. Some of the GMAs, particularly in the Perth Basin, have been further subdivided into groundwater management sub-areas to meet local groundwater management requirements. As a result most of the GMAs do not closely correspond with the groundwater provinces or natural physiographic regions.
The statutory areas for GMAs in Western Australia were obtained in digital format from the WRC and have been followed for the Audit. Some GMAs principally in the Perth (Basin) Province, have specific management plans or allocation quotas.
An unincorporated area (UA) is an area not included within a GMA. About 12% of Western Australia along the south coast and south western part of the State is a UA in which a number of small GMAs around town water supplies (eg. Bremer, Albany and Bolgart) are located.
For the purposes of the National Land and Water Resources Audit the term Groundwater Management Unit (GMU) was applied to a discrete aquifer, or part of an aquifer within a GMA or UA. In the sedimentary basins where aquifers may be superimposed on each other or the aquifer extends into several GMAs each aquifer or part of an aquifer is dealt with as a separate GMU. For the purpose of the Audit the UA was split into seven GMUs (W2-4, W9, W12, W34 and W171) corresponding with their respective groundwater provinces.
For the Audit all known major aquifers currently being exploited or considered likely to be exploited in the foreseeable future were identified in each GMA and their extent determined from the State Geological or Hydrogeological maps. The resultant GMUs were superimposed on a composite map showing groundwater provinces and groundwater management areas and numbered consecutively, (W1 - W174) commencing around the coast from the South Australian border and then through the central part of the State. Three GMUs not identified initially but subsequently recognised, were added to the end of the list. A total of 174 GMUs ranging from 1 km2 (Dwellingup) to 312,250 km2 (Canning) including seven in UA were recognised. The GMUs were also given names that reflect the geographic region; the geographic region and aquifer, or town water supply.
The GMUs are the basic areas used in the Audit. Data from them was aggregated into their respective groundwater provinces.
Groundwater recharge from rainfall may vary depending on rainfall conditions such as seasonal and annual variations in total rainfall and the intensity, duration and frequency of rainfall events. It is also affected by topography and drainage, soil cover, rock-types, land-use and other factors. In some areas groundwater recharge is increasing or decreasing as a result of changed land use such as clearing, urbanisation, or drainage.
In practice groundwater recharge has usually been estimated indirectly during regional groundwater investigations. The groundwater recharge has been estimated by dividing estimates of groundwater throughflow by the contributing area (average recharge = throughflow/recharge area), or from the ratio of chloride in rainfall to chloride in groundwater in recharge areas (average recharge = chloride in rainfall/chloride in groundwater x mean annual rainfall). These approaches provide results that are averaged over large areas and are generally considered to provide the most reliable recharge estimates for regional studies.
For the purpose of the Audit recharge factors for the Perth Basin and the remainder of Western Australia have been derived from available data or were estimated. The factors for the Perth Basin are derived from existing management plansmand for the remainder of Western Australia from a few groundwater investigations, or are estimated by reference to other areas and consideration of rainfall, topography and aquifer type.
In some areas such as in parts of the Perth urban area, which do not have management plans, or where groundwater allocation in confined aquifers (Leederville and Yarragadee aquifers) is based on throughflow (Davidson (1995), the area of the GMU does not reflect the size of the renewable resource. This is because of the regional extent of the aquifer concentrations of production bores in the GMU, and the large groundwater capture zone of artesian aquifers. Therefore, synthetic recharge factors based on throughflow divided by the area of aquifer were estimated so that the renewable resources could be related to the area of the GMU. A similar procedure was used for the Birdrong aquifer in the Carnarvon Basin.
The renewable or total groundwater resources were determined from the area of land surface or aquifer multiplied by the mean annual rainfall and by the applicable recharge factor for each defined area (see Section 4.2.1):
Renewable groundwater resources = area of land surface/aquifer x mean annual rainfall x recharge factor.
The areas were calculated by computer from the base maps at 1:2.5M scale, or larger scale for the Perth Basin, and the mean annual rainfall was interpolated from a Commonwealth Bureau of Meteorology map of mean annual rainfall (1998).
In existing groundwater management plans for some GMAs, computer modelling, discounting areas of parks and wetlands, and reducing the renewable resources by 25% - 70%, have been used to estimate volumes of water required to maintain wetlands.
For the purpose of the Audit a wetlands allowance of 0.40 of the renewable resources was adopted in areas with significant wetlands such as the Perth Coastal Plain (various GMUs) the Kimberley and Collie Provinces, and the extensive cave system on Cape Range (Gascoyne - Exmouth GMU). Elsewhere, the renewable resources (except sub-cropping aquifers), were reduced by 0.05 in recognition that all surface aquifers are likely to maintain some local wetlands or groundwater dependant vegetation.
To stabilise the seawater/groundwater interface, or minimise upconing of seawater where lenses of freshwater overlie seawater (eg. South West Coastal GMA) 0.3 to 0.5 of the renewable groundwater resources has been allowed in some existing management plans.
For the purpose of the Audit the seawater intrusion allowance was taken to be 0.25 of the renewable resource where allowances had not been made under existing management plans. The factor was only applied to sedimentary basins with known extensive unconfined aquifers bordering the coast. No allowance was used for fractured rock aquifers or confined aquifers, although local seawater intrusion is known.
Sustainable yields were based in the first instance on results derived from Groundwater Area Allocation Plans or (water) Management Plans for GMUs where these have been prepared (refer Reference list).
For most other GMUs/UAs within the State, the sustainable yield for each was determined by estimating the renewable groundwater resources and deducting allowances for wetlands and where appropriate for seawater intrusion. ie:
Sustainable yield = renewable resources - wetlands allowance - seawater intrusion allowance.
In the Perth basin, WRC believe that the most reliable estimate for sustainable yield of the confined aquifers is from Davidson 1995 Hydrogeology and Groundwater Resources of the Perth Region, WA; Geological Survey of WA Bulletin 142. The report indicates that the confined and superficial aquifers should be treated as an integrated system with a sustainable yield of between 275 to 498 GL/yr, and predicts that the falling heads of the Leederville and the Yarragadee may stabilise in 50 to 100 years respectively to the lower bound SY value. Current overall use is about 420 GL/yr and is approaching the upper limit. Subsequent initial modelling of the integrated system with an additional 80 GL/yr of use indicated potential unacceptable impacts on wetlands in some of the area. Recent monitoring has also indicated localised excessive watertable drawdowns that may be linked to the continuing falling heads of the confined aquifers. Consequently WRC believe that the sustainable yields for the confined aquifers should be set at the current levels of abstraction for the purpose of the Audit.
For some superficial aquifers within the Perth Basin (Jandakot, Mirrabooka, Gwelup, Yanchep and Wanneroo (including Pinjar)) sustainable yields were based on annual quotas. For the Rockingham, Perth and Gwelup Superficials, longterm monitoring indicates that water levels are rising and sustainable yields were based on current use.
Groundwater Management Plans apply to most of the Perth Basin. In these, various concepts about available groundwater supplies have been adopted. These include 'sustainable supply', 'maximum (groundwater) availability' and others. In parts of the Perth metropolitan area 'Underground Water Pollution Control Areas' have been declared around the major Water Corporation borefields in the Superficial aquifer.
Within these areas annual (production) quotas have been determined for the Water Corporation and for private abstractors. These have been arrived at by groundwater modelling and link abstraction to lowering of water table levels to pre-determined levels which should have minimal effects on some wetlands which have environmental/social values. The annual quotas (public plus private) are taken to be equivalent to the sustainable yield in the Jandakot, Mirrabooka, Gwelup, Yanchep, Wanneroo (including Pinjar) superficial aquifers.
In unconfined aquifers (ie. surficial and fractured rock aquifers) the depth to the top of the aquifer was assumed to be the water table level. This and the depth and thickness was obtained by reference to relevant reports and bore records.
In the confined aquifers (sedimentary basins) the depth and aquifer thickness were estimated from cross-sections and structure contours. Where possible an average depth and thickness were given, but in some cases the thickness and depth are highly variable as a result of the geological structure, (eg. Perth Basin) and where this applies it is noted under comments.
The minimum, maximum and mean groundwater salinity were determined by interrogating data in AQWAbase, the Water and Rivers Commission data base of bores and wells. The number of bores and minimum and maximum salinity readings were determined, and the mean was calculated. The results were then checked against a 1:2.5M groundwater salinity map of Western Australia and adjustments were made where necessary. For confined aquifers in the sedimentary basins the results were checked against management plans or relevant reports to ensure they gave the correct range of known salinity data.
The groundwater usage in each GMU is based on the Water and Rivers Commission Water Resources Licensing database (WRL). This was augmented with data from a report by Jackson (1999) which provides a compilation of licensed pumpage and estimated usage by purpose and aquifer for GMAs and for their sub-areas.
The WRL database has a data set current up to 1999/2000. To make the data set applicable to the 1996/97 base-year, post 1996/97 licences greater than 2000 ML were removed. However, difficulties were experienced where new licences replaced expired licences as there was no way to determine from the sequential numbering system used in the database whether the licence was new or a replacement. Consequently, there was some duplication of licences in the database possibly inflating the groundwater allocation in some GMUs.
Metering of groundwater abstraction is limited mainly to mining activities, some irrigation schemes, and public water supplies. Consequently, for the purpose of the audit the formal abstraction was assumed to equate to the licensed allocation.
It was found by (Jackson 1999), that usage was generally less than the groundwater allocation and therefore there is a margin of safety in the assumption.
In the Perth Province, from Rockmestic bores was based on the 1996 Australian Bureau of Statistics (ABS) Census of Population aingham in the south to Yanchep in the north domestic bores mainly used for reticulation were assumed to abstract 700 kL on average per year (Water and Rivers, undated). The total number of dond Housing for the Perth Metropolitan region, assuming that approximately 30% of households own and operate a domestic bore (the latter is based on preliminary results from a domestic water use study the Water Corporation is undertaking into domestic water usage patterns).
The distribution of bores within GMUs within the Perth Metropolitan region was based on applying landuse (urban, urban deferred, city) patterns (Bulletin 142, Department of Minerals and Energy, 1995) to the statistical sub-regional totals for separate houses, semi-detached houses and townhouses.
The quantity of free flowing artesian bore water in the Carnarvon area was provided by WRC and is based on estimates from a project established to cap these bores.
Water use by livestock was determined by obtaining numbers of sheep and cattle from Agriculture Western Australia. Livestock numbers were provided on a shire basis and aggregated to statistical divisions. The average water use by livestock was determined by the volume of water required by a sheep under normal conditions, referred to as a "Dry Sheep Equivalent" (DSE). DSE water use is measured in m3/head/yr, and values adopted for the Audit were consistent with values used in Review '85.
To determine the percentage of livestock water use from groundwater as opposed to surface water, Review '85 proportions were adopted, with some modifications on the basis of more recent regional planning experience. The volume of groundwater used by livestock was then summed on a GMU basis and compared to the volume licensed. Any shortfall in the licensed volume was assumed to be met by informal abstraction.
Categorisation Of Use
In the Audit four categories of use are recognised:
Category 1: Low level resource abstraction
Category 2: ` Medium level resource abstraction
Category 3: High level resource abstraction
Category 4: Over abstracted
The water use category was determined by comparing formal plus informal use as a percentage of the sustainable yield for each GMU.
Representative Licences and Monitoring Bores
Examples of the largest licensed allocations and of representative monitoring bores was selected by interrogation of the WRL and SWRISS databases respectively. The top 5% of the largest licensed allocations was selected as representing the major abstractors. For the monitoring bores the top 5% base on period of record, were identified, and from these representative monitoring bores were selected.
Changes in the geological understanding of Western Australia has resulted in changes to the number, extent and names of various provinces. In future some further changes may be needed.
The estimates of renewable groundwater resources underpin the estimates of sustainable yield. The recharge factors used to estimate the renewable groundwater resources are based on the following assumptions:
Groundwater recharge can be expressed as a proportion of mean annual rainfall irrespective of the timing of the recharge which occurs in the summer (north) and winter (south), and does not take account of episodic recharge from storm or cyclonic events;
Recharge to groundwater occurs over the entire surface area of a region and does not take account of runoff recharge along drainage lines;
Groundwater recharge is the volume of water which reaches the regional water table and may infiltrate down into artesian aquifer; recharge does not include soil water or water which may recharge local perched aquifers;
Recharge increases with increasing mean annual rainfall;
Different rates of recharge apply on surficial sediments, outcrops of sedimentary rocks and fractured rocks; and that
The recharge factors are conservative.
From consideration of the foregoing assumptions the shortcoming of the estimates of renewable resources should be appreciated. Nevertheless, it is expected that the estimates are in the correct order of magnitude and in most cases may be an underestimate. The figures are not absolute and can expect to be changed as a result of more detailed studies and with the developing understanding of the hydrogeology of Western Australia.
The present system of GMAs has evolved for various practical purposes but does not follow natural topographical or geological boundaries. If practicable a review of the GMAs should be undertaken to rationalise their boundaries, in particular so that the major Phanerozoic sedimentary basins are included in separate GMAs.
The UA in the south coastal and south-western parts of the State should be legislated as GMAs to enable management of anticipated groundwater problems in salinised farmland and some large undeveloped groundwater resources principally in the Eucla Basin.
The changes to the areas of the groundwater provinces; recharge factors which have be applied; and conceptual differences make any comparison between the present Audit and the 1985 Review impracticable. The difference between the methodologies used in the two reviews are summarised below:
|NLWRA 2000||1985 Review|
|Provinces||Thirty four provinces, area, and number changed.||Twenty nine provinces.|
|Recharge Factors||Various, depending on rock type; rainfall and topography; particular attention paid to Perth Basin.||Seven different factors applied dependent on rock type.|
|Groundwater Resources||Renewable resource (equivalent to major plus minor divertible resources).||Major divertible resources and minor divertible resources|
|Environmental Allowances||Various for wetlands and seawater intrusion.||None|
|Sustainable Yield||Renewable resource minus wetlands and seawater intrusion allowances.||No equivalent concept|
Audit Method Water Demand
The purpose of the demand scenarios is to estimate likely future demands on the resource that can be used to assist resource management, development and conservation, by categorising individual catchments and groundwater areas in terms of likely pressure on the resource in the year 2020. Projected demands were compared with sustainable yield estimates to look at the change in yield/demand characteristics over time. Demand projections were not estimated for the year 2050.
The methodology entailed the following steps:
- Western Australia was divided into 19 "Water Demand Regions". These were based on ABS Statistical Sub-Divisions. These regions are also used by WA Government Departments and the WA Regional Planning Commissions in land use and economic planning.
- "Indicator variables" for water use in 1996-97 were developed for 60 industry categories within each Demand Region using data on areas irrigated, mine production, employment, value added, stock numbers, population and households. The indicator variables data were mostly obtained from the ABS, but industry value added was obtained from the MONASH economic model database (Australian Academy of Technological Sciences and Engineering, 1999). The MONASH model used for the projections of employment and value added has 9 regions in Western Australia, based on the ABS Statistical Divisions. The employment and value added data in the MONASH data base were further divided into the 19 Demand Regions using ABS Census data on employment in each Statistical Sub Division in 1996.
- "First-pass" estimates of water use in 1996-97 were obtained by multiplying each of the indicator variables by an estimated water use coefficient. Water use coefficients were based on a number of studies, including Planning & Management Consultants Ltd (1996), Brooks & Peters (1988), Johnson (1995), Department of Primary Industries and Energy (1987), and Australian Academy of Technological Sciences & Engineering (1999). Assistance was also received from the ABS Water Account team, prior to their publication of the Water Account for Australia (Australian Bureau of Statistics, 2000).
- The "First-Pass" estimates of 1996-97 water use were adjusted using the information extracted from the Water and Rivers Commission Licensing Database. This adjustment required merging of the licensing data for SWMAs and GMUs and taking account of transfers of water from some SWMAs/GMUs to recipient Demand Regions. However, most SWMAs and GMUs were wholly contained in a Demand Region. For those that crossed the boundaries of two or more Demand Regions, discussions were held between the consultants and Water & Rivers Commission staff, and reference was made to detailed licensing data to arrive at a proportional split of water use at Level 1 between the respective Demand Regions. This process resulted in a set of estimates of water use in each Demand Region in 1996-97 for the 60 MONASH industry categories that agreed with the Level 1 totals in the licensing data base
- Projected growth rates for industry employment and value added to the year 2020 were obtained by using recent projections using the MONASH regional economic model. These projections draw on recent (post-Asian crisis) re-evaluations of prospects for the Australian economy. While economic growth is expected to continue to be strong throughout the projection period there has been some downward adjustment of projected growth rates of industry value added in the mining sector, compensated by upward adjustments in other sectors.
- Recent projections of growth rates for population in each Demand Region were obtained from the WA Ministry of Planning. These projections are based in part on the ABS population projections for Australia, with additional research on likely future population shifts within Western Australia. In using these projections it was assumed that the composition of dwelling types in each Demand Region would remain the same throughout the projection period. Typical water use rates for each dwelling type were incorporated in the projections.
- The future growth rates for industry value added and employment as projected by the MONASH model were next compared with past growth rates for indicator variables measuring physical production (e.g. areas irrigated and mine production), and with the apparent trend in total water use in Western Australia between 1983-84 and 1996-97. It was found that physical production and water use has generally grown faster than value added, while employment has grown slower than value added, physical production and water use. It was therefore decided to use growth rates for value added adjusted upwards for faster growth in physical production (and hence water use) than in value added within the mining and irrigation sectors.
- Water use was projected to grow at the same rate as value added, adjusted for physical production, based on the MONASH model-based projections of industry growth in each Demand Region, from 1996-97 to 2020-21.
- Discussions were held with key Western Australian Government Departments, in particular the Department of Resources Development and Agriculture WA and each of the Regional Planning Commissions, in order to compare the MONASH-based projections with known plans and major new projects throughout the State. It was found that the MONASH-based projections were in general agreement with planned developments region by region, but that in a few cases, where very large irrigation and mining projects were being planned, there would be faster growth in water use than had been projected using the MONASH model. In these cases estimates for the period 1996-97 to 2005-6 were adjusted upwards to take account of proposed new development, and subsequent growth was based on the MONASH trend rate in that region
The projections of water use in each demand region were next compared with available surface and groundwater resources to see the ways in which future demands could be met. This was done in the following manner.
- Current, 1996-97, water allocation in each SWMA and GMU was compared with the sustainable yield estimate. This gave an indication of "spare capacity" existing within each resource, that could be used to satisfy future demand.
- For each Demand Region, the likely future cost of water diversion and delivery to each of the major demand centres was estimated. It was then assumed that a least-cost supply plan would be adopted for each Demand Region, subject to withdrawals always being held within sustainable yield.
- In a few Demand regions it was apparent that projected water use could not be supplied from the sustainable yield. In these cases, rather than closing off the prospects for the particular industry in the initial demand region the likelihood of "demand displacement' to another, usually adjacent, region was considered. For example, it is quite feasible to grow certain irrigated crops in a number of Demand Regions.
- The above steps resulted in a projection of how the water use forecast for each Demand Region could be supplied at least cost, within sustainable yield estimates. In addition to the four basic categories of (i) reticulated surface water supply, (ii) self-extracted surface water supply, (iii) reticulated groundwater supply and (iv) self-extracted groundwater supply, (v) desalination and (vi) water re-cycling were considered. Several major new industrial developments in the two Pilbara Demand Regions already intend to use de-salinated sea water, and the Water Corporation is actively researching the contribution of desalination of both sea water and brackish surface supplies for Perth
Audit Methods - Water Resource Management
It is a prime intention of the Audit to assess the general state of water allocation in relation to demand pressures. Therefore, having estimated sustainable yields for both surface and groundwater resources, each individual resource unit was categorised in relation to the level of utilisation of the sustainable yield in that unit as shown in the table below. The Audit also classified the actual level of management of allocation for these resource units into response categories appropriate to different levels (categories) of utilisation. Statistical presentation of the gaps between categorised utilisation levels for each resource unit and the category of its actual management situation enables a general assessment of priority areas in the implementation of water allocation across the State.
Table .1: Resource Categories
|Categories of Use Level||C1||C2||C3||C4|
|Utilisation as % of Sustainable Yield||0-30%||30-70%||70-100%||>100%|
|Corresponding Category of Response||R1||R2||R3||R4|
For Groundwater, the water use category was determined by comparing formal plus informal use (based on allocation) as a percentage of the sustainable yield for each GMU. Categorisation for surface water was based on both allocation data, and water use data, although the former was used in the Audit. Results for surface water categorisation based on use can be found in the Audit's working papers (Sinclair Knight Merz/JDA Consultants 2000, Vol 3) held by the Water and Rivers Commission.
Categorisation for each GMU and SWMA was also undertaken using the projected water use demand in the year 2020.
A standardised checklist of management responses, appropriate for each of the four levels of resource utilisation, was established jointly with Water and Rivers Commission staff as part of the Audit. This checklist, as presented in Appendix A, presents the Commission's (reform) process goals for allocation and resource management which escalate according to Category of resource utilisation. These responses are set out under three prime criteria namely:
Resource Investigation and Monitoring
Allocation Planning & Sustainable Limits
Management of Use
For groundwater resources, the Water And Rivers Commission's draft report (Jackson 1999) which details current management responses for each sub-aquifer management area was used as the initial source information. Scores for the nine sub-criteria, plus a score for all sub-aquifers managed under licenses, were summed within each sub-aquifer management area using the proportional weightings shown in Table 6.2, then rolled up to the GMU level, weighted according to each sub-aquifer management area's Allocation Limit.
Table .2: Groundwater Management Response Roll-up Weightings
|Prime Management Response criteria||Management Response sub-criteria (Jackson 1999)||Roll-up Weightings|
|Resource Investigation and||RI||50|
|Allocation Planning &||POL||40|
|Management of Use||MU||30|
The overall management response for each GMU was then obtained from averaging the three prime criteria for the GMU. This overall result was then checked with Water and Rivers' senior and regional staff to ensure that it was representative of the level and nature of the management activity currently occurring within each GMU. Adjustments were made where the calculated response did not match the management activity.
The management of surface water resources was assessed in a similar way, however a pre-audit study like the Jackson groundwater study had not been undertaken. Consequently staff from Water and Rivers Commission met with senior staff from Resource Investigation and Allocation Branches, as well as key regional staff, to assess the current levels of management activity for all surface water management areas. These levels of management responses were assessed at the prime - criteria level, and the overall management response criteria for each SWMA were determined by averaging these three criteria.
Ideally, the management response for each GMU and SWMA should match its resource category as shown in Table 6.1 ie. a C3 resource should be managed at a R3 level, a C1 resource managed at a R1 level etc.
Management gaps for all GMUs and SWMAs were defined as the difference between the management response level and the resource category level for each respective GMU and SWMA. In other words, a C3 resource managed at R2 level would result in a gap of -1 (R2 - C3 = -1). Likewise a C2 resource managed at R1 level would also have a gap of -1 and a C4 resource managed at R1 would have a gap of -3. If the resource was being managed at the appropriate level, then it's gap would equal zero (R1 - C1 = 0, R3 - C3 = 0, etc).
Results of categorisation for all GMUs and for all SWMAs are respectively reported in Audit working papers (Sinclair Knight Merz Vol.3 2000 and Sinclair Knight Merz/JDA Vol.3 2000) held by Water and Rivers Commission.
Australian Academy of Technological Sciences and Engineering (1999). Water and the Australian Economy. Australian Academy of Technological Sciences and Engineering, Melbourne ISBN 1 875 61850 3.
Australian Bureau of Statistics (2000). Water Account for Australia 1993-94 to 1996-97. ABS Cat.No 4610, Canberra, ISBN 0 642 25662 4.
Aylmore, P.M., Luke G.J., and Hauck, E.J. (1994). Crop Irrigation Requirement Program, Technical Report 125, Horticulture and Resource Science Branch, Division of Plant Industries, Western Australian Department of Agriculture, 1994.
Brooks, D.B. and Peters, R. (1988). Water: the potential for demand management in Canada. Science Council of Canada, Ontario, ISBN 0 662 15907 1.
CSIRO Land and Water, Perth Laboratory (1997). The Hydrology of Lake Lefroy. A draft proposal to Western Mining Corporation, Kambalda Nickel Operations.
Department of Minerals and Energy, (1995). Hydrogeology and Groundwater Resources of the Perth region, Western Australia, Bulletin 142, W.A. Davidson, Geological Survey of Western Australia.
Department of Primary Industries and Energy (1987). 1985 Review of Australia's water resources and water use. Volume 2: water use data set. Australian Government Publishing service, Canberra, ISBN 0 644 08422 7.
GeoEng (1996). Potential Dams Sites in the Pilbara Region (DRAFT), completed for the Water & Rivers Commission, October 1996.
Hauck E.J. and Coles N.A. (1995). Farm Water Supply Reference Data for Rain Tanks and Surface Water, Western Australian Department of Agriculture, Feb 1995.
Ivanescu S and Ruprecht J. (2000). Surface Hydrology of the Pilbara Region - Summary Report, Water and Rivers Commission Surface Water Hydrology Report Series, Report No. SWH 32.
Jackson, M. (1999). Groundwater Allocation Situation Statements, Mid-West Gascoyne Region, North West Region, South Coast Region, South West Region and Swan Goldfields Agricultural Region, Draft Report prepared under contract for Water and Rivers Commission.
Johnson, T. (1995). Water use in economic and domestic activity. In: Environmental perspectives studies and statistics. Vol 2 p 65-76. Statistics Canada, Ottowa, ISBN 0 660 15573 7.
Luke, G. J. (1987). Consumption of Water by Livestock, Technical Report 60, Salinity and Hydrology Branch, Division of Resource Management, Western Australian Department of Agriculture, Dec 1987.
Luke, G. J., Burke, K.L., and O'Brien, T.M. (1988). Evaporation Data for Western Australia, Technical Report 65, Salinity and Hydrology Branch, Division of Resource Management, Western Australian Department of Agriculture, March 1988.
Patterson Market Research (1995). Executive Summary, Survey of Bore Ownership. Client: Water Authority of Western Australia.
Pearcey M. (1998). Surface Hydrology of the Murchison and Gascoyne Regions - Summary Report, Water and Rivers Commission Surface Water Hydrology Report Series, Report No. SWH 17.
Planning and Management Consultants Ltd (1997). IWR-MAIN Version 6.1 Water demand analysis software: Technical Overview. Planning and Management Consultants Ltd., Carbondale, Illinois.
Public Works Department (1984). Streamflow Records of Western Australia to 1982, Volume 1 Basins 601-612, Water Resources Branch, Public Works Department.
Public Works Department (1984). Streamflow Records of Western Australia to 1982, Volume 2 Basins 613-617, Water Resources Branch, Public Works Department.
Public Works Department (1984). Streamflow Records of Western Australia to 1982, Volume 3 Basins 618-810, Water Resources Branch, Public Works Department.
Ruprecht J and Rodgers S. (2000). Surface Hydrology of the Kimberley Region - Summary Report, Water and Rivers Commission Surface Water Hydrology Report Series (Unfinished Draft).
Stokes, R.A., Beckwith, J.A., Pound, I.R., Stone, R.R., Coghlan, P.C. & Ng, R. (1995). Perth's Water Future: A Water Supply Strategy for Perth and Mandurah, Water Authority of Western Australia, 1995.
Water Authority (1995). Review of Proposed Changes to Environmental Conditions. Gnangara Mound Groundwater Resources (Section 46).
Water Authority of Western Australia (1986). Gnangara Mound Groundwater Resources, Environmental Review and Management Programme.
Water Authority of Western Australia (1988). Collie Coal Basin, Water Resources Management Strategy. Water Resources Directorate, Groundwater Branch.
Water Authority of Western Australia (1989). Planning Future Sources for Perth's Water Supply (1989 Revision), Report No. WP 68, May 1989.
Water Authority of Western Australia (1989). South West Coastal Groundwater Area, Groundwater Management Review. Water Resources Directorate, Groundwater Branch.
Water Authority of Western Australia (1991). Jandakot Groundwater Scheme Stage 2 Public Environmental Review, Summary.
Water Authority of Western Australia (1991). Jandakot Groundwater Scheme Stage 2 Public Environmental Review, Volume 1.
Water Authority of Western Australia (1991). Jandakot Groundwater Scheme Stage 2 Public Environmental Review, Volume 2, Supporting Papers.
Water Authority of Western Australia (1992). Derby Groundwater Management Plan.
Water Authority of Western Australia (1993). Cockburn Groundwater Area Management Plan. Report No. WG 159.
Water Authority of Western Australia (1993). Wanneroo Groundwater Area Allocation Plan. Water Resources Directorate, Groundwater and Environment Branch.
Water Authority of Western Australia (1994). Broome Groundwater Management Plan, Volume 1.
Water Authority of Western Australia (1994). Bunbury Groundwater Area Management Plan. Water Resources Directorate, Groundwater and Environment Branch.
Water Authority of Western Australia (1994). Goldfields Groundwater Area Management Plan, Report No. WG157. Water Resources Directorate, Groundwater and Environmental Branch.
Water Authority of Western Australia (1994). Inventory of Potential Water Supply Schemes, December 1994.
Water Authority of Western Australia (1995). Arrowsmith Groundwater Area Management Plan. Water Resources Division, Water Resources Planning and Allocation Branch.
Water Authority of Western Australia (1995). Busselton-Capel Groundwater Area Management Plan, Report No. WG 205. Water Resources Division, Water Resources Planning and Allocation Branch.
Water Authority of Western Australia (1995). Jurien Groundwater Area Management Plan. Water Resources Division, Water Resources Planning and Allocation Branch.
Water and Rivers Commission (1996). Catalogue of Water Resources Information 1996, Volume 1: The South West Drainage Division.
Water and Rivers Commission (1996). Catalogue of Water Resources Information 1996, Volume 2: The Indian Ocean Drainage Division.
Water and Rivers Commission (1996). Catalogue of Water Resources Information 1996, Volume 3: The Timor Sea and Western Plateau Drainage Divisions.
Water and Rivers Commission (1996). Bunbury-Mandurah Region Water Resources Review and Development Plan, Water Resource Allocation and Planning Series, Report No. WRAP 1, October 1996.
Water and Rivers Commission (1996). Gascoyne Region Water Resources Review and Development Plan, Water Resource Allocation and Planning Series, Report No. WRAP 3, 1996
Water and Rivers Commission (1996). Pilbara Region Water Resources Review and Development Plan, Water Resource Allocation and Planning Series, Report No. WRAP 4, 1996.
Water and Rivers Commission (1997). Albany-Denmark Region Water Resources Review and Development Plan, Water Resource Allocation and Planning Series, Report No. WRAP 2, October 1997 (unpublished)
Water and Rivers Commission (1997). East Gnangara Environmental Water Provisions Plan, Public Environmental Review.
Water and Rivers Commission (1997). Encouraging Garden Bores in Perth. For Hon. Kim Hames, Minister for Water Resources.
Water and Rivers Commission (1997). Esperance Region Water Resources Review and Development Plan, Water Resource Allocation and Planning Series, Report No. WRAP 5, February 1997.
Water and Rivers Commission (1997). Busselton-Walpole Region Water Resources Review and Development Plan, Water Resource and Allocation Planning Series, Report No WRAP 6, April 1997 (unpublished).
Water and Rivers Commission (1997). Allocating Water for Perth's Future - Assessment of the Perth's Water Future Strategy, July 1997
Water and Rivers Commission (1997). Groundwater Allocation Plan, Swan Groundwater Area. Water Resource Allocation and Planning Series, Report No. WRAP 12.
Water and Rivers Commission (1997). The State of the Northern Rivers, Water Resource Allocation and Planning Report Series, Report No. WRAP 10, December 1997
Water and Rivers Commission (1998). Proposed Harvey Basin Surface Water Allocation Plan, Water Resource Allocation and Planning Series, Report No. WRAP 14, March 1998
Water and Rivers Commission (1999). Draft Interim Water Allocation Plan - Ord River, Western Australia, WRAP 2, May 1999.
Water and Rivers Commission (undated). Encouraging Garden Bores in Perth, report prepared for Hon. Kim Hames, Minister for Water Resources
Western Australia Water Resources Council (1984). Report No. 1 Water Resources and Water Use, Appendix C Water Use Survey Western Australia 1980/81.
Western Australia Water Resources Council (1987). Report No. 2 Water Resources and Water Use - Summary of Data for the 1985 National Survey, Appendix C - Water Use in Western Australia.
Western Australia Water Resources Council (1987). Report No. 2 Water Resources and Water Use - Summary of Data for the 1985 National Survey, Appendix A - Surface Water Resources in Western Australia.
Western Australian Planning Commission (1998). Statement of Planning Policy No. 6, Jandakot Groundwater Protection Policy. Western Australian Government Gazette, No. 117.
Some documents on this website are available as PDF files. Adobe Acrobat Reader is required to view PDF files.
Links to an another web site
Opens a pop-up window