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

Melbourne
Quantification approaches

Summary of quantification approaches

Table 1 outlines the quantification approaches used to derive the item volumes for the Melbourne region. For a more detailed description of the quantification approach, click on the relevant item name in the table.

Detail of quantification approaches

Water storage product data

Storages

Storage volumes at the start and end of the year were calculated using water level data (metres above Australian height datum) collected at each storage. Rating tables established for each storage were used to convert the height measurement to a volume. Storage capacity was calculated using the full supply level provided by the managing authority.

The volume of individual storages was aggregated to present the total storage volume for the region. The uncertainty range for the storage volume was not quantified.

The assumptions made were as follows:

• Storage–volume curves represent specifically surveyed parts of the storage and may not reflect the storage–volume relationship across the entire storage.
• Water storages are subject to sedimentation and other physical changes over time, which in turn affects the accuracy of the storage–volume curves.
• Storage capacity may differ from those published by storage operators due to rounding and uncertainty in the true values.

Climate grid data

Precipitation and evaporation on/from surface water

Monthly precipitation grids for the region were produced using daily data from approximately 6500 rain gauge stations in the country and interpolated to a 0.05 degrees (5 km) national grid (Jones et al. 2007).

Potential evaporation across the region was estimated using the Australian Water Resources Assessment system Landscape model (AWRA-L) version 3.0 (Van Dijk 2010). The AWRA-L model uses a modified version of the Penman-Monteith method to produce the potential evaporation. Daily AWRA-L potential evaporation grids for the region were produced based on daily gridded climate data (including precipitation, solar radiance and temperature) that were available on a 0.05 degree (approximately 5 km) national grid (Jones et al. 2007).

The precipitation and evaporation at each waterbody (i.e., storages) was estimated from the proportionally weighted average of grid-cells that intersected each water feature. The volume was then estimated by multiplying by the surface area of each waterbody. The average monthly surface area of the storages was calculated from daily storage levels and capacity tables.

The limitations associated with this approach are:

• Precipitation and evaporation estimates were subject to approximations associated with interpolating observation point data to a national grid detailed in Jones et al. (2007).
• The dynamic storage surface areas calculated from the levels and capacity tables represent a monthly average and therefore will not capture changes that occur on a shorter temporal scale.
• The total surface area of the surface water store within the Melbourne region included only the storages (and not the rivers).
• Melbourne Water's calculations of rainfall on water storages during the 2013–14 year were approximately 9.6% lower than modelled estimates by the Bureau. Melbourne Water uses rain gauges at each of its reservoirs to measure rainfall. Calculated volumes are generally assumed to have an accuracy of within +/– 5%. 
• Melbourne Water's calculations of evaporation on water storages during the 2013–14 year were approximately 19.7% lower than modelled estimates by the Bureau. Melbourne Water measures evaporation using the factored pan method. 

Uncertainty estimates were not available for the modelled precipitation and evaporation estimates by the Bureau.

Runoff to surface water

Runoff to surface water was estimated based on the AWRA-L Version 3.0 model streamflow outputs (Van Dijk 2010).

Using climate grid data for the Melbourne region (including precipitation, temperature, and solar radiation data), AWRA-L was used to estimate the runoff depth at each grid point within the region. Only runoff from the landscape is considered; therefore, the surface areas of the major reservoirs were excluded from the analysis.

The average runoff depth from the landscape into the surface water was determined as the weighted mean of the relevant grid-points within the region boundary. Points were weighted based upon the area they represented within the reporting region to remove edge effects (where the area represented is not wholly within the reporting region) and the effect of changing area represented with changing latitude. Runoff depth was converted to a runoff volume by multiplying runoff depth by the total area of the region (excluding storages).

Runoff estimates were subject to the assumptions of the AWRA-L model detailed in Van Dijk (2010). Uncertainty estimates were not available for the modelling method.

Werribee and Bacchus Marsh system allocation model

Surface water allocation remaining – individual users

The allocation remaining at 30 June 2014 was calculated as shown in Table 2.

Surface water allocation remaining for individual users calculated according to Table 2 aligns with the calculation method specified in the Werribee and Bacchus Marsh allocation model. Details of the allocation model are available on the Southern Rural Water website. The uncertainty estimate was not quantified for allocation remaining for individual users.

Annual Reports of water authorities

Inter-region claims on water

Remaining volume of water entitled at 30 June 2014 under inter-region claims was calculated as shown in Table 3.

Rights to remaining entitled water at Thomson Reservoir, Silver and Wallaby creeks, and Lake Eildon were the inter-region claims for the Melbourne region. The Melbourne retail water authorities' share of storage volume in the Thomson Reservoir and Lake Eildon at the end of the 2013–14 year was derived from the share of storage opening volume, inflows, diversions, and outflows or losses from the reservoir (download calculation data). Remaining volume at end of the year is not carried over to the following year from entitled water from Silver and Wallaby creeks. As a result, the opening and closing balance of the claim remains zero for this source.

Surface water allocation remaining – urban water system

The allocation remaining at 30 June 2014 was calculated as shown in Table 4.

Share of storage remaining for retail and regional water authorities, at the end of the year was recognised as carry-over as allocation remaining for the urban water system. The share of storages, which was used in the calculation method specified in Table 4, for each retail and regional water authority is available as a downloadable table.

The uncertainty estimate was not quantified for allocation remaining for the urban water system.

Surface water transfer under inter-region commitment

The volume of surface water diverted from the Melbourne region to Gippsland Water authority area (which is beyond the region boundary) was extracted from the Gippsland Water annual report 2013–14. A portion of the volume diverted by Gippsland Water was supplied by Melbourne Water which manages the Tarago Reservoir. This volume is published in the Melbourne Water annual report 2013–14.

Adjustment and forfeiture of inter-region commitments

The forfeiture volume for drought contingency allocation for Gippsland Water from Tarago Reservoir was allocation less diverted volume as carry-over provisions were not available. As formal annual allocations are not made for the Tarago River–Gippsland Water bulk entitlement, the volume of water allocated was equivalent to the volume of surface water actually diverted for this bulk entitlement and accordingly the forfeiture volume was considered as zero.

Increase of inter-region commitments

The volumes allocated under Tarago River–Gippsland Water bulk entitlement and drought contingency allocation for Gippsland Water from Tarago Reservoir were extracted from the Gippsland Water annual report 2013–14.

Reporting partner internal databases

Water received under inter-region claims

Surface water allocation announcements to the urban water system (Increase of urban claim on surface water)

Surface water allocation volume to the urban water system includes:

• increases to this share of storage through inflows such as rainfall and runoff for those bulk entitlements that include a share of storage
• increases in the entitlement equivalent to the delivery volume for those bulk entitlements that do not include a share of storage.

The breakdown of surface water allocation announcements (increase of urban claim) on surface water itemised by bulk entitlement and source is available as a downloadable table.

Uncertainty estimates were not quantified for the provided volumes.

Wastewater system

Metered and estimated data provided by water authorities via Bureau's urban water template

Wastewater collected

The volume of wastewater collected is estimated using the metered inflow to wastewater treatment plants and sewer mining plants within the region:

• minus any recirculation such as treated wastewater volume that was reported as discharge back to sewer in the region, to avoid double counting.
• plus any reported wastewater losses or egress from the system before the metering point measuring inflow to the treatment plants (e.g., through emergency relief structure).

Given wastewater volumes are typically measured at the treatment plants (and not at customer connections), the collected wastewater volume includes any variation due to (a) ingress of stormwater; (b) infiltration of groundwater; (c) unreported wastewater overflows to stormwater; and (d) exfiltration of wastewater to groundwater. 

Where inflow meter readings are not available, outflow meter readings have been used, which could underestimate the volume as it assumes no losses during wastewater treatment.

This volume does not include wastewater collected for individual or community wastewater management systems.  

Melbourne Water has a suite of bulk wastewater meters at their two major wastewater treatment plants, the Western Treatment Plant and the Eastern Treatment Plant. Melbourne Water uses formulas to apportion the wastewater volumes generated in the service areas of the three water retailers (City West Water, South East Water, and Yarra Valley Water). These apportioned volumes are reported by City West Water, South East Water, and Yarra Valley Water, and used in the 2014 Account for calculating the collected wastewater in the region. There is a discrepancy this year between the volumes reported by Melbourne Water as received from the retail water authorities versus the volumes reported by each retail water authority as collected and delivered to Melbourne Water WTPs. Wastewater volume received from Water Infrastructure Group is metered at Eastern Treatment Plant.

The uncertainty was estimated to be 0% to +/–20% based on meter specifications.

Entitled diversion of allocated surface water to the urban water system

The volume refers to allocated diversions from surface water sources to water treatment plants under the various bulk entitlements held by Melbourne's retail water authorities, including Western Water. Non-allocated diversions (mostly unregulated) are not included in the volume.

Metered raw water volumes at the sources were used to estimate the volume. The volume reported does not include water delivered by Melbourne Water to Gippsland Water (see Surface water outflows).

Meters used to measure the volumes have an accuracy of 0% to +/–5% in accordance with the manufacturer's annual bulk meter tests.

Entitled extraction of allocated groundwater to urban water system

Entitled extraction of allocated groundwater to urban water system was calculated and provided by Western Water as the total metered volume of groundwater taken from Lancefield Bore 3 and Glenfern Road bore. Meters are located on a pipe between the bore and the water treatment facility. Meter readings are recorded daily. Groundwater from Lancefield Bore 2 was not supplied to the urban system because of poor water quality. The uncertainty estimate was +/– 5% for the volume provided in accordance with manufacturer's annual bulk meter test.

Evaporation from urban water system

For the 2013–14 year, 15,657 ML evaporation loss from wastewater and recycled water systems was recognised by Melbourne Water, South East Water, and Western Water.

The volume is based on:

• calculations using Bureau's climate data and water balance approach through available inflow and outflow metering data
• metered treated wastewater volume disposal to evaporation lagoons.

No evaporation losses have been reported in the water supply system but only in the wastewater system. As no water was discharged to evaporation lagoons for maintenance, evaporation volume recognised by City West Water for Altona wastewater treatment was zero.

The uncertainty estimate for the reported volume was estimated to be +/–5% to +/–10%.

Urban water system leakage to landscape

Information on leakage to landscape from non-revenue potable water was received from Melbourne Water, South East Water, and Yarra Valley Water for the 2014 Account. The ‘leakage to landscape’ volume is assumed to be the non-revenue water associated with real losses, specifically due to pipe bursts from the urban water supply system. The non-revenue volume is calculated based on physical observations of bursts events.

Where pipe bursts and background leakage is provided by reporting partners as a combined volume, for simplification this volume was reported under Leakage from urban water system to groundwater as the volume related to leakage to landscape cannot be separated. City West Water and Western Water used this approximation. Melbourne Water assumed no leakage in the supply network associated with non-potable water, which is likely an underestimate of the leakage volume.

The uncertainty estimate was not quantified for the volume provided by Melbourne Water.  For the other volumes, the uncertainty estimate was estimated to be +/–10% to +/–20%.

Leakage from urban water system to groundwater

The ‘leakage to groundwater’ volume is assumed to be the non-revenue water associated with real losses, specifically due to background pipe leakage from the urban water supply system. Where there are available volumes associated with only pipe burst, this is reported under Urban water system leakage to landscape.

Non-revenue water was estimated using:

•  difference based on a water balance between metered water sourced and supplied to customers
• modelling software of network real losses (leakages and busts) and apparent losses (unauthorised/authorised unbilled use)
• time to repair leaks.

Leakage in the wastewater system is not reported and therefore the total leakage to groundwater is likely underestimated. Where non-revenue water real losses are reported as combined volume for pipe bursts and background leakage, these are also included in the reported volume, which may overestimate the volume. Melbourne Water assumed no leakage in the supply network associated with non-potable water, which is likely an underestimate of the leakages.

The uncertainty estimate was not quantified for the volume provided by Melbourne Water.  For the other volumes, the uncertainty estimate was estimated to be +/–5% to +/–20%.

Delivery to urban water system users

The volume delivered from the urban water system to users represents the delivery of water including potable, nonpotable, and recycled water to end users for urban consumption. Information for the volume was received from City West Water, Melbourne Water, South East Water, Western Water, and Yarra Valley Water.

Volumes provided by water authorities are based on customer meters, billing meters, on-site re-use water meters, and estimated non-revenue water volumes. They exclude recycled water use which is re-circulated within the wastewater treatment process.

Urban consumption consists of residential, commercial, industrial, municipal, on-site (water and wastewater treatment plant) use and small scale agriculture / irrigation.

The volume delivered to non-urban users (supply to irrigation schemes and the environment) is not included in the reported volume.

The following assumptions have been made in calculating the volume:

• The volume of non-potable water provided from Bunyip River supplied for use includes supply for residential, commercial, industrial, and municipal uses combined as it was not possible to separate the uses. Most of the meters were located at property boundaries.
• Western Water’s data for water use is based on metered readings with the assumption that 85% of the total potable water supplied was for residential purposes and 15% for commercial, industrial, and municipal use.  The volume is calculated deducting the water loss component associated with residential supply (assumed 12.67% of total supply).
• Part of the volume used on-site for wastewater treatment processes re-enters the system. Therefore, the volumes may not be accurate at some plants.
• Recycled water volumes supplied by the Eastern Irrigation Scheme for urban consumption have been included in the reported volume based on data provided by Water Infrastructure Group.

 For the reported volume, the uncertainty estimate was estimated to be +/–1% to +/–10%.

·       

Discharge from urban water system to surface water

The volume reported in the 2014 Account includes the metered flow of water from the urban water system for:

• disposal of treated wastewater to rivers and other surface water
• discharge of recycled water for environmental purpose
• return of excess water from the urban water supply system back to surface water.
  

 For the reported volume, the uncertainty estimate was estimated to be +/–5% to +/–10%.

Discharge from urban water system to irrigation scheme

The volume reported in the 2014 Account is the metered volume of non-potable water and recycled water supplied for use in Irrigation Schemes.

Melbourne Water provided the volumes of recycled water supplied to the Werribee Irrigation District (2,132 ML) and nonpotable water provided to Southern Rural Water's customers (112 ML). The volume associated with Eastern Irrigation Scheme (3,637 ML) is based on data provided by Water Infrastructure Group, though recycled water is sourced from Melbourne Water. 

Melbourne Water's recycled water supply from the Western Treatment Plant to Southern Rural Water for the Werribee Irrigation District was measured with magnetic flow meters at the interface of two authorities. The Western Treatment Plant logs data daily and reports quarterly. Magnetic flow meters are assumed to have an accuracy of +/–1 to +/–2%. Uncertainty information for the rest of the reported volume was not quantified.

Wastewater discharge outside of region

The volume included in the 2014 Account represents disposals from the wastewater system and recycled water system to the sea, estuaries, and inlets (which are considered outside of the region boundary). City West Water, Melbourne Water, and South East Water provided discharged volume to the 2014 Account.

For Melbourne Water, the volume was based on a mass balance calculation of all wastewater collected, treated, stored, and recycled at the Western Treatment Plant and the Eastern Treatment Plant. The uncertainty estimate was not quantified for this volume.

Volumes from City West Water and South East Water were based on metered data. The uncertainty for both of them was estimated as +/– 5%.

Transfer of water outside of region

Melbourne Water's supply of 111 ML of potable water to Barwon Water from Cowies Hill Reservoir was metered. Meters are mostly operated by Melbourne Water and are located at the interface between Melbourne Water and each of receiving authorities. The volume that is ‘billed’ to these authorities by the many billing meters operated by Melbourne Water is considered the reported volume. Billing meters are generally ultrasonic flow meters for larger pipes (greater than 600 mm in diameter) and magnetic flow meters for smaller pipes (less than 600 mm in diameter). Both types of meters have a notional accuracy of +/–1%.

Western Water transferred 240 ML of nonpotable water outside of the region from Mount Macedon to Woodend via its water supply infrastructure. This volume was metered; meters were read weekly. Uncertainty estimate was not quantified for the volume.

Other urban water system decreases

The volume reported in the 2014 Account represents the sum of the following three components:

• remaining non-revenue water from urban water supply system not reported as leakage to landscape and groundwater respectively
• losses from wastewater treatment system not reported as evaporation from urban water system
• known egress or exfiltration from the wastewater collection system occurring before metered inflow to wastewater treatment plants.

Remaining non-revenue water was estimated using:

• difference based on a water balance between metered water sourced and supplied to customers
• difference between metered supply into the urban water supply system and metered volume of water consumed (revenue water) and subtracting real losses
• modelling software of network real losses (leakages and busts) and apparent losses (unauthorised/authorised unbilled use)
• time to repair leaks
• difference between inlet meter and outlet meter of treatment plants for treatment losses.

Losses from wastewater system were estimated based on metered data between inflow and outflow/disposal/customer meters, or estimated based on observations.

The volume of wastewater in egress to the stormwater system for Yarra Valley Water (3ML) was estimated by using a mosaic ERS data processor that calculates spill duration and volume based on supervisory control and data acquisition (SCADA) monitoring data.

Western Water assumed that 12.67% of total water supplied is attributed to non-revenue potable losses. South East Water included infrastructure leakage, pipe burst, thefts, and leak allowances in the non-revenue potable water volume.

For Melbourne Water, nonpotable water supply losses were not included and nonpotable water lost from aqueducts was not included as these are located upstream of the seasonal storages.

The uncertainty for the provided total volume was estimated to be +/– 20% to +/–40%.

Southern Rural Water – Irrigation Planning Module Generation 2 database

Point return from irrigation scheme

Irrigation water returns from the Bacchus Marsh Irrigation District were metered at each outfall point that returns water to the Lerderderg River. This data was collated by Southern Rural Water and provided to the Victorian Department of Environment and Primary Industries. The uncertainty estimate was not quantified for the provided volume.

Stream monitoring data

River outflow from the region

Discharge from Bunyip, Yarra, Maribyrnong, and Werribee catchments within the Melbourne region to Port Phillip Bay and Westernport Bay were calculated using gauged streamflow data, plus the estimated ungauged flows in downstream subcatchments.

Gauged streamflow information is the sum of discharges during 2013–14 from the lowest stream gauges in the catchment that are above the tidal limit.  Discharge was derived from a telemetered flow level gauge and the water level was converted to a volume using a stage–discharge relationship.

Ungauged streamflow was calculated by extrapolating recorded flows to ungauged areas using the ratio of the mean average flows (MAF) computed for the gauged area compared with the MAF computed for ungauged areas.  The MAF values were based on the Sustainable Diversions Limit project (Department of Sustainability and Environment 2010a). These were updated in some catchments for the Central Region Sustainable Water Strategy (2006). The portion of the catchment that is ungauged is 38%.

The uncertainty estimate was not quantified for the calculated streamflows. In addition, following limitations apply for the streamflow calculations:

• Gauged streamflow measurements are based on the stage–discharge relationship at each gauge location. Stage–discharge relationships change over time and the accuracy measurement is dependent on the location.
• The accuracy of the MAF in the ungauged portion of a catchment is likely to be low whereas the accuracy of the gauged outflows is likely to be high.

Victorian Water Register

Entitled diversion of non-allocated surface water to users

Non-allocated water diversions for the 2013–14 year (13,682 ML) was the sum volumes for four catchments.

Non-allocated diversion volume is a combination of metered diversion data and estimates of non-metered diversions. Southern Rural Water meter surface water diversions for take and use licences in the Maribyrnong, Werribee, and Bunyip catchments. Melbourne Water meter surface water diversions for take-and-use licences in the Maribyrnong and Yarra catchments. Diversion data is submitted by those two authorities to the Victorian Water Register.

Where metered data were not available, the diversion was estimated using the following assumptions:

• diversion volume was assumed to be equal to zero for licences in the Yarra catchment (as per Melbourne water assumptions)
• diversion volume was assumed to be equal to the licensed entitlement volume for licences in the Bunyip, Maribyrnong, and Werribee catchments (as per Southern Rural Water assumptions).

Non-allocated diversion volume does not include entitled diversion of allocated surface water to the urban water system and entitled diversion of allocated surface water for individual users.

Following assumptions have been made to estimate unmetered diversions:

• The assumption that the volume diverted under take and use licences in the Bunyip, Maribyrnong, and Werribee catchments is equal to the entitlement volume is likely to overestimate the actual diversion.
• The assumption that the volume diverted under take and use licences in the Yarra catchment is equal to zero is likely to underestimate the actual diversion.

Metered diversions have an uncertainty of +/– 10% due to known errors of meters. The uncertainty estimate for unmetered estimates of diversion was not quantified.

Entitled diversion of allocated surface water to individual users

Diversion volume is the sum of diverted volume for high and low reliability water shares and the volume supplied by Southern Rural Water under agreements. Southern Rural Water meters these diversions in the Melbourne region. Diversion volumes for supply by agreements for the 2014 Account were obtained directly from Southern Rural Water. Metered diversions have an uncertainty of +/– 5% due to known errors of meters.

Adjustment and forfeiture of surface water allocation to individual users

Adjustment and forfeiture of surface water allocation to individual users was calculated as specified in Table 2 taking into account opening and closing balances, allocation announcement, and entitled diversions.

Surface water allocation announcements to individual users

Yearly allocations were calculated by multiplying entitlement volumes with relevant percentages of announced allocations. The percentages of announced allocations for high reliability and low reliability water shares were 100% and 15% respectively.

Entitled extraction of allocated groundwater to individual users

Metered data used in estimating entitled extraction has an uncertainty of +/–5% based on meter specifications. Estimated data has an uncertainty of +/–100% based on the broad assumptions applied.

Groundwater catchment statements

Aquifers

The Victorian Department of Environment and Primary Industries determined the volume of aquifers in groundwater management units to set a permissible consumptive volume for each aquifer.

Permissible consumptive volumes for the aquifers of groundwater management units were determined as follows:

• Cut Paw Paw GMA: the permissible consumptive volume is based on the through-flow method.
• Koo Wee Rup water supply protection area (WSPA): the permissible consumptive volume is based on numerical modelling and observed response to pumping.

• Frankston GMA: permissible consumptive volume was determined using rainfall recharge, hydrograph fluctuation, through-flow and aquifer storage.

• Lancefield GMA: permissible consumptive volume was determined on the rainfall recharge method.

• Merrimu GMA: permissible consumptive volume was derived from a rounded calculation of rainfall recharge.
• Moorabbin GMA, Nepean GMA, Wandin Yallock WSPA, and Deutgam WSPA: permissible consumptive volumes are based on the total volumes of existing licences issued for these groundwater management units.

Following assumptions/limitations apply to the estimated groundwater asset volume:

Bureau of Meterology - groundwater modelling

Groundwater flow from/to outside region

The Bureau estimated groundwater flow from/to outside region using data from the Port Phillip Catchment Management Authority's groundwater model (Department of Sustainability and Environment 2010) and following information:

Groundwater flow was calculated using a simple geographic information system (GIS) approach based on Darcy's law. Groundwater levels were interpolated for each season from reduced groundwater levels measured at monitoring bores using kriging with external drift and the 9" digital elevation model as an external driver taking into account the effect of the coastline on groundwater levels following the methodology presented in Peterson et.al. (2011). Seasonal groundwater flow grids were derived from groundwater level grids, aquifer thickness, and hydraulic conductivity using a modification of the ArcGIS Darcy Velocity tool. Groundwater flow across selected flow boundaries (Figure 1) was then calculated using a simple GIS analysis and seasonal values were aggregated to reporting period.

Figure 1 Lateral groundwater flow boundaries in the Melbourne region

Groundwater flow across the Melbourne region boundaries other than at the coast was assumed as negligible on an annual basis based on the fact that the northern and northeast boundaries represent a groundwater divide. Groundwater flow along the landward boundary of the region is thought to be minimal (Department of Sustainability and Environment 2010). A small amount of cross-boundary flow is likely in the Kinglake area due to the concentration of abstractions from the Kinglake GMA immediately to the north of the Port Phillip catchment management authority boundary.

Following assumptions were made in the estimation of groundwater flows:

• Regional flow was estimated for layers 1–5 of the Port Phillip groundwater model (Department of Sustainability and Environment 2010), which represent the sedimentary and basalt aquifers with the exclusion of the basement (layer 6). These productive aquifers are considered to be the most hydraulically conductive units and flow in other units is assumed to be insignificant.
• Consistent with the groundwater model report (Department of Sustainability and Environment 2010), groundwater flow in the Nepean Peninsula was calculated only for Layer 1. It was modelled as a fresh water lens in the highly permeable unconfined aquifer using the same GIS tool.
• Groundwater levels were estimated by assuming that all five hydrogeological layers within the Port Phillip groundwater model region are hydraulically interconnected. This assumption facilitated the interpolation of a groundwater potential surface from groundwater level measurements, as these measurements were limited in number. Groundwater levels were also assumed equal to 0 meters AHD at the coastline. These assumptions were used to generate seasonal groundwater level surfaces across the sedimentary area.
• The through-flow boundaries considered in the estimations are indicated in Figure 1. Flow across the remaining boundaries was assumed negligible on an annual basis because aquifer properties like hydraulic conductivity limit flow (e.g., fractured rock basement). The northern and northeast boundaries represent a groundwater divide with no through-flow, or groundwater flow was approximately parallel to the boundary (e.g., western boundary).
• The regional flow estimations were based on the interpolated groundwater level grids produced using kriging with external drift and the 9" digital elevation model as an external driver following the methodology presented in Peterson et.al. (2011). Use of different interpolation methods may impact the values of the groundwater level grids and hence the estimated regional flow.

The uncertainty in the field measured data (e.g., groundwater levels, hydraulic conductivity) was unspecified and unknown; the impact of such uncertainty on the groundwater flow was not estimated. Groundwater flow was estimated for a simplified boundary constructed from a series of line segments. The uncertainty surrounding this simplification was not analysed.

Water atmosphere vegetation energy and solutes (WAVES) model

Groundwater recharge from / discharge to landscape

Groundwater recharge from / discharge to landscape was estimated using:

• the Bureau of Meteorology National Climate Centre (NCC): Version 3 daily rainfall grids, Version 3 annual rainfall grids, daily maximum temperature grids, daily minimum temperature grids, daily satellite observed solar radiation grids, and daily vapour pressure deficit grids
• CSIRO: Australian Soil Resources Information System (ASRIS) soil information
• Bureau of Rural Sciences: land use mapping
• Victorian Department of Environment and Primary Industries: bore locations, groundwater level data, and aquifer attribution.

Groundwater recharge/discharge was estimated using the WAVES model (Zhang and Dawes 1998; Dawes et al. 1998). WAVES is a one-dimensional soil–vegetation–atmosphere–transfer model that integrates water, carbon, and energy balances with a consistent level of process detail. The input datasets required for WAVES include climate, depth to water table, soil, and vegetation data. The clipped sedimentary area was selected to estimate net recharge/discharge. The climate data used at selected points include rainfall, rainfall duration, maximum and minimum temperatures, vapour pressure deficit, and solar radiation. The relevant vegetation parameters required for modelling were selected from the WAVES user manual (Dawes et al. 1998). WAVES uses the soil hydraulic model of Broadbridge and White (1998) with saturated hydraulic conductivity, saturated moisture content, residual moisture content, inverse capillary length scale, and an empirical constant as input parameters calculated from soil properties accessed in the ASRIS database (Johnston et al. 2003).

The WAVES model has been used by CSIRO in its sustainable yields projects (Johnston et al. 2003) and the Bureau has built on this methodology. WAVES was run for all combinations of soil, vegetation, and depth to water table at each climate point. A groundwater recharge/discharge value was estimated for each 1 km × 1 km pixel across the region using annual rainfall, dominant soil and vegetation, and depth to water table. This recharge/discharge value can be positive or negative, due to evapotranspiration. Recharge was determined by summing the pixels with a negative estimate (grey areas in Figure 2) while discharge was determined by summing the pixels with a positive estimate (red areas in Figure 2).

Figure 2 WAVES model recharge areas

Following assumptions were made in the estimation of groundwater recharge/discharge:

• Assumptions made when developing the WAVES model (Dawes et al. 1998) are all applicable to the recharge/discharge estimations carried out for the Melbourne region.

• The Bureau of Rural Science's land use map of the Melbourne region was reclassified to three vegetation classes: annuals, perennials, and trees. The major vegetation classes modelled are C3 annual pasture, C3 perennial pasture, and eucalypt trees with a grassy understorey.

• Recharge/discharge was estimated to be within the clipped sedimentary area, considering the effects of shallow water table interpolated using kriging with external drift and the 9" digital elevation model as an external driver following the methodology presented in Peterson et al. (2011).

• Diffuse recharge to groundwater from irrigation applied to the landscape was not included in the estimate.

The uncertainty in the input parameters and the corresponding impacts on the modelled recharge/discharge values, and the uncertainty of the estimated recharge/discharge resulting from different recharge/discharge interpolation methods have not been analysed.

Bureau of Meterology - internal calculations

Adjustment and forfeiture of groundwater allocation to individual users and urban water system (Adjustment and forfeiture of urban claim on groundwater)

As carry-over of unused water allocation to the following year is not allowed, adjustment and forfeiture volumes were equal to the announced allocation minus extractions during the year.

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