Methods
The following section is a comprehensive list of method descriptions for all the items used in the water accounts. These methods are applicable for all accounting regions.
Summary of methods:
- AWRA-R model
- Water assets
- Urban utility data (Category 7 data)
- Water licensing database (Category 5 and 6 data)
- Groundwater models
AWRA-R model
AWRA-R model
AWRA-R is a river network model that represents key hydrological processes and diversions at a daily time step (Dutta et al. 2017; 2015). The model was used in the National Water Account to quantify river fluxes and stores along the river network. The river system is conceptualised in AWRA-R as a node-link network comprising nodes connected by river reaches. Gauged streamflow data are used where available. For ungauged portions of catchment, the landscape runoff from the AWRA-L model is used (Viney et al. 2015). River processes represented in the AWRA-R model are shown in Figure N1.
Figure N1 Conceptual diagram of AWRA-R reach showing model components
(from Dutta et al. 2015)
Rivers
The volume of water in the river channels on 30 June was estimated by using the daily water balance approach within the AWRA-R model. The water balance includes inflow at the upstream nodes and outflow at the downstream nodes; contributing catchment runoff; diversions for consumptive use; overbank flooding and floodplain return; rainfall, evaporation; and losses.
Precipitation and evaporation
Rainfall and evaporation into/from storages and rivers were calculated using climate data from the Bureau of Meteorology interpolated to 0.05 degree (5 km) national grids (Jones et al. 2009). Calculations were done on a daily time step, with the annual totals summed from the daily values.
Climate data for each water body at each time step were estimated from the proportionally weighted average of grid-cells that intersected the water body. Evaporation was estimated using Morton's shallow lake formulation (Morton 1983). Rainfall and evaporation volumes were then estimated by multiplying the surface area of each waterbody by the weighted average rainfall and evaporation, respectively. The average daily surface area of rivers was estimated using the AWRA-R model and the average daily surface area of storages was calculated from daily storage levels and capacity tables.
Inter-region inflow
Inter-region inflow represents the volume of surface water that flows into the region from rivers that cross the region boundary (e.g. Canberra region's Murrumbidgee River and Perth region's Avon River). It also includes the volume of water that flows into a region's surface water asset located outside the region boundary (e.g. Melbourne region's Thomson Reservoir and Perth region's Wellington Reservoir).
Inflows were estimated for rivers within the AWRA-R model based on observed flow data from the nearest gauging stations with missing values filled with simulated flows.
Runoff
Runoff to surface water was estimated using the modelled runoff from the AWRA-R model. Runoff within AWRA-R is in turn derived from landscape runoff modelled in the AWRA-L model, with a scaling factor applied within AWRA-R during the calibration process.
The AWRA-L model is a daily grid-based water balance model that is conceptualised as a small unimpaired catchment (Viney et al. 2015). It simulates the flow of water through the landscape from rainfall entering the grid cell through the vegetation and soil, and then out of the grid cell through evapotranspiration, runoff, or deep drainage to the groundwater. Its inputs include gridded climate, soil, vegetation, and topographic data. For more information see the Bureau of Meteorology's Australian Landscape Water Balance webpage.
Overbank flow and flood return
The AWRA-R floodplain module was used to model the volume of overbank flow from the river onto the floodplain, and the return flow from the floodplain back into the river. The module applies a simple storage-based floodplain model to each river reach. The floodplain modelling method is detailed in Dutta et al. (2013).
In the Murray–Darling Basin region, the volume of 'Floodwater harvested' during the year was subtracted from the AWRA-R output to establish the overbank flow volume.
Outflow
River outflow is estimated with the AWRA-R model using dummy nodes assigned at the end of of each river flowing out of the region. Observed flows (or simulated flows if observed flow is not available) at the most downstream gauges are routed to the dummy nodes. The residual catchment inflows not covered by the most downstream gauge are estimated using the AWRA-L model and are added to the routed flow to obtain the total outflow at the river mouth.
In the Canberra region, outflow refers to the volume of water that flows out of the region from the Murrumbidgee River. Outflow was estimated using observed data at a nearby gauge located downstream of the region boundary. It was assumed that only minimal runoff was generated between the boundary and the gauge.
Recharge: groundwater
[Canberra and Sydney only]
The AWRA-R river and groundwater interaction module was used to model the volume of surface water recharge to groundwater. The module simulates seepage based on the potential infiltration rate from the river, the available storage in the underlying aquifer and the aquifer's discharge rate. The equations used in the module are based on Doble et al. (2014).
River loss
The AWRA-R river and groundwater interaction module was used to model the volume of surface water recharge to groundwater. The module simulates seepage based on the potential infiltration rate from the river, the available storage in the underlying aquifer and the aquifer's discharge rate. The equations used in the module are based on Doble et al. (2014).
In the Perth region, the AWRA-R output has been assumed to represent river losses to landscape, rather than groundwater, as most river losses occur east of the Darling Escarpment outside of the coastal plain, where the aquifers are generally of low productivity or have non-potable water quality. On the coastal plain, where aquifers are of high productivity, it is assumed that the 'river-aquifer flux' is in the direction of groundwater discharge to rivers only and that all groundwater recharge is received via the landscape, not surface water.
Recharge: landscape
[Adelaide and Melbourne only]
The AWRA-L model version 5.0 (Viney et al. 2015) was used to estimate the volume of groundwater recharge from the landscape. The model simulates diffuse deep drainage, which is assumed to represent groundwater recharge, based on rainfall, soil conductivity, and evaporation rates from the ground for different vegetation cover. The diffuse deep drainage is the free drainage at the bottom of the deep soil layer (6 m depth) for each 5 km x 5 km stand-alone grid cell across the continent. The average deep drainage was estimated as the weighted mean of the relevant grid-cells within the region.
Water assets
Storages
Storage volume at the start and end of the year were obtained from the Bureau of Meteorology's water storage product. Storage volumes are calculated using water level data (metres above Australian Height Datum) collected at each storage. Capacity tables established for each storage were used to convert the height measurement to a volume.
The storage–volume curves represent specifically surveyed parts of the storage and may not reflect the storage–volume relationship across the entire storage. In addition, storages are subject to sedimentation and other physical changes over time that in turn affect the accuracy of the storage–volume curves.
In some regions, storage data were not available for the smaller storages. The storage capacities of these storages are a very small proportion of the region's total storage capacity and not including these storages in the account made no material difference to the region's total storage volume.
Lakes and wetlands
The volume of water in lakes and wetlands at the start and end of the year was calculated using water level data (metres above Australian Height Datum) collected at the lake. Capacity tables established for each lake were used to convert the height measurement to a volume.
Where metered data were not available, the volume of water in the lake was estimated based on the lake's capacity, that is, the lake was assumed to be full on 30 June. Given the water levels in these lakes are generally managed close to capacity throughout the year, the estimated volumes of these lakes are only slightly overestimated.
Aquifers
The volume of water in aquifers is estimated based on extraction limits associated with the region's groundwater management areas. These limits are provided in the region's water allocation plans and only change when the plan is updated or amended. Where aquifers do not have operational water allocation plans, or are not used for consumptive use, no groundwater volumes are estimated.
Urban system storages
The 'Urban system storages' volume represents the water held in distribution pipes and channels, and service reservoirs. This volume is estimated based on the size and dimensions of the service reservoir and distribution pipe network (i.e. it is assumed that all service reservoirs and pipes are full) and only changes when the network is augmented or altered.
Claims: surface water
Claims: groundwater
Claims: inter-region
The 'Claims: inter-region' volume refers to the amount of water still 'owing' to the region's water stores or systems on 30 June from outside the region. As there are no carryover provisions for these claims, the portion of water allocation (or claim) that has not been delivered to the region's stores or systems at the end of the water year is forfeited. Therefore, the inter-region claim at the end of the water year is 0 ML.
Urban utility data (Category 7 data)
Wastewater collected
The 'Wastewater collected' volume is estimated using the aggregated metered inflow to wastewater treatment plants within the region, minus any recirculation such as treated wastewater volume that was reported as discharge back to sewer in the region.
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.
Delivery: desalinated water
The 'Delivery: desalinated water' volume is metered at the outlet of the desalination plant. Desalinated water is generally delivered to a reservoir where it is then diverted by the utilities for urban supply.
In the Perth region, the desalinated water transferred to the reservoirs prior to consumption by urban water users is included in 'Supply system discharge: surface water'.
Supply system delivery: inter-region
The 'Supply system delivery: inter-region' volume refers to water transferred from sources outside the region boundary to the region's urban water supply system. It consists of potable and non-potable water and is based on metered information at the distribution infrastructure.
In the Perth region, water transferred to the supply system comes from Mundaring Reservoir. This reservoir lies within the region boundary but is not considered a surface water asset in the region as it primarily supplies the Goldfields and Agricultural Region outside the Perth region boundary.
Allocated diversion: urban system
The 'Allocated diversion: urban system' volume refers to surface water diverted to the region's urban water supply system under an allocation. It is measured using metered data collected at the outlet of the water source or using inflow data at the water treatment plant.
The metered inflows to water treatment plants are assumed to equal the metered outflow volume (i.e. no water losses occur during the transfer process).
Where metered data were not available, the volume of water taken was estimated based on historical metered usage.
Allocated extraction: urban system
The 'Allocated extraction: urban system' volume refers to groundwater extracted to the region's urban water supply system under an allocation. It is measured using metered data collected at the outlet of the water source or using inflow data at the water treatment plant.
The metered inflows to water treatment plants are assumed to equal the metered outflow volume (i.e. no water losses occur during the transfer process).
Where metered data were not available, the volume of water taken was estimated based on historical metered usage.
Non-allocated diversion: urban system
The 'Non-allocated diversion: urban system' volume refers to surface water diverted to the region's urban water supply system without an allocation. In the Adelaide region, this volume comprises water that was imported from the River Murray and stored within the region's storages. It is measured using metered data collected at the outlet of the water source or using inflow data at the water treatment plant.
The metered inflows to water treatment plants are assumed to equal the metered outflow volume (i.e. no water losses occur during the transfer process).
Non-allocated extraction: urban system
The 'Non-allocated extraction: urban system' volume refers to groundwater extracted to the region's urban water supply system without an allocation. It is measured using metered data collected at the outlet of the water source or using inflow data at the water treatment plant.
The metered inflows to water treatment plants are assumed to equal the metered outflow volume (i.e. no water losses occur during the transfer process).
Supply system delivery: urban users
The 'Supply system delivery: urban users' volume includes urban consumption of potable and non-potable water and is derived from (a) customer meters; (b) billing meters; and (c) estimated non-revenue water volumes.
Urban consumption consists of residential, commercial, industrial, municipal use and small-scale agriculture/irrigation use. It excludes water delivered to irrigation schemes and the environment.
Recycled water delivery: urban users
The 'Recycled water delivery: urban users' volume is derived from (a) customer meters; (b) billing meters; and (c) onsite re-use water meters.
Urban consumption consists of residential, commercial, industrial, municipal, and small-scale agriculture/irrigation use, as well as onsite use at the wastewater treatment plant. It excludes recycled water re-circulated within the wastewater treatment process.
Leakage: groundwater
The 'Leakage: groundwater' volume refers to non-revenue water associated with real losses, including background pipe leakage, pipe bursts, and tank leakage. These losses are calculated using the following equation:
Real losses = Non-revenue water – (Apparent losses + Unmetered authorised consumption)
Non-revenue water is water that is lost before it reaches the customer. It is estimated based on the difference between the metered volume of water supplied and the volume of water consumed (revenue water). In some regions, modelling software is used to estimate the losses across the network.
The volume of apparent losses comprises unauthorised consumption (e.g. water theft) and customer meter under-registration (e.g. meter inaccuracies) and is reported in 'Other supply system decreases'. The volume of unmetered authorised consumption, which includes fire use and internal operational use by utilities for cleaning of pipes, tanks and service reservoirs, is generally estimated using an infrastructure leakage index.
Discharge: sea
The 'Discharge: sea' volume is the metered volume of disposals from the wastewater system and recycled water system to the sea, estuaries, inlets and portions of rivers and streams with tidal impacts (which are considered outside of the region).
Where metered disposal data are not available, the volume is estimated based on the difference between metered inflow to a wastewater treatment plant and metered volume of recycled water used.
In South East Queensland, advanced wastewater treatment plants also discharge reverse osmosis concentrate and excess purified recycled water to sea.
Supply system discharge: surface water
The 'Supply system discharge: surface water' volume is metered and includes return of excess water from the urban water supply system back to reservoirs for balancing.
In the Perth region, potable water is also discharged to rivers from the urban supply system for environmental purposes (riparian releases) and is metered at each environmental release point.
Wastewater and recycled water discharge: surface water
The 'Wastewater and recycled water discharge: surface water' volume refers to the disposal of treated wastewater to rivers and other surface water, as well as the discharge of recycled water for environmental purposes. It is measured using metered outflow data from the wastewater treatment plant.
Treated wastewater disposal to rivers and streams that are estuarine in nature, or subject to tidal impacts, are not reported in this volume, but reported in 'Discharge: sea'.
Where metered data were not available, the volume of treated wastewater discharged to rivers was estimated based on historical metered discharges.
Discharge: landscape
The 'Discharge: landscape' volume is the metered treated wastewater discharge to landscape and/or infiltration ponds, where the primary purpose is disposal of the effluent rather than using the effluent for irrigation purposes. In the South East Queensland region, this volume also includes discharge of excess treated water and reverse osmosis concentrate from advanced water treatment plants.
Where metered disposal data are not available, the volume was estimated based on the difference between metered inflow to a wastewater treatment plant and metered volume of recycled water used. This volume may include discharges to landscape that make their way into groundwater.
Managed aquifer recharge
The 'Managed aquifer recharge' volume refers to potable, non-potable, and recycled water recharged into aquifers. It includes recycled water injected into the aquifer, as well as treated wastewater discharged to infiltration ponds where it infiltrates into the groundwater store.
The volume of aquifer recharge is based on metered data collected at the wastewater treatment or recycling plant. Where treated wastewater is discharged to infiltration ponds, it is assumed that this entire volume infiltrates into the aquifer; however, it is likely that some water would be lost through evaporation.
Supply system delivery: irrigation scheme
The 'Supply system delivery: irrigation scheme' volume refers to water delivered to the region's irrigation schemes from the urban water supply system. It is based on metered data.
Recycled water delivery: irrigation scheme
The 'Recycled water delivery: irrigation scheme' volume refers to water delivered to the region's irrigation schemes from the urban recycled water system. It is based on metered data.
Supply system transfer: inter-region
The 'Supply system transfer: inter-region' volume refers to water transferred outside the region boundary from the region's urban water supply system. It consists of potable and non-potable water and is based on metered information at the distribution infrastructure.
Wastewater transfer: inter-region
The 'Wastewater transfer: inter-region' volume refers to wastewater transferred outside the region boundary from the region's wastewater system. It is based on metered information at the distribution infrastructure.
Other supply system decreases
The 'Other supply system decreases' volume is the non-revenue water associated with apparent losses (which comprises unauthorised consumption and customer meter inaccuracies) and any remaining non-revenue water from the urban water supply system (not reported in 'Leakage: groundwater').
This volume of non-revenue water is estimated using one or more of the following:
- the difference based on a water balance between metered water sourced and supplied to customers
- the 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 water treatment plants for treatment losses
- assuming a set percentage of the metered supply volume is non-revenue water.
Other wastewater and recycled water system decreases
The 'Other wastewater and recycled water decreases' volume includes losses from the wastewater treatment system and losses during the management of treated wastewater.
Losses from the wastewater system were estimated based on metered data or from observations. Wastewater overflows or spills, which may occur at emergency relief systems built into the network or uncontrolled points at manholes and network leaks, were estimated based on observation or monitoring of the sewer network.
Water licensing database (Category 5 and 6 data)
Allocation remaining
For licences that have a 1 July–30 June water management year, the allocation remaining refers to the portion of unused allocation that can be carried over to the next year. For some licences, there is no carryover provision and the portion of water allocation that has not been taken at the end of the year is forfeited. In these cases, the allocation remaining at the end of the water year is 0 ML.
For licences where the water management year commences on the date the licence is issued and is different to the standard 1 July–30 June water year, the allocation remaining at 30 June represents the unused component of the annual allocation for the licence.
The allocation remaining on 30 June is calculated as shown in Table N1.
| Account | |
| Opening balance at 1 July | |
| add | Allocation |
| less | Allocated abstraction |
| less | Adjustment and forfeiture |
| equals | Closing balance at 30 June |
Allocations refer to the maximum amount of abstraction allowed during the year and is announced annually. It is usually a percentage of the licence entitlement, which is determined after a review of the region's water resources at the start of the water management year. In some regions, subsequent additional announcements may be made throughout the year if additional water becomes available.
For licences that have no carryover provisions, forfeiture is calculated as the total annual allocation minus the volume of water taken during the water year. Licences that are terminated during the year are also considered to be forfeitures. Where carryover provisions exist, forfeiture is calculated as the total annual allocation minus the volume of water taken and the carryover.
Allocated abstraction: individual users
Allocated abstraction to individual users refers to water taken for private and commercial use. The entitled abstraction of allocated water by individual users (both surface water and groundwater) during the licensed water year is derived from a combination of metered data and estimates. Where metered data were available, the abstraction was calculated as the volume of water taken during the year. Where metered data were not available, the volume of abstraction was usually estimated to be the full licensed allocation (i.e. it was assumed 100% of the allocation was taken).
For some licences, the volume of water taken was estimated:
- based on historical usage
- based on modelled data
- by applying a pre-determined usage rate (e.g. a set volume per property size or bore)
- by assuming a set ratio of water take to entitlement volume.
There is generally insufficient information relating to actual abstraction to provide more accurate estimates of abstraction for all licences, particularly individual users.
Non-allocated abstraction: individual users
Non-allocated abstractions to individual users refers to water taken for private and commercial use. In the Perth region, non-allocated extraction refers to domestic garden bore use.
Where metered data are available, the abstraction is calculated as the actual volume of water taken during the year. Where metered data are not available, the volume of water taken was estimated:
- based on historical usage
- based on modelled data
- by applying a pre-determined usage rate (e.g. a set volume per property size or bore)
- by assuming a set ratio of water take to entitlement volume.
Allocated abstraction: irrigation scheme
The 'Allocated abstraction: irrigation scheme' volume refers to water diverted from surface water storages or extracted from aquifers to the region's irrigation schemes under an allocation. It is measured using metered data collected at the outlet of the water source.
Non-allocated abstraction: irrigation scheme
The 'Non-allocated abstraction: irrigation scheme' volume refers to water diverted from surface water storages or extracted from aquifers to the region's irrigation schemes. It is measured using metered data collected at the outlet of the water source. In the Adelaide region, recycled water injected into the aquifer (see 'Managed aquifer recharge: individual users') is subsequently supplied to the irrigation scheme for re-use.
Allocated abstraction: environmental purposes
The 'Allocated abstraction: environmental purposes' volume refers to water taken from storages, rivers or aquifers under an allocation for an environmental purpose. It is measured using metered data collected at the outlet of the water source.
Allocated abstraction: inter-region
The 'Allocated abstraction: inter-region' volume refers to water diverted from surface water storages or extracted from aquifers and pumped outside the region boundary under an allocation. It is measured using metered data collected at the outlet of the water source.
Abstraction: basic rights
Abstractions for basic or statutory rights usually refers to water taken for riparian water rights, cultural water rights, or stock and domestic purposes. Where metered data are not available, the volume of water taken is usually estimated using a pre-determined usage rate (e.g. a set volume per property size or bore). The set volume may be established using small-scale metering projects in the area or it is based on best practice and water requirements as recommended by the relevant government water agency.
Delivery: inter-region agreement
The 'Delivery: inter-region agreement' volume refers to raw, potable, or non-potable water transferred via pipeline from outside the region boundary to the region's surface water store under an inter-region agreement. The volume is usually metered at the pipeline pump station.
Delivery: inter-region
The 'Delivery: inter-region' volume refers to raw, potable, or non-potable water transferred via pipeline from outside the region boundary to the region's surface water store. The volume is usually metered at the pipeline pump station.
In the Melbourne region, part of the inter-region delivery volume comprises water diverted from the Silver and Wallaby creeks, located outside the region boundary, to the region's storages via an open channel. The metered volume of water delivered to the storages also includes catchment runoff into the channel; therefore, the portion of this volume that comes from the Silver and Wallaby Creeks was estimated based on historical data.
Managed aquifer recharge: individual users
The 'Managed aquifer recharge: individual users' volume refers to potable, non-potable, and recycled water recharged into aquifers from private and commercial users. The volume of aquifer recharge is based on metered data collected at the treatment plant. In the Burdekin region, metered data are not available, and the volume is estimated balancing recharge credit details for active licences.
Transfer: inter-region (from surface water)
The 'Transfer: inter-region' volume refers to surface water diverted from the region's reservoirs and pumped outside the region boundary. It is measured using metered data collected at the outlet of the water source.
Leakage: landscape (from surface water)
The 'Leakage: landscape' volume refers to seepage losses from the region's surface water storages. It is usually based on estimated data.
In the SEQ region, leakage was estimated by subtracting net evaporation loss, based on the AWRA-R model, from the modelled estimate of total loss (i.e. seepage and evaporation loss) provided by the Department of Natural Resources, Mines and Energy for several of the region's major storages. Where total water loss was not modelled for a storage, it was assumed no leakage occurred at that storage.
In the Ord and Perth regions, leakage was estimated based on historical metered data collected at the region's storages. Given the annual metered loss changed little from year to year, it was assumed that leakage to the landscape during the reporting year was equivalent to the average annual leakage during the monitoring period.
Delivery (irrigation scheme)
The 'Delivery' volume refers to water supply to irrigation scheme users within a scheme area and is based on consumers' meter readings. Where customers' meter readings are not available for a scheme, the metered data at the pumping station was used (i.e. assuming no water losses occur during the transfer process).
Point return: irrigation scheme
The 'Point return: irrigation scheme' volume refers to surplus irrigation water that returns to a river from an irrigation scheme area. Irrigation water returns are usually metered at the outfall point. Where metered data are not available for a scheme, the return flow was estimated based on historical or modelled data.
Leakage: landscape (from irrigation scheme)
The 'Leakage: landscape' volume refers to seepage losses during the transfer of water from the surface water storage to the irrigation scheme area via an open channel. The leakage was estimated as the difference between the metered diversions from the dam and the metered deliveries to the irrigation scheme area.
Discharge: user (surface water)
The 'Discharge: user' volume refers to treated wastewater from private and commercial users (including power stations) to rivers. It is measured using metered discharge data.
Return flow: environmental purposes
The 'Return flow: environmental purposes' volume refers to environmental water returned to rivers. It is based on estimated data provided by the Murray–Darling Basin Authority for Sustainable Diversion Limit (SDL) resource units in Victoria only.
Floodplain harvesting
Floodplain harvesting refers to water taken from the landscape as a result of heavy rainfall events and overbank flood spilling. This volume is estimated based on a combination of user returns and local knowledge. Currently, information is available only for Queensland and New South Wales areas within the Murray–Darling Basin region.
Conveyance losses
Conveyance losses refers to seepage losses during the transfer of water via open channel from the rivers to the users. The seepage was estimated as the difference between the metered diversions from the river and the metered deliveries to the user. In the Murray–Darling basin, these losses are only calculated for areas within Victoria (where they are referred to as 'physical and transfer losses'); losses in other areas within the region are already incorporated within the diversion volume.
Groundwater models
GIS-based approach
[Adelaide, Murray–Darling Basin, Melbourne only]
Inter-region flows
Regional and coastal groundwater flow into and out of the region was calculated using a simple GIS approach based on Darcy's Law. A set of bores with current data was selected, including any bores within 20 km of the region's boundary. Where no bores were present close to the boundary, the interpolated groundwater level surface was extended to the boundary and used to estimate groundwater flow across the boundary (this flow is small in magnitude).
Groundwater levels were interpolated to a groundwater-level grid for each season using the ArcGIS Topo-to-Raster tool. Seasonal groundwater-flow grids were then derived from these groundwater-level grids along with aquifer thickness and hydraulic conductivity data, using a modification of the ArcGIS Darcy velocity tool. Groundwater flow across selected regional and coastal boundaries (Figure N2) was then calculated using a simple GIS analysis, and seasonal; values were aggregated to the reporting period.
Figure N2 Map of lateral groundwater flow boundaries in the
Adelaide (top) and Melbourne (bottom) regions
Regional groundwater outflow was only estimated for the region's most hydraulically conductive aquifers. Flow across boundaries not included in this quantification was assumed to be negligible due to limited flow (e.g. in fractured rock) or could not be estimated because limitations of the method prevented its application.
FEFLOW groundwater model and Mike 11 hydraulic model
[Daly only]
The Department of Environment and Natural Resources uses the Finite Element Subsurface Flow system (FEFLOW) to estimate the natural water movement to and from the groundwater store within the Daly region. FEFLOW estimates groundwater movement for the entire extent of the Oolloo Dolostone Aquifer and the Tindall Limestone Aquifer, which extends beyond the Daly region boundary (Figure N3). The volumes reported in this account refer to the natural water movement that occurs within these aquifers within the Daly region boundary.
Figure N3 Groundwater model area relative to the Daly region
boundary
The Oolloo Dolostone and Tindall Limestone aquifers are karstic and were modelled as an equivalent porous media with relatively limited storage. The groundwater model was calibrated using regional aquifer parameters to reproduce the observed groundwater levels and discharge to the rivers, as outlined by NRETAS (2010).
Inter-region flows
The groundwater model derives the lateral flux by defining the appropriate water balance zones and calculating the volume of water flowing across each boundary on an annual basis. Detailed information on the model calibrations are provided by NRETAS (2010).
Recharge: landscape
Diffuse recharge from the landscape into the region's aquifers was estimated using FEFLOW. Recharge into the aquifers occurs via the following pathways:
- direct recharge of excess soil moisture
- precipitation 'channelled' through the unsaturated zone via macropores
- localised indirect recharge of surface water that is channelled into karstic features such as dolines (sinkholes).
Detailed information on the model calibrations are provided by NRETAS (2010).
A limitation of this method is that it does not quantify the increase in recharge during wetter periods in the rainfall record when compared to observed groundwater level and streamflow data.
Recharge/discharge: surface water
The flow between aquifers and rivers is estimated using FEFLOW in combination with the one-dimensional river hydraulic model MIKE 11. The flow interactions between surface water and groundwater are estimated where the surface water channels in the MIKE 11 model are coupled to the aquifer boundaries in the FEFLOW groundwater model. Detailed information on the model calibrations are provided by NRETAS (2010).
There is limited understanding of actual river/aquifer interactions, especially with respect to flows from the river to the groundwater system. It is likely that, when FEFLOW is coupled with MIKE 11, groundwater recharge from rivers is overestimated during large flow events.
PRAMS and PHRAMS groundwater models
[Perth only]
The Department of Water and Environmental Regulation uses the Perth Regional Aquifer Modelling System (PRAMS) version 3.5 and Peel–Harvey Regional Aquifer Modelling System (PHRAMS) to estimate the natural water movement to and from the groundwater store within the Perth region (Davidson and Yu 2008; URS 2009).
PRAMS estimates groundwater movement for the area north of Mandurah. PHRAMS estimates groundwater movement for the Peel–Harvey area south of Mandurah. The volumes reported in this account refer to the natural water movement that occurs within each model area within the Perth region boundary (Figure N4).
Figure N4 Groundwater model areas relative to the Perth region
boundary
Both models were initially developed for the purpose of estimating and assessing the impacts of changes in climatic conditions and varying extraction rates on the aquifers, not for the purposes of preparing water accounts. These models have since been modified to also provide data for water accounting.
Inter-region inflow and outflow
PRAMS and PHRAMS were used to estimate groundwater flows to and from outside the region. The models derive the lateral water movement between aquifers within the region and outside the region by defining the appropriate water balance zones and calculating the volume of water flowing across each boundary on an annual basis.
All groundwater flow to and from outside the region is via the north and south boundaries and the coastline. There is no groundwater flow between the model areas and the Darling Range in the eastern part of the region due to the geology of that area.
For estimating groundwater movement between the region's aquifers and the ocean, both models apply a constant head at the coastline to estimate the volumes flowing through each boundary over the year. For the Peel–Harvey area, PHRAMS assumes that the estuary inlets along the coastline form part of the boundary.
Recharge: landscape
PRAMS and PHRAMS were used to estimate groundwater recharge from the landscape. PRAMS calculates the recharge of water into the Perth region aquifers from the unsaturated zone above (i.e. the landscape store). The model delineates a series of horizontal cells called representative recharge units, and collates data on:
- land use, vegetation classifications, leaf area indexes, and soil classifications (spatial datasets)
- water table depths and plant root depths
- climatic data throughout the region.
The CSIRO WAVES model was then used to calculate flows from some of the specific land use areas, such as agriculture, pine plantations, and native bushland (simpler models are used for general land use areas including residential, industrial, and parkland areas). The Vertical Flux Model calculates recharge on a daily basis and MODFLOW was used to do the time step calculation (Xu et al. 2008).
PHRAMS calculates the inflow of water into the Peel–Harvey model area and assumes that most of the inflow is recharge from rainfall. The CSIRO WAVES model is used to estimate the maximum annual recharge based on the following equation:
Recharge = 0.8 x Rainfall – 280
The annual recharge and annual pan evaporation were distributed into monthly amounts using a monthly distribution table. The monthly accounts were then applied to the specific geological areas (which have their own recharge rates according to soil types and land cover) to calculate total recharge.
The two groundwater models use different techniques to calculate recharge. PRAMS is a more complicated and sophisticated model than PHRAMS. PRAMS uses daily climatic data to determine total recharge during the year, whereas PHRAMS is based on annual data inputs.
Recharge/discharge: surface water
PRAMS and PHRAMS were used to estimate water flow between the region's aquifers and surface water store. The models assume that all groundwater flows between the aquifers and the surface water stores occurs from the aquifers (i.e. there is no recharge from surface water), which is consistent with measured and simulated discharges. It is also assumed that there is no groundwater discharge to the major surface water storages, only to the region's rivers and drains.
PRAMS removes water from drain and river cells when the water table rises above the specified invert level of the drain cell. The volume of water removed is the volume of groundwater discharged to surface water.
PHRAMS uses a simplified drain package developed within MODFLOW to calculate the discharge to these drains and rivers from the aquifer. Two classes of drains were assumed:
- major drains that are permanent and deep (including major rivers)—conductance is calculated at 10,000 m2 /day and a depth of 2 m
- minor drains—conductance is calculated at 10,000 m2 /day and a depth of 1.5 m.
Groundwater discharges to drains and rivers were calculated when the local groundwater level rises above the drain bed elevation.
Perennial lakes provide major groundwater sinks in the water table aquifer and are subject to rainfall and evaporation. These were included in the water table aquifer balance and modelled accordingly.
Discharge: landscape
PRAMS and PHRAMS were used to estimate groundwater discharge to the landscape. The models calculate evapotranspiration from the saturated zone of the aquifers, which is considered to be equal to the groundwater discharge to landscape. Note that this should not be confused with evapotranspiration from the unsaturated zone, which is rainfall water that has entered the ground in the unsaturated zone but is removed before it reaches the water table at the top of the saturated zone.
Both models use the MODFLOW evaporation module to calculate evapotranspiration from the saturated zone open water wetland surfaces and near surface water table areas.
MODFLOW and water table fluctuation models
[Murray–Darling Basin only]
Natural groundwater movement was estimated by the NSW Department of Industry using MODFLOW and water table fluctuation methods in selected Sustainable Diversion Limit (SDL) units across the region (Figure N5). It was assumed that no groundwater movement occurred outside of these areas.
More detail on MODFLOW is available at the MODFLOW website (United States Geological Survey 2013).
Figure N5 Sustainable diversion limit areas where
groundwater flows were modelled
Recharge/discharge: landscape
MODFLOW and water table fluctuation models were used to estimate discharge and recharge to and from the landscape. In MODFLOW, evapotranspiration from the landscape was estimated and assumed to represent groundwater discharge.
Groundwater recharge is both an input to and an output from a groundwater model. Several models estimate recharge as a percentage of rainfall. The magnitude of recharge (as a percentage of rainfall) can be adjusted during the calibration of a groundwater model so that the observed groundwater levels are reproduced in model outputs as accurately as possible, typically for a period of around 20 years if data are available.
Recharge/discharge: surface water
MODFLOW and water table fluctuation models were used to estimate water flows between the region's aquifers and surface water store.
Groundwater discharge into the river is modelled when groundwater levels are higher than river water levels; groundwater recharge from the rivers is modelled when groundwater levels are lower than river water levels. The river levels are usually based on the monthly average from a gauge close to the groundwater model cell. MODFLOW also has a subroutine to represent drains. When this is activated and groundwater levels are above the base of the drain, water flow to the drain is estimated and this water volume is removed from the cell of the groundwater model.