National Water Account 2018

South East Queensland: Methods for final account

Image of Brisbane River (istock © Wendy Townrow)

Summary of methods

There were five key methods for establishing item volumes in the 2018 Account. Click the down arrow in the table below to view the list of items derived by each method type. For detailed information about each method scroll down this page or click on the links in the table.

 

Methods approach

Water storage product data

AWRA-R model

Metered and estimated data provided by water authorities

Operational Data Storage System: seepage data

Water resourcing licence database and meter readings

 

Detail of methods

Water storage product data

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 volume of individual storages was aggregated to present the total volume for the line item as detailed in the supporting information table. The uncertainty range for the storage volume is +/–5%.

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.
  • Storages are subject to sedimentation and other physical changes over time that in turn affect the accuracy of the storage–volume curves.

 

Water table aquifer

The water in the aquifers is assumed to equal the total entitled maximum volume extractable from the Central Lockyer Groundwater Management Area for the Central Lockyer water supply scheme and from the Cooloola Sandmass subartesian aquifer for the Cooloola Shire Council.

 

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 at 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.

 

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'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).

 

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.

 

Metered and estimated data provided by water authorities

Leakage: groundwater

The 'leakage: 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 and also includes volumes that were historically reported under ‘leakage: landscape’ which accounted for pipe bursts, losses in water treatment, and disposal to sewer from the water supply system.

Non-revenue water is estimated using:

  • the difference based on a water balance between metered water produced and revenue water (metered/estimated customer consumption charges); and/or
  • modelling software of network real losses (leakages and bursts) and apparent losses.

Leakage in the wastewater system is reported under 'other wastewater system decreases'.

Where non-revenue water real losses are reported as a combined volume for pipe bursts and background leakage, with no breakdown, this was reported in 'leakage: groundwater', which may overestimate the volume.

 

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 is 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.

Some disposals to Brisbane River, Albert River, Logan River, Bremer River, Tingalpa Creek, Eprapah Creek, and Cabbage Tree Creek are considered discharge to sea as these are estuarine at the site of the disposal.

Advanced wastewater treatment plants within the region also discharge reverse osmosis concentrate and excess purified recycled water to sea.

The estimated uncertainty of this volume was +/– 20%.

 

Discharge: user

The Water Tracking and Electronic Reporting System (WaTERS) contains both wastewater treatment plant discharges, and industrial and commercial discharges. These data are collected, measured and reported by third parties (licence holders). WaTERS was queried for commercial and industrial discharge volumes in the 2017–18 year.

This volume includes treated wastewater discharge directly to surface water and sea water from industrial and commercial businesses, rather than discharging to urban wastewater collection system.

 

Discharge: wastewater

The 'discharge: wastewater' volume is metered and includes:

  • disposal of treated wastewater to rivers and other surface water
  • discharge of recycled water for environmental purposes.

Treated wastewater disposal to rivers and streams which are estuarine in nature, or subject to tidal impacts, are not reported in this volume, but reported as discharge outside the region (to sea).

The estimated uncertainty of this volume was +/– 20%.

 

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. Also included in this volume is any other managed treated wastewater discharges not reported in:

  • discharge: surface water
  • discharge: sea.

This volume includes discharge of excess treated water and reverse osmosis concentrate from advanced water treatment plants.

Where metered disposal data is 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.

This volume may include discharges to landscape that make their way into the groundwater.

The estimated uncertainty of this volume was +/– 20%.

 

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, to avoid double counting.

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.

The estimated uncertainty of this volume was +/– 20%.

 

Delivery: desalinated water

The 'delivery: desalinated water' volume is metered at the outflow from the Gold Coast desalination plant (also known as the Tugun desalination plant).

The estimated uncertainty of this volume was +/– 20%.

 

Supply system delivery: urban users

The 'supply system delivery: urban users' volume includes urban consumption of potable and nonpotable water and is derived from:

  • customer meters
  • billing meters, and
  • estimated non-revenue water volumes.

Urban consumption consists of residential, commercial, industrial, municipal use and small scale agriculture/irrigation uses.

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

The estimated uncertainty of this volume was +/– 20%.

 

Other supply system decreases

The 'other supply system decreases' volume is assumed to be the non-revenue water associated with apparent losses, the remaining non-revenue water from the urban water supply system (if not reported in 'leakage: groundwater'); and 'own use' which is the volume of water used by the utilities on site for purposes such as wash down, toilet flushing and watering gardens.

Where pipe bursts and background leakages are provided as a combined volume, for simplification this is reported as 'leakage: groundwater' because the leakage volume to landscape cannot be separated.

Remaining non-revenue water is estimated using:

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

The estimated uncertainty of this volume was +/– 40%.

 

Recycled water delivery: urban users

The 'recycled water delivery: urban users' is derived from:

  • customer meters; and
  • billing meters onsite re-use water meters.

The volume excludes recycled water re-circulated within the wastewater treatment process.

Urban consumption consists of residential, commercial, industrial, municipal, onsite (external to the treatment process) use, small scale agriculture/irrigation uses, and ‘other’ use which includes non-revenue recycled volumes due to pipe-bursts, leakage, apparent losses, advanced treatment system and distribution losses, and other non-revenue recycled water.

Volumes supplied to commercial, industrial and municipal customers also included advanced treated water.

The estimated uncertainty of this volume was +/– 20%.

 

Wastewater and recycled water discharge: surface water

The 'wastewater and recycled water discharge: surface water' is metered and includes:

  • disposal of treated wastewater to rivers and other surface water
  • discharge of recycled water for environmental purposes

Treated wastewater disposal to rivers and streams which are estuarine in nature, or subject to tidal impacts, are not reported in this volume, but reported as discharge outside the region (to sea).

The estimated uncertainty of this volume was +/– 20%.

 

Other wastewater and recycled water system decreases

The 'other wastewater and recycled water system decreases' volume is the sum of the following components:

  • losses from the wastewater treatment system
  • known losses from the wastewater collection system
  • known egress or exfiltration from the wastewater collection system occurring before metered inflow to wastewater treatment plants
  • losses during management of treated wastewater
  • inclusion of advanced treated water.

Losses from the wastewater system are estimated based on the metered inflow and outflow/disposal/customer meters or estimated based on observations.

Wastewater overflows or spills are estimated based on observation or monitoring of the sewer network. This may occur at emergency relief systems built into the network or uncontrolled points at manholes and network leaks.

The estimated uncertainty of this volume was +/– 40%.

 

Other decreases

'Other decreases' represents transfers of supplemented allocations out of the South East Queensland region. This represents the surface water transfers out of the region; no diversions for use within the region are included.

Although the Queensland Department of Natural Resources, Mines and Energy has records of entitlement, allocation and diversions from storages in the water management system database, data were needed from Toowoomba Regional Council to determine the diversions transferred out of the South East Queensland region to the town of Toowoomba. Toowoomba is located outside the South East Queensland region, on the Great Dividing Range and obtains much of its town water supply from within the South East Queensland region.

Water is pumped out of Lake Perseverance and Lake Cressbrook by the resource operation licence holder (Toowoomba Regional Council) to Toowoomba via a series of tanks and minor storages to Mount Kynoch water treatment plant. Potable water is then supplied to the town of Toowoomba.

There were no volumes reported in 2017–18.

 

Operational Data Storage System: seepage data

Leakage: landscape

'Leakage: landscape' is the loss that occurs from the water supply scheme storages. Where storage loss was not specifically evaluated as part of resource operating licence reporting requirements, the storage loss allowance detailed in the plan was used as an estimate. This was done by adding the storage loss allowances calculated for each month, based on the storage surface area at the start of month and the application of the difference between monthly storage loss factors in the applicable resource operating licence tables. The Moreton and Logan Basin resource operating licences provide storage loss tables for Lake Wivenhoe, Lake Somerset and Lake Maroon, Cedar Grove Weir and Bromelton Off–Stream Storage, Lake Atkinson and Lake Moogerah.

The value for each storage was calculated as follows:

  • For a storage, net evaporation loss was calculated by subtracting precipitation on surface water from the evaporation from surface water. If the calculation resulted in a negative value, the net evaporation loss was considered as zero.
  • This net evaporation loss was subtracted from the resource operating licence loss (provided by the Department of Natural Resources, Mines and Energy) to calculate the adjusted storage loss for the volume. This is to prevent double counting because the resource operating licence loss includes net evaporative loss as estimated by the department. If the resulting value was less than zero, no value was considered for the storage.

The volumes are from application of the resource operating licence calculation and therefore include evaporation losses. No adjustment was made to the calculation.

The Moreton and Logan Basin resource operating licences list loss factors to apply when estimating losses from storages where the storages are part of the water supply scheme. Where the storages are not part of a scheme, losses were not available and could not be quantified accurately.

Losses from the storages that form part of a water supply scheme have been estimated and reported where information was available to allow accurate quantification. Therefore:

  • transmission losses were not reported in the Moreton or Gold Coast water plan areas
  • storage losses were not reported in the Gold Coast Water Plan area.

 

Water resourcing licence database and meter readings 

Allocation remaining

The water allocation remaining for a water licence at the end of the reporting year is the unused component of the annual allocation. As there is no carryover provision for water supply licences in the South East Queensland region, the portion of water allocation that has not been abstracted at the end of the water year is forfeited. Therefore, the allocation remaining at the end of the water year is 0 ML.

 

Adjustment and forfeiture

The portion of water allocation that has not been abstracted at the end of the licence water year is forfeited (i.e., there is no carryover of entitlements). Therefore, forfeiture is calculated as the total annual allocation for each licence minus the allocation abstraction during the licence water year.

 

Allocation

Queensland water licences are issued with an annual abstraction amount specified and with annual compliance arrangements in place.

The maximum amount of abstraction under a water entitlement is announced by the resource operations licence holder on an annual basis. The announced allocation is made after a review of storage and aquifer levels in the region on the first day of the water year (1 July). Subsequent additional announcements may be made throughout the year if additional water becomes available.

More information on these allocations and the associated water access entitlement is given in the Water rights and use note.

 

Non-allocated diversion: surface water

The 'non-allocated diversion: surface water' volume is calculated from the volume of surface water diverted (metered at the source) and inflow to water treatment plants.

North Stradbroke Island Water Treatment Plant sources water from both surface water and groundwater. The percentage of surface water abstracted was estimated based on production logs of treated water from each water source and this percentage was applied to the combined outflow metered volume of the plant.

Where metered inflows to water treatment plants are not available, these volumes are assumed to equal the metered outflow volume (i.e. no water losses occur during the treatment process).

The estimated uncertainty of this volume was +/– 20%.

 

Non–allocated diversion: urban system

The 'non-allocated diversions: urban system' volume refers to surface water that is sourced from unregulated water source and/or source not managed using entitlements and allocations. For water sources managed through entitlements and allocations, refer to 'Allocation diversion: surface water'.

The calculation is based on metered raw water extraction from surface water and inflow to water treatment plants. Raw water supplied directly as untreated (nonpotable water) is the metered extracted volume from the water source. Where metered intakes to water treatment plants were not available the intake volumes were estimated using metered outflow data, assuming that no water losses occurred during the treatment process.

North Stradbroke Island Water Treatment Plant sources water from both surface water and groundwater. The percentage of surface water abstracted was estimated based on production logs of treated water from each water source and this percentage was applied to the combined outflow metered volume of the plant. In previous years, all water was assumed to be sourced from surface water.

The estimated uncertainty of this volume was +/– 20%.

 

Allocated diversion: individual users 

The ‘allocated diversion: individual users’ volume represents the volume of water diverted from surface water by non-urban (excluding Seqwater and Toowoomba Regional Council) holders of supplemented allocations. 

Supplemented allocation diversions were provided by Seqwater for each water plan area. The current resource operations licence reporting requirements do not allow for reporting by 'type' of use. The volume was calculated by removing the urban from the total supplemented allocation diversion. This represents the remaining high-priority holders and all medium-priority holder diversions.

Seqwater has accepted metered data provided by water supply scheme operators. The volume calculated excludes distribution loss.

Diversions for the following rural-based water supply schemes were not necessarily solely for irrigation purposes and may have included some supplemented allocation diversions for urban purposes:

  • Central Lockyer
  • Lower Lockyer
  • Warrill Valley
  • Mary Valley
  • Logan River.

The data were derived from measured data and no uncertainty was quantified.

 

Allocated diversion: surface water

The 'allocated diversion: surface water' volume is calculated from the volume of surface water diverted (metered at the source) and inflow to water treatment plants or directly to major customers.

Where metered inflows to water treatment plants are not available, these volumes are assumed to equal the metered outflow volume (i.e. no water losses occur during the treatment process).

The estimated uncertainty of this volume was +/– 20%.

 

Non-allocated extraction: groundwater

The 'non-allocated extraction: groundwater' volume is calculated from the volume of groundwater extracted (metered at the source) and inflow to water treatment plants.

Where metered inflows to water treatment plants are not available, these volumes are assumed to equal the metered outflow volume (i.e. no water losses occur during the treatment process).

The estimated uncertainty of this volume was +/– 20%.

 

Diversion: statutory rights

‘Diversion: statutory rights’ volume consists of diversions based on riparian water authorisations. The total diversion is estimated by multiplying the total number of properties with a riparian water authorisation by an assumed diversion rate of 2 ML per property.