South East Queensland
Quantification approaches
Summary of quantification approaches
Table 1 outlines the quantification approaches used to derive the item volumes for the South East Queensland region. For a more detailed description of the quantification approach, click on the relevant item name in the table.
Bureau = Bureau of Meteorology
DNRM = Queensland Government Department of Natural Resources and Mines
DSITIA = Queensland Government Department of Science, Information Technology, Innovation, and the Arts
Detail of quantification approaches
Water storage product data
Storages
Storage volume was measured at the start and end of the 2013–14 year by using gauged water level height(s) for individual storages. The height measurement was converted to a volume using the storage-volume curve(s) of the storage.
The volume of individual storages was aggregated to present the total volume as detailed in the supporting information table. The uncertainty was not quantified.
The assumptions made were as follows:
Storage-volume (rating) tables are constructed from surveyed parts of the water 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 that affect the accuracy of the storage-volume tables.
Stream monitoring data
River outflow from the region
The runoff at the most downstream gauges of the major rivers within the SEQ region were received from the Queensland Government Department of Natural Resources and Mines (DNRM). The runoff downstream of these gauges was calculated using Australian Water Resources Assessment Landscape (AWRA–L) model version 3.0 (Van Dijk 2010) outputs. The gauging stations considered in this calculation covered 65% of the total area of SEQ catchments and relevant flow data were received from DNRM. The rest 35% of the total area was ungauged and it had to be modelled to estimate the flow volumes. It was estimated that out of 1,699,479 ML of runoff to surface water, approximately 57% was stored in the storages and the rest of the runoff went to the rivers. The following river gauging stations and the Pumicestone passage were considered to estimate the outflow from the region (Figure 1):
- Coomera 146010A
- Currumbin Creek 146012A
- Tallebudgera Creek 146095A
- Nerang River 146002B
- Logan River 145014A
- Brisbane River 143001C
- Caboolture River 142001A
- South Pine River 142202A.
Figure 1 Gauging stations used to calculate total outflow to sea
Daily AWRA–L runoff were produced based on daily gridded climate data that were available on a 0.05 degree (approximately 5 km) national grid. The catchments of the downstream river sections were defined using the Australian Hydrological Geospatial Fabric (AHGF) stream network. The average runoff depth from the landscape into the surface water was determined as the weighted mean of the relevant grid points within the catchment boundary. Points were weighted based upon the area they represented within the catchment boundary. Mean runoff depth was converted to a runoff volume by multiplying runoff depth by the catchment area of the relevant end point of the river (excluding reservoirs).
To estimate outflow to the sea, the water balance equation was applied on the measured surface water volume at the upstream gauging station and estimated surface water volume at the near-sea outlet for the listed rivers, water diversion for the WTP, wastewater disposal to the surface water within the catchment from the WWTP, change in storages, rainfall volume directly on to the storages and evaporation from the storages.
It was assumed that the gauging station flow data are reliable and the water balance equations are valid. A comparison of alternative 'extrapolation' methods has not been undertaken.
This contributing area below the gauging stations is 7,310 km2, approximately 35% of the total area of the SEQ region. Based on a water balance equation equation, estimated outflow to the sea is approximately 904,491ML, which is 53% of runoff to surface water reported in the Statement of Water Flows (1,699,479 ML). Given that the ungauged component of the SEQ region lies mainly on the Moreton, which contains a large number of rivers, creeks and estuary, it is likely that this area will generate a large amount of runoff. Moreover, river allocation rules were not considered in estimating the flows and outflows within the region. Therefore, the uncertainty in the estimate could not be quantified.
Climate grid data
Precipitation and evaporation on/from surface water
Monthly precipitation grids for the region were produced using daily data from approximately 6,500 rain gauge stations in the country and interpolated to a 0.05 degree (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:
- 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 SEQ region included only the storages and not the rivers.
Runoff to surface water
Runoff to surface water was estimated based on the AWRA–L version 3.0 Van Dijk (2010) streamflow model outputs.
Using climate grid data for the SEQ 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 connected surface water store 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).
The total runoff to surface water in 2013–14 was 1,699,479 ML, which was only 24% of the runoff generated in the 2012–13 year. The reason behind this reduction in runoff was due to significantly lower rainfall (681 mm) in 2013-14. It was estimated that 57% of the runoff was stored in the storages in the region and the rest of the runoff entered to the rivers downstream of the storages.
The runoff estimates were subject to the assumptions of the AWRA–L model detailed in Van Dijk (2010). The uncertainty could not be unquantified.
Water resourcing licence database and meter readings
Water allocation remaining (or claims on water)
Announced allocations for the Lower Lockyer WSS's water year (1 April–30 March) were obtained from Seqwater. Metered quarterly use data were extracted from DNRM database 'Water Scheme Operator Report'. Any unused allocation remaining at the end of the water year (i.e. 31 March) was forfeited; and there was no carryover of allocation between water years. The allocation remaining at the end of the 2013–14 year (30 June 2014) was calculated by subtracting the first quarter use (1 April–30 June) from the announced allocation made on 1 April 2014.
It was assumed that all entitlement, allocation and diversion data within the Water Scheme Operator Report were accurate and current at the time of data extraction.
The allocation remaining at 30 June 2014 was calculated, as shown in Table 2.
| Account: Individual users | |
| Opening balance (at 1 July 2013) | |
| add | Water liability increase (allocation announcement) |
| less | Entitled abstraction of allocated water |
| less | Water liability decrease (forfeiture) |
| equals | Closing balance (at 30 June 2014) |
Adjustment and forfeiture of water allocation/claim on water
Allocation carryover from one water year to the next does not occur in the SEQ region. All unused allocation at the end of a water year is forfeited.
Entitled abstraction of allocated water to individual users
Supplemented allocation diversions were provided by Seqwater for each WRP area. The current resource operation plan reporting requirements do not allow for reporting by type of use. This volume was calculated by removing the urban diversions from the total supplemented allocation diversion. This represents the remaining high-priority holders and all medium-priority holder diversions.
Metered data were obtained from resource operations licence holder for licensed groundwater allocation extractions for the Central Lockyer WSS for the 2013–14 year.
It was assumed that all entitlement, allocation and extraction data within the water management system were correct and up to date at the time of data collection.
Diversions for the following rural-based WSSs were not necessarily solely for irrigation purposes, and may have included some supplemented allocation diversions for urban purposes:
- Central Lockyer WSS
- Lower Lockyer WSS
- Warrill Valley WSS
- Logan River WSS.
The data were derived from measured data and no uncertainty was quantified.
Water allocation announcements (or increase of claim on water)
The volume was calculated by multiplying the nominal allocation volume (equivalent to entitlements in the 2014 Account) stated in the resource operations plan (ROP) or interim resource operations licence (IROL) by the announced allocation percentage. Data were then sorted into water security type and WSS. Urban holders of supplementary licences were then removed individually from the data and included in the surface water allocation announcements for urban water system.
Interim water allocations are provided for the Central Lockyer, Warril Valley, and Lower Lockyer WSSs under IROLs dated July 2008, August 2009, and July 2008 respectively.
The announced allocation percentage varies between priority groups and between WSSs, and is announced on the first day of the water year by the resource operation licence holders. If an announced allocation percentage is initially below 100%, subsequent announcements may be made to increase the percentage. The percentage cannot be reduced during a water year and once the announced allocation percentage reaches 100%, no further increases to the limit can occur.
Urban holder entitlements were defined as high-priority group supplemented entitlements held by Seqwater or Toowoomba Regional Council. The volumes of entitlement were obtained from the Moreton, Logan Basin, and Gold Coast resource ROPs schedule of water allocations. Announced allocation of 100% was given for all urban utility's entitlements for the 2013–14 year, making the allocation announcements equal to the nominal entitlement volume.
Other organisations may hold supplemented entitlements for some form of urban use but, as urban use is not identified on entitlements, these could not readily be identified.
The uncertainty estimate was not quantified for allocation announcements.
More information on these allocations and the associated water access entitlement is given in the Water rights, entitlements, allocations and restrictions note.
Metered and estimated data provided by water authorities via UrbanSAT data collection spreadsheet and urban contextual information
Discharge from urban water system (to surface water)
The volume of discharge to surface water from urban water system 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 purposes
- return of excess water from the urban water system back to surface water / reservoirs for balancing.
The disposal of treated wastewater to rivers and streams that are estuarine in nature or subject to tidal impacts are not reported in this volume, but reported as discharge outside the region (to estuary/sea).
The uncertainty was not quantified.
Entitled abstraction of allocated water to urban water system
Diversion of allocated surface water volume refers to the surface water source that is managed through entitlements and allocations. For unregulated water source and/or sources not managed using entitlements and allocations, refer to 'Entitled diversion of non-allocated surface water'.
The calculation is based on metered raw water extraction from surface water and inflow to WTPs.
Raw water supplied directly as untreated (nonpotable water) is the metered extracted volume from the water source.
Where metered intakes to WTPs were not available, the intake volumes was estimated using metered outflow data and assumed that no water losses occurred during the treatment process.
This volume 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 derived from metered extracted volume from the water source.
The uncertainty estimate was not quantified.
Entitled abstraction of non–allocated surface water to urban water system
Entitled diversion of non-allocated surface water 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 'Entitled diversion of allocated surface water'.
The calculation is based on metered raw water extraction from surface water and inflow to WTPs.
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 and assumed that no water losses occurred during the treatment process.
North Stradbroke Island WTP 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 uncertainty estimate was not quantified.
Entitled abstraction of non–allocated groundwater to urban water system
Entitled diversion of non-allocated groundwater volume refers to the groundwater source 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 'Entitled diversion of allocated ground water'.
The calculation is based on metered raw water extraction from groundwater and inflow to WTPs.
Raw water supplied directly as untreated (nonpotable water) is the metered extracted volume from the water source.
Where metered intakes to WTPs were not available, the intake volumes were estimated using metered outflow data and assumed that no water losses occurred during the treatment process.
Groundwater treatment plants in Bribie Island and Stradbroke Island were not considered as they are located outside the SEQ region.
The uncertainty was estimated in the range +/– 20%.
Discharge from urban water system to groundwater
The ‘leakage to groundwater’ volume provided in this Account is assumed to be the non-revenue water resulting from background pipe leakage from the urban water supply system.
Non-revenue water is estimated using:
- difference based on a water balance between metered water sourced and supplied to customers, and/or
- modelling software of network real losses (leakages and bursts) 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 to be underestimated.
Estimated non-revenue water with combined pipe bursts and background leakage, are also included in the volume, which may overestimate the volume.
The uncertainty is estimated to be in the range of 20-40%.
Urban water supply system
The storage volume of the urban water supply system is comprised of two components: the distribution pipe network and the service reservoirs. The volumes of water in the pipes and tanks were obtained from Seqwater, QUU, Council of the City of Gold Coast, Logan City Council, Redland City Council, Unitywater and Toowoomba Regional Council.
Due to lack of availability of actual storage volumes on 30 June 2014, the entire capacity for each tank and water main for the utilities in the SEQ region was included for this volume; however, QUU incuded all the pipes it owns. The pipe volumes for the portion of Toowoomba Regional Council within the SEQ region was approximated using average pipe capacity.
Wastewater system
This is the estimated volume of wastewater (from tanks and open lagoon systems) that is stored in the region's wastewater system at the end of the reporting year.
Recycled water system
This is the estimated volume of recyled water (from tanks) that is stored in the region's recycled water system at the end of the reporting year. The data was supplied by the Council of the City of Gold Coast.
Wastewater collected
The volume of wastewater collected is estimated using the metered inflow to WWTPs and sewer mining plants (sewer mining involves taking water directly from a sewer -practically anywhere- and treating it onsite in preparation for an intended use) 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 WWTPs (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 were 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.
Unitywater estimated the volume of wastewater collected within the SEQ region boundary, which is a subset of Unitywater's total operational area. The volume estimate is based on a pro-rata adjustment of the total wastewater by the customer connections located inside and outside the SEQ region boundary. The difference between this volume and the metered inflow to WWTPs located within the region is the volume of wastewater exported by Unitywater outside the SEQ region boundary (but still within Unitywater’s operations). This is referred to 'Transfer of water outside of region'.
The uncertainty estimate was not quantified.
Delivery of water from outside region to urban water system
Delivery of water from outside the region consists of all potable, nonpotable, wastewater and recycled water transferred from outside into the SEQ region. The volumes are based on metered information in the distribution infrastructure.
Some of the WTPs located outside theSEQ boundary may supply into SEQ region via the SEQ water grid. The volume imported is derived from meters available at the outflow point at the treatment plants as well as meters located within the water grid or within local reticulation networks.
North Stradbroke Island is located outside the SEQ region. It is assumed that the entire volume of water produced at North Stradbroke Island WTP is imported into the SEQ region via the Eastern Pipeline Interconnector and that none of this volume is used on the island .The imported volume is likely to be overestimated due to this assumption.
Metered 2013–14 data was used to derive the net volume of water imported into the SEQ via the Northern Pipeline Interconnector.
The uncertainty estimate was not quantified.
Delivery of desalinated water to urban water system
Delivery of desalinated water volume is based on metered desalinated water outflow from the WTP.
The meter manufacturer (Promag) estimates an uncertainty of measurement of 0.26 to 0.37%.
Evaporation from urban water system
The reported volumes of evaporation from the SEQ urban water system are based on:
- calculation using the Bureau's climate data
- calculation using water balance approach through available inflow and outflow metering data and/or
- metered volume of treated wastewater discharged to evaporation lagoons.
Losses through evaporation were reported in the wastewater system but not in the urban water supply system.
The uncertainty estimate was not quantified.
Delivery to urban water system users
The volume delivered to urban water system users represents the delivery of water to end users for urban consumption and includes potable, nonpotable and recycled water.
Volumes are based on customer meters, billing meters, on site re-use water meters, and estimated non-revenue water volumes. It excludes recycled water use that is re-circulated within the wastewater treatment process.
Urban consumption consists of residential, commercial, industrial, municipal, on site WTP and WWTP use use and small-scale agricultural irrigation.
For information on non-urban consumption, refer to 'Discharge from urban water system to surface water, for environmental flows'.
The volumes include advanced treated water supplied for use within the SEQ region.
Unitywater estimated the volume of water consumption within the SEQ region, which is a subset of its Unitywater's operational area. The volume estimate is based on a pro-rata adjustment of the total water use by the customer connections located inside and outside the SEQ region.
Three WTPs operated by Redland City Council (Amity, Dunwich and Pt Look Out WTP) are located outside the SEQ region; therefore, their volumes of treated water were excluded from reported volume.
Water treated by the North Stradbroke Island WTP is assumed to be entirely imported into the region and is therefore included in the reported volume.
For simplification, urban consumption relating to QUU, Council of the City of Gold Coast and Logan City Council were reported fully even though there are small areas of their operations located outside of the SEQ region.
The uncertainty was not quantified.
Wastewater discharge outside of region
Wastewater discharge out of region volume represents disposals from the wastewater system and recycled water system to the sea and estuaries (inlets and portions of rivers and streams with tidal impacts), which are considered outside of the region boundary. The volume is based on metered data.
Some disposals to Brisbane River and its tributaries are considered discharge to estuary/sea as they are estuarine through much of the Brisbane area and therefore classified as discharge outside of the region.
The AWTPs within the SEQ region also discharge reverse osmosis concentrate and excess purified recycled water to sea.
Where metered disposal data is not available, the volume is estimated based on the difference between metered inflow to a WTP and metered volume of recycled water used.
The uncertainty was not quantified.
Other wastewater discharge
Other wastewater discharge volumes consist of metered treated wastewater discharged to landscape and/or infiltration ponds, where the primary purpose is disposal of the effluent rather than using the effluent for irrigation purposes. Refer to 'Delivery to urban water users' for the volume of recycled water used for agricultural or irrigation purposes.
Also included in this volume (Other wastewater discharge) is any other managed treated wastewater discharges not reported in:
- discharge to surface water
- discharge out of region.
Where metered disposal data is not available, the volume is estimated based on the difference between metered inflow to a WTP and metered volume of recycled water used.
This volume may include discharges to landscape that make their way into the groundwater.
The uncertainty estimate was not quantified.
Transfer of water outside of region
Transfer of water outside of region consists of all potable, nonpotable, wastewater and recycled water transferred outside of the SEQ region. The volumes are based on metered information in the distribution infrastructure. For the SEQ region, this also includes advanced treated water.
Wastewater exported by Unitywater is estimated by pro-rata adjustment of the total metered inflow to all its WWTPs based on the number of customer connections within the SEQ region, minus the metered inflow to WWTPs located within the region boundary.
Unitywater customer connections located inside and outside of the SEQ region is approximated based on GIS scan of the water infrasturctures.
The uncertainty estimate was not quantified.
Other urban water system decreases
Other urban water decreases volume represents the sum of the following three components:
- remaining non-revenue water from the urban water supply system (if not reported in 'Leakage to landscape' and 'Leakage to groundwater', respectively)
- losses from wastewater treatment system (if not reported in 'Evaporation from urban water system')
- known egress or exfiltration from the wastewater collection system occurring before metered inflow to WWTPs.
Non-revenue water was estimated using:
- difference based on a water balance between metered water sourced and supplied to customers, and/or
- 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 bursts) and apparent losses (unauthorised/authorised unbilled use), and/or
- time to repair leaks, and/or
- difference between inlet meter and outlet meter of WWTPs for treatment losses.
Losses from wastewater system are estimated based on metered data between inflow and outflow/disposal/customer meters, or estimated based on observations.
Ingress to stormwater or exfiltration to groundwater is 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.
No nonpotable water losses were reported and likely an underestimate of the losses in the system.
The uncertainty estimate was not quantified.
Urban water system leakage to groundwater
The leakage to groundwater volume is assumed to be the non-revenue water associated with real losses, specifically that resulting from background pipe leakage from the urban water supply system.
Where there are available volumes associated with only pipe burst, this is reported in 'Leakage to landscape'.
Non-revenue water is estimated using:
- difference based on a water balance between metered water sourced and supplied to customers, and/or
- modelling software of network real losses (leakages and bursts) and apparent losses (unauthorised/authorise unbilled use)
- time to repair leaks.
Leakage in the wastewater system is not reported and therefore the total leakage to groundwater is likely to be underestimated.
Where non-revenue water losses are reported as combined volume for pipe bursts and background leakage, these are also reported in this volume. In that case, it may overestimate the volume.
The uncertainty is estimated in the range +/- 30%.
Operational Data Storage System: seepage data
Surface water leakage to landscape
Storage loss is the loss that occurs in the WSS storages. Where storage loss was not specifically evaluated as part of ROP reporting requirements, the storage loss allowance detailed in the ROPs 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 ROP tables. The Moreton and Logan Basin ROPs 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 ROP loss (provided by DNRM) to calculate the adjusted storage loss for the volume. This is to prevent double counting because ROP loss includes net evaporative loss as estimated by DNRM. If the resulting value was less than zero, no value was considered for the storage.
The volumes are from application of the ROP calculation and therefore include evaporation losses. No adjustment was made to the calculation.
It has been assumed that the water management system database data were current, accurate and correct.
The Moreton and Logan Basin ROPs list loss factors to apply when estimating losses from storages where the storages are part of the WSS. Where the storages are not part of a WSS, losses were not available and could not be quantified accurately.
Losses from the storages that form part of a WSS 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 WRP areas
- storage losses were not reported in the Gold Coast WRP area.
Derived from storage loss estimates. DNRM reliability and accuracy rating is B4 (Queensland Government Department of Environment and Resource Management 2011).
Groundwater information and allocation
Water table aquifer
The entitled maximum volume extractable from the benefitted area of the Central Lockyer WSS was provided by DNRM. Detailed groundwater modelling of the benefitted area of the Central Lockyer aquifer has been undertaken by DNRM to determine the sustainable volumetric limit for extractions.
This volume is applicable to the Implementation Area 1 of the Central Lockyer GMA.
There was no uncertainty associated with the provided volume. The maximum entitled volumetric limit of medium priority interim water allocation that can be extracted from Implementation Area 1 of the benefitted area of groundwater in the Central Lockyer Valley WSS was confirmed.
Entitled extraction of non-allocated groundwater to users
Licensed extraction data were compiled for the Cressbrook Creek Alluvial GMA. Metered extraction data from the Central Lockyer WSS non–benefitted Area for the 2013–14 year were available.
The licensed metered extraction data have been underestimated due to the lack of data for three of the four GMAs. In future years, licensed metered extraction data may become available for other GMAs.
The uncertainty estimate was not quantified.