National Water Account 2016

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Key findings

Climate and water

Water Accounting Statements

Supporting information

Region description

Reference information

South East Queensland: Methods

Summary of methods

Table N4 outlines the methods 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.

Table N4  Methods used to derive item volumes

Detail of methods

Water storage product data

Storages

Storage volume at the start and end of the year was 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 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.

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.

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 provisions 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, entitlements, allocations and restrictions note.

Stream monitoring data

Outflow

Outflow to sea was based on a combination of observed streamflow data and runoff estimates from the AWRA-L version 5.0 model outputs.

First, the total river outflow was estimated using flow data collected at the most downstream gauging stations nearest to the outlet to the sea (see Figure N1). These data were used to determine the total annual discharge (in ML) at each station during the year.

Figure N1 Gauging stations used to calculate total outflow to sea

The catchment area upstream of these gauging stations is approximately 75% of the South East Queensland region area (Figure N2). The AWRA–L version 5.0 model was used to estimate the outflow from the contributing area below the gauging stations (approximately 25% of the region area).

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

The average runoff 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 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 modelled region (excluding storages).

The approach was subject to the assumptions of the AWRA-L model detailed in Viney et al. 2015.

Figure N2 Gauging stations used to calculate runoff

Based on a water balance equation (that integrates diversion to water treatment plants, treated wastewater discharge to sea and surface water, evaporation from and precipitation on storages in the ungauged area), total outflow from the contributing area below the gauging stations was derived. The volume of flow in the 'ungauged' portion of the region was added to the total annual streamflow in the gauged portion upstream of the gauging stations to estimate a total outflow to sea volume.

Gridded climate data

Precipitation and evaporation

Monthly precipitation grids for the region were produced using daily data from approximately 6,500 rain gauge stations across the country and interpolated to a 0.05 degree (5 km) national grid (Jones et al. 2009). The precipitation 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 the surface area of each waterbody by the weighted average precipitation. The average monthly surface area of the storages was calculated from daily storage levels and capacity tables.

Evaporation from water bodies was calculated on a daily basis using the Morton's shallow lake formulation (Morton 1983a, 1983b, 1986). For annual evaporation estimate, there is no difference between shallow and deep lake evaporation (Sacks et al. 1994). The climate data required for the Morton's method are maximum temperature, minimum temperature, vapour pressure and solar radiation. The climate data for each waterbody (i.e. storages) was estimated from the proportionally weighted average of grid cells that intersected each water feature and input to the Morton's program to obtain the evaporation values. The volume was then estimated by multiplying the surface area of each waterbody by the evaporation values.

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 South East Queensland region included only the reservoirs and urban lakes. River channels were not included.

Runoff

Runoff to surface water was estimated based on the AWRA–L version 5.0 (Viney et al. 2015) streamflow model outputs.

Using climate grid data for the South East Queensland region (including precipitation, temperature and solar radiation data), AWRA–L model was used to estimate the runoff depth at each grid cell 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 cells within the region boundary. Cells 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 approach was subject to the assumptions of the AWRA–L model detailed in 5.0 Viney et al. (2015).

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 uncertainty estimate was +/– 20%.

Discharge: user

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 2015–16 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 uncertainty estimate 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 uncertainty estimate 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 uncertainty estimate was +/– 20%.

Delivery: desalinated water

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

The uncertainty estimate 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 uncertainty estimate 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 uncertainty estimate 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 (water and wastewater treatment plant) 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 uncertainty estimate 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 uncertainty estimate 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 uncertainty estimate 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 and Mines 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 2015–16.

The Department of Natural Resources and Mines reliability and accuracy rating is B2 (Department of Environment and Resource Management 2011).

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 plan 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 plan tables. The Moreton and Logan Basin resource operating plans 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 plan loss (provided by the Department of Natural Resources and Mines) to calculate the adjusted storage loss for the volume. This is to prevent double counting because the resource operating plan 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 plan calculation and therefore include evaporation losses. No adjustment was made to the calculation.

The Moreton and Logan Basin resource operating plans 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 resource plan areas
• storage losses were not reported in the Gold Coast Water Resource Plan area.

The Department of Natural Resources and Mines reliability and accuracy rating is B4 (Queensland Government Department of Environment and Resource Management 2011).

Water resourcing licence database and meter readings

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 uncertainty estimate 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 uncertainty estimate 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 resource plan area. The current resource operations plan 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.

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 uncertainty estimate 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 uncertainty estimate 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.