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National Water Account 2017

Canberra: Methods

Lake Burley Griffin, Canberra. Photograph: © Perry Wiles

Summary of methods

Table N3 outlines the methods used to derive the item volumes for the Canberra region. For a more detailed description of a method, click on the relevant item name in the table.

 

Table N3  Methods used to derive item volumes

Assets
Approach or data usedItemSource
Water storage product dataStoragesBureau of Meteorology and Icon Water
Water storage product dataLakes and wetlandsNational Capital Authority and Environment, Planning and Sustainable Development Directorate
AWRA-R modelRiversBureau of Meteorology
Not quantiifed
  • Water table aquifer
  • Underlying aquifers
 

 

Liabilities
Approach or data usedItemSource
Water Sharing Plan for the Murrumbidgee Unregulated and Alluvial Water SourcesDepartment of Industry, Lands and Water
Water resource information database Environment, Planning and Sustainable Development Directorate 

 

Inflows and outflows
Approach or data usedItemSource
Stream monitoring data Icon Water
Gridded climate data and AWRA-L modelBureau of Meteorology
AWRA-R modelBureau of Meteorology
Metered and estimated data provided by water authoritiesIcon Water and Queanbeyan–Palerang Regional Council
Not quantified
  • River and floodplain losses
  • Groundwater discharge
  • Groundwater inter-region inflow
  • Groundwater inter-region outflow
  • Recharge: landscape
 

 

Abstractions
Approach or data usedItemSource
Water resource information databaseEnvironment, Planning and Sustainable Development Directorate
Metered and estimated data provided by water authoritiesIcon Water and Queanbeyan–Palerang Regional Council
Not quantified
  • Allocated abstraction: individual users
  • Surface water: other statutory rights
 

 

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 Surface water note. The uncertainty range for these volumes 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.

Lakes and wetlands

The volume of water in lakes and wetlands is based on both measured and estimated data. The volume of water in Lake Burley Griffin at the start and end of the year was calculated using water level data (metres above Australian Height Datum) collected at the lake. Rating tables established for the lake were used to convert the height measurement to a volume.

The volume of water in Lake Ginninderra and Lake Tuggeranong was estimated based on the known capacity of the lakes, that is, the lakes were assumed to be full at 30 June 2017.

The assumptions made were as follows:

  • Water levels in Lake Ginninderra and Lake Tuggeranong are generally managed within 200 mm of full supply level throughout the year. Therefore, the estimated storage volumes of these lakes are considered to be only slightly overestimated.
  • At present, abstraction from Lake Ginninderra and Lake Tuggeranong is limited to volumes that would have negligible effect on the volume of the lakes (<50 ML).
  • The capacity of Lake Burley Griffin is based on survey data collected at the time of construction and fill in 1964.

 

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)
Figure N1 Conceptual diagram of AWRA-R reach showing model components (from Dutta et al. 2015)

 

For further detail on the AWRA-R model, its assumptions and its calibration refer to Dutta et al. (2015; 2017).

 

Rivers

The volume of water in the river channels at 30 June was estimated by using the daily water balance approach within AWRA-R. The water balance includes inflow at the upstream nodes and outflow at the downstream nodes; contributing catchment runoff, reservoir contribution, irrigation diversion and return; overbank flooding and floodplain return; loss to groundwater; anabranch flow; rainfall; and evaporation.

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 for rivers were carried out on a daily time step using the AWRA-R model. Calculations for storages were done on a monthly time step. Annual totals were summed from the daily or monthly 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 monthly surface area of the storages was calculated from daily storage levels and capacity tables.

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).

 

Gridded climate data and AWRA-L model

Runoff

Runoff to surface water in the Canberra region was based on streamflow estimates from the AWRA-L version 5.0 model outputs (see the Australian Landscape Water Balance model website).

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

Runoff from the landscape is divided into three components: runoff into the major storages; runoff into farm dams; and remaining runoff in the region. Runoff into farm dams was not considered in this item.

The runoff from the catchment contributing to major storages and the remaining runoff within the region were separately calculated.

 

Figure N2Runoff area to storages and modelled area within the Canberra region
Figure N2 Runoff area to storages and modelled area within the Canberra region

 

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. 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 limitations associated with this approach are:

  • The runoff estimates were subject to the assumptions of the AWRA-L version 5.0 model detailed by Viney et al. (2015).
  • The estimated runoff corresponds to the runoff expected from an unimpaired catchment. The impairment on runoff from farm dams was estimated using a farm dam water balance model (farm dam algorithm written by the Bureau of Meteorology). Where this was applied, the runoff estimates inherited the approximations, assumptions, caveats, and the parameters used in the farm dam water balance model.

 

Water Sharing Plan for the Murrumbidgee Unregulated and Alluvial Water Sources

Allocation: individual users

The Water Sharing Plan for the Murrumbidgee Unregulated and Alluvial Water Sources 2012 details the rules for surface water and groundwater allocations for access licences with share components.

Allocation remaining

The remaining surface water and groundwater allocation corresponds to the volume of water allocation that can be carried over between water years. The water allocation remaining at 30 June 2017 is calculated as shown in Table N4.

 

Table N4 Calculation of water allocation remaining
 Account
 Opening balance at 1 July 2016
addAllocation
lessAllocated abstraction
lessAdjustment and forfeiture
equalsClosing balance at 30 June 2017

 

Adjustment and forfeitures: individual users

Carry-over of unused allocation is allowed in Water Sharing Plan for the Murrumbidgee Unregulated and Alluvial Water Sources 2012. While carryover of unused surface water allocation is allowed for access licence holders, due to limited data availability the carryover volume could not be quantified. Therefore, for the purposes of the National Water Account, the closing balance of remaining allocation is zero.

 

Water resource information database

Allocation: urban system

Water access entitlement volumes were obtained from the ACT water resource information database. The total annual announced allocation for the 2016–17 year was considered to be 100% of the urban water licence entitlement volume for Icon Water and Queanbeyan–Palerang Regional Council. There is no distinction between regulated and unregulated flows in the urban water access entitlement. Water to service this licence was diverted from both regulated and unregulated sources.

Adjustment and forfeiture: urban system

Allocated water that had not been diverted was considered as forfeited.

Non-allocated diversion: individual users

Surface water non-allocated diversion includes diversions of unregulated flows under multi-use licences for nonpotable water within the ACT. It includes licensed diversions within urban area for unspecified purposes and licensed diversions for all purposes outside the urban area.

Individual licensees submit monthly meter readings to the ACT Environment Protection Authority (EPA) on an annual basis. Where a licensee has not provided meter data, the EPA estimates usage based on historical usage data. The uncertainty range for these volumes is +/–5%. Uncertainty can not be quantified for estimated usage where meters were not read.

Non-allocated extraction: individual users

For non-allocated groundwater extraction in the ACT, individual licensees submit meter readings for each month to the ACT EPA once per year. Where a licensee has not provided meter data, the EPA may assume use as 100% of entitlement or it may estimate the usage based on historical usage data. The uncertainty range for these metered volumes is +/–5%. Uncertainty can not be quantified for estimated usage where meters were not read.

 

Stream monitoring data

Inter-region: inflow / outflow

The river inflow to the region represents the volume of surface water that flows into the Canberra region from the upstream Murrumbidgee River. The volume is recorded as the sum of flows at Murrumbidgee River upstream of Michelago Creek (gauging station 41000272) and Micaligo at Michelago Creek, both located close to the ACT border (Figure N3).

The river outflow from the region represents the volume of water that flows out of the Canberra region from the Murrumbidgee River. The volume is recorded at Murrumbidgee River at Hall's Crossing (gauging station 410777) (Figure N3).

Water level in the river was monitored at these sites and converted to a flow volume using a rating table. The daily flows from these sites during the reporting year were used to calculate the annual streamflow.

The limitations associated with this approach are:

  • The level of uncertainty of these gauging stations is estimated at +/– 20 % during low to medium flows and the uncertainty during high flows is ungraded. This is based on four manual physical flow gaugings performed per year. At these sites the water surface level is measured constantly by on-site equipment. This water level is used to estimate a flow rate, based on a rating curve produced by physical flow gauging in as many flow conditions as possible.
  • As Murrumbidgee, Micaligo and Halls Crossing sites are located not far away from the Canberra region boundary it was assumed that minimal runoff was generated between the catchment boundary and the monitoring site.
  • There is some uncertainty in the flow rates. The river flows have not been gauged under all flow conditions, and the river channel can change from time to time due to deposition and movement of river sediments. It impacts the cross-sectional area of the channel and changes the velocity of the water.

 

Figure N3 River network used in AWRA-R model for the Canberra region
Figure N3 Gauging stations used to calculate river flows  to and from the region

 

Metered and estimated data provided by water authorities

Allocated diversion: urban system

The allocated diversion: surface water volume is calculated from the volume of surface water diverted (metered at the source). The uncertainty range for these volumes is +/–5%.

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

Non-allocated diversion: urban system

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.

This is the metered volume of potable water discharged from the urban water supply system to Googong Reservoir, to take advantage of storage capacity. This volume is not counted as part of the volume diverted under Icon Water’s entitlement. The estimated uncertainty range for these volumes is +/–5%.

Wastewater collected

The volume of wastewater collected 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 to avoid double counting

The assumptions made were as follows:

  • Given wastewater volumes were typically measured at the treatment plants (and not at customer connections), the collected wastewater volumes included any variation due to (a) ingress of stormwater; (b) infiltration of groundwater; and (c) unreported wastewater overflows to stormwater. 
  • Where inflow meter readings were not available, outflow meter readings were used, which could underestimate the volume as they assumed no losses during wastewater treatment.
  • The volume of wastewater collected does not include wastewater for individual or community wastewater management systems.

Uncertainty information:

  • The uncertainty of the volume of wastewater collected is estimated to be of the order of +/–20%.
  • The uncertainty in the estimated volume of storm water and / or groundwater ingress is in the order of +/- 50%.

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:

  • 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 range for these volumes is +/–10%.

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 surface water / reservoirs. The estimated uncertainty range for these volumes is +/–10%.

Wastewater and recycled water discharge: surface water

The volume of wastewater and recycled water discharged to surface water volume is metered and includes:

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

The estimated uncertainty range for these volumes is +/–10%.

Leakage: groundwater

The real losses component of non-revenue water reported as leakage: groundwater is based on both avoidable and unavoidable losses (including pipe network background leaks, pipe leaks and bursts, tank and service reservoir leakage, and overflows) and is calculated using the following equation:

Real losses = Non-revenue water – (Apparent losses + Unmetered authorised consumption).

The volume of apparent losses comprises two components: unauthorised consumption (e.g., water theft); and customer meter under-registration (e.g., meter inaccuracies).

The following assumptions were made:

  • 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.

The uncertainty estimate was not quantified for this volume.

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 as discharge to surface water.

Information on discharge of treated wastewater to landscape was received from Icon Water regarding Outward Bound Sewage Treatment Plant.

The volume provided in the 2017 Account has been estimated and the uncertainty estimate was not quantified.

Other supply system decreases

The 'Other supply system decreases' volume was assumed to be the non-revenue water associated with apparent losses, and the remaining non-revenue water from the urban water supply system (if not reported in 'Leakage: groundwater' ).

The non-revenue volume was calculated based on physical observations of bursts events. Real losses reported related to pipe leakage is reported in Leakage: groundwater.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 was 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 following assumptions were made:

  • Non-potable water losses were not reported and losses in the system were likely to be underestimated.

The uncertainty estimate was +/–20% for the provided volume.

Recycled water delivery: urban users

The recycled water delivery: urban users is derived from:

  • customer meters
  • 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, and small scale agriculture/irrigation uses.

The estimated uncertainty range for these volumes is +/–5%.

Other wastewater and recycled water system decreases

The volume reported in the 2017 Account represents the sum of the following components:

  • losses from wastewater treatment system
  • known losses from the wastewater collection system
  • known losses during management of treated wastewater.

The losses from the wastewater system were estimated based on metered data, or estimated based on observations. Wastewater overflows or spills were estimated based on observation or monitoring of the sewer network. This may have occurred at emergency relief systems built into the network or uncontrolled points at manholes and network leaks.

The uncertainty for the provided volume was not quantified.