Canberra
Quantification approaches
Table 1 outlines the quantification approaches used to derive the line item volumes for the Canberra region. For a more detailed description of the quantification approach, click on the relevant item name in the table.
Detail of quantification approaches
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. Rating 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 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, which in turn affects 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 2014.
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.
Service reservoir data
Urban water supply system
The volume in the service reservoirs was reported as the volume on 1 July 2014. The volume in the pipe network was calculated based on the pipe lengths and nominal internal pipe diameters as recorded in the Geographic Information System (GIS) database. This includes both nonpotable and potable water pipes. It was assumed that all the pipes were full on 30 June 2014. The uncertainty range for these volumes is +/–10%.
Asset database
Recycled water system
The volume in pipes is calculated using ACTEW Water's Esri GIS asset database, and assumes all pipes in the network are full. Two storage tanks are used for recycled water, the LMWQCC nonpotable water tank and the Lower Russell tank. These are assumed to have a combined storage of approximately 1 ML to give a total system storage of 2 ML (rounded to nearest ML).
Stream monitoring data
River inflow to region / River outflow from the region
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 at Angle Crossing (station 41001702) along the Murrumbidgee River located close to the ACT border (Figure 1).
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 Halls Crossing (station 410777) along the Murrumbidgee River (Figure 1).
Figure 1 Gauging stations used to calculate flows to and from the region
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 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 both Angle Crossing 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.
Climate grid data
Precipitation on and evaporation from surface water
Monthly precipitation grids for the region were produced using daily data from approximately 6,500 rain gauge stations and interpolated to a 0.05 degrees (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 were 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 major storages was calculated from daily storage levels and capacity tables. In the Canberra region, the surface area of the four storages was calculated dynamically and the surface area of the three urban lakes was a static value produced from the Australian Hydrological Geospatial Fabric (AHGF).
The limitations associated with this approach are:
- The precipitation and AWRA-L potential evaporation estimates were subject to approximations associated with interpolating the observation point data to a national grid as detailed in Jones et al. (2007).
- The dynamic storage surface areas calculated from the levels and storage rating tables represent a monthly average and therefore will not capture changes that occur on a shorter temporal scale.
- The use of the static default AHGF surface area is an approximation only. It represents the lakes at capacity and therefore likely results in an over-estimation of precipitation and evaporation on the lakes.
- The total surface area of the surface water store within the Canberra region included only the reservoirs and urban lakes. River channels were not included.
Runoff to surface water
Runoff to surface water in the Canberra region was based on streamflow estimates from the AWRA-L model outputs. Using climate grid data for the Canberra 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 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 off–channel water storages; and remaining runoff in the region. Only runoff into the surface water store excluding runoff into off–channel water storages was considered in this line item.
The runoff from the catchment contributing to major storages and the remaining runoff within the region were separately calculated.
Figure 2 Runoff model 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 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 limitations associated with this approach are:
- The runoff estimates were subject to the assumptions of the AWRA-L model detailed by Van Dijk (2010).
- The estimated runoff corresponds to the runoff expected from an unimpaired catchment. The impairment on runoff from off–channel water storages was estimated using an off–channel water storage 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 for total grid point area.
Water Sharing Plan for the Murrumbidgee Unregulated and Alluvial Water Sources
Surface water and groundwater allocation announcements / abstractions / adjustment and forfeitures
The surface water and groundwater allocation remaining corresponds to the volume of water allocation that can be carried over between water years. The Water Sharing Plan for the Murrumbidgee Unregulated and Alluvial Water Sources 2012 details the rules for access licences with share components. According to these rules, carry-over of unused allocation is allowed. While carry-over of unused surface water allocation is allowed for access licence holders, due to limited data availability the carry-over volume could not be quantified. Therefore, for the purposes of the National Water Account, the closing balance for the water allocation remaining is zero.
The water allocation remaining at 30 June 2014 is calculated as shown in Table 2.
| Account | |
| Opening balance (at 1 July 2013) | |
| add | Water liability increase (allocation announcement) |
| less | Entitled abstraction of allocated water |
| less | Water liability decrease (forfeiture) |
| Closing balance (at 30 June 2014) |
Water resource information database
Surface water allocation announcements / adjustment and forfeiture: urban water system
Water access entitlement (WAE) volumes were obtained from the ACT water resource information database. The total annual announced allocation for 2013–14 year is considered to be as 100% of the ACTEW Water urban water licence volume. Any volume of water allocated under urban water licence that has not been diverted is considered as forfeited. There is no distinction between regulated and unregulated flows in ACTEW's urban WAE. Water to service this licence was obtained from both regulated and unregulated sources.
Entitled diversion non-allocated surface water to users
Entitled diversion of non allocated surface water includes diversions of unregulated flows under multi-use licences for nonpotable water within the ACT. It includes licensed abstractions within urban area for unspecified purposes and licensed abstractions for all purposes outside of 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.
Entitled extraction of non-allocated groundwater to users
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 is 100% of entitlement or they may estimate the use. 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.
Metered and estimated data via UrbanSAT- Data request spreadsheet and UrbanSAT Notes document
Entitled diversion of allocated surface water to urban water system
This comprises the metered volumes from ACTEW water diverted from each surface water sources:
- Googong Reservoir
- Bendora Reservoir
- Cotter Reservoir
- Murrumbidgee River.
This volume excludes water returned/discharged back to Googong Reservoir from Bendora Reservoir, Cotter Reservoir and/or Murrumbidgee River to take advantage of the storage capacity in the Googong Reservoir. This volume is instead reported as the entitled diversion of non-allocated surface water to urban water system. The uncertainty range for these volumes is +/–5%.
Entitled diversion of non-allocated surface water to urban water system
This refers the diversions from surface water that are not counted against ACTEW Water's entitlement. To take advantage of storage capacity, ACTEW Water can transfer water from the Murrumbidgee River to the Googong Reservoir. It is the metered volume from ACTEW Water released from the urban water supply system and discharged back to the Googong Reservoir. The uncertainty range for these volumes is +/–5%.
Wastewater collected
Metered volumes from ACTEW Water and QCC of water inflow to each waste treatment plant:
- Fyshwick Sewage Treatment Plant (STP)
- Lower Molonglo Water Quality Control Centre (LMWQCC)
- Outward Bound STP
- Uriarra STP
- Queanbeyan STP
From the above total, volume returned from Fyshwick STP to LMWQCC for further treatment was subtracted.
For the 2013–14 year, ACTEW Water estimated that the metered wastewater volume at LMWQCC included 1,729 ML of net ingress of stormwater (and groundwater) to the sewer system. This volume is calculated by comparing calculated annual dry weather inflow to measured annual inflows, with the difference assumed to be ingress to the sewer system (Table 3). The dry weather inflow volume is calculated by multiplying the volume of inflows to LMWQCC during a dry week by 365/7 to give an annual volume. The dry week used this year was 7–13 September 2014, when the inflow volume was 582 ML. Therefore, the dry weather inflow would be 30,326 ML.
| Description | Volume (ML) |
| Total inflows into LMWQCC | 32,055 |
| Base-flow inflows over year | (30,326) |
| Total | 1,729 |
The following assumptions were made:
- The estimation of volume of stormwater ingress is based on the assumption that in the dry reference week there is no net gain or loss of stormwater and/or groundwater into or out of the sewer system.
- Stormwater ingress was estimated only for the inflow to the LMWQCC as the data for other STPs were not available.
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%.
Delivery to urban water system users
The volume of water delivered to urban water system users by ACTEW Water and QCC is derived from:
- customer meters based on charge code for residential, commercial, industry, municipal, agricultural/irrigation use
- local meters for other use
- on site meters for on site use
The associated limitations associated include the the potential for errors in the measured data used to derive volumes. For example, where an incorrect charge code has been applied to some meters.
Uncertainty information:
- Potable water: The uncertainty estimated is +/– 10%.
- Recycled water: The uncertainty estimated is +/– 5%.
Discharge from urban water system to surface water
The total volume of water discharged from the urban water system to surface water within the Canberra region is comprised of two components:
- discharge to surface water from the urban water supply system
- discharge to surface water from the wastewater system.
They are metered volumes from ACTEW Water and QCC. The uncertainty range for these volumes is +/–10%.
Evaporation from urban water system
In Canberra region, evaporation from urban water system refers to the volume of water loss through evaporation at the STPs. ACTEW Water and QCC consider major water loss at the STPs as the loss through evaporation and calculates this volume as the difference between the known inflows and outflows to STPs and subtract the recycled water produced/supplied for use.
Urban water system leakage to groundwater / other urban water system decreases
The leakage to groundwater includes pipe bursts and background leakage from pipes, service reservoirs, and service connections prior to the delivery to customers in the Canberra region. The remaining losses (other non-revenue water) is taken as other urban water system decreases.
The losses from the urban water supply network is the difference between the system input volume and the total of the billed water exported (supplied to Queanbeyan), billed metered consumption, billed unmetered consumption, unbilled metered consumption, unbilled unmetered consumption, unauthorised consumption, and customer meter under-registration.
QCC calculates the total volume of losses as the combined volume of non-revenue water (pipe bursts, leakage and other losses) from the Queanbeyan potable water supply system. This is calculated by using the difference between what QCC purchases from ACTEW and what QCC sells to its customers.
The associated limitations are:
Losses from the water supply network cannot be distinguished from the background leakage and losses due to pipe bursts, and therefore a combined estimate is provided.
This combined volume of losses is presented as leakage to groundwater since leakage to landscape cannot be quantified.
Climate grid data and waterbodies spatial dataset
Off-channel water storages / Precipitation on, evaporation from, runoff into, and water abstraction from off-channel water storages
The Canberra region was divided up into five subregions for the purpose of estimating the water balance of the off-channel water store. Four of the subregions were the catchments of the major storages and the fifth was the remaining land.
The private store consisted of off-channel storages filled primarily by rainfall-runoff. These were determined from waterbody mapping provided by Geoscience Australia and were waterbodies that were greater than 50 m from built-up areas in the Canberra region. The catchment of each individual storage was determined via analysis of the 9 arc-second digital elevation model (DEM).
A water-balance based farm dam algorithm written by the Bureau of Meteorology was used to determine the volume of water stored in off-channel water storages. The code was provided inputs in the form of climate from gridded climate datasets, runoff from the Australian Water Resources Assessment system Landscape model AWRA-L model version 3.0 (Van Dijk 2010) and dam details derived from spatial data.
Monthly precipitation data were produced by the Bureau. They were based on daily data from approximately 6,500 rain gauge stations and interpolated to a 0.05 degree (approximately 5 km) national grid (Jones et al. 2007). The average precipitation depth across the Canberra subregions was determined as the weighted mean of precipitation occurring from the relevant grid points within the region boundary. Points were weighted upon the area they represented within the Canberra landscape 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. The average precipitation depth was used as an input into the farm dam algorithmthe and converted the depth of precipitation to a volume using the surface area of off-channel water stores within a region.
Using climate grid data for the Canberra region (including precipitation, temperature and solar radiation data), AWRA-L version 3.0 (Van Dijk 2010) was used to estimate the runoff depth at each grid point within the region. The average runoff depth was converted to a volume by multiplying depth by the total area and was used as an input into the farm dam algorithm.
The potential evaporation estimate produced by the AWRA-L version 3.0 (Van Dijk 2010) was used to calculate evaporation from the private water store. The AWRA-L model uses a modified version of the Penman-Monteith method to produce the potential evaporation. The potential average evaporation depth across the Canberra subregions was determined as the weighted mean of potential evaporation occurring from the relevant grid points within the region boundary. The farm dam algorithm was used to determine the amount of water available for evaporation from individual private storages. It determines the water stored in each off-channel water store at each time point and determines the volumetric potential evaporation by multiplying potential evaporation by reservoir surface area. It assumes that actual evaporation will occur at the same rate as potential evaporation unless the reservoir empties, at which time evaporation will cease.
The farm dam algorithm determines the water stored in each off-channel water store at each time point and the volume of water abstracted from the private water store. It assumes that water will be abstracted from the off-channel water store at the rate required unless off-channel water store empties, at which time, abstraction will cease.
The associated limitations are:
- The gridded climate input data are subject to approximations associated with interpolating observation point data to a national grid detailed in Jones et al. (2007).
- The spatial extent of waterbodies is subject to the assumptions and methods associated with the data provided by Geoscience Australia.
- The use of a 9 arc-second DEM to determine catchment area may result in off-channel water stores being assigned a catchment much larger or smaller than the true catchment. In some cases an off-channel water store may be assigned the catchment of a stream line hundreds of metres away.
- The estimated volume available in storage for evaporation is subject to the assumptions associated with the farm dam algorithm and the parameters used.