Murray–Darling Basin
Quantification approaches
Summary of quantification approaches
Table 1 outlines the quantification approaches used to derive the item volumes for the Murray–Darling Basin region. For a more detailed description of the quantification approach, click on the relevant item name in the table.
1s71 Reporting obligations of Basin States – a Basin State must, within 4 months after the end of a water accounting period for a water resource plan area in the Basin State give the Murry–Darling Basin Authority a written report about water availability, allocation, diversion, trade and compliance with long–term annual diversion limit (Water Act 2007).
Detail of quantification approaches
Water storage product data
Storages, regulated rivers—river weirs and locks, lakes
Storage volume was measured at the start and end of the year by using gauged water level height(s) in metres Australian height datum (mAHD) for individual storages, weirs, locks and lakes. The height measurement was converted to a volume using the storage-volume curve(s) of the storage, weir, lock and lake.
A complete list of all reported storages can be found here.
The assumptions and limitations of this approach were:
- Storage-volume curves represent specifically surveyed parts of the water storage, and may not reflect the storage-volume relationship across the entire storage.
- Rivers and water storages are subject to sedimentation and other physical changes over time, which in turn affect the accuracy of the storage-volume curves.
HYDRO database and height-volume relationship
Regulated river—weirs and locks
River levels were directly measured and converted into volumes using capacity tables for the individual weirs and locks, including locks 6–10 and 15 and Mildura Weir.
A complete list of all reported 'Regulated river-weirs and locks' can be found here.
The assumptions and limitations of this approach were:
- The capacity of the lock is taken to be the volume contained in the lock at target storage/full supply level.
- The dead storage associated with the locks is taken to be the volume in storage at the lower level of the operating range.
- This approach allows for comparative measure across years and is preferred to estimating the total volume behind the lock wall, which cannot be accurately measured.
- The accuracy of the capacity tables employed was not evaluated.
- Euston Weir volume excludes the Euston Lakes.
- Mildura weir was lowered for maintenance works during June 2013. Mildura Weir was back to full supply level (36,586 ML) on 20 July 2013.
- Information provided in this line item may have been based on Cap valleys in the HYDRO database, which may not align perfectly with SDL resource units.
Regulated rivers—river channels
The volumes of water stored in river channels upstream of the South Australian border were modelled and do not include dead storage.
The volumes of water stored in river channels downstream of Lock 1 were interpolated from capacity tables of height-volume relationships established by the Murray–Darling Basin.
A complete list of all reported Regulated river channels can be found here.
The assumptions and limitations of this approach were:
- Reliable information on dead storage for the volumes upstream of the South Australian border is not available. Dead storage calculation within river channels upstream of the South Australian border is complex and is assumed to remain static over the years.
- Data included in this item has been compiled specifically for this account.
- Information provided in this item may have been based on Cap valleys in the HYDRO database, which may not align perfectly with SDL resource units.
Lake capacity data
Lakes
The volumes of water stored in Lakes Ginninderra and Tuggeranong were estimated from their capacity, assuming that they were full at the start and end of the year.
The volume of water stored in Lake Burley Griffin was estimated by the National Capital Authority.
A complete list of all reported 'Lakes' can be found here.
The assumptions and limitations of this approach were:
- 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.
- The capacity of Lake Burley Griffin is based on survey data collected at the time of construction and fill in 1964.
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 degree (approximately 5 km) national grid (Jones et al. 2009).
The potential evaporation 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 were produced based on daily gridded climate data that were available on a 0.050 (approximately 5 km) national grid.The daily gridded climate datasets used to produce this estimate included downward solar irradiance, and maximum and minimum air temperature. The methods used to generate these gridded datasets are outlined in Jones et al. (2009).
Precipitation and evaporation at each waterbody were estimated from the proportionally weighted average of grid-point cells that intersected each storage, lake or weir (water feature). The volume was then estimated using the surface area of each waterfeature. Surface area varied dynamically with changing storage level for storages, lakes and weirs where the relationship between storage level and surface area has been derived; where this relationshis was not available the static Australian Hydrological Geospatial Fabric (AHGF) surface area was used.
The assumptions and limitiations of this approach were:
- The estimates were subject to approximations associated with interpolating observation point data to a national grid detailed in Jones et al. (2009).
- The dynamic storage surface areas calculated from the levels and capacity tables represent a monthly average and therefore do 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 water features at capacity and therefore likely results in an overestimation of precipitation on the water features.
Runoff to surface water
Runoff to surface water was estimated based on the AWRA-L version 3.0 (Van Dijk 2010) model output and a water balance algorithm written by the Bureau of Meteorology.
Using climate grid data for the MDB region (including precipitation, temperature and solar radiation data), AWRA-L estimated 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, off-channel water storages and other mapped waterbodies were excluded from the analysis.
Runoff from the landscape is divided into two components: runoff into the surface water store (surface water storages and weirs, rivers and drains) and runoff into off-channel water storages. Only runoff into the surface water store was considered here.
The average runoff depth from the landscape into surface water was determined as the weighted mean of the relevant grid-points within the MDB 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 MDB 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 surface water storages, weirs and off-channel storages) and was used as an input to the water balance algorithm.
The assumptions and limitations of this approach were:
- Runoff estimates were compared to historical flows at unimpaired catchments within the MDB region for the 2013–14 year and found to be a reasonable representation of the runoff in this region for this year.
- 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 local catchment storages is estimated using a local catchment storage balance model. Where this is applied, the runoff estimates inherit the approximations, assumptions and caveats of the local catchment storage water balance model and the parameters used.
Streamflow data
River outflow from the region
Flows into Menindee Lakes from the Barwon–Darling watercourse were based on metered discharge data and subsequent calculations.
Flows through the barrages were estimated based on the number of barrages open, the duration of their opening, and the flow rates across the barrages.
s71 Water resource report data and Snowy Hydro internal database
Inter-region claim on water
Each Snowy water year, Snowy Hydro Limited (Snowy Hydro) must release the required annual release (RAR) to the Tumut River, and the Murray River. The RAR is set at the commencement of the Snowy water year for delivery over the next 12 months. the volume of inter-region claim on water is the balance of the RAR at 30 June 2014.
The volume is calculated as shown in the following table.
| Calculation | Description |
| Fixed annual calculated yield for the development | |
| add | dry inflow sequence volume (DISV) as at 1 March from previous Snowy water year (1 May 2013 to 30 April 2014) |
| less | releases made during previous Snowy water year in excess of the previous year's RAR adjusted by the DISV at 1 March |
| less | water allocation from prior Snowy water year for environmental releases |
| add | other RAR adjustment |
| equals | RAR at the commencement of the Snowy water year (1 May) |
| less | accountable release1 to 30 June |
| less | DISV increase at 30 June |
| equals | RAR remaining at 30 June |
1The accountable release volume at 30 June 2014 is a preliminary estimate only and subject to confirmation and revision
Snowy Hydro RAR:
- Snowy Hydro RAR at the commencement of the Snowy Water Year (1 May) is based on the calculations in the Snowy Water Licence.
- Snowy Hydro RAR remaining at 30 June adjusts the RAR at 1 May by the estimated progressive releases (ML) from 1 May to 30 June.
Inputs to the calculation of the RAR include:
- 1,062 GL for the Murray River and 1,026 GL for the Tumut River–the precorporatisation RAR
- the dry inflow sequence volume
- environmental water savings transferred from the Murrumbidgee River and the Murray River to the Snowy River or the montane streams
- recognition of when Snowy Hydro has made a water release in advance of the Snowy water year
- transfers between the Tumut River and the Murray River
- recognition of water deals between Snowy Hydro and downstream irrigators (both the borrowings and the subsequent paybacks).
- any other RAR adjustment.
Increase of inter-region surface water claim on water
Increases in the RAR that Snowy Hydro was required to deliver to the Tumut and the Murray rivers, and a claim by Grampians Wimmera–Mallee Water in the Glenelg catchment were calculated as shown in the following table.
| Calculation | Description |
| Fixed annual calculated yield for development | |
| less | Snowy water allocation |
| less | dry inflow sequence volume (DISV) increase over the year |
| add | other RAR adjustment |
| equals | increase of claims against Snowy Hydro |
| add | Glenelg River |
| equals | Total increase of inter-region claim |
The assumptions and limitations of this approach were:
- Snowy Hydro claim: Numbers were estimated at the commencement of the water year, and subject to revision and confirmation at the end of the year.
- Inflows to Lake Hume for the River Murray are subject to a formula for calculating the respective New South Wales and Victorian shares, which is 50% between New South Wales and Victoria with some adjustments.
Delivery of water under inter-region agreement to surface water
s71 Water resource report data were derived from measured data. Other data were measured or extracted from reports by Snowy Hydro.
Decrease of inter-region surface water claim on water
Total decrease of claims against Snowy Hydro's RAR was calculated as the sum of the following components:
- repayment of water deals
- reduction in RAR for Snowy River deals (Mowamba)
- Snowy Water licence–reduction agreed between parties for the 2014–15 year
- relation volume reduction (due to irrigatiors entitlement's reaching full allocations and fullness of downstream storages)
- reserved as directed by the NSW Office of Water under clause 13.2 of the Snowy Water licence to facilitate a potential inter-valley transfer
- allocated for the drought account
- call out of relation volume that occurred in previous water year
The assumptions and limitations of this approach were:
- Snowy Hydro claim: Numbers were estimated at the commencement of the water year and subject to revision and confirmation at the end of the year.
River inflow to the region
The discretionary flow made by snowy Hydro to Murray and Tumut rivers and the inflow from the Barwon–Darling Watercourse SDL resource unit into the Lower Darling SDL resource unit at Menindee lakes was based on metered discharge data and subsequent calculations. The upstream end of the Menindee Lake was the boundary for the Northern and Southern Basins.
The uncertainty estimate for s71 Water resource report data is +/– 5%.
s71 Water Resource Report State inputs
Other surface water assets
The volume of water stored in Rocky Valley Reservoir, owned by a hydro-electric operator, was provided to the Murray–Darling Basin Authority as part of the s71 Water Resource Report Victorian input. The calculations used to derive the storage values were not provided. The volume does not include dead storage.
The assumptions and limitations of this approach were:
No orders can be placed on the storage for delivery of water to the entitlement system and thus does not reflect a volume that can be used to support the total volume in storages. It is potentially an asset, although there is some doubt about when the asset can be claimed because it is not available to settle claims for water until the hydro-operator physically makes the release.
Surface water allocation remaining: users and urban water supply; surface water allocation announcement: users and urban water supply; entitled diversion of allocated surface water: users and urban water supply; and adjustment and forfeiture of surface water allocation: users and urban water supply
Volumes of allocation remaining (carryover), allocation announcements, allocation diversions and adjustment and forfeiture of allocations were calculated by the States and Trrotories and provided by the s71 Water Resource Report State inputs, which are either measured, modelled or estimated data.
- Water sharing plans, water resource plans and the water legislation of each State and Territory specify the classes of licences that are permitted to carry forward any unused volumes and rules attached to the volume that may be carried forward.
- Allocation announcements are usually the entitlements on issue multiplied by the percentage allocation announced.
- Allocation diversions are metered or estimated based on user meter readings.
- Adjustment and forfeitures of allocations were calculated using a water balance approach and s71 Water Resource Report State inputs and were checked to ensure that the closing balance reconciled.
State and Territory specific entitlement conditions relevant to allocation remaining (carryover), allocation announcements, allocation diversions and adjustment and forfeiture of allocations are provided below.
Queensland
- Reliable information distinguishing volumes for urban and non-urban entitlements was not available; therefore the volumes reported for users include urban and non-urban entitlements and there are no volumes reported for urban entitlements.
- In the 2013-14 year, carryover of resource cap was only permitted in the St George (Condamine–Balonne sustainable diversion limit [SDL]). The Border and Macintyre Brook are continuous share schemes where water is carried over by continuous accounting . Carryover did not apply to all other water resource planning (WRP) areas within Queensland.
- In the Condamine–Balonne SDL carryover does not relate to bringing forward unused allocation. Rather, it provides for the resource Cap to be increased in the current year dependent on water use in the previous year.
- In the Queensland Border Rivers SDL, information was not available to separate the water available at the end of the previous year from the allocation announced during the year. The allocation announcement for the Queensland Border Rivers SDL resource unit includes both the allocation announcement during the year and the remaining water available at the end of the previous year, and carryover is reported as zero.
- The allocation announcement for the Condamine–Balonne SDL and the Borders Rivers water supply scheme within the Queensland Borders River SDL resource unit is calculated on use plus available water remaining at the end of the water year; however, a part of Macintyre Brook scheme is subject to announced allocation, but it is gradually moving to continuous accounting.
- For continuous accounting systems in the Condamine–Balonne and Border Rivers, it was not possible to calculate the adjustment and forfeiture volumes due to lack of information.
New South Wales
- Volumes reported include environmental entitlements in New South Wales Sustainable Diversion Limit resource units.
- Urban volumes refer to major and local water utility classes as well as to high security town water supply classes. Water use for cultural, industrial, research, community, and education activities have been categorised as non-urban.
- In calculating allocation announcements, impacts of implementing new water sharing plans and abolishing existing plans have been taken into account.
- The allocation announcement volume for Murrumbidgee NSW and Murray NSW includes the allocation announcements associated with river conveyance and bulk irrigation conveyance licences within the Coleambally and Murrumbidgee, and Murray irrigation areas respectively. These bulk irrigation conveyance licences are held by irrigation corporations to provide for losses within their distribution systems.
- Usually unused allocation balances are forfeited for entitlement classes: stock and domestic, community and education, and research and Aboriginal culture.
- Allocations remaining for several stock and domestic entitlements in Macquarie–Castlereagh, Lachlan, and New South Wales Murray SDL resource units, and conveyance entitlements in New South Wales Murray SDL resource unit were negative volumes. This could be due to and overdraft of surface water allocation (advance drawing), overuse breach of licence condition, or accounting/licensing anomalies. These anomalies may arise as a result of (a) some entitlement holders' licence accounts were not updated to accommodate late transactions at the time of collecting data for this item; and (b) the entitlement holder holds many licences but the accounting was on one licence only (the anomalies continue until consolidating licences and fixing in the database occurs).
- In the Murrumbidgee water resource plan (WRP) area, irrigators may 'borrow' water from the Snowy Scheme. This borrow is made under a contractual agreement between the irrigator and the Snowy Scheme. The volume contracted is then credited by New South Wales Office of Water to the individual account of the irrigator, allowing the irrigator to order water from the water assets administered by New South Wales Office of Water. In parallel, the Snowy Scheme transfers the physical water into Blowering Reservoir in the Murrumbidgee WRP area. When the irrigator is able in subsequent years to repay the debt, it notifies New South Wales Office of Water, which debits the account from the volume previously borrowed, thus reducing the allocation announced earlier in the year.
Victoria
- Reliable information distinguishing volumes for urban and non-urban entitlements was not available; therefore the volumes reported include urban and non-urban entitlements.
- Volumes reported include environmental entitlements.
- Volumes reported are shown in the source valley, even if the water was taken in a different destination valley. Therefore, all entitlements in the Goulburn SDL resource unit have their entitlement volumes shown in that area, rather than the destination valleys of the Loddon or the Campaspe.
- Once an allocation has been made, regardless of its class, it goes into a single allocation account. Therefore, allocation diversion, allocation remaining (carryover) and adjustment and forfeiture volumes are not specified as high reliability water share or a low reliability water share and are reported as combined high and low reliability water share.
South Australia
- Volumes reported include environmental entitlements.
- No carryover was permitted for South Australian Murray entitlements at the end of the 2013–14 year.
Australian Capital Territory
- No formal allocation announcement is made to extract water from storages. The allocation announcement for the year is assumed to be equal to the total entitlement volume.
Assumptions and limitations
The assumptions and limitations of this approach were:
- Only New South Wales and Queensland carryover data is shown by a specific security class. This reflects the carryover rules in the WRPs.
- Inclusion of urban carryover volumes may likely overestimate carryover in the States of Victoria and Queensland.
- The allocation announcement for environmental volumes reflects allocations made under various environmental water programmes. It is possible that the total volume allocated during the year could be higher than the volume reported due to data availability limitations.
- Volumes may have been based on Cap valleys in the HYDRO database that may not align perfectly with SDL resource units.
Uncertainty information includes:
- The uncertainty value for the New South Wales s71 Water Resource Report data provided in this item is +/–10%.
- Uncertainty of allocation announcements may in part be due to existing entitlements being converted into a different class, new entitlements issued, or entitlements cancelled following commissioning of a water saving infrastructure project.
- Uncertainty reported for diversion at the abstraction point accounts for possible errors in the data collection process.
- A single metered abstraction point may provide water to a range of users, under various types of entitlements (e.g. stock and domestic class). When this happens, the jurisdiction may split the metered abstraction into several classes of entitlements or types of users, according to priority rules governing the entitlements. This split has an inherent uncertainty that is not considered here.
- Estimates of uncertainty of the diversions are indicative accuracy of bulk diversions at the abstraction point on the river only and do not provide an uncertainty of diversion at the diversion point.
s71 Water Resource Report State input data uncertainty percentages and the measurement method applied that relates to the reported percentage and uncertainty percentage for each entitlement class for each jurisdiction are available in the following downloadable table.
Groundwater allocation remaining: users and urban water supply; groundwater allocation announcement: users and urban water supply; entitled extraction of allocated groundwater: users and urban water supply; and adjustment and forfeiture of groundwater allocation: users and urban water supply
Volumes of allocation remaining (carryover), allocation announcements, allocation extractions and adjustment and forfeiture of allocations were calculated by the States and Territory and provided by the s71 Water Resource Report jurisdictional inputs that are either measured, modelled or estimated data.
- Water sharing plans, WRPs and the water legislation of each State and Territory specify the classes of licences that are permitted to carry forward any unused volumes and rules attached to the volume that may be carried forward.
- Allocation announcements are usually the entitlements on issue multiplied by the percentage allocation announced. Allocations may be made for urban, stock and domestic, or irrigation purposes under a single class of licence in the particular WRP area. Where the purpose was not known, and it was a general class of licence, the groundwater allocation announcement was included under 'aquifer' entitlement class.
- Allocation extractions are metered.
- Adjustment and forfeiture of groundwater allocations was calculated by deducting the allocation extraction from the allocation announcment, with the exception of Angas Bremer and Marne Saunders prescribed wells areas in South Australia. Adjustment and forfeiture for these areas was calculated by deducting the allocation extraction and carryover from the allocation announcement.
State and Territory specific entitlement conditions relevant to allocation remaining (carryover), allocation announcements, allocation diversions and adjustment and forfeiture of allocations are provided below.
New South Wales
- GS32 NSW Border Rivers Alluvium includes both upstream Keetah Bridge and downstream Keetah Bridge alluvial groundwater sources.
- GS33 NSW Border Rivers Tributary Alluvium includes Macintyre and Ottleys Creek alluvial groundwater sources.
- GS47 Upper Namoi Alluvium are sourced from the Upper Namoi Zones 1–12.
Victoria
- Carryover of unused groundwater allocations is allowed in some groundwater management areas in Victoria; however information was not available.
South Australia
- Water sharing plans for GS2 Eastern Mount Lofty Ranges, GS6 SA Murray and GS7 SA Murray salt interception schemes were yet to commence or data were unavailable for these groundwater SDL resource units.
- Carryover of unused allocated groundwater is permitted in the State of South Australia for the Angas Bremer and Marne Saunders prescribed wells areas. Rules applying to the carryover of unused groundwater in these areas are described in the Water Allocation Plan for the Angas Bremer Prescribed Wells Area and the Water Allocation Plan for the Marne Saunders Prescribed Wells Area.
Assumptions and limitations
The assumptions and limitations of this approach were:
- The calculation of water made available may be affected by licences that have been cancelled or created part way through the year.
- SDL resource units other than those reported may have relevant volumes; however, information was not available for the 2014 Account.
Entitled diversions of non-allocated surface water to users
Volumes reported were provided through s71 Water resource report State and Territory inputs and are based on metered diversions and estimates:
- Australian Capital Territory sustainable diversion limit (SDL) area: Individual licensees submit monthly meter readings to the Australian Capital Territory Environment Protection Authority on an annual basis. Where a licensee has not provided meter data, the EPA estimates usage based on historical usage data.
- Other SDL resource units: Volumes reported were either measured, modelled or estimated.
State and Territory specific diversion information includes:
Queensland
- Data includes unsupplemented irrigation water allocation with flow conditions, unsupplemented irrigation allocation without flow conditions, and unsupplemented water licences diversions.
- Reliable information distinguishing volumes for urban and non-urban entitlements was not available; therefore, the volumes reported for users include urban and non-urban entitlements and there are no volumes reported for urban entitlements.
New South Wales
- Volumes include supplementary diversions in the regulated system and unregulated diversions in the unregulated systems.
- Volumes include a volume of water diverted via the Fish River Water Supply Scheme under a commercial agreement.
- Urban volumes refer to major and local water utility classes, as well as high security town water supply classes. Water use for cultural, industrial, research, community, and education activities have been categorised as non-urban.
Australian Capital Territory
- The volume reported includes diversions of unregulated flows under multi-use licences for non-potable water within the Australian Capital Territory. It includes urban use for licensed abstraction within the urban area, and other use for licensed abstraction outside the urban area.
- The volume reported for Murrumbidgee NSW includes Australian Capital Territory supplies for which Murrumbidgee New South Wales sustainable diversion limit area is the supply source.
- The volume reported includes regulated diversions made from the Murrumbidgee River for urban purposes.
South Australia
- Urban diversions include the Metro-Adelaide and the South Australian country town allocation diversions. The diversions to Metro-Adelaide are part of the River Murray entitlements and are pumped from within the MDB region to Adelaide.
Assumptions and limitations
The assumptions and limitations of this approach were:
- A single metered abstraction point may provide water to a range of users under various types of entitlements (e.g. stock and domestic class). When this happens, the jurisdiction may split the metered abstraction into several classes of entitlements or types of users, according to priority rules governing the entitlements. This split has an inherent uncertainty that is not considered here.
- Information provided in this line item may have been based on Cap valleys in the HYDRO database that may not align perfectly with SDL resource units.
- Estimates of uncertainty of the diversions are indicative accuracy of bulk diversions at the abstraction point on the river only and do not provide an uncertainty of diversion at the diversion point.
The s71 Water Resource Report jurisdictional input data uncertainty percentages and the measurement method applied that relates to the reported percentage and uncertainty percentage for each entitlement class for each jurisdiction are available in the following downloadable table.
Surface water point return from irrigation scheme
The volume was based on metered discharge data provided in the s71 Water resource report jurisdictional inputs.
Information on point returns from irrigation schemes was only provided for Murrumbidgee and Victorian Murray river systems within the Southern Basin. There was no measured data available for the other irrigation areas, particularly in the Northern Basin within the MDB region.
The uncertainty estimate, except for the returns in the Broken Creek irrigation system, is +/– 5%. The uncertainty estimate for the Broken Creek irrigation system, is +/– 40%.
Overbank flood spilling
Estimates of overbank flood spilling are made by local officers based on a combination of user returns and local knowledge. This information is reported in the s71 Water resource report jurisdictional inputs.
The assumptions and limitations of this approach were:
- Information on overbank flood spilling volumes was only available for Queensland and therefore only includes the Northern Basin.
- In the volume reported (which is abstracted overland flow), it is possible that the whole volume may not be from overflows from river channels because it was not possible to distinguish between harvesting from landscape and river overflows.
The uncertainty estimate for the volumes reported is +/– 40%.
s71 Water resource report jurisdictional inputs and Bureau regulations data
Trade and lease of surface water and groundwater entitlements; Trade of surface water and groundwater allocations within the region
All data pertaining to trade and lease of entitlements and allocations within the Murray–Darling Basin were obtained from s71 Water resource report jurisdictional inputs and Category 6 data provided to the Bureau.
The assumptions and limitations of the approach were:
- In general all trade was occurring within sustainable diversion limit areas that are predominantly regulated or supplemented; however, trade in both regulated (supplemented) and unregulated (unsupplemented) systems occurred in Queensland.
- The Warrego sustanable diversion limit area in Queensland is predominantly unsupplemented but contains the supplemented Cunnamulla water supply scheme. All the allocation trade within the Warrego region is assumed to be within Cunnamulla water supply scheme.
s71 Water resource report jurisdictional inputs and jurisdictional water sharing plans
Other groundwater assets
The extractable volume of groundwater (groundwater asset) was estimated as the sum of :
- sustainable diversion limits (SDL) volumes based on information provided by the Murray-Darling Basin Authority
- basic landowner rights or unlicensed stock and domestic rights (where these are not included in the long–term extraction estimates in the WRP)
- for New South Wales the volume of supplementary access licence that was available for the 2013–14 year.
The assumptions and limitations of this approach were:
- SDL resource units other than those reported may have relevant volumes; however, information was not available for the 2014 Account.
- Volumes reported are based on information available at the data collection stage for the account. It is likely that any subsequent changes to groundwater information in the WRP areas after the data collection stage have not been included in the above tables
Groundwater extractions: other statutory rights
Groundwater extraction data were obtained from the relevant clauses in the jurisdictional groundwater plans and s71 Water resource report jurisdictional inputs.
The assumptions and limitations of this approach were:
- It was assumed that the volume reported is the same as the water requirements estimated for these rights at the commencements of the water management plans.
- The volume is likely to be underestimated as limited data was available.
Surface water access entitlements for other statutory rights, non-allocated diversions and allocated diversions; Groundwater access entitlements for other statutory rights and allocated diversions
Entitlement volumes were obtained from jurisdictional water sharing plans and s71 Water resource report jurisdictional inputs.
The assumptions and limitations of this approach were:
- Information for some SDL resource units has been extracted from draft water sharing plans and represent estimates only.
- The entitlement volumes reported are the initial volumes of the water sharing plans. The actual volumes of entitlements during the 2013–14 year may be different from the initial volumes on issue at the time of the water plans' commencement due to conversions between classes or issue of new entitlements. Note that trade (ownership transfer), water savings projects or buy–back of entitlements for environmental purpose do not change the volume entitled within a class but only its ownership.
Jurisdicational water sharing plans
Surface water diversions: other statutory rights
Diversion volumes were estimated as equal to the total volume of basic landholder rights detailed in the water sharing plan at the commencement of the plan. No information was available for sustainable diversion limits outside NSW.
Bureau of Meteorology internal calculations
River and floodplain leakage, evaporation and errors
A water balance approach was adopted in calculating river and floodplain leakage, evaporation and errors. The calculations were based on hydrological boundaries of river catchments within the region. Total inflows less total outflows and changes in surface water storage for surface water in a reporting unit (a WRP area) was considered as the river loss (river and floodplain leakage, evaporation, and errors) for the same unit. Details of the calculation method applied in the water balance approach are as follows.
The volume for the WRP area (stated in the table provided under 'Supporting information'), for which necessary details are available, is equal to:
I – O – ΔS
where:
I is total inflow to the WRP area
O is total outflow from the WRP area
ΔS is change in total surface water storage during the 2013–14 year in the WRP area.
Total inflow to the WRP area was calculated using the following equation:
I = R1+R2 + P +Qi
where:
R1 is rainfall runoff to surface water
R2 is return flows (Groundwater discharge, point return from irrigation scheme, discharge from urban water system and delivery of water under inter-region agreement)
P is precipitation on surface water
Qi is inflow from upstream water resource plan areas (estimated using relevant streamflow gauge data, not applicable to all WRP areas).
Total outflow (O) was calculated using the following equation:
O = D+E +Qo
where:
D is diversions from surface water (discharge from surface water to groundwater, overbank flood spilling, entitled diversion of non-allocated and allocated surface water to users and urban water supply)
E is evaporation from surface water
Qo is outflow to downstream WRP areas or sea (estimated using relevant streamflow gauge data, not applicable to all water resource plan areas).
Change in surface water storage (ΔS) in the water resource plan area is the difference between total storage volumes at the end and beginning of the 2013–14 year. Storage information is available in the ‘Supporting information’ note.
The assumptions and limitations of this approach were:
- Assumptions made for individual volumes (see the above method for input variables) from which values were used as input variables may affect the accuracy of the calculations.
- A water balance approach was adopted in calculations (total inflows less total outflows and changes in surface water storage).
- At present, attempts to calculate the volume on small spatial units are limited by the resolution of available data, particularly diversion and return data at present. The Bureau is looking to implement the AWRA-R model over the next 2–3 years, which will be able to better attribute some of the inputs for the calculation and attribute these inputs to individual river reaches.
Other groundwater increases/decreases
Groundwater increases and decreases resulting from changes in long-term extraction estimates and basic land-owner rights were calculated by the Bureau of Meteorology and based on s71 Water resource report jurisdictional data.
It was assumed that groundwater basic right is included in the permissible consumptive volume provided in relevant water sharing plans if no information is available to decide otherwise.
Bureau groundwater modelling; GIS dataset of bore locations and groundwater levels; sustainable diversion limit area boundaries
Regional and coastal groundwater inflow to and outflow from the region
Regional groundwater flow across the MDB regional boundary was only considered to be significant in the area near the mouth of the River Murray in South Australia. Inflow from the Northern Basin to the Southern Basin was considered negligible and could not be quantified. The boundary through which groundwater flow was estimated is highlighted in Figure 27 in 'Supporting information' note. Groundwater inflow was estimated for the unconfined aquifer (Murray Group Limestone and Parilla Sands) and confined aquifer (Renmark Group) that underlie this boundary.
Groundwater flow was calculated using a simple geographic information system (GIS) approach based on Darcy's Law. Groundwater levels were interpolated for seasons using the ArcGIS Topo-to-Raster tool from reduced groundwater levels measured at monitoring bores
The Geofabric version 2.0 (Bureau of Meteorology 2011a) was used to estimate aquifer thickness. The hydraulic conductivity values were sourced from the Mallee Prescribed Wells Area – Murrayville Water Supply Protection area groundwater model, Department of Water, Land and Biodiversity Conservation, South Australia (Barnett and Osei-bonsu 2006). The transmissivity values were calculated by multiplying the aquifer thickness with the relevant hydraulic conductivity.
Seasonal groundwater flow grids were derived from groundwater level grids, aquifer thickness and hydraulic conductivity using a modification of the ArcGIS Darcy Velocity tool. Groundwater flow across selected flow boundaries was then calculated using a simple GIS analysis and seasonal values were aggregated for the 2013–14 year.
The assumptions and limitations were as follows:
- Regional flow estimations were provided for the Murray Group Limestone Aquifer, which was chosen to represent the unconfined aquifer and the Renmark Group Aquifer. These were considered to be the main aquifer systems that cross the boundary of the MDB region.
- It was assumed that no major groundwater flow occurs between the sustainable diversion limits (SDL) areas of Northern Basin and the Southern Basin. This was due to the groundwater flow within the fractured rocks (Lachlan Fold Belt: Lachlan and Western, Kanmantoo Fold Belt, and Orange Basalt) being local, therefore regional flow was negligible. In addition, most of the central–eastern boundary represents a no-flow boundary (groundwater divide). Regional groundwater inflow in the Western Porous Rocks is also small because it is a small area with low groundwater flow gradients (resulting from low groundwater recharge). It was assumed that groundwater outflow from the upper Darling Alluvium was small due to the small outflow area. Interaction with the river would be the main recharge/discharge process in the area, with regional lateral outflow being a secondary process. Inflows and outflows for the Southern Basin were assumed to occur at or near the coast line only; all the other boundaries were assumed no-flow boundaries mostly representing a groundwater divide.
- Groundwater levels in the unconfined aquifer were assumed to be 0 mAHD (metres above Australian height datum) along the coastline.
- Groundwater flow from the GAB to the MDB and groundwater abstraction from the GAB were not evaluated for the 2014 Account due to lack of data (although this vertical leakage is recognised to be important in some SDL resource units).
Uncertainty information
- The uncertainty estimate was not quantified.
- The uncertainty in the field-measured data (e.g. groundwater levels, hydraulic conductivity) was not specified and unknown, and hence the impacts of such uncertainty on the calculated groundwater flow were not estimated.
- The regional flow estimations were based on the interpolated groundwater level grids produced using a simple GIS analysis. Use of different interpolation methods may impact on the values of the groundwater level grids and hence the estimated regional flow; however, a comparison of this methodology was carried out using a simple groundwater flow model developed on MODFLOW model (United States Geological Survey 2013). The results from the two methodologies indicated a 6–7% difference.
- Groundwater flow was estimated for a simplified boundary constructed from a series of line segments. Groundwater flow across this boundary was calculated using the method described above. The uncertainty surrounding this simplification was not analysed.
Estimated change in groundwater stored in aquifers
Change in extractable storage is estimated using a simple geographic information system (GIS) approach based on measured groundwater levels and aquifer properties. Firstly, groundwater levels at the start (1 July 2013) and the end (30 June 2014) of the 2013–14 year were estimated. This was achieved by considering all groundwater level measurements between March 2013–October 2013 and March 2014–October 2014, respectively, and using the measurements closest in time to interpolate the start and end levels. The estimated groundwater levels on the start and end dates were then spatially interpolated to grids using kriging with external drift and the 9" Digital Elevation Model (DEM) as an external driver following the methodology presented in Peterson et al. (2011). The change in volume within the sedimentary area was calculated using these interpolated groundwater level surfaces.
These volumes were multiplied by appropriate specific yield values (Commonwealth Scientific and Industrial Research Organisation and Sinclair Knight Merz 2010a and 2010b) to convert the volume to a change in groundwater storage. Finally, change in storage was only considered within a 10-km mask of each groundwater observation bore to ensure an appropriate influence from the change in each bore and the volume was reported for the water table aquifer only. Groundwater storage outside these buffer areas was assumed constant throughout the year given that there is no data available.
The uncertainty in the field-measured data (e. g. groundwater levels, specific yield) was not specified and hence the impacts of such uncertainty on the change in storage were not estimated.
The assumptions and limitations were as follows:
- Change in groundwater storage outside the buffer areas is assumed zero given that no data is available for calculation.
- Change in groundwater storage was not calculated for confined aquifers. Under normal circumstance, the annual change in storage is considered to be negligible for confined aquifers due to their very low storage coefficient, which is much lower than the specific yield of water table aquifers (Freeze and Cherry 1979, Johnson 1967). As long as confined aquifers remain saturated, changes in piezometric levels (i. e. aquifer pressure) usually cause small changes in water volumes stored in the aquifers; the changes are equivalent to the volumetric expansion/contraction of the water and the pore space.
- The specific yield values used in each water table aquifer are presented in the downloadable table.
- The change in storage estimations were calculated from the interpolated groundwater level grids produced using kriging with external drift and the 9" DEM as an external driver. Use of other interpolation methods may impact the values of the groundwater level grids and hence the estimated values for change in groundwater storage.
Groundwater inflow to a SDL resource unit from another SDL resource unit
The regional groundwater flow across selected SDL resource units within the Northern and Southern Basins was considered. The selected SDL resource units represent major groundwater resources for the Northern Basin. Groundwater flow was estimated for the unconfined and selected confined aquifers that underlie these boundaries. Refer to the 'Quantification approach' for regional groundwater flow for more information on the method used to calculate regional groundwater flow across selected SDL resource unit. The downloadable table provides the calculated groundwater inflow to an SDL resource unit from another SDL resource unit for both Northern and Southern Basins.
The assumptions and limitations were as follows:
- Regional flow estimations were provided for the aquifers indicated in this downloadable table only. This, together with the fact that not all the hydrological processes within the Northern and Southern Basins have been taken into consideration, means the total regional inflows to each of the basins are not comparable with that provided in the downloadable table.
- The Geofabric version 2 (Bureau of Meteorology 2011a), and Southern Riverine Plains groundwater model (Goode and Barnett 2008) were used to estimate aquifer thicknesses. The hydraulic conductivity values were sourced from Mallee Prescribed Wells Area – Murrayville Water Supply Protection Area groundwater model (Barnett and Osei-bonsu 2006), Southern Riverine Plains groundwater model (Goode and Barnett 2008) and the report on sustainable extraction limits derived from the recharge risk assessment method – New South Wales (Commonwealth Scientific and Industrial Research Organisation and Sinclair Knight Merz 2010a and 2010b). The transmissivity values were calculated by multiplying the aquifer thickness with the relevant hydraulic conductivity.
- It is possible that small differences occur between the University of Melbourne database and the DSE groundwater database (from which bore locations and groundwater level data in Victoria were sourced).
Regional flow estimations are provided for the SDL areas as detailed in this downloadable table. Due to the fact that not all the hydrological processes within the Northern and Southern Basins have been taken into consideration, the total regional inflows to the Northern Basin are not comparable with that provided in the table.
The uncertainty in the field-measured data (e.g. groundwater levels, hydraulic conductivity) was not specified and unknown, and hence the impacts of such uncertainty on the calculated groundwater flow were not estimated.
The regional flow estimations were based on the interpolated groundwater level grids produced using kriging with an external drift from 9" DEM and simple GIS analysis for the water table and confined aquifers, respectively. Use of different interpolation methods may impact on the values of the groundwater level grids and hence the estimated regional flow; however, the regional flow estimated with interpolated groundwater levels using GIS analysis was compared with a simple groundwater flow model developed on MODFLOW model (United States Geological Survey 2013). The results from the two methodologies indicated a 6–7% difference.
Groundwater flow was estimated for a simplified boundary constructed from a series of line segments. Groundwater flow across this boundary was calculated using the method described above. The uncertainty surrounding this simplification was not analysed.
Bureau groundwater modelling using climate grid data, soil data, land use data
Groundwater recharge from/discharge to landscape
The method described below applies to the following groundwater sustainable diversion limit areas:
- GS64 Upper Condamine Alluvium (Central Condamine Alluvium and Tributaries)
- GS65 Upper Condamine Basalts
- GS27 Lower Murray Alluvium (shallow; Shepparton Formation)
- GS46 Upper Murray Alluvium
- GS8 Goulburn-Murray (Ovens-Kiewa sedimentary plan)
- GS8 Goulburn-Murray (Victorian Riverine sedimentary plan)
- GS9 Wimmera-Mallee (Sedimentary plan)
- GS01 Angas Bremer (Quarternary sediments and Murray Group limestone
- GS03 Mallee Murray Group limestone
- GS05 Peake-Roby-Sherlock (unconfined)
Groundwater discharge was estimated along with diffuse groundwater recharge volumes using the water atmosphere vegetation energy and solutes (WAVES) model (Zhang and Dawes 1998; Dawes et al. 1998). In the recharge calculations, depth to water table was considered for all regions where the depth to water table was shallow. A shallow water table was assumed to be where the depth to the watertable was 4 m or less below the ground surface. The shallow water table was interpolated using kriging with external drift and the 9" DEM as a physical constraint following the methodology presented in Peterson et al. (2011). Where the water table was not shallow, free drainage conditions were assumed. For SDL resource unitss with a shallow water table, the model may produce a net discharge from groundwater over the calculation period. The recharge within the MDB region was determined by summing the spatially interpolated positive recharge estimates.
The assumptions and limitations of this approach were:
- The assumptions made in developing the WAVES model as described in Dawes et al. (1998) were all applicable to the recharge estimations carried out for the MDB region.
- The national land use grid (Australian Bureau of Agricultural and Resource Economics and Sciences 2010) was reclassified to three vegetation classes that include annuals, perennials, and trees. The major vegetation classes modelled were C3 annual pasture, C3 perennial pasture and eucalypt trees with a grass understorey for SDL areas to the south of 31oS; and C4 annual pasture, C4 perennial pasture and eucalypt trees with a grass understorey for the SDL resource units to the north of 31oS.
- Annual recharge was estimated using a shallow water table surface estimated by interpolating measured groundwater levels.
The uncertainty in the input parameters and the corresponding impacts on the modelled recharge values were not studied. The uncertainty of the estimated recharge resulting from different recharge interpolation methods was not estimated.
NSW groundwater model
Groundwater recharge from/discharge to landscape
The method described below applies to the following groundwater sustainable diversion limit areas:
- GS24 Lower Gwydir Alluvium
- GS29 Lower Namoi Alluvium
- GS40 Peel Valley Alluvium
- GS47 Upper Namoi Alluvium
- GS26 Lower Macquarie Alluvium
- GS25 Lower Lachlan Alluvium
- GS44 Upper Lachlan Alluvium
- GS28 Lower Murrumbidgee Alluvium (shallow; Shepparton Formation)
- GS31 Mid-Murrumbidgee Alluvium
Recharge volumes were calculated for the selected SDL resource unitss listed above applying New South Wales groundwater models based on MODFLOW (United States Geological Survey 2013) modelling process. Discharge volumes were calculated where the MODFLOW evapotranspiration routines were activated to represent groundwater discharge.
Groundwater recharge is both an input to and an output from a groundwater model. There is no single method for estimating recharge used in the New South Wales groundwater models; however, several models estimate recharge as a percentage of rainfall. The magnitude of recharge (as a percentage of rainfall) can be adjusted during the calibration of a groundwater model so that the observed groundwater levels are reproduced in model outputs as accurately as possible, typically for a period of around 20 years if data are available.
The assumptions and limitations of this approach were:
- Groundwater models make many assumptions and approximations to represent a water balance (United States Geological Survey 2013).
- Several of the New South Wales groundwater models assume estimation of recharge volume as a percentage of rainfall.
Uncertainty of recharge/discharge estimates was not evaluated for the New South Wales groundwater models.
Groundwater recharge from/discharge to surface water
Groundwater interactions with surface water (discharge to and recharge from) can be represented in MODFLOW models in several ways. Options that have been used in the New South Wales groundwater models are the MODFLOW river package and the MODFLOW drain package (USGS 2013).
Groundwater flow into the river is modelled when groundwater levels are higher than river water levels and water flow is out of the river when river water levels are higher than groundwater levels. MODFLOW also has a subroutine to represent drains. When this is activated and groundwater levels are above the base of the drain, water flow to the drain is estimated and this water volume is removed from the cell of the groundwater model.
For more details about MODFLOW calculations, see documentation at the MODFLOW website (USGS 2013).
The assumptions and limitations of this approach were
- Groundwater models make numerous assumptions and approximations to represent water balance (refer to the MODFLOW website for more details).
- Estimates of water level in rivers that are input to groundwater models are usually taken to be monthly average levels, and the levels would usually have a high level of uncertainty unless a river gauge is located within the groundwater model cell.
The uncertainty estimate was not quantified. It is currently not feasible to estimate the uncertainty of modelled groundwater recharge from surface water from outputs of a MODFLOW groundwater model.
Estimated changes in groundwater stored in aquifers
New South Wales groundwater model outputs were used to evaluate the changes in groundwater storage. The change in groundwater storage derived from the groundwater models in New South Wales included all the groundwater model layers (not just the water table aquifer layer).
Details on the limitations of groundwater models used by NSW Office of Water can be accessed through its webpage on Water accounting.
It is currently not feasible to estimate the uncertainty of modelled change in extractable storage from outputs of a MODFLOW groundwater model.
Groundwater inflow to a SDL resource unit from another SDL resource unit
The outputs of the New South Wales groundwater models available within selected SDL resource units were used. The downloadable table provides the calculated groundwater inflow to an SDL resource units from another SDL resource units for both Northern and Southern Basins.
It is currently not feasible to estimate the uncertainty of modelled regional flow from outputs of a MODFLOW groundwater model.
Details on the limitations of groundwater models used by NSW Office of Water can be accessed through its webpage on Water accounting.
Internal database
Discharge from surface water to urban water system
Treated wastewater discharged to the surface water store was measured at wastewater treatment plant outflow flow meters.
Estimated uncertainty is +/– 5%.
Water Information and Licence Management Administration system
Managed aquifer recharge: other schemes
Recharge volumes were metered.
Climate grid data and waterbodies spatial dataset
The farm dam algorithm: Off-channel water storage volume and precipitation on, evaporation from, runoff into and abstraction from off-channel water storages
The farm dam algorithm written by the Bureau of Meteorology was used to determine the volume of water held in and the movement of water to/from off-channel water storages. Data input to the model included gridded climate datasets; runoff from the AWRA-L version 3.0 (Van Dijk 2010) model; and dam details derived from spatial data (surface area, volume, location and catchment area).
The MDB region was divided into 105 regions as shown in Figure 1 for the purpose of modelling the off-channel water storages. The off-channel water storages consists of those storages filled primarily by local catchment runoff. These identified off-channel storages are shown in Figure 2. They were determined from waterbody mapping conducted by Geoscience Australia in 2007 as those that:
- are not named storages (assuming that any storage with a name is unlikely to be a off-channel water storage); and
- are above 600 m in elevation; and/or
- are below 600 m in elevation in areas that receive greater than 400 mm per annum in precipitation and are not within 50 m of a major or perennial stream.
The above rules attempt to divide storages into those that are likely to be filled primarily by local catchment runoff and those which are filled by abstraction from surface water, groundwater or floodplain harvesting. The catchment of each storage was determined via analysis of the 9" DEM.
Figure 1 MDB region divided into 105 regions for modelling off-channel water storage volumes
Figure 2 Off-channel storages in MDB region used for modelling volume, precipitation, evaporation, runoff harvesting and abstraction
Source: Waterbody mapping conducted by Geoscience Australia in 2007
The farm dam algorithm performs a water balance on each individual storage at each time step using runoff and precipitation as inflows; and spills, evaporation and usage as outflows. The volume of water held in storage is an output of this water balance. The algorithm estimates abstraction based on the assumption that water will be abstracted from the off-channel water storage at the rate required unless the off-channel water store empties, at which time, abstraction will cease.
Precipitation on, evaporation from and runoff harvesting into off-channel water storages were estimated using the same methods for surface water storages.
The assumptions made were as follows:
- The estimated volumes are subject to the assumptions associated with the farm dam algorithm written by the Bureau and the parameters used.
- The gridded climate input data are subject to approximations associated with interpolating observation point data to a national grid detailed in Jones et al. (2009).
- The spatial extent of water bodies are subject to the assumptions and methods associated with the data provided by the Geoscience Australia.
- The use of a 9" DEM to determine catchment area may result in off-channel water storages being assigned a catchment much larger or smaller than the true catchment. In some cases, an off-channel water storage may be assigned to the catchment of a stream line hundreds of metres away.