Water resources - Availability - Australian Capital Territory
Australian Capital Territory
Australian Capital Territory Overview
In comparison with the States and the Northern Territory, the ACT's water resources are not significant but they are an integral and valued part of the natural landscape and are critical to the future economic development of the Territory. Water, its availability and use, has been a key driver in shaping the ACT. The availability of an adequate and good quality water supply was a key determinant of the location of the ACT when it was established in 1909. A significant proportion of the ACT's water resources has now been developed to support the needs of the national capital, which include a high proportion of parks and gardens. In addition, Canberra has a large number of smaller lakes and ponds designed to protect downstream water quality in the Murrumbidgee and to enhance recreational and aesthetic amenity.
The ACT lies entirely within the upper part of the Murrumbidgee River catchment as an 'island' within NSW. The Murrumbidgee River itself is a major feature of the ACT entering from NSW in the south and returning to NSW through the northern border.
While in the past water supplies have been sufficient to meet requirements, there is likely to be increasing demand on the water resources of the ACT as a result of the continued growth and diversification of the ACT and surrounding region. It should also be noted that Canberra is the largest urban area in the Murray-Darling Basin in which there is significant pressure on the available water resources. In this context the ACT is committed to sustainable and equitable management of its water resources and the protection of associated environmental values.
Surface Water Reporting Units
The ACT is entirely within the Murrumbidgee catchment and the major tributaries draining the Territory are the Cotter, Gudgenby and Molonglo Rivers. The Murrumbidgee Basin covers an area of 84,700 km2, of which the ACT occupies 2,400 km2, representing 3% of the whole basin. The Murrumbidgee River rises to the southwest of the ACT. It flows some 30 km before reaching Tantangara Reservoir in NSW, where most of its flow is diverted to Lake Eucumbene. The river then flows for a further 150km in NSW and then through the ACT to Burrinjuck Reservoir to the north of the ACT in NSW.
Groundwater Reporting Units
The ACT is entirely within the Upper Murrumbidgee River Catchment. The ACT catchment has been subdivided into three Groundwater Management Units 410.a, 410.b and 410.c which correspond to the Management Areas for surface water resources. It includes an area of NSW from which the ACT draws surface water resources. The total surface area of the GMU is 3626 square kilometres. The ACT takes a conservative approach to groundwater management providing for efficient use and ensuring the protection of the aquifers and associated environmental values. Within the Groundwater Management Unit, it is thought that there is scope for further use of groundwater for rural purposes.
For further information on water in the ACT, go to the Envoronment ACT website.
How much surface water does Australian Capital Territory have?
Hydrology
For the purposes of the Audit the ACT contribution has been subdivided into three SWMA's: 410.a, 410.b and 410.c which include some regulated streams as well as unregulated components. 410.a represents the main catchments of the ACT to the west of the Murrumbidgee River. Its predominant uses comprise urban water supply, conservation, forestry and rural land use. 410.b comprises the Murrumbidgee River corridor and associated small streams. This sub-catchment includes a mixture of rural and urban activities. It also contains pine forests and offers a wide range of recreational and conservation opportunities. 410.c comprises the Molonglo River catchment and includes mainly urban and rural activities. It includes an area of NSW from which the ACT draws water resources.The climate in the ACT is essentially continental, with hot summers and cold winters. Rainfall is strongly affected by the landform. Summer rainfall tends to occur as storms with more prolonged gentler rainfall in winter. Mean annual precipitation ranges from 800 to 1000 mm in the mountainous zone (410.a) in the western part of the ACT to 500-600 mm in the lower city areas. The mean annual potential evaporation across the ACT is around 1300 mm per year.
Available Resource
The mean annual stream-flow of the ACT Management Area is 520 GL. Of this, 320 GL is designated by the Environmental Flow Guidelines as environmental flow, leaving 200 GL available for consumptive use.
Currently, the ACT licenses diversions of around 62.7 GL a year mostly for urban water supply, representing about 5% of the upper Murrumbidgee Catchment runoff. Of this around 55% is returned as highly treated effluent.
For ACT waterbodies there are four elements that are built into environmental flows as follows.
- Low flow based on the 80th percentile flows calculated on periods of not more than a month.
- Flushing flows required to ensure that channel structure and the dependent ecological processes are maintained. For ACT rivers other than water supply catchments, the short duration of high volume flows and a limit on abstraction of 10% of flows over the 80th percentile, ensures that flushing flows occur.
- Special purpose flows which have been set to meet spawning requirements in the Cotter River. A flow adequate for spawning has been defined as the 50th percentile monthly flow during the spring months (September, October and November) and 80th percentile monthly flow for the months August and December to March.
- Maintenance of lake and pond levels to protect macrophytes. For urban lakes and ponds the maximum drawdown as a result of abstraction is 0.2 m below spillway level.
Around 14% of the Territory is urban area and this has significantly changed the flow patterns of streams in that area. In addition flow variability in the Murrumbidgee River is attenuated by the return of treated effluent at a relatively constant rate. The other major land uses in the ACT are conservation 53%, forestry occupying 10% of the ACT and rural uses representing around 23% of the ACT (ACT Government, 1999).
The total developed surface water resource for the ACT Management Area represents approximately 16% of the total streamflow. Much of the remaining 84% of the total surface water resource refers to water that is unable to be developed, largely for environmental reasons.
The sustainable yield has been determined as the maximum volume of water that could be diverted after taking account of in-stream environmental water requirements. For the ACT Management Area, the total sustainable yield is estimated to be 200 GL per year representing 38% of the total streamflow. Of this yield, 42% has been developed for use.
The management area with the most highly developed surface water resource is 410.a with a developed yield of 54.7 GL per year. This represents 76% of the total developed yield in the ACT Management Area and reflects the nature of the Cotter catchment dedicated for urban water supply.
| Basin/Surface Water Management Area | Mean Annual Run-off (GL/yr) | % of state | Natural mean annual out-flow (GL/yr) | In-flow (GL/yr) |
|---|---|---|---|---|
| Murrumbidgee River A | 298 | 57.24 | 247 | 0 |
| Murrumbidgee RIver B | 81 | 15.43 | 872 | 802 |
| Murrumbidgee RIver C | 143 | 27.32 | 177 | 49 |
How saline are Australian Capital Territory's surface water resources?
Table: Surface water resource by salinity class for divertible yield (GL)
| Surface Water Managemnet Area | <500 mg/l (GL/yr) | 500 - 1500 mg/l (GL/yr) | 1500 - 5000 mg/l (GL/yr) | 5000 -14000 mg/l (GL/yr) | >14000 mg/l (GL/yr) | Total volume (GL/yr) |
|---|---|---|---|---|---|---|
| Australian Capital Territory | 255 | no data | no data | no data | no data | 128 |
| Murrumbidgee RIver A | 180 | no data | no data | no data | no data | 90 |
| Murrumbidgee RIver B | 5 | no data | no data | no data | no data | 3 |
| Murrumbidgee RIver C | 70 | no data | no data | no data | no data | 35 |
How much of Australian Capital Territory's surface water resource has been developed?
The major storages in the ACT Management Area are Googong Reservoir, Corin Reservoir, Bendora Reservoir and Cotter Reservoir. The total storage capacity of these is around 216 GL. There are also a number of other smaller lakes and ponds the primary purpose of which is for water quality protection.
How committed are Australian Capital Territory's surface water resources?
Categorisation was based on the percentage of use to sustainable yield. The ACT Management Area is categorised as level two - Medium Level Resource Development. No areas have been over-developed.
| Basin/SWMA | Volume diverted (GL/yr) | Sustainable (GL/yr) | Diversion Development class |
|---|---|---|---|
| Murrumbidgee RIver A | 51 | 125 | MEDIUM DEVELOPMENT |
| Murrumbidgee RIver B | 2 | 7 | LOW DEVELOPMENT |
| Murrumbidgee RIver C | 16 | 69 | LOW DEVELOPMENT |
The volume diverted is the total volume of the SWMA's surface water resources diverted for use both within the management area and for export to other management areas.
A four-class classification system was developed to provide a simple method to communicate the status of the use and allocation of Australia's water resources in relation to sustainable water management.
It is important to recognise that adequately quantifying a sustainable flow regime or sustainable yield and consequent operating rules is a complex matter. State, Territory and scientific agencies continue to develop and apply methods and measures for determining sustainable flow regimes and sustainable yields.
This categorisation provides a general guide only. Please refer to the State and Territory Overview and Technical reports for detail on the analysis methods used.
| Category | Development status | |
| 1 | <30% | Low development |
| 2 | 30 - 70% | Moderate development |
| 3 | 70 - 100% | Highly developed |
| 4 | 100% | Overdeveloped |
* Water use as a percentage of sustainable flow regime (surface water) and sustainable yield (groundwater)
How much groundwater does Australian Capital Territory have?
Hydrology and Available Resource
In the GMU, groundwater occurs in two types of aquifer: fractured rock and alluvial. The area contains mainly fractured rock aquifers, which are overlain in places by minor, high-yielding aquifers in superficial, unconsolidated, alluvium/colluvium. Transmissivity is generally low except in highly fractured areas ranging from 0.15 to 53 m2/day. Storage coefficient has a value ranging from 0.0004 to 0.00005.
In the typical fractured rock aquifer in the area, the depth limit of significant open fractures is generally about 100 m, below which the aquifer can be considered essentially impermeable. The fractured rocks are mainly volcanic rocks. Alluvial aquifers occur in relatively recent unconsolidated deposits of silt, sand and gravel in river valleys and basins. They are exploited and can be a locally significant source of water. Bore yields in fractured rock vary from 0.25L/s through to 5.7 L/s.
Within the ACT Groundwater Management Unit (GMU), there is low level use and there is some limited scope for its further development for rural supply and possibly for supplementary urban supply. It is estimated that the groundwater resource in the GMU available for use is around 7 GL per annum.
Sustainable Yield and Environmental Allocation
The estimation of sustainable yield for groundwater in the GMU's has been made taking account of environmental requirements and is therefore substantially less than the maximum sustainable yield.
Total recharge in the GMU's is calculated to average 73.1 GL per year. The ACT Environmental Flow Guidelines and the Water Resources Management Plan recognise that there are links between groundwater and surface water which need to be considered when determining allowable extraction. In particular, on a regional scale, groundwater is a major contributor to the base flow of rivers and streams. Intensive use of groundwater is likely to lead to significant stress on these waterways.
In this context, the ACT takes a conservative approach to groundwater management, particularly in light of the absence of reliable information. Groundwater abstraction in the ACT has therefore been limited to 10 percent of average annual estimated recharge. Over the entire GMU this is around 7 GL per annum.
How committed are Australian Capital Territory's groundwater resources?
Table: Allocation volumes (GL/yr in each development category)
Note: "GMU"=Groundwater Management Unit "UA"=Unallocated Area
| Province | Over | High | Med | Low | Total (GL/yr) | |
|---|---|---|---|---|---|---|
| Lachlan | GMU | 256 | 198 | 58 | 27 | 538 |
| UA | no data | no data | no data | 71 | 71 |
A four-class classification system was developed to provide a simple method to communicate the status of the use and allocation of Australia's water resources in relation to sustainable water management.
It is important to recognise that adequately quantifying a sustainable flow regime or sustainable yield and consequent operating rules is a complex matter. State, Territory and scientific agencies continue to develop and apply methods and measures for determining sustainable flow regimes and sustainable yields.
This categorisation provides a general guide only. Please refer to the State and Territory Overview and Technical reports for detail on the analysis methods used.
| Category | Development status | |
|---|---|---|
| 1 | <30% | Low development |
| 2 | 30 - 70% | Moderate development |
| 3 | 70 - 100% | Highly developed |
| 4 | 100% | Overdeveloped |
* Water use as a percentage of sustainable flow regime (surface water) and sustainable yield (groundwater)
How saline are Australian Capital Territory's groundwater resources?
Table: Groundwater resource by salinity class
| Province | <1500 mg/l (GL/yr) | 5000 mg/l (GL/yr) | 14000 mg/l (GL/yr) | >14000 mg/l (GL/yr) | Total volume (GL/yr) | |
|---|---|---|---|---|---|---|
| Australian Capital Territory | GMU | 102750 | ||||
| UA | ||||||
| Lachlan | GMU | 342,635 | 268 | 6 | 7 | no data |
| UA | no data | no data | no data | 429 | no data |
How much water does Australian Capital Territory trade?
The Total reported Volume Traded in Australian Capital Territory is 0 GL; in 0 transactions.
The State and Territory water management agencies continue to consider water use efficiency and optimisation strategies within existing infrastructure (e.g. water supply efficiency, precision irrigation and scheduling, water recycling, trading and pricing) as part of water resource development planning.
Recognising that water is a finite resource, the States and Territories have developed water allocation systems where security and reliability are assigned to entitlement, trading is provided so water can be moved to high value uses and the choices of individuals are maximised.
Part of the decision-making framework to enable and facilitate water trading, changes in water allocation and definition of rights to water is the need for water use monitoring. Water use monitoring will assist decision-making and provide an opportunity over time to evaluate the effectiveness of allocation policies.
Environmental water requirements
The Water Resources Act gives clear priority to the provision of environmental flows by requiring that Environmental Flow Guidelines be prepared setting out the flows necessary to protect aquatic systems within the ACT Management Area. The environmental flows are determined by the requirements of the four different categories of ecosystem defined for the ACT Management Area, namely water supply, natural, modified and created. The Water Resources Act also requires the preparation of a Water Resources Management Plan, which describes the water resources of the ACT and identifies water available for allocation. The Plan is developed on the basis of the Environmental Flow Guidelines and no allocation of water can be made unless it is in accordance with the Plan. Licences to take water ensure that water use is in accordance with the Plan.
Further information
- Australian Capital Territory Water Resources Assessment 2000 Report
- Australian Capital Territory Water Resources Assessment 2000 Technical Report
- report from the study of Streamflow data and modelled streamflow
- Link to data available for download on the:
- extension of unimpaired monthly streamflow data and regionalisation of parameter values to estimate streamflow in ungauged catchments (NLWRA 2000)
- Surface Water Management Areas
- Groundwater management units and provinces - ARC/INFO export
- Link to the Map Maker to make a map using this information.
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