Water resources - Availability - Victoria
Basin & Surface Water Management Area: Barwon River
Introduction
This section presents information about surface water quantity and sustainability. For simplicity of communication, sustainability measures are based on assessing the level of water use and/or allocation with the quantity of water required to fulfil a sustainable flow regime (environmental water provision) - this has been expressed as a sustainable yield.
Vital statistics:
| Mean Annual Run-Off (Natural) (ML/yr) | 250,800 |
|---|---|
| Mean Annual Outflow (Natural) (ML/yr) | 250,800 |
| In-stream commitment (Total available flow - imported water - sustainable yield) (ML) | 180,200 |
| Sustainable Yield - Developed Yield (ML) | 24900 |
| Divertible Yield (ML/yr) | 90,700 |
| Developed Yield (ML/yr) | 45,700 |
| Sustainable Yeild (ML/yr) | 70,600 |
| Yield, Security of Supply | |
| Current Development Category | MEDIUM DEVELOPMENT |
| Diversion (ML/yr) | 40,060 |
| Total Available Water | 250,800 |
PLEASE NOTE:
Mean Annual Flow:
The Mean Annual Flow of the Barwon River Basin was estimated using the natural flows at the furthest downstream gauge (Station No. 233200). This assumes negligible contributing inflow contributions from the catchment between this gauge and the basin outlet.
Mean Annual Outflow:
The flow in the Barwon River increases downstream. The flow is therefore greatest at the catchment outlet and represents both the Mean Annual Runoff and the Mean Annual Outflow (for undeveloped conditions). (Refer to the description of the method for determining the MAF).
The mean annual outflow under current development conditions was estimated as the difference between the outflow estimated under natural conditions and the average annual diversions. This assumes negligible storage and river losses.
Developed Yield:
The developed yield refers to the annual volume of water that is available for diversion at a defined level of reliability, taking account of environmental water requirements.
The bulk entitlement conversion process, initiated in Victoria in the early 1990s, has involved a comprehensive assessment of the developed water resource. The bulk entitlement volume represents the maximum volume of water that can be diverted at specified locations with current infrastructure in place and with consideration given to the original design intent of the water supply system. The bulk entitlement volumes have been derived using Resource Allocation Models (REALM) of the various supply systems.
For the majority of basins in Victoria the developed resource has been fully allocated. Hence, for these basins the developed yield is equivalent to the average annual allocation.
For the Barwon River Basin the developed yield (and average allocation) has been defined as the average diversion that would occur when the maximum entitlements within the basin are taken up. The average diversion from the Geelong Water Supply System has been estimated using the Resource Allocation Model (REALM) of the system.
The average regulated diversions from the White Swan system (located in the upper reaches of the catchment on the Leigh River) has been reported as 90% of theBE cap as this cap is an upper limit.
The average unregulated diversions were determined as 90% of sum of the private diversion licence volumes in the basin. 90% of the licence and entitlement volumes is assumed to represent the likely upper limit to the long term average diversions for these users.
Divertible Yield:
The divertible yield has been defined as the average annual volume of surface water that can be diverted utilising both existing infrastructure and potential infrastructure under the ultimate level of development. In Victoria, potential future dam sites have been identified as part of an earlier study, which considered the options for surface water development in the State. The study was published by the previous Rural Water Commission of Victoria in June 1986 and was titled "Long Run Incremental Cost of Annual Regulated Flow in Victorias River Basins" (Alexander and Haydon 1986). An essential component of the study involved the determination of the incremental costs of future water resource developments in Victoria. A rapid appraisal method for assessing storage yield and construction costs at possible dam sites was developed which allowed selected sites to be ranked on a comparative basis. The construction cost was based on the volume of the dam embankment, catchment area and a parameter obtained from a relationship derived from existing dam embankment construction costs.
The main assumptions adopted in the assessment of potential storage sites and the estimation of yields from storages are listed below:
- Only streams carrying large flows in relation to the total annual basin yield and having a salinity of less than 1600 EC units (1000 mg/l) were investigated for possible storage sites.
- The yield estimation method is based on 95% supply security (a one in twenty year failure to supply unrestricted demands), an urban demand pattern and retention of 20% of storage capacity for dead storage and drought security carryover.
Some factors that are likely to influence actual storage costs and yields were not considered within the scope of the study. For example, costs associated with spillway construction, road construction, and land purchase were not taken into account in the cost equation. Other factors not considered included environmental considerations, variable demands, potential inter- and intra- basin transfers, site geology and water treatment requirements.
For this Audit, the divertible yield was reported as the sum of the developed yield for the SWMA and the incremental yield from the potential storage sites identified in the study noted above.
Dam sites with an effective cost greater than $2000/ML, as determined in 1985 (equivalent to around $3300/ML in 1996),were not included in the estimate of divertible yield as these were considered to be uneconomical.
For the Barwon River Basin one potential dam site has been identified, providing an increase in system yield of 45 GL.
How has flow regime changed in Barwon River?
Change in Flow Regimes:
A high proportion of the yield of the Barwon River Basin is from the Barwon River above key gauge 233218, which contributes approximately 64% of the yield. The upper Leigh River also contributes a high proportion (~25%). The mean annual flow varies from 59,100 ML at key gauge 233215 on the Leigh River to 221,900 ML at the Pollocksford Station (233200) near Geelong.
The Barwon River and its tributaries exhibit highly seasonal flow patterns with between 80% and 90% of the annual flow occurring in the winter/spring. The rivers in the Basin are perennial, although flow can become quite low in the summer and autumn months. The highest flows in the basin are recorded in September contributing about 24% of the average annual flow (51,525 ML/annum at Pollocksford). The lowest flows in the year occur during March contributing between 0.5% and 2% of the average annual flow (1,700 ML/annum at Pollocksford).
The main on-stream storage impacting on the flow regime of the Barwon River is the West Barwon Reservoir, which has a capacity of 20,900 ML. The storage lies at the headwaters of the Barwon and is operated by Barwon Water to supply Geelong and surrounding towns. The impact of the storage is to reduce the total volume flowing down the river system. At key site 233218 on the Barwon River, average spring flows are marginally reduced. However average autumn flows are reduced by up to 52%, summer flows by up to 34% and winter flows are reduced by up to 26%. Regulation and diversion has had a minimal impact on Leigh River flows. Below the confluence of the Barwon and Leigh rivers at key site 233200, average winter and spring flows remain relatively unchanged. However summer and autumn flows are reduced by 31% to 46% respectively. There has been no significant change in the seasonal flow pattern.
Trade and Transfer - a bit of give and take:
Water use efficiency and optimisation strategies within existing infrastructure (eg. water supply efficiency, precision irrigation and scheduling, water recycling, trading and pricing) are part of the modern water resource development planning tool kit. 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.
Measurement Stations in Barwon River
Summary surface water measurement station statistics
| Name | Stream gauge ID | Mean annual flow (ML/yr) | Mean annual flow (mm) |
|---|---|---|---|
| Stream guage 233200 | 233200 | 221,888 | 71 |
| Stream guage 233215 | 233215 | 57,301 | 97 |
| Stream guage 233218 | 233218 | 126,551 | 106 |
Modelled unimpaired stream-flow sites in Barwon River
Over 300 sites across Australia were modelled to predict the unimpaired (natural) stream-flow. The long time series of stream-flow data are important for both research and management of Australia's hydrological and ecological systems. A simple conceptual daily rainfall-runoff model was used to extend the stream-flow data.
The model estimates stream flow from daily runoff and potential evapotranspiration data. The parameters of the model are first calibrated against the available stream-flow data. The optimised parameter values are then used to estimate monthly stream flow from 1901 - 1998.
For further information please refer to : Project Report - Stream Flow Study
Table: Summary unimpaired stream flow sites statistics:
| Station Name | Mean annual runnoff | Mean annual rainfall (mm) |
|---|---|---|
| LEIGH AT MOUNT MERCER | 98 | 738 |
| WARRAMBINE CK AT WARRAMBINE | 41 | 688 |
Further information
- Victoria 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
- Link to the Map Maker to make a map using this information.
Key
Links to an another web site
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