Water resources - Overview - Victoria
Basin & Surface Water Management Area: Otway Coast
Introduction
The Otway Coast Basin covers the southern coastal region of south-west Victoria from east of Torquay to west of Peterborough and has an area of 3,876 km2 (2% of the State). There are several stream networks in the basin that originate on the southern slopes of the Otway Ranges and flow southwards into the southern ocean. The Curdies River is the only system that does not originate in the Otway Ranges. The catchment of Curdies River is characterised by a relatively flat landscape. The Gellibrand River drains the western end of the Ranges and has several tributaries including Olangolah River, Kennedy's Creek and Carlisle River. Other major river systems in the Otway Coast Basin include the Aire, Barham, Cumberland, St George, Erskine and Anglesea Rivers. There are no major storages in the Otway Coast Basin, however there is a network of pumping stations and weirs that divert water to supply towns in the basin and larger ones outside, such as Colac and Warrnambool.
Over the main ridge of the Otway Ranges, the annual average rainfall reaches 2,000 mm. Rainfall reduces to around 900 mm in the central coastal region, 800 mm to the far west and 600 mm to the far east, which is as a result of the rain shadow effect from the Otway Ranges.
The mean annual flow of the basin is 750,000 ML, which represents 3.7 % of the total runoff generated in the State.
Approximately 60% of the basin is still covered by hardwood native forests. In the west of the basin, where the hardwood forests have been extensively logged, dairying and cattle grazing are the principal primary industries, and potato growing is also significant.
Average annual water use in the Basin averages 12,180 ML - 47% for rural use, 25 % for irrigation, and 28% for urban and industrial use.
(Note: The reported volume of water used represents the total water consumed within the basin. This estimate of water use does not account for the volume of reclaimed or returned water and does not include water that is allocated for use in other management areas).
Approximately 1,650 ML of water is imported from the Barwon River Basin annually to supply urban demands. Water exported from the basin totals about 8,820 ML each year. This water is exported to townships in the Hopkins and Corangamite basins.
Vital Statistics:
| Area: | 3,876 Km2 |
|---|---|
| Total storage volume: | 2,772 |
| Total surface water use: | 12,180 ML/yr |
| Development category: | LOW DEVELOPMENT |
| Mean annual run-off: | 750,000 ML/yr |
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)
PLEASE NOTE:
Sustainable Yield:
While Victoria has a variety of programs under way aimed at identifying, improving and protecting environmental water requirements, the necessary investigations take considerable time and resources.
Given the short time frame of the Audit, it was necessary to make some broad assumptions, and use a variety of approaches, to derive estimates of the sustainable yield for surface water management areas (SWMAs) in Victoria. Consideration was given to environmental water requirements (known and likely), existing user rights, and related social and economic impacts. The reported allocations to the environment represent the water that can currently be maintained or made available in an attempt to meet environmental water requirements.
The sustainable yield of the Otway Coast Basin was determined by calculating the total volume of water that can be extracted from the river system (during May to November) such that the degree of change to the natural flow regime is not unacceptable, as defined by the achievement of a rating of 5 for the Hydrology sub-index of the Index of Stream Condition (ISC). This method is described in further detail in the Victorian Technical Report.
This approach is considered to be relatively conservative and the estimate of sustainable yield should only be considered as an interim measure, pending the outcome of detailed environmental flow assessments.
In the longer term, there may be further scope for freeing up additional water to improve environmental regimes by improving distribution and water use efficiencies (other options for improving environmental regimes will be considered as part of the Victorian River Health Strategy). In SWMAs where a significant portion of the available resource is committed to a downstream SWMA, there is also potential for trading of entitlements between the two SWMAs. This will result in a change to both the sustainable yield and the environmental allocation in both SWMAs. Trade out of a SWMA would decrease the sustainable yield of the SWMA and a trade of water rights into a SWMA would increase the sustainable yield. However, the sum of the sustainable yields for the two SWMAs would remain unchanged.
PLEASE NOTE:
Categorisation:
The categorisation of SWMAs in terms of the current level of water resource development has been determined with consideration given to the level of allocation and actual diversion of the resource relative to the assessed sustainable yield.
Five development categories have been defined:
Category 1: Low level of development: 0-30% Category 2: Medium level of development: 31-70% Category 3: High level of development: 71-99% Category 3*: Fully developed: 100% Category 4: Over allocated/used resource: >100%
The development category for the Otway SWMA has been reported at a low level of development (Category 1) with respect to allocation and diversion.
How saline are the surface water resources in the Otway Coast surface water management area?
Table: Surface water resource by salinity class.
| Total Volume, Divertible Yield (ML/Yr) | |
|---|---|
| Total volume (ML/yr), DIVERSION | 204,100 |
| <500 mg/l (ML/yr) | 173,485 |
| 500 mg/l (ML/yr) - 1500 mg/l (ML/yr) | no data |
| 1500 mg/l (ML/yr) - 5000 mg/l (ML/yr) | 30,615 |
| 5000 mg/l (ML/yr) - 14000 mg/l (ML/yr) | no data |
| > 14000 mg/l (ML/yr) | no data |
Major water storages
Table: Major water storage areas:
| Storage name: | Capacity (ML) |
|---|---|
| Painkalac Dam | 410 |
| Allenvale | 226 |
| Olangolah Weir | 136 |
| West Gellibrand Dam | 2,000 |
| Total | 2,772 |
Further Information
- View the Victoria Water Resources Assessment 2000 Report
- View the Victoria Water Resources Assessment 2000 Technical Report
- Link to data available for download on the:
- Surface Water Management Areas
- Data from the 1985 Review of Australia's Water Resources and Water Use
- Link to the Map Maker to make a map using this information.
- For more information about water and other natural resource issues link to www.dse.vic.gov.au