About the area
- The Otway Coast basin is in south-west Victoria. It encompasses the numerous small creeks and rivers that flow to the coast from the Otway Ranges, the largest being the Gellibrand and the Curdies rivers.
- Annual rainfall in the basin ranges from below 600 mm in the eastern-most extent to over 1,200 mm in the elevated south around Cape Otway.
- The moderate to steep forested Otway Ranges dominate the centre of the basin, while the remainder is largely covered by cleared farmland.
More information on water management and accounting is detailed in Water .
2021-22 overview
Available water
Slightly less water was available than the previous year.
Licensed diversions from unregulated streams
There were more restrictions on licensed diversions than the previous year.
Water use
About the same of water was diverted for consumptive purposes than the previous year.
When compared to the previous year, in 2021-22:
- less rainfall was received, catchment inflow was lower and storage levels peaked and declined at similar levels
- there were more restrictions on licensed diversions from unregulated streams
- about the same amount of water was diverted from the basin for consumptive uses.
Climate
Rainfall
In 2021-22, rainfall in the Otway basin was average in most areas, lower than the previous year. Rainfall was:
- above average in the Otway National Park around Apollo Bay
- average elsewhere in the basin west from the Aire River and in the north-east from around Lorne to Torquay.
River basin water balance
In 2021-22, 21,752 ML of water was diverted for consumptive uses: town, domestic and stock, irrigation and commercial supply, about the same as the previous year (22,449 ML).
Water balance table
The table below shows the total volumes of water available and supplied from water resources in the Otway Coast basin in 2021-22.
Table 1: Water balance, Otway Coast basin
Storages
Major — greater than 1,000 ML — on-stream storages in the Otway Coast basin are included in the water balance.
Storage levels
Storage levels in the Otway Coast basin were 100% on 30 June 2022.
The same as the previous year
Storage levels were 100% on 30 June 2021.
Table 2: Storage levels, Otway Coast basin
Catchment inflow
Catchment inflow represents the volume of water flowing into the waterways of a basin. It is calculated to be the difference between the total outflows, the known inflows and the net change in storage volume.
The amount of water flowing into Bass Strait represented 97% of the catchment inflows in the basin in 2021-22.
Above average inflow received
Catchment inflow was 140% of the long-term average of 733,300 ML.
Less than the year before
Inflows received were lower than the previous year (159% of the long-term average).
Wastewater treatment plants
Water treated at wastewater treatment plants can be used to supplement water available in the basin. Water discharged to waterways from treatment plants is included as an inflow to the water balance.
Information on treatment plants is now reported in the Water Supply local reports for the water corporation responsible for managing the plant.
In this basin, wastewater treatment plants are managed by Barwon and Wannon .
Small catchment dams
Water harvested, used and lost by small catchment dams (farm dams) is included in the water balance.
Table 3: Small catchment dams, Otway Coast basin
Entitlements and compliance
Entitlements provide the basis for how water is shared in the basin.
Entitlement volumes
Rights to water in the Otway Coast basin are shown in table 4 below.
Entitlement volumes represent a maximum volume that can be taken in a one-year period. The volume available in a particular year is dependent on the rules for allocating water set out in the entitlement and the seasonal conditions in that year, which varies. The rules for allocating water under an entitlement can differ between entitlements and systems. This affects the ability and likelihood of water being taken in a particular year.
Table 4: Annual entitlement volumes at 30 June, Otway Coast basin
Available water and take under entitlements
Total water available under entitlements represents the volume of water that was available to be taken by entitlement holders in 2021-22. The volume includes seasonal allocations and net trade into the basin.
Water taken
There was 17,466 ML used in 2021-22, about the same as the year before (17,628 ML).
Restrictions on licensed diversions from unregulated streams
Two streams were placed on restrictions throughout 2021-22, compared to none the previous year.
- A stage 1 roster was in place on Carlisle River from April through to the end of June 2022.
- A ban on diversions was also in place for Curdies River in February and April to June 2022.
- All other streams were unrestricted for the year.
Available water and take table
This table shows the volume of available water and the volume taken under entitlements in 2021-22.
More information on available water and take has been detailed in the How do we account for surface section on the How do we account for water page.
In 2021-22, about the same amount of water was taken under entitlements as the previous year.
Table 5: Available water and take, Otway Coast basin
Compliance
Compliance against water entitlements is reported for this basin in three areas:
- entitlement issued: the volume of entitlements issued in a basin does not exceed formal caps, and has not increased without appropriate approvals
- water taken: the volume of water taken during the year does not exceed the volume considered to be available for consumptive and/or in-stream use during that year
- bulk entitlement provisions: holders of entitlements do not breach any provisions that are documented in their bulk entitlement orders.
Total entitlement volume
There was an allowed increase in the total entitlement volume from the previous year. See note below.
Total volume diverted
The total volume diverted (17,466 ML) was within the volume available for the year (34,864 ML).
Individual bulk entitlements
No individual bulk entitlement holder took more than the annual volume made available to them.
Exceptions to compliance
Individual bulk entitlement holders complied with all provisions in their entitlements.
Note to increase in total entitlement volume:
- 200 ML of take and use licence was issued for a small catchment dam on a waterway due to a surface water auction in the Curdies system.
Water for the environment
Environmental watering sites
There are no environmental entitlements in the Otway Coast basin, so no active environmental watering occurs.
However, important sites and environmental values in the Otway Coast basin that depend on water for the environment include:
- Aire River (a heritage river) and more specifically the Lower Aire wetlands, which are nationally significant
- the Aire River estuary, which is state-significant
- the upper Aire River, which is a representative river
- Elliot River, Parker River, Grey River, Carisbrook Creek and Smythes Creek, which are ecologically healthy waterways
- native fish communities (such as river blackfish and Australian grayling) and their habitats (such as remnant riparian vegetation)
- lakes Costin and Craven
- endangered, flow-dependent ecological vegetation classes including estuarine wetland and swamp scrub
- the native bird population including the great egret (a Victorian endangered species), Cape Barren goose and Australasian bittern
- native mammals including platypus and swamp antechinus
- macroinvertebrate communities in Elliot River, St Georges River and Wye River.
Environmental water reserve
In 2021-22, water for the environment in the Otway Coast basin comprised:
- water set aside for the environment through the operation of passing flow conditions:
- on consumptive bulk entitlements held by Barwon Water and Wannon Water
- on licensed diversions
- all other water in the basin not allocated for consumptive uses: this water also provides social, recreational and cultural benefits.
Management responsibilities
Management of water in the Otway Coast basin is undertaken by various parties
| Authority | Management responsibilities |
|---|---|
| Southern Rural Water |
|
| Wannon Water |
|
| Barwon Water |
|
| Corangamite Catchment Management Authority |
|
| Water supply system | 2021-22 (ML) | 2020-21 (ML) |
|---|---|---|
| Apollo Bay | 393 | 367 |
| Colac system | 3,491 | 3,494 |
| Lorne | 356 | 402 |
| Otway system | 8,429 | 8,450 |
