Construction of Rosslynne Reservoir began in February 1971 with the river diversion along the right hand side of the creek, which is now the main outlet conduit, and was essentially complete by July 1974.
Following studies that showed the dam did not meet industry standards for flood capacity, temporary works to lower the risk were carried out in November 1996, whilst investigation and design work was completed on a permanent dam safety upgrade. This involved raising the embankment by about 0.5m by installing an impervious membrane on the downstream face of the bankette.
In October 1998, rockfill was placed on the upstream face of the embankment to give the dam a uniform upstream batter slope of 1.8 horizontal to 1 vertical up to a level of 451.5m AHD. Previously, some sections of the upstream slope had been as steep as 1.33 horizontal to 1 vertical, which was no longer considered acceptable.
In 2000, major upgrade works were completed that brought the dam into line with modern industry standards. The works improved the flood capacity by raising the embankment by 1.9m and installing an 85m long secondary spillway on the right abutment. Filters were also installed on the right abutment to reduce the risk of piping.
The reservoir provides additional water supplies to the townships of Sunbury and Gisborne and provides irrigation water to river diverters along the Maribyrnong River.
|Dead storage||199 ML|
|Surface area||198 Ha|
|Full supply level||450.90 m AHD|
|Catchment area||90 km2|
|Maximum height||37.0 m|
|Crest length||87 m|
|Discharge capacity||72,000 ML per day|
|Crest length||87 m|
|Discharge capacity||69,000 ML per day|
Rosslynne Reservoir is located on Jackson’s Creek, 3 kms north-west of Gisborne.
A Bulk Entitlement Order is a set of operating rules for a reservoir.
At Southern Rural Water (SRW) we deal with the following Bulk Entitlement Orders:
- Yallourn Energy
Because more than one organisation or group can have shares (or entitlement) in the water being held in a reservoir, each shareholder must follow rules about:
- the volumes that can be taken from the reservoir, system or waterway
- costs of managing the system, and how they are shared
At a number of reservoirs, SRW acts as the storage manager on behalf of all shareholders.
As a storage manager, we:
- allocate water (both increases and decreases) according to the inflow and capacity shares held by shareholders
- ensure that we meet the rules for passing flows downstream for environmental purposes
- release water to meet a shareholder’s request
Passing flows are a vital part of our Bulk Entitlement Orders and are met before allocation requests are supplied.
Environmental Entitlement Orders spell out a whole pattern of environmental flows that are required downstream of a reservoir – from how long they last, to how frequently they flow and how large they are.
Environmental flows are designed to mimic the natural conditions of rivers. It is not just about the amount of water but also the timing and quality. In each order, environmental flow requirements are low during the summer and autumn, and are much higher during winter and spring.
Environmental flows are vital to supporting the river’s ecological processes. High flows provide triggers for fish breeding and supply water for fish passage, so that they are able to move up and down rivers to appropriate habitat. They also keep estuaries open and provide recreational opportunities. Low flows in summer maintain fish refuges and connect habitats. Spring floods regenerate wetlands and floodplains and replenish the river channel.
To make sure that we comply with the rules about passing environmental flows, we:
- perform random checks at points along rivers, to ensure that customers are taking only the amount of waterthey have ordered
- maintain a number of gauging stations with alarms that alert us of unusual changes in water levels.
For more information contact us on 1300 139 510 or visit www.srw.com.au.
SRW's role during floods at Rosslynne Reservoir
Rosslynne Reservoir is not designed to manage floods
Southern Rural Water helps to provide river flow information during floods
Please keep clear of dams and spillways during floods
Rosslynne Reservoir capacity is 25,400 megalitres (ML) and is managed by Southern Rural Water.
This reservoir was not designed to manage floods. It simply stores water for various uses including water supplies for the townships of Sunbury and Gisborne and irrigation water for river diverters along the Maribyrnong River.
Operating Rosslynne Reservoir during floods
Rosslynne Reservoir has a fixed crest spillway, so that once it is full any excess water coming into the reservoir will flow over the spillway into Jackson Creek. Therefore Southern Rural Water does not have the ability to deliberately surcharge (over fill) the reservoir.
This reservoir also does not have the ability to pre-release enough water to have any effect on a possible flood, but it can help reduce flood peaks by temporarily storing water if room is available, however, once the lake is full, it has little impact on flows.
When we know high rainfall is possible, our staff work closely with other agencies such as the SES, local councils and the Bureau of Meteorology to provide information on the flows passing through our structures to assist them in their operations.
Southern Rural Water provides daily updates on its website (www.srw.com.au) about the water levels in local storages and also has a web page which has links to Bureau rainfall forecasts, flood warnings, river levels and emergency assistance provided by the SES.
We strongly recommend that if you are in a flood prone area that you and your family familiarise yourself with the SES’s "Flood Safe information brochure" and take all necessary precautions.
Contact us on 1300 139 510 for more information or to make an appointment to chat to one of our assessment staff.
More information can also be found at www.srw.com.au
The majority of the reservoir is used for urban supply by Western Water and for this reason, the reservoir is closed to the public.