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.
RESERVOIR Capacity 25,368 ML Dead storage 199 ML Surface area 198 Ha Full supply level 450.90 m AHD Catchment area 90 km2 EMBANKMENT Maximum height 37.0 m Length 340 m PRIMARY SPILLWAY Crest length 87 m Discharge capacity 72,000 ML per day SECONDARY SPILLWAY Crest length 87 m Discharge capacity 69,000 ML per day
SRW's role during floods at Rosslynne Reservoir
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 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.
Please keep clear of dams and spillways during floods
Contact us on 1300 139 510 for more information or to make an appointment to chat to one of our assessment staff.
The majority of the reservoir is used for urban supply by Greater Western Water and for this reason, the reservoir is closed to the public.