7 September 2021
Flows in all the rivers are now receding.
The flow on the Latrobe has now dropped below minor flood level at Thoms Bridge. The release from Narracan is also below the equivalent minor flood level for the Latrobe River at Rosedale.
The release at Lake Glenmaggie has been decreased to 6,500ML/d which is also below minor flood level, and the storage level is steady at 173,000 ML.
2 September 2021
Vic Emergency warnings of flooding across Eastern Victoria this Friday 3rd and weekend of 4th and 5th of September 2021.
A significant rain event is forecast for Friday 3 and Saturday 4 September 2021. SRW staff are working at storages over the next few days to make small releases from Glenmaggie to create air space.
Cowwarr recreational areas remain closed to the public.
Community warnings during floods
Victoria State Emergency Service (SES) is the control agency for flood, storm, tsunami and earthquake in Victoria, and is the responsible Authority for issuing emergency information and warnings to communities.
Detailed information from SES regarding regarding flood warnings and any community notifications can be found on the VicEmergency website emergency.vic.gov.au
Southern Rural Water has approval from SES to provide updates about releases from our storages, while SES remains responsible for issuing community warnings and managing flood information.
Please follow SES advice on safe road travel during heavy rain events. Heavy rainfall often causes localised flooding of land, roadways and drains. Never drive through floodwaters.
You can also join our SRW Eastern Storages Updates Facebook group to make sure you never miss one of our posts regarding our storages at Lake Glenmaggie, Cowwarr Weir, Lake Narracan and Blue Rock Lake. We’ll post there regularly during high-outflow events.
Lake Glenmaggie –
Update: Monday 20 September 2021 - 13:00 hrs
The release at Lake Glenmaggie is 3,500ML/d which is also below minor flood level, and the storage level is steady at 173,000 ML.
Outflows: 3,500ML/d - Southern Rural Water staff will continue small releases as part of ongoing management.
Total capacity: 177,640 ML
Storage volume: 173,000 ML
Cowwarr Weir – Minor Flood Levels
Update: Monday 6 September 2021 – 13:00 hrs
Thomson River – Cowwarr Weir:
Note – there is damage at Cowwarr Weir with work being completed to clear debris from June storms. Access is still strictly prohibited to the public.
Minor flooding is likely to occur at Thoms Bridge and Rosedale from Sunday morning.
Minor flooding may develop along the Thomson River at Cowwar Weir from Sunday night and Wandocka overnight Sunday into Monday. Minor flooding may extend downstream to Sale Wharf during Tuesday.
The Latrobe River system flow remains steady, Moderate Flood Level at Thoms Bridge and Minor Flood Level at Rosedale remain.
Please note, all recreation areas at our storages remain closed until further notice.
No access to Cowwarr Weir is allowed.
Upstream of Cowwarr Weir: 5,960 ML/d
Flow: 10,060 ML/d – This has reached the Minor / Moderate Flood Level. The gates of the weir have been lifted above water level to allow free flow as levels drop.
When flow reaches 8,000 ML/d upstream of Cowwarr Weir and is expected to rise, access to the low-level bridge at Cowwarr Weir cannot be guaranteed.
The official flood warning levels for the Thomson River upstream of Cowwarr Weir are:
Minor Flood Warning 8,000 ML/d
Moderate Flood Warning 20,000 ML/d
Major Flood Warning 40,000 ML/d
The official flood warning levels for the Thomson River at Wandocka, downstream of Cowwarr Weir, are:
Minor Flood Warning 9,460 ML/d
Moderate Flood Warning 15,100 ML/d
Major Flood Warning 24,300 ML/d
Blue Rock Lake – Low inflows
Update: Saturday 4 September 2021 – 20:00hrs
Current flow of Tanjil River upstream of Lake Blue Rock is 429ML/d and expected to rise overnight and peak later on Saturday. Lake Blue Rock is full with downstream flow currently at 533ML/d.
Total Capacity : 208,000ML
Current storage level: 100%
Calculated inflows into Blue Rock Lake:
Total releases – on the Tanjil River down stream of Blue Rock Lake:
1, 727 ML/d – falling
Tanjil River levels are decreasing with Minor Flood Level now reported.
Official Flood Warnings – Tanjil River at Tanjil South
Minor Flood Warning: 7,500
Moderate Flood Warning: 11,700ML
Major Flood Warning: 18,500ML
Notes: For more information on flood warnings visit the Bureau of Meteorology website and emergency.vic.gov.au for all notifications. SES is the agency responsible for alerting communities about the possibility of flooding.
Please note, all recreation areas at our storages remain closed until further notice.
Lake Narracan – Minor/Moderate Flood Levels
Update: Monday 6 September 2021 - 13:00hrs
Lake Narracan is being kept at approximately 60% full with outflows matching inflows.
Inflows are slowly dropping. The Latrobe River system flow remains steady, Moderate Flood Level at Thoms Bridge and Minor Flood Level at Rosedale remain.
Calculated inflows into Lake Narracan: 9, 096 ML/d
Current release downstream: 9,064 ML/d
Calculated expected flow Latrobe River at Thoms Bridge: 7,515 ML/d
Official Flood Warning trigger levels on the Latrobe River at Thoms Bridge
Minor Flood Warning: 8,200ML/d (4m)
Moderate Flood Warning: 11,600ML/d (5m)
Major Flood Warning: 102,000ML/d (6.5m)
Official Flood Warning trigger levels on the Latrobe River at Rosedale:
Minor Flood Warning: 6,000 ML/d (4m)
Moderate Flood Warning: 17,650 ML/d (4.8m)
Major Flood Warning: 31,300 ML/d (5.5m)
Latrobe River Yallourn to Traralgon Creek:
Minor flood levels are being experienced on the Latrobe River to Traralgon Creek.
Note: For all information on current flood warnings visit the Bureau of Meteorology website and emergency.vic.gov.au or the Vic Emergency app for all notifications. SES is the agency responsible for alerting communities about the possibility of flooding.
Please note - all recreation areas at our storages remain closed until further notice.
A one in 100-year flood is a flood that has a 1 in 100 or 1% chance of occurring in each and every year.
In a 70 year lifetime there is a 50/50 chance of a 1 in 100 flood being exceeded at any location.
Can you have two 100-year floods in one year?
Yes, two 100-year floods can occur one after the other.
Who is in charge of responding to the floods?
The Victoria State Emergency Service (VICSES) is the control agency for flood response works in partnership with support agencies such as DEPI to manage responses to flooding.
How does Victoria’s flood warning system work?
Flood warning information is acquired through the Victorian streamflow gauging network.
The network has 750 gauging sites that serve a range of purposes, including 283 that are used as primary flood warnings sites.
Other sites are used to provide further back up information and flash flooding information. Data collected is immediately made available to those organisations that require it.
Who develops flood maps?
Melbourne Water and Catchment Management Authorities develop flood maps for areas at risk.
These maps are used for both land planning and by the SES to provide flood information during flood emergencies.
Flood maps have been completed across the state for the 1 in 100-year flood. In a number of key areas across the state, this is supplemented by additional information on flood extent and height for a range of flood sizes.
What is a levee?
A levee is a natural or man-made mound or wall to confine floodwaters.
Levees can reduce the risk of flooding for adjacent properties, but no levee can eliminate all flood risk.
Levees can also increase the risk of flooding downstream through the loss of natural floodplain storage or increase flooding to unprotected area.
Who is responsible for maintaining levees?
- Private landowners are responsible for maintaining levees on their land. They may be required to obtain a planning permit to undertake works from their local Council.
- Local councils and/or Melbourne Water are responsible for maintaining levees which protect urban communities.
- There are a smaller number of levees on public land built many decades ago which have no clear ownership responsibility.
Why don’t water corporations hold back more water during flooding events to protect downstream communities?
Most water corporation dams were built to capture sufficient water to meet the supply needs of the community.
They have very little additional capacity to mitigate the impacts of flood events on developments located on flood plains.
In extreme floods, dams simply cannot hold back the massive volumes of water that flow into a reservoir over a short period of time. Dams must spill water once the capacity of the reservoir is reached and allow the water to continue its passage through the water courses and across the floodplains.
Dam spillways are designed, however, to allow extreme floods to pass through the reservoir without compromising the dam structure itself, thereby reducing the impact on downstream communities.
Who is responsible for dam safety?
Under Victorian legislation dam operators and owners are responsible for dam safety.
The Minister for Water maintains sufficient oversight of dam safety to ensure responsibilities are being met and to intervene where required.
What would cause a dam to fail?
Dams can fail if water flows over the dam wall during high rainfall or floods.
This is because the capacity of the spillway is not able to pass the flows safely.
Also, where construction and materials are inadequate, dams can fail due to piping and erosion and subsequent water flow through the embankment or foundation of the dam.
Does vegetation in and around streams have an impact on flooding?
In major floods, such as January 2011 , flood height is controlled primarily by the intensity and amount of rainfall, not vegetation.
Vegetation along riverbanks can have a beneficial effect on flooding in lowland areas as it slows the rate of water movement.
However, in large floods, the main control on local flood level will be through constrictions that choke the flow down. These are usually road embankments, or bridge openings. Such constrictions are much more important than the local effect of vegetation.
How safe is floodwater?
Floodwater can contain contaminants like animal waste, agricultural chemicals and petrol. Avoid swimming in floodwaters, swollen creeks, rivers and other tributaries at all times.
If you are unsure whether it is safe to swim in a river that has been affected by floodwaters, seek advice from the local council.
Is my water ok to drink?
Floodwater can contain contaminants like animal waste, agricultural chemicals and petrol.
For those members of the community who are on a town supply of drinking water, the relevant water corporation will advise its customers if the tap water is unsafe to drink, use for cooking, cleaning or bathing via local media and their websites.
For those members of the community on private water supplies (tanks, bore water), advice on managing these supplies post flood is contained in the Department of Health’s flood recovery packs which are available at relief and recovery centres and on the DHS website.
What about water for stock?
Floodwater can contain contaminants like animal waste, agricultural chemicals and petrol and may be dangerous to stock.
Advice on managing these supplies post flood is contained in the Department of Health’s flood recovery packs which are available at relief and recovery centres and on the DHS website.
Flood history at Glenmaggie
Flood history at Glenmaggie
Below shows a comparison of flows into Glenmaggie and flows out of Glenmaggie for the ten highest floods on record.
Glenmaggie – ten largest floods (ranked on outflows)
Peak inflow – 250,000 to 300,000
Peak outflow – 147,600
Peak inflow – 123,000
Peak outflow – 110,600
Peak inflow –102,000
Peak outflow – 88,900
Peak inflow –108,000
Peak outflow – 88,100
Peak inflow – 83,200
Peak outflow – 77,000
Peak inflow – 69,700
Peak outflow – 75,500
Peak inflow – 62,600
Peak outflow – 66,500
Peak inflow – 91,000
Peak outflow – 62,400
Peak inflow – 69,000
Peak outflow – 59,000
Peak inflow – 93,700
Peak outflow – 58,000