Goulburn-Murray Water held a webinar on Thursday 6 July 2023 to share information about how Lake Eppalock is managed and the role the storage plays during times of flood.
Below is a recording of the webinar. You can also download a copy of the presentation.
Questions from the webinar
How far in advance would the release of water had to commence to accommodate the October 2022 rainfall?
The inflows Lake Eppalock received during October 2022 was over 1,800 per cent of the monthly average and more than twice the previous record inflow for October.
In October alone, 343 GL flowed into Lake Eppalock, which is more water than the storage can hold at full capacity. From July to November 2022, Lake Eppalock recorded 579 GL of inflow, almost twice the amount the storage can hold. Therefore, even if Lake Eppalock had been empty in July, there still would have been a significant amount of water passing through the storage in the months that followed.
What does the term ‘full supply level’ mean? How is Lake Eppalock able to mitigate flood by storing above this level?
‘Full Supply Level’ is the level where the water in the storage is equal to the top of the spillway.
The Lake Eppalock embankment walls are nearly 5.2 metres higher than that of the spillway. These embankments help temporarily hold water back and allows the water level to exceed the full supply level, enabling outflows from the storage to be less than inflows.
Who is the environmental water holder?
There are two environmental water holders who have water entitlements in the Campaspe system and are supplied from Lake Eppalock: The Victorian Environmental Water Holder, and the Commonwealth Environmental Water Holder. The North Central Catchment Management Authority places water orders for delivery rates on behalf of the water holders.
What percentage of water in Lake Eppalock is bulk entitlement?
Lake Eppalock is a capacity shared storage. GMW manages 82% of the volume and Coliban Water manages 18%. Each Water Corporation holds a bulk entitlement specifying the rights to take or store water. The Bulk Entitlement documents can be accessed via the Water Register website
The Victorian Environmental Water Holder also holds an environmental entitlement in the Campaspe system.
What went wrong with the BoM forecast in October 2022?
Exact rainfall totals are very difficult to forecast accurately. The rainfall in the Lake Eppalock catchment was over three times the monthly average and the highest on record for October. The response to the rain received generated the highest October inflows on record, double the previous maximum.
Now GMW has the data, do you have triggers for notifications?
Flood warnings are issued by the Bureau of Meteorology and then shared by the SES via the VicEmergency app. GMW works with both agencies to provide information on catchment conditions and storage levels to help inform these warnings.
People can stay up to date with the latest warnings at the Bureau of Meteorology Flood Warning Summary webpage
Are there any proposals to change legislation to allow for more pre-releases at Lake Eppalock? With climate change leading to more extreme weather events, how is GMW working with the government to ensure future flood events are mitigated?
The Department of Energy, Environment and Climate Change Action (DEECA) is leading an assessment of the operating arrangements at Lake Eppalock, with input from Water Corporations, Catchment Management Authorities and Local Council and has engage an independent consultant to undertake the modelling and develop a report.
This assessment will explore whether changing the operational arrangements or infrastructure options for Lake Eppalock would have reduced the impact of flooding to downstream communities and what would be the cost of doing so.
This is a technical assessment which will be an important input into the work the Campaspe Shire with support from North Central CMA are doing in reviewing flood mitigation strategies in the Campaspe Region. Community members input will be sought in the review of the Rochester flood plan, which includes mitigation activities.
The scope of the assessment and progress can be found at the DEECA Lake Eppalock operating arrangements assessment webpage
What reason is there to have Lake Eppalock so full? Surely it would be better to have the lake at 90 per cent?
GMW manages the lake, it doesn’t own the water. Coliban Water, environmental water holders, and farmers are the main entitlement owners. To release more water from Lake Eppalock, GMW would generally require the water holders to order more water.
However, GMW is able to release water from Lake Eppalock when the storage is expected to fill and forecast inflows will replenish the water released. This ensures that water holders are not losing the water being stored in Lake Eppalock for them.
How does the recent rainfall play into the current modelling?
Any decisions on pre-releasing water must take into account numerous factors.
Catchment conditions, both upstream and downstream of storages, forecast rainfall, current storage levels, and the potential impact on landholders, all factor into decisions to release water.