Some flood-impacted residents of Rochester are calling for modification of the Lake Eppalock dam to allow for flood mitigation.
Photo by
Chris Braden, G-MW
Some flood-impacted residents of Rochester are calling for modification of the Lake Eppalock dam to allow for flood mitigation.
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A state government review of the lake, now under way, is looking at the feasibility of new release gates or bigger valves.
Large volumes of water pouring down the Campaspe River decimated the town in last October’s floods.
Eppalock, the main storage on the Campaspe River, above Rochester, reached three metres above full supply level at the height of the deluge.
A technical assessment of the operating and infrastructure arrangements at Lake Eppalock is being conducted by the Department of Energy, Environment and Climate Action in consultation with the North Central Catchment Management Authority, Goulburn-Murray Water, Coliban Water and Campaspe Shire Council.
A department spokesperson said the assessment had started, with findings to be published in the second half of this year.
“Once complete the assessment’s findings will support the Campaspe Shire Council review of flood plans for Rochester and help inform future flood mitigation strategies,” the spokesperson said.
The assessment will consider possible infrastructure options for Lake Eppalock, to identify if there are any opportunities to mitigate flooding downstream.
The rights of existing entitlement holders will be considered in the assessment, including any upstream impacts on landholders.
The department said the review would look at possible infrastructure options, such as larger release valves or the installation of gates on the dam wall, that could potentially support the operation of Lake Eppalock prior to, and during flood events.
Several submissions to the Victorian parliamentary inquiry on the 2022 floods have queried the impact of Eppalock on the Rochester inundation.
Wayne Park has told the review his home has been flooded twice. He blames the obstruction of water flow caused by the Waranga Mallee Channel.
“The other problem for Rochester is the management of the water in Lake Eppalock. Eppalock should be used to help mitigate downstream floods,” Mr Park said.
“The water should be compulsorily released at night though a turbine to generate zero-carbon electricity when the dam is 80 per cent full.
“This should extend to full-time generation when Eppalock is 90 per cent full. This could be done without more engineering at the moment.”
Maree Trail who runs a Rochester community Facebook page has complained that there were insufficient warnings for the Rochester community, and argued that Eppalock should be better managed to provide flood mitigation.
She appealed for the installation of flood-gates to increase the discharge.
Tony Royden and Janet Webb argued for an engineering solution
“There needs to be better control over Eppalock and an ability to release substantial amounts of water when a trigger point is met.
“This could generate electricity and prevent major flooding in Rochester and downstream.
“When Eppalock is full it only takes one major local rain event to flood our town and downstream communities.
“A protocol should be developed about safety margins in Eppalock storage, combined with weather forecasts and recent history.“
G-MW Water Storage Services general manager Martina Cusack said the spillway at Lake Eppalock was a fixed-crest spillway, which meant G-MW was unable to release more water than the maximum capacity of the outlet valve of 1800 ML/d.
“During spill events, downstream flows are governed by how high the storage level exceeds the full supply level,” Ms Cusack said.
“In contrast to fixed-crest spillways, gated spillways, like Cairn Curran, can be managed to release larger amounts of water before they spill.
“Campaspe Weir was built to divert water to the Campaspe Irrigation District, but is no longer used for water diversion after the irrigation district closed.
“Higher flows spill over the weir, and therefore it has negligible effect on river flows during times of flood.
“Water is still used for irrigation by those who divert water directly from the Campaspe River.”
The Rochester Flood-Mitigation Group is also arguing for better release mechanisms on Eppalock.
State Member for Murray Plains Peter Walsh (left) with Rochester flood mitigation committee members Stuart Murray (back), Dave Christie and Tracie Kyne at the Lake Eppalock emergency spillway showing the incredible flood damage. Photo: Luke Hemer
During the October 2022 floods, outflows peaked at 103,000 ML/d on October 14, yet on October 13, inflows peaked at 235,000ML/d.
G-MW figures show both these figures were historical highs.
The storage reached a maximum of 134 per cent of capacity, almost three metres above the full supply level.
The risk of spill in the Campaspe system in 2023-24 is about 60 per cent.
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