Subsidence and future coal allocations in Gippsland
- Go to new Land subsidence page here as well for update information on Gippslands subsidence
What is subsidence?
Subsidence is a natural process in certain landscapes where there are porous sediments and rocks, or where they are highly soluble. Subsidence can affect clay, peat, some silts and some sands, limestones with large underground voids and can be associated with mining activity and old mine workings.
Over the last 40 years, pumping groundwater for irrigation, removal of groundwater for open-cut coal mining operations (dewatering) and substantial groundwater extractions related to ongoing offshore oil and gas production in Bass Strait have lowered groundwater levels in the Latrobe Aquifer at a rate of approximately 1 m per year.
This is because the rate of natural aquifer recharge is not sufficient to compensate for the rate of extraction by industry, resulting in permanent change to the Gippsland lands.
Why does subsidence matter?
Subsidence is of great importance because it is irreversible once it has occurred.
The majority of cases of subsidence recognised so far have been found to have developed due to increased extraction of groundwater, mainly from oil and gas extraction.
It is land sinking as opposed to coastal inundation from sea levels rising.
What is of particular concern is that as of Aug 24th 2013, the Napthine Government refuses to release to the public the most recent 2012 seismic and subsidence reports yet they continue to promote new open cut mines in Latrobe Valley, onshore unconventional gas extraction and a new rail and port development in the very area of Ninety Mile Beach where the land is sinking and sits on unstable fault lines. Go to Morwell Mine Fire March, 2014 for our most recent disaster in a coal mine and the information stills remains hidden. This is your government at work allowing their liberal corporate mates to bleed the very ground we depend on to make their riches and then piss off and leave that spectacular area of Gippsland in ruin. Go to Farmers Rally about subsidence reports here and Ignite EL 4416 here for the story on Dr John White and his grand plans for Gippsland
Subsidence can cause many additional problems including:
- changes in elevation and slope of streams, canals and drains, affecting the rate of flow;
- damage to bridges, roads, railroads, electric power lines, storm drains, sanitary sewers, canals and levees;
- damage to both private and public buildings;
- failure of well casings causing reduction in the quality and yield of extracted groundwater;
- tidal inundation of low-lying coastal areas that were previously above high-tide levels.
Potential for artificial recharge-
In order to maintain mine stability the LV mines need to extract groundwater from artesian aquifers
beneath the mine. This groundwater is currently utilised in the cooling cycle for the Hazelwood
and Loy Yang power stations prior to being treated and discharged into the Latrobe River system
As the LV mines deepen, significant energy (and cost) is required to pump groundwater to the
The perception of the regional impacts of the mining operations is also gaining a higher public profile.
Through artificial recharge, possibly using existing bores for aquifer re-injection, the perceived benefits include:
- reduced operational costs,
- stabilisation of regional groundwater pressures,
- reduction in subsidence rates and
- demonstration of the power industry’s commitment to good environmental management
The following information are excerpts from:
PIT SLOPE STABILITY AND GROUND MOVEMENTS ASSOCIATED WITH THE DEVELOPMENT OF LOY YANG POWER MINE
SOURCES OF GROUND MOVEMENTS
Ground movement will result whenever there is a change in the stress field applied to the ground.
This is particularly evident within the compressible strata contained within the Latrobe Valley Depression.
The largest source of ground movement in the areas adjacent to Loy Yang Power Mine is that associated with the open cut development. The major factors contributing to the occurrence of ground movements adjacent to Loy Yang Power Mine are: -
- Aquifer depressurisation resulting in regional subsidence;
- Relief of tectonic stresses during coal excavation with consequential horizontal and vertical displacements;
- Drainage of the “unconfined” groundwater from the batter faces resulting in consolidation of the coal;
- Rotation of the coal blocks, due to differential consolidation of the supporting strata adjacent to the mine, resulting in horizontal movements;
Meanwhile, the Baillieu government still pushes on for more open-cut mines.
You would have to be in la-la land if you think this government cares
about the farmers and the environment.
In relation to the 2007 mine collapse at Yallourn the Mining Warden report made a startling conclusion, noting:
“The open cut mines in the Latrobe Valley are very large excavations. The mines are not rigid structures, they are highly deformable and the deformations spread a long way outside the mine perimeters… They are in part surrounded by natural and man-made infrastructure.
This infrastructure is often quite rigid or inflexible. In an engineering sense deformable structures next to inflexible infrastructure can result in some incompatibility, which in a wider context means risk.”
On June 6 2012, the Morwell River collapsed into the Yallourn coalmine in the Latrobe Valley. The river, perhaps Australia’s most poorly treated, has been moved six times to allow access to new coal deposits. The day after the mine site collapsed, TRUenergy dammed the river in two places, diverted the flow of the river into their mine pits, and shut down most of the power station.
The Victorian government is proposing to allocate 13 billion tonnes of Latrobe Valley coal in 2012/13 in the hope of establishing an export coal industry. That’s equivalent to 13 mines the size of the Hazelwood pit. We currently have just three mines in the Latrobe Valley, and persistent and serious problems are emerging. From an emissions perspective developing new brown coal mines and export industries is ridiculous. From a local environmental perspective in the Latrobe Valley the cumulative impacts of mines on rivers and groundwater, agricultural land and community health is reckless.
If lessons are to be learnt from this disaster, it’s that Victoria’s regulatory environment and mine operators cannot be relied upon to cope with the proposed massive expansion of brown coal mining across the state, let alone the serious threat to the health of our environment and communities that it would create. The Baillieu government is not doing Victorians any favours by increasing our reliance on highly polluting and damaging coal.
TRUenergy has plans for future diversions of the Morwell River, and if the Baillieu government and federal energy minister Martin Ferguson’s plans to turn the Latrobe Valley into the Pilbara are realised, more rivers will be interfered with. The Morwell River diversion was justified by sophisticated modelling exercises that predicted that the diversion would cope with all but a 1 in 10,000 year flood event. While flooding in Gippsland in June was serious, the region floods regularly and it certainly wasn’t a 1 in 10,000 year flood ever.