Study measures the environmental impacts of longwall mining subsidence

While underground longwall mining does not have the same, obvious impacts of open-cut mining on surface environments, it can nevertheless cause serious changes to the topography and ecology of an area.

After the coal seam at a longwall operation has been removed, the earth above will generally collapse to fill the void, causing the surface to slump.

This surface slumping, known as Longwall Mine Subsidence (LWMS), can permanently alter the environment and the way it functions.

According to Dr Paul Frazier, the Hunter and New England regional manager for environmental services firm Eco Logical Australia, LWMS can change water flow patterns and soil characteristics.

“Almost every longwall mine that is developed will cause surface subsidence, but the consequences will depend on the location,” he told Australian Mining.

“In certain places, a significant drop can redirect the overland flow of water run-off and even cause it to pond.

“There have definitely been instances of surface vegetation dying and tree roots being disturbed, which can increase erosion.”

Frazier coordinated an extensive three year project to study the impact of subsidence of three longwall minesites; the Kestrel mine in the Bowen Basin, the Beltana mine the Hunter Valley and the Dendrobium operation in the Illawarra region.

The team developed a convenient and more accurate way for mines and the community to monitor the impacts of LWMS.

“Longwall minesites can be quite large, with panels up to several kilometres long,” Frazier said.

“On-ground monitoring using traditional field surveys is practically impossible at that scale.

“You would need to have lots of people in the field for a long time, meaning there are associated costs and safety risks.”

Frazier said the team studied the affects on the vegetated and agricultural environments above and nearby longwall areas.

At the conclusion of the study, the team had not found any major changes to the vegetation or the agricultural production at the selected studies.

“We employed a combination of ground sampling, high-resolution satellite imagery and airborne laser scanning to measure changes to crops, pastures and native vegetation,” he said.

“We used Quickbird, Ikonos and Spot high-resolution multi-spectral satellite imagery and Lidar airborne laser scanning.

“These techniques and technologies are widely available in the mining industry; we just implemented them in a unique way.”

According to Frazier, this method provides total coverage of a mine’s footprint, giving greater assurance to the local communities.

 

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