Getting green on subsidence

SUBSIDENCE has long been a topic of debate between the mining industry and environmental groups, with the former maintaining it has the problem under control and the latter insisting the controls are not enough.
Getting green on subsidence Getting green on subsidence Getting green on subsidence Getting green on subsidence Getting green on subsidence

New research will develop methods to monitor the effects of subsidence on vegetation.

Christine Feary

Published in March 2008 Australian Longwall Magazine

A new project from the University of New England, which received approval for ACARP funding in December 2007, aims to develop methods to monitor the effects of subsidence on vegetation.

UNE’s Dr Paul Frazier said the project will give the industry a better handle on what’s going on in the environment, and help it to understand and potentially manage the problem better.

“We’ve got pretty good handles on the topographic changes that occur after subsidence . . . with level surveying that can tell us how much topographic change has happened.

“What we suspect is that longwall mine subsidence doesn’t have much effect on surface vegetation, however this will vary from mine to mine. Our job is to develop methods to measure and quantify the effects, if any, on the surface grasses, crops and trees.”

There are a couple of ways that subsidence can impact upon vegetation, first of all by releasing coal seam methane gas. Dr Frazier said when gas is liberated in an intense burst it can kill vegetation by heating up the soil and depriving plants of oxygen.

It can also change surface and groundwater flow patterns, diverting water away from water-dependent vegetation and waterlogging soil or causing water to collect in other areas.

Finally, root shearing can occur when differential subsidence takes place, as the ground shifts and cracks open up.

The exact impact of that subsidence depends on a number of factors, including the type of vegetation, the landscape, and the slope and geology of the area.

Dr Frazier said the impact of subsidence on a gently sloping area with thick soil is likely to be less than on a rocky area with thin soil and large trees.

He said that by giving mining companies a way to measure the impact of subsidence on vegetation the companies will be able to understand the potential impacts of their work.

“Providing reliable, quantitative assessment of landscape change will also assist the industry develop future sites and liaise with the community and government.

“What [the project] really means is a better way, a cheaper way, and a less risky way, depending on the landscape, of monitoring their mining area.”

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