By PHILIP HOPKINS

 

NEW research into soil revegetation by Federation University at Churchill is helping to pave the way to successfully rehabilitate the Latrobe Valley’s coal mines.

The study, commissioned by the Cooperative Research Centre for Transformations in Mining with support from FedUni and the state government, comes against predictions of a changing climate. Victoria is forecast to have higher temperatures and a drier climate, with declining winter rainfall but more extreme thunderstorms in summer.

“This would likely cause both an increase in soil drought conditions and the possibility of soil erosion with intense rainfall runoff,” the study says.

Key points of the research include:

  • These climate conditions require new ways to rehabilitate mine sites to ensure that vegetation grows successfully and landforms are stable;
  • Experiments have found that drought forced vegetation to explore deeper soil depth for access to water;
  • Underlying coal beneath the soil cover can store water and provide water to plant roots over extended periods of time, mitigating drought, and;
  • Vegetation on deeper cover has a much greater chance to thrive, increasing the chances of successfully rehabilitating coal mines.

The research notes that a drier climate could affect the survival and density of vegetation soil cover on rehabilitated coal mines, as well as increasing the risk of erosion. It details that increasing the depth of soil cover allows vegetation to grow roots deeper so it can survive drought.

The project team, which included FedUni’s Professor Thomas Baumgartl, used measured data and hydrological modelling to simulate soil moisture and water flux. The data showed the importance of fracture flow of water through coal.

The Latrobe Valley’s climate from 2021 was extrapolated to simulate future climate scenarios, and these were used to guide soil column experiments to assess the water content of the soils and plant growth. Vegetation was planted in the soil columns and a range of soil cover and climate scenarios were modelled.

The results were heartening: plants under drought conditions grew their roots deeper, searching for and extracting water from the coal below.

Professor Baumgartl said the new data had implications for mine rehabilitation.

“To most effectively rehabilitate landforms that can withstand future climate conditions, increasing the depth of soil cover designs – to a certain point – could be a means to provide more opportunity for vegetation to establish and thrive in the long term,” he said.

Specifically, plant roots grew to their maximum at the interface between the soil and the coal, down to a depth of 0.9 metres and may have the potential to grow deeper. A lot less water is stored and available to plants in shallow cover (0.4 metres) compared to deep cover (0.9m), the research found. This may be caused not only by the smaller soil volume, but by the existence of cracks in the coal affecting the drain age of water.

Verification of numerical hydrological modelling by measured soil moisture and water flux data showed the importance of considering fracture flow of water through coal.

The research noted that constructed soil covers found in mine rehabilitation are commonly finite in depth, have limited water available to support vegetation, and may be exposed to greater drought risk under future climate conditions.

“To best design effective rehabilitated landforms for future climate conditions, the water balance of soil cover designs must be better understood, to assess and guide the establishment of viable vegetation cover in the long term,” the research found.