Impacts of Mine Subsidence on the Strata & Hydrology of River Valleys - Management for Undermining Cliffs Gorges & River Systems

THIS REPORT IS PROVIDED AS A SET, COMPRISING C8005, C9067 & C18015

ACARP Has funded work since March 1999, in order to gain a better understanding of the impacts of underground coal mining on creeks, river valleys, gorges and clifflines. The research work was funded in two stages and the final report on the first stage of the work (C8005), was completed in March 2001. This report describes the work completed in the second stage of the project and should be read in conjunction with the report on the first stage of the work.

Prior to commencement of this project, there had been considerable public comment, and expressions of concern, regarding the impacts of mining on creeks and rivers in the Hunter Valley, water storage reservoirs in the Southern Coalfield, escarpments and cliffs in the Southern and Western Coalfields and the Cataract River Gorge, at Tower Colliery.

Numerous longwall extractions have already been completed and many more longwalls are planned beneath creeks, river valleys, gorges and clifflines in the NSW Coalfields. Indeed, the very nature of the topography makes it virtually impossible to avoid such features. All of the current coal mining operations in the Southern Coalfield, and most of those that are planned in future, are taking place in areas of steep topography and are likely to have some impact on creeks, river valleys, gorges, clifflines and associated infrastructure.

The research work was undertaken by a multi-disciplinary team of researchers and the various aspects of the work were split broadly into the four sections described below:

• Management of the project, literature search, state-of-the-art review, empirical study, development of empirical predictive techniques and preparation of the final report, incorporating the work of other researchers. (Waddington & Associates Pty Limited, trading as Waddington Kay & Associates, using data supplied by collieries, the NSW Dams Safety Committee and Sydney Catchment Authority)
• Surveys and monitoring of ground movements, geological investigations and hydrological studies, rock classification and testing and in situ stress measurements. (BHP supported by external consultants)
• Numerical modelling and development of numerically based predictive methods. (CSIRO Petroleum)
• Design and construction of a physical scaled model that can be used to illustrate the underlying mechanisms of strata movements for a range of different mining scenarios. (The School of Mining Engineering at the University of New South Wales)

This report includes an additional state-of-the-art literature review and comprehensive discussion on the findings that have arisen from the empirical studies, the numerical modelling work and the physical modelling facility. The research work has provided new insights into the mechanisms involved as creeks, river valleys, gorges and clifflines are undermined and has resulted in new methods for the prediction and assessment of subsidence impacts.

The final output from the research project will be a management information handbook, to assist coal mining companies that are planning to mine in areas of steep topography. The handbook will include a CD copy of the reports on the first and second stages of the research project for ease of reference. The importance of ongoing research in this area can not be overemphasised, since future longwall approvals might well depend upon it.