Engineers Australia

Impacts of longwall mining and coal seam gas extraction on groundwater regimes in the Sydney Basin: Part 1 – Theory

S. E. Pells and P. J. N. Pells


The mathematics steady state and transient downwards Darcian flow are given for full or limited recharge and saturated homogenous ground, layered ground, and for unsaturated flow. Data are presented from a physical model that supports the theoretical analyses.

A hypothesis is presented for unsaturated hydraulic conductivity in the Triassic rocks of the Sydney Basin. The theoretical analyses coupled with the important inferences from unsaturated hydraulic conductivity provide valuable aids to understanding possible impacts of depressurisation due to underground coal mining and coal seam gas extraction in the Sydney Basin.

It is acknowledged that flow through jointed rock masses is very complex, and there are limits to the applicability of the equations of flow through porous media. However, as with elastic theory in geomechanics analyses, it is considered that the rigor gained from Darcian flow analysis assists greatly in avoiding flawed thought processes in hydrogeology.