title: Estimation of the Change in Storage Capacity above Mined Longwall Panels.
abstract: Accurate estimation of the change in groundwater storage capacity (S) above mined longwall panels is vital for analysis of postmining void water level recovery in coal mines, and assessment of water quality impacts. At present, there is no generalized representation of the spatial distribution of changes in S around a panel. Current estimates are generally bulk averages with high uncertainty, precluding calculation of groundwater velocities in various parts of the subsurface. In this work, a recently published hydrogeological conceptual model of longwall caving is used in conjunction with observations from borehole extensometers, goaf height measurements, and pumping/drawdown records for mine pools to develop a subsurface spatial distribution of changes in S following longwall caving, with reduced uncertainty in their magnitudes. The assumption of saturation in the disturbed zone proved critical for obtaining accurate results and in reconciling widely varying published estimates of S. Results indicate that the goaf and collapsed zones each absorb over 30% of the mined volume, and about 20% is absorbed by the surface subsidence trough. The increase in S in the collapsed zone is inversely proportional to the amount of surface subsidence. The conceptual model is updated with these results to present the spatial distribution of S after caving. The results allow calculation of water velocities in various zones, and may provide greater accuracy in estimation of water level rebound and water quality processes. Most of the S participating in groundwater flows is provided by defects rather than the matrix.
authors.affiliation: Associate Subsurface Hydrologist, Coffey Geotechnics, Level 18, Tower B, Citadel Towers, 799 Pacific Highway, Chatswood, NSW, 2067, Australia. paul.tammetta@coffey.com.
authors.forename: Paul
authors.initials: P
authors.lastname: Tammetta
mesh_terms: D060587:Groundwater; D008906:Mining; D035501:Uncertainty; D014867:Water; D060753:Water Quality
chemical_list: D014867:Water